Severe Storms Expected For The Next Few Days

Good morning everyone! I've got to be brief today so I apologize for not walking through the entire forecast process like I normally would. I'm on the road right now and I'm typing this on my phone so there will probably be a few typos as well, we'll work it out though.

Today's Target

Severe storms are expected to break out later this afternoon from Missouri to Tennessee. The greatest corridor of severe storms appears to be from southeastern Missouri through southern Illinois and Kentucky. The primary threat is damaging winds across the area mentioned but severe hail and a few tornadoes are on the table as well. I'm targeting southern Illinois into western Kentucky where I think more discrete supercellular storms should initiate this afternoon before upscale growth occurs and a more linear system takes shape. This is where I think the greatest tornado and hail threat exists too, although embedded tornadoes are possible throughout the night.

The Setup

Briefly looking at current obs and mesoanalysis we can see a shortwave trough evident as a subtle cyclonic "kink" in the mid-level flow and a speed max (40kts) over the central plains. Showers and storms are already ongoing with the vertical motion associated with this feature and this could play a role in limiting some development today (although I think storms erupt anyway). A plume of sufficient lapse rates is established over the central CONUS and this will advect eastward atop the moist sector. Surface analysis shows a thera-e axis surging into the region and 70ºF dew points already in place. Ample sunshine and this moisture advection are/will contribute to moderate-strong destabilization across western KY/southern IL. With the advance of the shortwave and upper-level speed max we'll see ascent increase and this should result in more robust storm initiation by late-afternoon. 

12z HRRR indicates ample destabilization in response to high theta-e air and strong diurnal heating. Note the "blobs" of stable air, that is a result of convection/outflow in that area.

 This is just one model run but the 12z HRRR supports the current forecast showing widespread storm development this afternoon.

This 30-40kt 850mb flow may aid the increase of low-level rotation, especially into this evening. 

With MLCAPE on the order of 2000-3000j/kg and 30kts of deep-layer shear we can expect updrafts to be organized and storms to be strong. Shear profiles are somewhat favorable for rotating cells, especially in the more discrete storms, and I think a risk for hail, and maybe a tornado or two exists. As I said, this is my target today. Storm-relative winds coupled with cold pool interactions will result in upscale growth with perhaps multiple linear segments developing across KY/IL/IN/TN. Embedded circulations will still be possible although the primary threat will transition to damaging winds through the night. 

More severe weather is expected the next few days and I'll break that down in this evening's update. It currently looks like the target will be in the northern Plains plains for Friday and back into southeast MO to Western TN for Saturday. 

Stay tuned for updates during the next few days as it looks like we'll be putting some road behind us. 

Alberto's Landfall and Severe Weather Chase Potential through the Weekend

It's been somewhat active the last couple days hasn't it? Tornadoes in the high plains, flooding in the East, and Alberto finally made landfall in Florida. Tonight we're going to dive in to Alberto's impact as he tracks Northward through the Tennessee Valley first, including where I think a severe storm and flood threat will exist, then we'll break down tomorrow's severe threat in the plains and identify some target areas for that.

Subtropical Storm Alberto's Landfall and Impacts

As of the time I'm typing this subtropical storm Alberto just recently made landfall in the Florida panhandle and was continuing his track northward, turning slightly northwest.  

I expect this will be the track from here on out as he moves northwest into western Tennessee and Kentucky on Tuesday and Illinois/Indiana toward the Great Lakes on Wednesday. While he will be generally weakening over the next 48-72hrs his impacts will not go unnoticed. 

Flood Threat Across The Tennessee Valley

The most prominent threat associated with Alberto is the heavy rainfall and flooding. When forecasting a flood threat I'm essentially looking for a few key factors; a source of deep, rich moisture, a degree of instability to trigger convection and enhance rates, and a source of mesoscale/synoptic lift (preferably slow moving). That said, flood/flash flood potential certainly exists over Tennessee/Kentucky as a very moist air mass, characterized by dew points in the upper 60's-low 70's and PWAT values in the 1.8"-2" range, is already established across the region upstream from Alberto. 

