2018-03-04 EVENT: OK/KS

[Dan Robinson]

A nice negatively-tilted shortwave trough will spread strongly diffluent flow aloft over a dryline in the central Plains on Sunday afternoon and evening as a narrow tongue of moisture in the form of mid to upper 50s dewpoints makes its way northward into central Oklahoma and Kansas. Lapse rates could be better, but are adequate enough.

The negative is mainly the meager moisture and a strong capping inversion shown between 700-850mb. NAM shows no precip through 00z (end of its range at the time of this post), while the GFS is not breaking anything out until after 03z. Also, surface winds are not shown backing much, even after the LLJ starts kicking in at sunset.

This looks like a couple of photogenic supercells after dark (should be nice for nighttime lightning) from near Wichita down to OKC. I don't see this as a worthy opportunity for a long haul chase, but that could change if the moisture situation improves.

 

[Jeff Duda]

Hoooeee, are there some differences between our two favorite models! One says there's just enough moisture & instability to squeeze out a tornado if storm mode cooperates, while the other one says "better luck next time". Looks like major differences in how each model is handling the PBL evolution is a likely culprit. One seems to mix out just ahead of the dryline whereas the other one keeps the moisture in close to the boundary. The NAM's forecast doesn't seem to make as much sense, however, so at least as of now I would tend to favor the GFS solution.

Definitely could be an excellent first chase for southern Plains chasers - a good one to warm up your gear and strategies on.

 

[Quincy Vagell]

If this was a month later in the season, we'd probably be looking at a notable, if not significant severe weather event.

The shear will almost undoubtably be there, as models generally agree on clockwise-curved, enlarging hodographs late Sunday afternoon and evening. LCLs should remain well below 1000m and at least marginal instability is expected be realized, especially south of the KS/OK border. The dryline should surge eastward into the theta-e axis, perhaps faster than some model progs, while the system looks favorable, synoptically, as well.

However, one major issue is the warm sector. The models keep considerable cloudiness around, limiting the quality and size of the warm sector.

Only a narrow area around the southwestern Oklahoma vicinity is progged to have both favorable low level moisture, along with at least a possibility of convective temperatures being approached.

The issue is that even within NAM range (taken with a large grain of salt this far out), only a very tiny area (1-3 counties) comes within a couple of degrees of convective temperatures. The 00z NAM also shows no convection along the dryline. Widespread >75% cloud cover across areas east of the dryline in Oklahoma limits maximum surface temperatures to the mid-60s, generally, immediately ahead of the dryline. Given the forecast mid-level "warmth," we're going to need surface temperatures at least 5F warmer to overcome the capping inversion.

Synoptically, Sunday is actually quite similar to 2/28/12, however, the warm sector this weekend is significantly smaller and in return, much less impressive.

If we had a deeper trough, a la 2/23/07, better forcing and mid-level cooling would result in substantially greater certainty of convective initiation along the dryline.

Even the evolution of the surface low is not entirely clear. The 12z ECMWF shows a 995mb low up near I-80 in central Nebraska at 00z Mon, while the operational NAM still shows a focused low over western Kansas at the same time. The 00z GFS was somewhere between, while the 21z SREF shows substantial variability, ranging from an OP NAM solution to a more elongated low over the mid-Missouri Valley/Siouxland. It should be noted that the 00z GFS has improved the low levels thermodynamics enough to hint at convection along the dryline in western Oklahoma and even parts of Kansas.

Once we get into higher resolution model range and the operational models have some time to converge on a solution, then confidence may increase in severe prospects. Right now, the severe threat appears fairly conditional and perhaps less exciting than one would expect for such a scenario in early March. The ongoing drought and cloud cover issues east of the dryline don't help matters either.

Synoptics: Check
Shear: Check
Instability: Good enough, given the shear
Capping: A glaring issue given limited surface heating
Convective initiation: Highly conditional

Regardless of the exact placement, a 995mb low in the central Plains in April would generally result in a regional severe weather episode. March is a different story, especially early in the month, where a drought is ongoing and low level thermodynamic profiles already look fairly meager.

