05/08/05 FCST: Northern/Southern/Central Plains

I have been monitoring for several GFS runs now of a potent storm system that will make its way through the Plains States during the day on Sunday.

You can see a dryline push its way eastward (by the 0Z GFS run) and compared with the day on Saturday, we will have more 60 degree or higher dewpoints to work with along a wide swath from the Gulf to the Great Lakes. The 6Z GFS from NCEP is showing a wide band of precipitation moving its way eastward through NE/KS/OK/TX. Also from the same GFS run, there are two upper level storm systems at 0Z Monday, one in western Kansas at 1004mb, and one in southwestern Minnesota at 1003mb. However, the 0Z GFS shows weaker upper level winds of 30-40 knots through much of the Plains States with the best upper level winds located into eastern Iowa and western Illinois.

Many NWS HWO's from KS/MO/OK/NE/IA mention of possible severe for Sunday. Graphic for this forecast can be found on "My Chase Forecasts" link on my signature. I'll update it when I get back from the hospital to check on the baby (still has jaundice).
 
Well - we're talking about six days out, but since Friday and Sunday seem to hold the first potential we've seen in quite a while, it won't hurt to start some conversation. Looks like some potential exists for severe across much of eastern Kansas and Oklahoma on Sunday. Nice winds appear to be setting up ahead of the developing low over MN, currently fcst at 1002mb. Something I notice, however, is the swath of cool air still pooling over eastern Kansas into Missouri at 0z Mon, left over from Friday's system ... warmth looks like it will build just ahead of the approaching boundary, further west in Kansas, but to the east the temps may be struggling in the 50-60 range. With TDs in the 60 degree range, hopefully rapid airmass recovery ahead of the frontal boundary will allow for something severe to develop. Will have to wait and see ... we have nearly a week to talk about it. :)
 
Just for talk, I have a better feeling about Sunday. It figures... another way to get in trouble with mama. :wink:

I think my wife has grown pretty used to these Mother's Days turning into chase days. I cannot recall the last Mother's Day that was chase-free.

Back on subject, I think the setup looks all too interesting for Sunday. I do believe we'll have a good opportunity of finally seeing some activity right here in the central Plains.
 
Looks like early potential target for Sunday may be shaping up in N Central TX. WAA still ongoing, bringing >65 surface td up to Red River, with 40-50kt westerly flow at 500mb. Moreover, surface map now shows a low developed over lower TX panhandle by 00z with attendant SE surface winds across central and eastern TX and fairly sharp wind shift line. Dewpoint gradients show dry line making a gallant eastward push, with a hint of a bulge ahead of surface low. CAPE - check, SRH - check, low LCL/LFC's - check, deep layer shear - half-check.

Perhaps some potential northward of this area through central OK and central KS - certainly lift present in those areas also - but surface wind fields a little less defined, and I don't particularly like the higher humidity at 700mb up there. Besides, greater precip accumulation forecast further north calls into question how discrete the convection will be.
 
Sunday will be a gameday target decision, I think outflow boundaries are gonna decide the fate of Sunday. If the main wave is a bit north, and if there is an outflow boundary or two to play with on Sunday, I wouldn't doubt to see several tornado reports. You can really infer anything this far out still, I'm going to be interested to see if SPC includes a hatched area on the Day 3.
 
The 0Z Eta is looking very interesting indeed for NC OK on Sunday. By 0Z Monday, the Eta has decent 500 mb flow (35 kts) superimposed on southeasterly surface winds in association with what looks like a mesolow on a dryline bulge. Dewpoints in this area are progged to be ~ 65, 0-3 km helicity over 400 m^2/s^2, and 0-1 km helicity of 150-200 m^2/s^2. CAPE is forecasted by the Eta to be ~2500 J/kg in the same area.

Three things stand out to me about this latest Eta run. Here they are in no particular order:

1) It's a 72 hour forecast, and the previous forecast for this time seemed to have the mesolow feature in SW OK, NW TX, underneath weaker mid-level flow, but with higher CAPE. For a weak low like this, trying to pin down a position this far out is difficult if not impossible.

2) The most favorable area is very small on this run (although the same was true on May 12th last year, and look what happened then).

3) If something like this were to actually verify, the setup would be very fine indeed, especially if there were a stronger/larger region of decent westerly mid-level flow!


