04/20/05 FCST: South/Central/High Plains

Okay, I'll bite on this finally. I've been watching things progress over the last couple of days on the models and things look decent at least for Wed. As far as the morning of goes, Nam and GFS are highly different right now as far as the wind fields go, but I'm gonna base this forecast off the GFS since it is the only one showing 0z for Wed.

Looks to be some morning precip around S. Oklahoma/N. Texas which will clear out by the early morning. I wouldn't expect any boundaries laid by this will be west enough to effect the show in the evening. By 0z, precip is broke out in the E. Texas Panhandle along the dryline. Capes are at ~2000 at this time from Abilene to Childress, so things will pop, but as far as tornadic activity, it looks to be limited due to poor speed sheer, but directional sheer will be good. If there is a disturbance that kicks through that is presentely undetected by the GFS, then things could get very interesting on Wed, but I just don't see it just yet. I hope I'm wrong, seeing the flatlands out west would do a soul good at this time of year.

As far as Thu goes, if things stay more isolated (unlike what's indicated right now), shear improves and capes still look like they're in the 1500-2000 range, if overnight convection puts an outflow boundary down, and we get some isolation, there could be a decent storm or two to chase in the area on Thu, but this is all a wishcast right now and its more a wait and see attitude on things right now..
I'll bite for Wednesday, as well.

The new 12Z NAM shows this day as having some good potential for severe weather. We have CAPES of 2500-3500 J/Kg in a wide swath from Altus, OK to just SW to Topeka, KS. SRH will be highest in SC/SW Kansas around Pratt, values up to 300. LI's will also be highest in this area, -8 possible in the area around Pratt, SW-ward. Td's in OK and KS are progged to be in the lower to mid 60's, with surface air temperatures around 70-80 degrees, warmer the further south. Still the thing that might kill this storm, like Tuesday's setup over northern and central Kansas is the lack of 500mb winds. Low pressure at 1004mb is centered south of Lubbock, TX. I would target Pratt, southward to Woodward, that general vicinity. I'm on baby watch, so I won't be able to head out.

Personally, for a system in the Southern Plains, I got my eyes on Friday, around OKC, SE-ward.
Well, just as nick said, CAPE, Helicity and moisture (although modified gulf air) are all going to be good. But what really concerns me is the mid level winds. 500mb winds are terrible (sw @ 20 kts). Speed shear is not going to be there however, directional shear will be okay: se at surface to sw at 700mb. High CAPE, low shear days mean chasable storms but will be HP's and will rain themselves out.
My target area would be SC KS to extreme NW OK (might as well just say Harper County, thunderstorms seem to like it there. :lol:
As far as 500 winds go, I just took a jog around the area forecast office's discussions and they all agree that the models are underplaying the winds and aren't handling the wave strengths very well. This seems to be confirmed with the wave today not being forecasted as strong as it really is..
Here is what the 12Z GFS shows for 00Z Friday 22nd April (Thursday 21st April 6PM CDT):

Didn't you mean 7pm CDT? Maybe I'm off but seems standard time 0z 6pm and daylight savings is 7pm. Standard time we are 6 hours from zulu but as we 'spring forward' we move the clock forward and so only 5 hours different then right?

As for the rest of the discussion on Mon, Tue, and Wed of this week. My biggest concern is the placement / strength of the 500mb / 300mb winds. I think that is the deal breaker or maker.
Upper level winds (500mb & 300mb) are going to be too weak to support supercells both Tuesday and Wednesday over the central plains (according to the 00Z Monday NAM).

Right now I see only two possibilities for supercells:
1) Moisture and instability become sufficient northwest of the low near the Nebraska/Kansas/Colorado border where the 300mb winds will be near 40 knots.

2) A storm is able to ride a baroclinic zone and ingest vorticity into its updraft.