 

[Brandon Centeno]

An otherwise awesome looking setup looks to be extremely limited by:

1) Cloud cover. The warm sector cannot adequately destabilize due to widespread cloud cover. Recent frontal intrusion and resultant modifying airmass leads to widespread cloud cover. With perhaps only glancing influence of the ejecting trough, the primary source of lift would be the dry line circulation itself. With a muted density gradient owing to the presence of cloud cover east of the dry line, we are possibly talking about a weakened dry line circulation.

2) There's a sliver of clearing along/just ahead of the dry line according to a few models (NAM3k, GFS). NAM 3k offers up a dry line bulge, suggesting enhanced synoptic/mesoscale lift in this area, and enhanced shear. Even so, the area looks capped. The stronger dynamics being confined to the north could very well keep us from seeing anything farther south due to a dearth of mid-level cooling.

The moisture is actually not that bad, with upper 50s and even some 60s progged to creep in. It seems to be cloud cover and an inability to cool the base of the EML that will do this one in.

 

[Jeff Duda]

The GFS has some pretty slim lapse rates regardless of any cloud cover or surface thermodynamics. The NAM has better mid-level lapse rates, but part of that is due to the presence of the cap and the shallower PBL.

Even if clouds turn out not to be a huge issue, this event does not appear to have outbreak potential.

 

[Royce Sheibal]

For those of you located way too far north for things to logically happen this time of year, I present my thoughts.

Looking at the EURO: a narrow line of up to 1k SBCAPE likely to spread up into E NE and W IA after dark. GFS isn't too far off, and with surface TD's near 50 with 0-1km shear of 40+kts, I think we might have ourselves a late night mini-supercell hail scenario. There will likely be a bond-chillingly cold surface inversion preventing anything serious from happening, but considering that I had nickel-sized hail from a thunderstorm/freezing rain event last month at 22F surface temps, anything seems possible. The totally nuts vort max pushing in from the west will only boost the hail threat between 03 and 06z for most of the Mo-Valley area, so a few borderline severe to severe size hail storms are possible. Reminds me of a similar setup in early April a few years back that did significant damage to roofs and cars with unusual cold-surface storms that dropped 1.5" hail for a sustained period in SW Omaha.

So no chasing for the northerners, but we might need to get our snow shovels out again.

 

[Quincy Vagell]

Even the "best" parameter space on the 00z 3km NAM across the eastern Texas panhandle (dryline bulge) shows convective temperatures in the 75-80F range with almost no shot at coming close to reaching those values. Lapse rates in the sfc-800mb layer are ugly, while the overall kinematic profile looks quite favorable and elevated instability is not lacking. Cloud-cover and time of year will likely result in a non-event.

I'm still not entirely writing this event off, as it falls on a weekend and it's the first event that the least bit interesting, locally, but I wouldn't hold my breath.

 

[Brandon Centeno]

GFS continues to look mildly interesting, with perhaps its most potent runs yet. NAM and 3km NAM do not push the dry line far into OK, mixing out dewpoints ahead of the dry line in the E TX PH. GFS is virtually uncapped along the entire OK portion of the dry line by 21z, before building in a small inversion by 00z.

While this could certainly support robust surface-based convection, and keep storm mode relatively discrete, the warming temperatures certainly seem to indicate some degree of subsidence occurring in the mid levels. Pretty much all models, parameterized or explicit, fail to develop precip along the dry line. Some CAMs, although pretty much useless at this range, *attempt* to develop convection along the dry line but fail miserably.

Curious if there may be a subtle wave causing subsidence over W OK in the wake of the convection farther east.

 

[Drew Terril]

NAM and 3km seem to be increasing the strength of the cap, as well as drawing the dryline even further west, but not pulling the moisture further west with it. Neither show anything firing along the dryline, and the entire warm sector being socked in with cloud cover all day.