EDIT: just looked at the 250 mb winds, and they are very weak, considering that the trough axis lies right over this region. This may be a negative in that the weak anvil-level flow might induce HP-like character to the storms, by not evacuating small hydrometeors far enough away from the updraft.
Dan
 
For the Northern Plains, Sunday looks similar to Saturday. System might fill slightly but I expect more moisture to work with. The best convergence looks to be from eastern SD down into eastern KS. The best low level shear looks to be in eastern SD and northeastern NE where the LLJ will have an easterly component. Downside in this area is shear looks weak above 500 mb. Better upper level winds to be found in KS and OK. Day 2 convection is a function of Day 1 activity which I suspect will be rather active making a target difficult but I like eastern SD at the moment. Will edit if needed when 12z runs are out.
 
I don't know what the NAM Model has done to Sunday, but if it verified, it made it a lot better for east central Kansas into southeastern Nebraska.

At 18Z Sunday, the NAM model is showing a wide swath of very unstable air in east central Kansas into southeastern Nebraska with SBCAPE values exceeding 3,000 J/Kg. There is an upper level system (999mb) centered in south central Nebraska at this time, and just to the immediate south and east of the system and dryline, there is a wide swath of 65+ degree dewpoints reaching as far east as Lafayette County, Missouri. Lifted Index values of -8 and lower are found throughout most of east central Kansas and into Nebraska where values may reach lower than -10. 500mb winds of 30-40 knots are found throughout eastern Kansas and into eastern Nebraska. Should this verify, we will have earlier initiation (maybe as early as Noon-1PM) for potential severe weather, but the forecast for 0Z Monday shows this action to all have died off by then. This is something that is certainly worth watching, for those who intend to be in Kansas/Nebraska during the day on Sunday.

Graphic for my opinion on risk area can be found on the "My Chase Forecasts" link below.
 
Well just got back from a two day bust so I am going to make this quick...

The latest NAM 0Z run seems to have bullseye on western and central OK tomorrow afternoon. Cape from 1500 to 2000 and some nice shear to go with it. I know SPC is having an issue with the ongoing precip in central tx but according to the latest run no major probs for OK. However, I am sure things will be different in the morning we shall see. Thats about as far as I am getting into it I tired and pissy.

Mick
 
My main concern lies with weak 500mb flow, which the 0z NAM shows to be ~20kts. Without much mid-upper level flow, I think the storms are going to have a hard time evacuating the precipitation to avoid having it fall back into the updraft... 0z NAM currently showing 0-6km shear of 20-25 kts primarily (patchy 30kts), which is really marginal for supercells. Otherwise, CAPE and helicity look pretty good in OK, particularly by 0z, with 2000-2500 CAPE and 150-350 m2/s2 0-3km SRH. I think that, given the low-level shear and instability, a brief tornado is possible, but I can't imagine that any mesocyclone will persist for long owing to the very weak deep-layer shear. I have quite a bit to do tomorrow, so I probably won't go out unless I see >40kts at 500mb....
 
Originally posted by Jeff Snyder
My main concern lies with weak 500mb flow, which the 0z NAM shows to be ~20kts. Without much mid-upper level flow, I think the storms are going to have a hard time evacuating the precipitation to avoid having it fall back into the updraft... 0z NAM currently showing 0-6km shear of 20-25 kts primarily (patchy 30kts), which is really marginal for supercells. Otherwise, CAPE and helicity look pretty good in OK, particularly by 0z, with 2000-2500 CAPE and 150-350 m2/s2 0-3km SRH. I think that, given the low-level shear and instability, a brief tornado is possible, but I can't imagine that any mesocyclone will persist for long owing to the very weak deep-layer shear. I have quite a bit to do tomorrow, so I probably won't go out unless I see >40kts at 500mb....

Just woke up from a wonderful dream I was chasing a tornadic storm that was barely moving in my home county and had tornadoed off and on for a good time. I took this as a great omen and took to the models. And what do I see? Whereas the NAM was showing only 20 knot 500mb winds at 18z the ruc has 40kt+ and more westerly at that same time across OK! Given those differences I was almost ready to pack it in knowing that OK would be socked in with clouds and rain or something, and there is a bit of cloud cover forecasted, its mostly high stuff AND its not on the dryline at that time. Not to mention the cape will be 2500+ if things verify all up and down the dryline and it looks like our sleeper day in the making may be happening.