Southerly flow throughout the eastern half of the surface-low will help advect even more moisture into the area and convergent flow associated with Alberto's circulation along with interaction of an upper-level trough will definitely be enough to bring swaths of heavy rainfall to the area. Rain has already been ongoing well in advance of Alberto but the heaviest rain will begin with the arrival of the low-pressure center itself timed favorably with afternoon heating Tuesday afternoon. We'll get into the severe threat shortly but this rain will continue through the evening, and into Wednesday morning in Kentucky, before finally exiting to the North. Stray showers are possible in Alberto's wake as well but there is often strong subsidence following the passage of troughs like the one upstream and regardless, the heaviest rain will exit with Alberto. I think a swath of significant rainfall is possible in the western Carolinas and another 2"-3" of rainfall likely, particularly along I-65, and obviously the stronger storms will be capable of producing higher totals. This will likely result in flash flooding issues with heavy rain occurring the previous leading to saturated soil and flood guidance already being approached.

GFS Accumulated Precip through 12z Wednesday Morning. The GFS is a little more West with the corridor of highest totals than the ECMWF is but it's been handling the current track of Alberto pretty well. More importantly, it appears to account for the fact that the heaviest rainfall has been occurring nearest the center of Alberto's circulation and along a pseudo warm front in the Northeast quadrant since landfall. The ECMWF and UKMET models seem a bit more broad with the precip

High-Res CAM guidance has been supporting the recent GFS runs as well. Based on recent trends with Alberto, I chose to use a blend of GFS and NAM3k guidance to forecast heavy rain. This is not to say heavy rain won't occur elsewhere, it will, it just points toward where the longest duration of heavy rainfall will occur.

The SREF (Under-utilized in my opinion) shows similar output as above with swaths of heavier rainfall in central TN/western KY associated with the center of Alberto and another swath of heavy rain from northern GA into the Carolinas. Graphic above shows 700-500mb Vertical Velocity and 3hr QPF. This is meant to identify areas where ascent and precip are suggested concurrently by the model, hopefully helping to increase certainty. 

Severe/Tornado Threat As Alberto Moves Northward

I'll start this part off by saying that it's somewhat different forecasting severe weather, and specifically tornadoes, with a tropical cyclone. For one, you don't typically see the high instability you see when forecasting more "conventional" tornado setups, often mitigated by extensive cloud cover/rainfall. Another is the lack of deep-layer shear. Deep-layer shear is very unfavorable for tropical systems, and even though we aren't looking at a tropical system per se anymore, the environment that spawned it still needed to support tropical development to even get this far. This usually results in embedded convection in feeder bands of tropical cyclones that quickly devlop low-level circulations without a deep, persistent mesocyclone (although occasional mesocyclones are noted). They are most likely going to be identified by tighter velocity couplets, sometimes briefly preceded by a convergent velocity signature. 

The northeast quadrant (on a Cartesian plane) of tropical cyclones is the climatologically favored zone for these tornadoes to develop, and this is due to a few reasons.

This diagram, actually taken from one of my first college textbooks (Understanding Weather and Climate 7th Ed. by Aguado & Burt), plots the position of 373 embedded tornadoes between 1948-1972. 

Perhaps later in the hurricane season when I'm preparing to intercept a hurricane/tropical storm I'll really get into the nuts and bolts of all that but it basically has to do with the fact that shear profiles are traditionally much more favorable for both non-mesocyclonic tornadoes and mini-supercells. There are also subtle baroclinic zones that tend to develop here (think a storm ingesting vorticity as it rides along a frontal boundary).

Now that we've got a little bit of foundation put down let's see how it applies in the short-term. As Alberto's remnants drift forward areas in the northeast quadrant will have some increased potential for tornadoes, based on everything we just mentioned. We still need to assess the environment though and better delineate the risk area. It's no help to just blanket half of the Country with a threat, and it's definitely no use to do that when targeting for a chase, a target area of 1000^2mi isn't going to help anyone. For tomorrow's situation I timed out where Alberto will be when diurnal heating really gets going. Today's analysis shows that he's slowed down quite a bit so this looks most likely to be in central TN as he will move through there through mid-afternoon. Like I said, you don't typically see the intense instability you see in other setups but steep low-level buoyancy will enhance convective cell development and low-level vortex stretching. Forecast models are progging marginal, but sufficient instability across KY/TN for Tuesday and it's in line with what we saw in a similar setup today so it seems realistic. Plus, any breaks in cloud cover will help localized buoyancy build even more. 

