05/07/05 FCST:Central Plains

[Mickey Ptak]

I don't really know where all this bla bla bla is coming from about moisture return . Sure it may not be perfect as far as 70+ Td GULF moisture, but 60-65 Td are still relatively good for supercell development (I’ve seen them in less). I know it's May and they should be in the 70's but I take what I can get. It is still a ways out but I personally don’t think moisture is going to be a problem.


Over TX,OK,KS, and NE
500mb at 50 kt.
300mb at 60-80kt

With the upper air dynamics as good as they look now and 60+ Td. I will be chasing.

Mick

 

[Chris Allington]

Im liking Sunday alot more, especially for NE... We will not have any good boundaries here in Eastern NE until Sunday afternoon, assuming the models verify. The OAX AFD sums it up well...they show DP's steadily increasing to near 60 beginning Thursday night and continuing through Sunday. They also mention that instability "spikes" on Sunday afternoon, when we will have the best dynamics to work with. This weekend/ early week may be interesting for many, even with modified continential air only.

 

[Jay McCoy]

I am not that worried about the moisture in the panhandle this weekend. The fetch isnt pure guld moisture but thats not uncommon and you dont have to have upper 60Td's in west Texas to have huge storms.Mid 50's and up work quite well around here. Just makes for more LPish style storms. I like saturday more than friday. the low sets up and the dryline should sharpen. it should be very dry behind the line with westerly winds so convergence isnt an issue.

I just hope all those that are so pessimistic about this weekend will decide it isnt worth it and stay home so the roads wont be so crowded. makes for an easier chase. We will sent ya some pics :wink: j/k

 

[Mike Johnston]

Seems like what we have is a set of average to good, but certainly not overwhelming, synoptic factors aligning this weekend. On the positive side, we are looking at at least minimal threshholds in place for buoyancy, moisture, heating, low level inflow and directional shear based on a forecast which has remained pretty consistent, over good chaseable territory. At this point, it appears we will be dealing with many small question marks, but no major question marks as long as the big-picture forecast holds. Although currently forecast parameters do not obviously suggest significant tornado outbreak, what is heartening about the setup is good probabilities of supercell/severe environment along with an upside kicker should we see enhancement in any one or two factors.

Of course, it is a little discouraging to see that surface front pushing S across the gulf this week, but pretty good prospects for rate of warm air advection to make up for it. Given just forecast margin of error and climatological norms, dewpoints across the area could easily be 3-4 degrees higher than currently forecast.

If you just average out the checklist at this point, looks like W OK would be preliminary target. Again, no overwhelming parameter values and I will not recite what everyone can see, but just enough of each ingredient. Character and location of surface lifting mechanism(s) might remain somewhat of a guessing game until 12-24 hrs out, but whatever is out there on the western horizon will likely be steered through with the 500mb flow - just follow the surface moisture convergence and wind shift forecast.

BTW, I am not so excited by the northern plains setup. In particular, precipitation forecast of 0.2 to 0.4 inches in the hours leading up to Saturday makes me wary of cloud cover/daytime heating - especially so far north. I suspect this may be a case where forecast parameters that look good on paper are overwhelmed by a reversion to the climatological norm.

 

[Jim Bishop]

:?

I'm having a very hard time ascertaining where people are getting information to conclude that this coming weekend's system looks to have good Gulf moisture to work with.

The models maintain surface-HI pressure on the east coast most of this week - and by Saturday May 7th's morning this HI pressure seems settled in to stay over SC - with it's dirty big foot planted right in the gulf. This brings northeasterlies in the GoM until at least 12Z Saturday (look at MSLP on the models).

Accordingly, by the forecast period, dewpoints are struggling to reach 60oF around the Red River. IMO, this does NOT bode well for moisture - especially out west in the TX/OK Panhandles where many are alluding their targets to be.

This system may be worth chasing just because we've hardly had anything out that way to chase recently, and it might be one of the final encores for the Southern Plains' 2005 season. But I wouldn't get my hopes up, nor expect the Gulf to be "open for business" - because it's not. I don't like my fetch coming from Kentucky, personally......

It takes a helluva lot more than just plain southerly winds over the central and southern Plains to give you the true GoM moisture you're looking for......that wind can suck and suck and suck for weeks on end - but if it's origin is the east coast......you're hosed.

KR

Granted this won't be 100% true Gulf of Mexico moisture being advected over Texas. But I don't see why this is such a hinder on the setup. GFS is forecasting low 60 dpts over the Texas Panhandle and all of West Texas by 00Z Sunday. You don't need 70 degree dewpoints for a good setup, ESPECIALLY for the high plains. All you really need are 55dpts out there because of the higher elevation. Hell, 850mb dpts are forecast to be 12C, that's fine!

This does't even take into account evapotrasperation. West Texas has received rainfall for the past 2 days and it's not over yet. Shoot, Amarillo had measurable snowfall on Monday (very strange)!! Anyways, southerly winds Friday evening and all day Saturday will be plenty for quite a bit of evapotrasperation to kick those dewpoints up a few degrees.

Honestly, I think some of us are still spoiled from last year's wealth of incredible setups. This setup isn't perfect, but the thermodynamic conditions will still be supportive of severe storms.