But on a PS note, this is coming from a chaser that is not going to be able to chase in his home state of Oklahoma for TWO weeks due to Senior crap in HS, so I'm trying to find every reason possible to go tommorow, but man, compared to the ETA, there are some big differences right now compared to the RUC

Here's one optimistic chaser for tommorow, but I'm not chasing unless there's something big brewing tommorow, as I DO have a couple of papers to write.
 
LATEST NAM MOVES DRYLINE A BIT FARTHER E
THAN PREVIOUS RUN...TO JUST W OF A PNC-OKC-SPS LINE AT 00Z. RUNS
HAVE BEEN CONSISTENT IN LAUNCHING CONVECTION ALONG AND JUST E OF
DRYLINE AROUND 21Z. SIMILARITIES TO SCENARIO 2 YEARS AGO TODAY -
WHEN AN F4 TRACKED THROUGH MOORE AND SE OKC - ARE ALMOST SPOOKY.

Ok, I forgot about this being the two year anniversary, and with my dream AND with the 06z nam going the same route at the RUC, I sure hope that here at 4:50am, I'm not about to wake up and realize I was just dreaming. This looks amazingly too good to be true, but if those mid 60+ tds get all the way up here, which depends on those storms south of the Red River, I'm gonna be going tommorow regardless of location. But all in all, this leaves me good enough reason to be moderately excited about tommorow, as OUN AFD goes on to mention the possibility of a higher end event if things come together just right AND the storms to the south don't inhibit moisture return, but hey, our luck here in the S. Plains has to turn around to an event actually being better than advertised sometime.
 
Originally posted by Jeff Snyder
My main concern lies with weak 500mb flow, which the 0z NAM shows to be ~20kts. Without much mid-upper level flow, I think the storms are going to have a hard time evacuating the precipitation to avoid having it fall back into the updraft... 0z NAM currently showing 0-6km shear of 20-25 kts primarily (patchy 30kts), which is really marginal for supercells. Otherwise, CAPE and helicity look pretty good in OK, particularly by 0z, with 2000-2500 CAPE and 150-350 m2/s2 0-3km SRH. I think that, given the low-level shear and instability, a brief tornado is possible, but I can't imagine that any mesocyclone will persist for long owing to the very weak deep-layer shear. I have quite a bit to do tomorrow, so I probably won't go out unless I see >40kts at 500mb....

Regarding OK...

The latest RUC is showing 300-400 0-3km SRH developing WSW of OKC by 0z, with 2500-3000 j/kg CAPE as well. From current SPC mesoanalysis, it appears that the NAM CAPE forecast magnitudes (3000-3500) may verify a bit better, but I also don't like its helicity forecast (not meshing with reality), so I suppose I can't really take it's CAPE forecast. Regardless, CAPEs in the 2500-3000 will be likely and there may be signficant low-level shear, so brief tornadoes remain possible / likely in my mind. Tds >63 are finally nearing OUN, and winds are backed to the SSE west of OUN. Actually, current OK mesonet showing very odd surface wind field, with winds out south of Altus from the SE, but SW to the east of there (strong sfc diffluence). Winds are SE in NE OK, but Tds remain only near 60F. With decently strong SW or SSW to the west of a Blackwell to Altus line, I'd think that the dry air would mix rather rapidly eastward with time. I'm hoping that winds to the south of OUN will turn to southeast a bit more to draw in the >63-65 Tds in southeastern and east-central OK currently. TCU/CU developing along the dryline down in western TX, but with full insolation across much of southcentral/central OK ahead of the dryline, I'd expect destabilization to occur rather rapidly (hopefully not mixing out the better Tds though).

Unfortunately, 500mb flow remains forecast to be 20kts by 0z... With such weak flow in the mid-upper levels, I agree that supercell structures will be relatively brief. That said, given the instability and low-level shear (should the RUC solution verify), I do see a couple/few brief tornadoes possible across the OK portion of the risk area. I may meander to the southwest of OKC in a couple of hours if it appears that this situation will unfold as I hope (though I really hope we'll see a magical increase in 500mb to 50kts)...
 
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