HRRR shows sufficient destabilization across the region tomorrow. 

The main reason the tornado threat will exist tomorrow is due to the enhanced low-level shear profiles we mentioned. This looks to be maximized from North Georgia into East/Central Tennessee and Kentucky. Forecast soundings show around 100-150m^2/s^2 0-1km SRH in this region and this will be supportive of low-level rotation, particularly in the stronger cells that are able to redistribute this rotation back to the surface. 

Above: HRRR and SREF model guidance showing 0-1km SRH and ensemble probability and mean 0-1km SRH, respectively.

There may very well be instances tomorrow with relatively unimpressive rain showers that show signs of low-level rotation, I've seen this multiple times when chasing inland tropical systems. I think the greatest tornado threat is going to be in central TN but I can't rule them out anywhere in western KY either. Understand that I'm not forecasting major tornadoes and that's not what I'm chasing. A phrase you hear a lot with squall lines is "brief, weak tornadoes", and I hate that because I don't want to undermine any severe weather threat and build complacency, but we're not expecting huge tornadoes, at least not in the Tennessee Valley. 

Central Plains Severe Weather Potential

The most classic chase target tomorrow is the central plains. While there are a few different locations someone could target I really see two primary areas to be. They both center around the dryline across western KS into the OK panhandle. A large, elongated area of low-pressure is established from the southern plains all the way into Minnesota and there will be severe storms associated with this entire area given steep lapse rates advecting over a moist boundary-layer however the focus for chasing tornadoes seems to be OK/KS. Don't misread this, ALL severe weather is serious and I don't want other severe storms to be ignored or "written off" because they aren't tornadoes. I'm choosing to focus on forecasting supercells and tornadoes here for the purpose of chasing supercells/tornadoes. 

Now that that's out of the way let's get back to it. The boundary-layer is already sufficiently moist across the plains and continued southerly flow associated with the surface-low will only act to further moisten the boundary-layer. Dew points are already near 70F into OK and are in the low 60's northward.

0z observed sounding indicate deep moisture,14-16C dew points at 850mb, across eastern OK and TX, extending into southeast KS. 

 The big question mark tomorrow is the current convection and how it will modify the environment. Given their current eastward progress however, I don't think the current storms will limit things. The bigger uncertainty arises with the potential for morning convection. Should storms initiate in central KS Tuesday morning then they could overturn the atmosphere a bit and this may come into play. I would most certainly get up early in the morning to perform some nowcasting and assess the environment because these storms will likely limit the areal extent of later, more robust convection and if someone was playing the northern target then they may need to make some quick adjustments. Either way, the strong theta-e advection and diurnal heating will result in moderately strong destabilization ahead of the dryline (2000-3000j/kg MLCAPE) by afternoon.

HRRR guidance indicates moderate-strong destabilization taking place by mid-afternoon across western KS/OK. Convective influence is noted in NE and MO. Also plotted is 0-6km shear. The deep-layer shear is more parallel to the surface boundary in KS which suggests to me that storms will become linear muvh more quickly as opposed to western OK where boundary-relative shear will allow storms to initiate along the boundary and move away, remaining semi-discrete. It's important to note that storms in OK may face problems with short residence time along the boundary and if they move out of the area of forcing too quickly they may have trouble staying organized.

 Deep-layer shear associated with an ejecting shortwave will be on the order of 30-40kts, sufficient for organized convection. Forecast hodographs tomorrow are supportive of supercells, at least initially, and low-level curvature suggests low-level rotation is supported. 0-3km MLCAPE is forecast to be between 75-100j/kg across south central KS (I usually want to see about 100j/kg 0-3km CAPE or more for tornadoes).

SREF "composite" plot of  showing the ensemble mean MUCAPE, effective shear vectors, and 0-3km SRH. Areas where favorable values of these ingredients overlap suggest supercells may be supported, assuming you actually have storms in that area.

This graphic can get a little noisy but it's one of my personal favorite "secret weapons". It shows low-level MLCAPE and I don't usually expect tornadoes with less than 100j/kg. That's just a rough guideline though and I will never bail on a chase because of any one parameter. Regardless, it shows 0-3km CAPE in the range I like to see anyway.  