GFS, while more generous on T/Td west of US-81, and showing a nice bulge in the dryline along the Red River, also indicate cloud cover over all of the warm sector. NAM and 3km also indicate a bulge in the dryline at a similar latitude, just farther west. I suspect, that if there is any clearing during the day in the warm sector, it will be in SW Oklahoma and NW Texas; probably somewhere in the vicinity of Frederick to Altus to Vernon.

 

[Quincy Vagell]

As relatively narrow as the low-level moisture plume appears tomorrow, I did some digging and if FWD observes a 64F dew-point at 00z Mon, that would (narrowly) exceed the highest value in 65 years of data for 00z 3/5. The 18z 3km NAM progs a 64F dew, with the 18z GFS showing 63F. The average dew-point for the time of year at 00z is in the mid to upper 30s. Reference: SPC Sounding Climatology Page

There is actually fairly good confidence that 60F dew-points will be realized as far north as southwestern Oklahoma, which is not very common for this early in the season. Considering the extreme drought in place across the southern High Plains, maybe this is a good sign of things to come. I know a few others have offered analysis that suggests a winter drought does not automatically suggest a spring "severe drought." Recent rains over the past few weeks across eastern portions of the southern Plains have helped scale back drought conditions east of I-35 as well. Considering the source region for moisture in early Spring is generally the Gulf of Mexico, it won't hurt moisture trajectories if that region avoids falling back into moderate or worse drought conditions.

 

[Drew Terril]

I believe it was @Dan Robinson who provided some outstanding information regarding a lack of correlation between winter drought and a quiet spring.

After taking a look at the latest runs, everything seems to be pulling more moisture further north and, in the case of NAM and 3km, further west as well. NAM seems to be cutting back on the temperature inversion, although it still shows up strong on soundings from the 3km. I think that ultimately, cloud cover is still going to be what kills the setup, but everything else seems to be there, which is surprising this time of year.

 

[Brandon Centeno]

Latest guidance has not yet convinced me this thing is *totally* dead. Truly will have to see what cloud cover looks like in the morning hours.

SREF plumes seem to indicate *much* warmer max temps than deterministic guidance does. lots of spread still. Not entirely sure how to feel about this. Probably more likely than not that cloud cover is widespread but just have to wait and see.

 

[Quincy Vagell]

Tomorrow is just an odd looking day. The latest HRRR out to 20z is rather aggressive with warming in portions of southern Kansas, with convective temperatures being approached, but limited moisture, as dews hang in the low to mid-50s. At the same time, it also shows the area in the general vicinity of Childress with just enough heating to make it interesting. Only minimal SBCIN by the end of the run and still another hour or two of heating. Even so, that area experiences "too little, too late" and I'd stress getting too excited over cherry-picked soundings that only show a very narrow sliver of favorable parameter space. Even those areas will still need more heating to breach the capping inversion.

My gut still says that it's a no-show event. I worry that even if a few echoes do manage to flare up, the updrafts will struggle to sustain themselves, especially with downstream cool air and cloudiness over western Oklahoma. I've seen this happen before where convection manages to initiate in a narrow instability corridor, but the "cells" junk out nearly as fast as they first formed. That, and/or you'll have slop going up east of the moisture axis, near/east of I-35, also well east of greater forcing.

The bigger story will likely be the fire danger threat on the west side of the dryline.

P.S. The RGEM (mixed track record with severe setups) shows 80/60 conditions over Wilbarger County, TX at 21z with a continued faint signal of convection in far western Oklahoma.

 

[Quincy Vagell]

It's too bad forcing is weak in vicinity of the dryline. Temperatures in far southwestern Oklahoma have risen into the mid and even upper 70s with dew-points near 60. Despite very minimal capping, convergence along the dryline will likely be insufficient to cause any convection to initiate. At least the moisture return was well-modeled. Per NWS OUN, dews are in the 99th percentile for the time of year in the area. Until next time...