Otherwise, any storms that form will quickly be undercut by their own outflow.
May be worth noting that a chance for severe storms has also developed in Northeast Colorado for Wednesday. A frontal system is expected to pass through NE Colorado on Tuesday, then retreat northward again on Wednesday actin as the focal mechanism. Low level moisture is expected to move into the area. With help from a potential Denver Cyclone, we could have some added convergence, although I think the action will fall along the northward-moving frontal system. CAPE values of 1000-1500J/kg are nosing in behind the system into NE Colorado along with a small tounge of theta-E. Some 50s TDs are also nosing in as well, which is more than sufficient for storms here in NE Colo. Good shear also appears to be forecasted for the area, so severe storms are a possibility with the potential for landspoutish type tornadoes. There's a big ol' bulls-eye of 400 3km SRH right over NE Colorado on Wednesday as well with some 50/100 1km over the same areas...

While I was hosting Kansas as my target on Wednesday, I may elected to play it closer to home Wednesday and see how NE Colorado shapes up in the forecasts over the next 24 hours.

EDIT, BTW folks, all your strong 500mb winds are sitting over Colorado as well! :wink: 35 to 40 all across Eastern and Northeastern, CO... Kansas still sitting near 20... models still won't change their minds out that way.
I am liking southcentral/southeastern NE/KS border area. NAM is showing >3500 j/kg sbCAPE just to the north of the surface front, in an area of very strong low-level shear (200-400 m2/s2 0-3km SRH) given east-northeasterly sfc winds, easterly 850mb winds, and southwesterly 700mb winds. The magnitude of low-level shear and instability would suggest a threat for tornadoes, though the relatively weak mid-level flow would argue for short-lived mesos. That said, given the easterly flow in the low-levels, the net 0-6km deep-layer shear is in the 30-35kt range, which would support supercells given the strong instability. I'd be thinking about a significant tornado risk in this area if we had strong mid-level flow. Alas, we don't, so we'll see...
Originally posted by Tony Laubach
May be worth noting that a chance for severe storms has also developed in Northeast Colorado for Wednesday.

This has held for the last two operational NAM runs, so improved confidence in this scenario coming together. Agree - this region looks the best - but potential may exist further east as well for slow moving cells tracking along the front. Edge of the stronger cap along the KS/NE border - so either this slipping further south or the boundary setting up farther north would enhance the chances for surface-based convection to develop. Deep layer shear looks good across the zone along/north of front - but better west. Upper level shear much better west, HP mode appearing more likely to the east - but with lower LCL. Shear profiles over CO look great for aesthetic storms - but high bases could preclude significant tornadic activity. Looks like it could be a decent chase day though for folks in the region. Maybe Sterling to Goodland looks best right now.

Glancing at the latest ETA runs, NE Colorado still looks pretty good. The 500mb does show the LOW over Idaho with good difluence over the NE Colorado with nice speeds over the area. The 850 winds are nice as well in terms of direction sheer over NE Colorado with winds from the SE. Flow from the southwest at 500mb over flow from the southeast at 850 not only means great directional and speed shear, but upslope as well.

Temps progged to be in the 60s and 70s across NE Colorado with a nose of 50s TDs moving in over the area as well over the SFC low. LIs in the -4 range, so definately nothing wrong with instability. CAPE values are good for the High Plains with values over 1000J/kg and approaching 1500J/kg in some areas in extreme Northeast Colorado.

3km SRH values are at least 200 all over NE Colorado with values approaching 400 over the Sterling/Julesburg areas, sweeping back along I-80 in southern Nebraska. Low level SRH at 1km is only about 50 over the Northcentral/Northeast part of the state with values climbing into the 200s over the Julesburg area in the far northeast corner of the state. Not much CINH over the area either.

As it stood right now, I'd likely head up I-76 for at least Fort Morgan, maybe even as far as Sterling on Wednesday afternoon. The ETA breaks out precip in a bulls-eye over an area from about Fort Collins eastward towards Fort Morgan. I would think the better storms would be east where the better instability and shear would be, so at 48 hours out, I would say someplace I-76 between Fort Morgan and Sterling.
One of my biggest concerns with Wednesday over NE Colorado is the temps. The FROPA on Tuesday will leave parts of NE Colorado (from south of I-70 northward) on the cool side of the front. Temps only being forecasted in the 50s and 60s could seriously hinder convective development. Also, the latest NWS Denver AFD mentions CIN as an issue in areas further east. In glancing at the 12z ETA, I see where CIN is being forecasted, but there's also a hole in NE Colorado. As you move North and East where some of the best conditions are, the CIN actually begins to increase. I guess I'm not seeing an issue with CIN over parts of NE Colorado, so I'm not overly concerned with this issue. I guess this is one of those forecasting steps; sticking to what YOU know as opposed to giving in to what NWS/SPC/ETC are saying about a situation.