 This suggests the potential is there for tornadoes, maybe a strong tornado or two. My hang up tomorrow however is whether or not storms will even be able to initiate and take advantage of the ingredients. I always want to see lid strength indices of -1C and below and tomorrow they are in the +2 and above range. This could be an issue. I would not bank an entire forecast on one index at all but this is certainly something to monitor in real-time if following along tomorrow, especially considering there is some reason to buy this given the morning convection. 

This can also appear like a noisy product due to the high resolution but I like to use it from time to time. It depicts areas of moisture convergence. It is subject to influences from terrain but if you have a knowledge of the area you're looking you can apply it easily. Looking across western OK and KS you can see what almost looks like the areas of enhanced cumulus (cloud streets) we'd expect to see when convective initiation is imminent. This corresponds with moisture surging northward here and warmer colors indicate convergence, and you can infer ascent from this. This is a decent proxy for identifying the "burst point". This data supports the thinking that storms will fire in central KS (where convergence is strongest) and then fire in western OK.

All in all I expect the earlier storms to be confined to the area of Hays, KS into NE. The target options, as I see them, will be either the area near Hays where earlier initiation would allow for the opportunity to chase storms that will likely be supercellular before upscale growth occurs, or the "burst point" further to the South between Woodward, OK and Pratt, KS where storms would have the benefit of "cleaner" inflow and one could "stairstep" to continue playing the tail-end charlie. Any of these storms will be capable of large hail and damaging winds of course and will be dangerous regardless of whether tornadoes occur or not. It's also worth mentioning that I always get up early on chase day because things happen overnight and the best target the night before may not be the best target the day of. I've seen tornadoes on days when I changed my target by 100mi at 7am on chase day based on the position of boundaries or other mesoscale features. This is why it is imperative to perform solid analysis using current observations, radar, and satellite data. A good forecast won't mean anything if you bank on last night's HRRR and sleep until 1pm and wake up thinking storms are about to fire only to realize the dryline surged a little more eastward than expected and now you're sitting 80mi West of it, chilling in 30 degree dew points and clear skies. With all of this in mind, I personally think the southern play is the better option. That would put me somewhere near Woodward, OK or just along the OK/KS border. I expect linear forcing along the boundary and boundary-relative flow to result in upscale growth and I think that although initiation is more difficult to anticipate in this area it's the area where discrete supercells will be most likely for the longest time.

I hope everyone enjoyed tonight's post, I tried to be as detailed and informative as possible. As always, thanks for following along and we'll start picking apart this weekend's setup next time.

Chase Forecast for Holiday Weekend Tropical Storm

  Good evening everyone! We actually do have a little bit to cover tonight with this subtropical system in the Gulf of Mexico to isolated severe storms across the Plains, so let's do it. I'll start off by saying that I am packed up and ready to hit the road but I am still debating on whether I'm going South to cover the subtropical-low or heading West to chase occasional severe storms out there so today's chase forecast will simply break down all of it and take a look at all the options on the table. I'm probably targeting a marginal, but realistic tornado threat in the Gulf States as our subtropical system makes landfall. An areal tornado threat can't really be outlined at this point because there is too much uncertainty regarding where the storm goes but I expect at least some increase in tornado probs as we get closer to "go time" and he's making landfall. Enough of my rambling though and let's dive in to the interesting stuff...the analysis.

Subtropical Storm "Alberto"

Coincidentally, during the typing of this blog, the NHC issued advisory #1 at 15z and dubbed Invest 90L as "Alberto". This isn't unexpected as it has been organizing slowly for a few days and myself and others were eyeballing this potential for over a week now but nonetheless it means that things are developing as anticipated, at least up to this point. Alberto is currently located just East of the Yucatan peninsula of Mexico (19.5N 88.0W as of 13z). GOES East shows a broad area of convection in the Caribbean associated with this storm and the low-pressure circulation is more defined than it was even last night. It's not the tightest circulation by any means and the entire western half of the storm is fairly dry, only broken cumulus fields indicated the center if the low, but that is likely due to the land-interaction of the peninsula.

I expect conditions to become a little more favorable for organization over the next 36-48hrs, coinciding with Alberto's emergence into open water. When analyzing/forecasting tropical weather I prefer to assess water temperatures after I make an initial analysis & diagnosis of the storm itself using satellite imagery, radar, etc. (This is always preceded by the usual analysis and diagnosis of the atmosphere at-large) This is just the way I prefer to do it because, for one, it's fairly easy to analyze by simply looking at buoy obs and maybe some remote sensing data to fill in the gaps, but also the release of latent heat that occurs in tropical/subtropical storms over warm water is essentially the "fuel" that they use to survive & thrive.

Recent buoy observations, along with NOAA-19 and GOES satellite-derived data to fill in gaps where observations don't exist (errors occur due to cloud cover, etc) show SST's across the GofM in the 26C-28C range with a corridor of warmer water through the central Gulf and relatively cooler water eastward toward Florida. Some slight warming is possible with air temps potentially reaching 30ºC+, this could support a 1-2ºC increase. You generally want to see SST's of 27C+ to support tropical development, although like anything else in meteorology these values are just rough guidelines. The track of the storm will be key because it will determine if Alberto can hang out over the warmer open water or if it will be influenced by slightly cooler water near Florida. Our subtropical storm is currently parked in between two ridges with one to its West over Mexico and another off the East coast of Florida and these will be big players in steering Alberto as he drifts generally northward. The general motion should be to shoot the gap between these ridges, so to speak.

 Windsat satellite-derived wind fields. Errors can occur because this technology isn't perfect but areas of 30kts+ are evident.

Special "Nighttime Visible" satellite imagery from the NPP VIIRS satellite via the Naval Research Lab. Note the broad area of enhanced convection near the Yucatan peninsula.

Satellite-derived 6hr precipitation totals. Retrieved from the Naval Research Lab NexSat Program.

The above image shows the 700-850mb streamlines and is a good proxy for the steering layer of 1000mb-1010mb tropical cyclones. It seems reasonable that the Bermuda high will shift slightly eastward while Alberto drifts northward. I am not going to take a stab at landfall or anything yet and please forgive me for not explaining EVERYTHING that affects a tropical cyclone's track, like trochoidal motions, beta effects due to vorticity, and other factors like the Coriolis force, but the likely track seems to be through the central Gulf, although an embedded synoptic trough across the southern CONUS may draw the storm toward it, as often happens, so that is a variable worth monitoring. Either way, at this point I'm tentatively watching somewhere from the Florida panhandle to Louisiana. Heavy rainfall, strong winds, and dangerous rip tides will be likely along the West coast of Florida and the southern Alabama, Mississippi, and perhaps Louisiana coasts.

Now that I have a rough area for this thing to go let's look at how it may evolve. Wind shear has been relatively strong across the region, which has been part of the reason it was slow to organize, however it is expected to weaken somewhat. Honestly, the wind shear is probably going to be the main inhibiting factor going forward. We should see further intensification but I think the regional shear will be enough to mitigate a more intense storm. There will still be impacts and I don't think it's wise to write off any storm but it's just to say that I think this is one environmental influence that will prevent a more robust threat. 

I also assessed upper-level divergence and lower-level convergence. These factors tie in together and are related to mass-removal within the column of the cyclone. Continued removal of mass within the storm will result in pressure falls and I believe we will see a slow deepening/intensification. I'm not convinced we'll even see a sub 1000mb low yet but there appears to be enough ventilation to help sustain the cyclone as it moves northward to the CONUS.

Graph depicting output from 21 different numerical models suggesting possible trends in overall wind shear across the Gulf of Mexico in the coming days.

GFS output for wind shear over the next 30hrs. It does show a weakening of shear aloft but it's still painting a corridor of flow resulting in 30-40kts of deep-layer shear in some areas. I like to see roughly < 30kts to feel confident in increasing potential of a stronger tropical storm. This is not the "be all, end all" and as I said earlier, these guideline values are simply bases to refer to. Assigning any rigid, arbitrary "limits" to the fluid processes of which we're dealing with can and will get you in trouble at some point as nature doesn't recognize our thresholds. 