Waiting on the 0z ETA run which should hopefully be in within the next 60 to 90 minutes... anxiously awaiting to see what the upcoming run holds in comparison to what's been forecasted previously.
0Z NAM shows more potential for severe weather across the eastern parts of Kansas, south of Interstate 70 during the afternoon and early evening on Wednesday. 500mb winds are picking up a little to the east in Missouri which is a good sign that severe weather is becoming possible in the area. CAPE values of up to 4000 J/Kg can be expected in an area in Kansas from Kansas City southwest to Wichita. Lifted Index values of up to -10 is expected in Franklin, Miami, Linn, and Anderson counties in Kansas. SRH remain at 100-150. Dewpoints are progged to be in the upper 60's if not nearing the 70 degree mark in the same area. I expect with some model increases in the 500mb winds, we could see some potent severe weather activity in eastern Kansas. Local chase? Maybe!

My graphic for this forecast can be found on the forecast link on my signature.
Yes, looks like severe indices Wed will be most favorable of the season thus far for KS. Besides the capital question mark of upper level winds, I have a feeling the small question mark will the lifting mechanism. In selecting target for Wed chase, choice may come down to proximity to stationary front, NE KS, or heading down to Wichita with surface trough approaching from the west?
Based on the 00Z Tuesday NAM, northeast Colorado east and southeast into southwest Nebraska/northwest Kansas looks pretty good. Orographic lift along the high plains, coupled with frontogenitic forcing should be plenty to break the cap. With 40-45 knots at 300mb, and souhteasterly 850mb winds, shear will be supportive of supercells, some tornadic.

I am concerned about the front undercutting the storms from the north, and also about the availablitly of low level moisture as far west as northcentral/northeast colorado. However, I believe the tornado risk to be fairly significant nonetheless, especially for short lived tornadoes *if* the boundary does tend to undercut the storms.
A good friend observed to me today that this system "appears to be going to hell in a handbasket". And I couldn't put it any better way. I am likely getting this boards' reputation as the most pessimistic forecaster....if I can be classed as a forecaster. Guesscaster?

Well - I'd sure LOVE to go out and chase. I could even have got off work for a reasonable amount of time (discounting the fact that I have to be in the office every morning this week at 8.30am to open up, and at least until my bosses sidle in around 10.30am). But I'm afraid I can't go out there stomping around just because I want to chase. There have to be some *realistic* opportunities, too.

The upper system is NOT playing nice - and I think the models may have at least a vague handle on it's track now, too. It's hanging way out west, filling, and will likely fart off to the east as a shadow of its former self come Friday.

Like everyone else, glancing at the CAPE signatures for 0Z Thursday makes me wonder if I am blowing the year's world-ending severe fest...

>>Image removed due to redundancy<<

But I don't - can't - chase CAPE signatures/bullseyes. It's all very well running the latest run of the models through your brain and regurgitating it on here - but that doesn't do anyone any good. I don't care if northwestern Kansas is going to have a MONSTER 4,000 CAPE come this forecat period. Why? Because forecasting the type of storms that I will drive over a state away for requires a balancing of several different ingredients.......the mystical CAPE being only one of them.

I can't conjure up an upper system for this low-level instability even if I tried - it's not there. Like I said before - it's not playing nice and I think I'm just going to have to admit to that.

I want to chase - but this system isn't it - not Tuesday, not Wednesday, not Thursday.

Also - the day we WERE eyeing-up optimistically (Thursday) appears to be hosed due to a crashing cold front, too. It's just not going to happen with this one, folks......

I have Wednesday afternoon off work as per normal, so if anything happens on the dryline down here in the southern Plains we will likely be all over it. But looking at data myself, and also reading how pessimistic SPC are in their wordage for DY1, 2 &3 - I'm not going to drive great distances for this in April.


PS - Condolencies to Ryan McGinnis about his car - nothing worse than not seeing very much out there AND causing yourself a great deal of headache and expense......sorry, Ryan.