Another factor to consider is the possibility of tropical cyclone induced tornadoes. The SPC hasn't been able to delineate an areal risk for tornadoes associated with Alberto yet because of the variability in the track but I anticipate they will eventually. Tropical cyclones are often able to produce embedded tornadoes, particularly in the northeast quadrant. In the simplest terms, this results from favorable wind fields, especially in the low-levels where southeasterly flow and surface friction often enhances the probability for circulations to develop. You can usually identify enhanced hodograph curvature and favorable wind profiles in this region. This is something I've assessed when I've chased hurricanes/tropical storms in the past and it is currently the area I'm leaning most toward trying to identify and targeting for my chase this weekend. My initial target looks to be in the region of the extreme southeast Louisiana coast to the western tip of the Florida panhandle but that may change.

The GFS (and other guidance as well) picks up on this increased low-level shear and is painting an area of pretty high storm-relative helicity values (500+m^2/s^2 0-3km) in southern Mississippi. This isn't to show exactly where I think the greatest tornado potential will be but is just to demonstrate the enhanced low-level shear that often occurs in tropical cyclones.

So before we compare the model guidance with what I've put together here, let's summarize. I'm thinking our subtropical storm Alberto will finish crossing the Yucatan Peninsula of Mexico before emerging over open Gulf water at which point he'll drift northward, undergoing a slow deepening as he does. Some wobble is possible given mesoscale eccentricities and a nearby synoptic trough but overall it looks like a generally northward track. Heavy rainfall, flooding, gusty winds, and dangerous rip tides are likely this weekend along Florida's West coast and by late weekend/Memorial Day along the southern Gulf coast. Once making landfall it is uncertain how quickly Alberto, eventually an extratropical low, will phase with the mean westerly flow but heavy rainfall/thunderstorms will be possible across the southeast CONUS into the Tennessee Valley. 

"Spaghetti Plot" of numerous forecast models showing simulated tracks of our cyclone. It seems that some of the models are picking up on the tendency for tropical cyclones to be drawn toward synoptic troughs, which is producing decent clustering of tracks supporting my forecast, however, there is still considerable spread with just as many models diverging from that track too. There are several outliers which need to be noted as well. Remember, the trend is your friend! If the models are trending toward a certain outcome then there is always a reason why and it should be investigated further. That said, a solid conceptual model needs to exist and a forecast should ALWAYS come from detailed analysis, diagnosis, and prognosis with model data being used to help guide us along *after* we've already made our own assessments ofhow the atmosphere will evolve over space and time.   

Deterministic model guidance from the GFS and even the NAVGEM. These are only isolated model graphics but they are a good proxy for the forecast I've come up with because they have "Alberto" taking a slight northwest jog before landfall and that's the way I'm leaning. I don't think this is going to be such a strong storm that it shows a lot of "deviant motion" so it seems it will be even more susceptible to mid-tropospheric flow and features. Like I mentioned earlier, given the tendency for these cyclones to be "drawn in" toward synoptic troughs I am anticipating that the trough to its northwest will influence its track. There's also a tendency for tropical cyclones to propagate toward areas where they are producing maximum latent heat release and that could play a role in this outcome too.

Above is the GFS output for total QPF through Tuesday evening (7pm CT). This is just to show the potential for flooding in many locations because widespread heavy rain is likely regardless of how "Alberto" evolves, although areas that see a more direct hit will of course see higher precip totals. After landfall the remnant extratropical-low will likely still be responsible for rainfall across the TN Valley but I didn't go past 102hrs because, 1: a passing frontal system begins to influence QPF totals in the output and I haven't assessed this system much yet so I don't want to lend any credence to it until I have, and 2: after 96hrs I start questioning the legitimacy of the GFS even more than usual because it starts to show the effects of mounting uncertainty stemming from each previous forecast hour (related to "chaos theory")

That will do it for tonight, I'll post updates throughout the weekend because at this point we're in the monitoring stage. It's going to be all about tracking in real-time as "Alberto" emerges over the open Gulf, plus we'll have more Air Force recon data to work with so that'll help. I said several days ago that this system could flirt with category 1 hurricane strength, and even though confidence is higher that it maintains tropical storm intensity, I still think there's an outside chance that it can if it manages to stay over the central Gulf where the longer residence time over warmer water may compensate for the influence of shear. Regardless of what anybody calls it, do not ignore this storm if you're in any if the threatened zones. There will be flooding risks, strong wind gusts, and dangerous ocean currents. Simply monitor official sources for information, assess your situation, and be smart. I'll get into the upcoming severe risk in the northern plains and upper Mississippi River Valley with tomorrow's post.
Stay cool folks, the next adventure is right around the corner.
DKK

Chase Forecast: Sunday 20 May 2018

  Man ole man, what a tricky forecast for the next several hours. This is going to be a fairly brief post today so I apologize if it lacks the usual detail you're accustomed to reading on this blog. I'm currently sitting here in my office awaiting storm development later this afternoon so I don't have too long to type this but we'll look at some of what we're working with. This is NOT a banner chase day as there just isn't too much that's favorable for organized severe weather but it's a local setup so I'm going to take a chance on some "mesoscale magic". Uncertainty is also extremely high for today and the model guidance has no run-to-run or model-to-model consistency either so there isn't much ability to even fall back on the models as a last resort to reign things in. All is not lost though and I think we can still develop a reasonable forecast based on what we do have so let's get to it.

Starting with a quick look aloft we can see that upper-air support is weak today. Higher heights/ridging are in place over the Ohio Valley/Great Lakes with an upper-low upstream over Nebraska and a convectively-aided shortwave over Oklahoma. A core of 30-40kt 500mb W/SW flow is over northern Indiana/Ohio/, central Illinois, and back into Missouri. This isn't particularly strong but it's sufficient to help with some degree of updraft organization. I think the better deep-layer shear is going to be displaced to the North of the moist sector but there could be some overlap in southern Indiana/Iliinois and particularly in the Missouri bootheel where colder temps aloft (-10 to -12C) will steepen lapse rates a bit more.

A complicated surface scenario will be a key player this afternoon. A weak, 1016mb surface-low is centered over northern Missouri with a slow/stalled front extending eastward through Illinois/Indiana and a cold front extending southward through Oklahoma. The moist sector is characterized by mid 60's dew points spreading into central Illinois/Indiana and upper 60's-low 70's into Arkansas and PWAT of 1.5"-1.7" through central Missouri. An army of outflow boundaries are also evident after a combination of radar, satellite, and surface obs analysis. This is a huge complicating factor as they are difficult to identify in some cases. There is one that is particularly noticeable in southern Illinois/Indiana tracking SE into the Owensboro, KY area and another in SE Missouri tracking SE. This air mass is currently convectively overturned and strongly capped. A plume of marginal, but "good enough" mid-level lapse rates (6.5-7C/km) are spreading across the area and some destabilization of the boundary-layer is destabilizing somewhat. RAP derived MLCAPE suggests 1000j/kg throughout the moist sector with an axis of 2000-3000j/kg (may be a little aggressive) over eastern Arkansas.

I have to quickly hit on target areas and hazards and then I have to go so forgive the rapid ending. Convective initiation may seem "random" in some cases (it's not actually "random" but may appear that way). It's difficult to anticipate where initiation will occur for sure but I have identified a few areas where it seems most likely and where the environment is more conducive for sustained convection, perhaps severe weather.

We'll most likely see continued elevated showers and storms due across the upper Ohio Valley due to isentropic ascent North of the surface front. I expect we'll see scattered storm initiation along various outflow boundaries throughout the day and that will be more favorably timed with peak diurnal heating to support some stronger storms.

I had intended on targeting southern Indiana but given the extent of overturning of the air mass in that area I have decided to target western Kentucky. The SPC has been maintaining that the Illinois/Indiana is more supportive, and perhaps they're right given better shear, but I'm not so sure initiation occurs there and I feel better across western Kentucky where more unstable air is surging into the area and capping is weaker/weakening. The current position and motion of two more evident outflow boundaries also leads me to believe these are more predictable areas of storm development. Hazards will be marginally severe hail and damaging winds. Tornado risk is low today so I'm not expecting much in that regard, but these situations with intersecting boundaries and terrain influences can cause localized rotation and if an updraft is able to ingest that vorticity and redistribute it to the surface then there becomes an outside chance at brief circulations/non-mesocyclonic tornadoes. Weak storm-relative mid-level flow suggests that a messy, multicell storm mode is most likely. The organization/consolidation of cold pools is another question mark as this could result in continued updraft development and growth into linear/bowing segments.

All in all I'm not expecting a big day but I'll be in western Kentucky seeing what happens. I still think that's the most likely area, along with western Tennessee, to see strong storms so we'll see how the outlooks address this in the next 6-8hrs.