Happy Chasing

 

[Nic Wilson]

Tonight's May 4th 00z run of the GFS looks the best yet with nice a nice veering wind profile out ahead of the dryline across Western OK and TX and progged Td's into the low 60's with high temps up around 80. The 500 mb winds aren't screaming by any means, but a nice SSW trajectory of 45 knots is seen by 7pm Saturday evening ahead of the dryline. Surface winds are 15 kt out of the SSE, but still much too far off to trust that forecast. The GFS also fails to break out dryline precip. for the same time period which should be viewed as a positive since one would hope the GFS wouldn't pick up on discrete development (e.g. supercells).

It should also be noted that the NAM is significantly slower than the GFS at 84 hours (12z Sat.) with its 500 mb jet lagging behind about 100 miles to the west. The GFS and ECMWF have had good agreement though, so I would definitely lean toward the GFS solution knowing the initialization difficulties of the NAM when trofs are still off-shore. But this should be watched in the next couple runs. Western Oklahoma better be ready for some traffic jams as every chaser and their mother will probably be out on this one!

 

[Glen Romine]

Finally starting to get some input from the NAM on this event, and GFS providing about as consistent a picture as one can hope for this far out. Appears there will be a weakening open wave trough somewhere in the central Rockies by Saturday, with a series of weak short waves radiating out over the weekend. Surface ridge forecast to remain firmly in place along the Gulf coast through early Saturday, but elevated moisture transport and pooling appears to result in a pocket of more substantial moisture in the upper plains - upper MS River valley depending on which model you look at, as well as improving moisture across the southern plains. Shear profile forecasts are weak, but probably adequate given strength of mid-level lapse rates for supercells. Where is the million dollar question, as cap strength looks sufficient to limit convection along the weakly convergent dryline without some upper support - but with perfect timing between forcing arriving at peak heating storms could be possible across a broad stretch. Otherwise, weaker cap across the northern plains/upper MS River valley could offer some storms there as well, but quality of moisture looks overdone in the models imo, and shear is marginally adequate, but at least some convection looks possible. That said, last night's ECMWF paints a potentially favorable scenario across eastern CO-western KS to split the difference. This system isn't forecast to make landfall until saturday morning, so I wouldn't focus too much on the model forecasts until then, but it appears there is at least reason to keep a watch on things.

Glen

 

[Mike Johnston]

Wow, I am a little concerned about developments appearing on the latest Eta runs. First and foremost, I asked myself the question - with obvious strong southerly flow at 850mb 00zSat to 00zSun over the plains, why aren't we seeing higher surface dewpoints in southern & central plains by 00zSun? After looking more closely, I don't think it has to do with source/quality of moisture, but rather to the alignment of the height contours with isolines at that level. Both gradients are aligned more or less SWtoNE all the way up to central IA - when the height contours are parallel with the isolines, advection is minimized. As the contours become perpendicular across northern plains, advection is maximized and, sure enough, we see pooling of higher surface dewpoints than exist hundreds of miles to the south much closer to the "source."

Second, the surface low to move over ND is now forecast to deepen over the period to 997mb by 00zSun. Although enough of a southward trough is shown to result in some backing of surface winds in NCentral TX and W OK at 12zSat, I am a little concerned that things are beginning to look too unidirectional close to the surface. Still on the plus side, an SRH pocket of 150-200 m2s2 showing over NW TX and W OK at 00zSun on the Eta run, and good directional crossover of 500mb & 850mb flow over same area.

 

[Bill Tabor]

Right now after looking at today 12z NAM it looks like this system is a bit all over the place with the primary low being far north and dryline extending all the way through SD, NE, KS, and TX. I can't make up my mind on this system but at the moment appears the primary area would be MN and perhaps eastern SD,eastern ND, possibly northeast NE, and northwest IA. CINH appears fairly strong across the southern plains and helicity seems to move eastward along with the northern area leaving the south in a bit of a lurch. However far southeastern TX panhandle does seem to have some stuff to watch.

I don't particularly like what I am seing cause even if I was in KS/NE on Fri it's still a drive up to SD/MN for Sat and that probably puts me out of position for Sunday.

Someone call the weather gods and tell them we want it further south.

 

[Jeff Snyder]

I've only briefly looked at the prospects in the TX/OK/KS area, and it looks "okay". Mid-upper level flow is sufficient, though not terribly strong, yielding "sufficient" deep-layer shear of 30-40kts (00z NAM). The crappy fact that we're YET AGAIN dealing with modified continental air is quite depressing, as the 00z NAM is showing upper-50 Tds across most of the Plains, which, when combined with temps near 80, yields very high LCLs and a limited tornado threat. Instability is in the moderate range for most of the area (2000-2500 j/kg sbCAPE), but I'm very frustrated by the fact that we can't get any real juice up here.

I mean, seriously... It'll be mid-May before we get real Gulf moisture into the Plains, and that's just plain ridiculous! We usually at least see a couple of days with upper-60 Tds in April, and at least a day or two of low-70 Tds by early May... Instead, we've dealt with meager low-60 Tds (at best), which obviously hasn't netted much of anything as far as warm-sector convection is concerned... With the high LCLs courtesy of ~20 degree T-Td deficits, combined with only "sufficient" other conditions (moderate CAPE, moderate deep-layer shear, relatively low SRH), I'm not holding out much hope for tornadoes on Saturday. The CAPE and shear do appear to be enough for supercells, though I highly doubt that, if tonight's NAM verifies, we'll see a tornado event in the area on Saturday....

 

[Ben Prusia]

Personally, I am starting to diss on the setup in the TX/OK area for Saturday. Moisture is going to be the biggest problem and the 0Z NAM only shows that area heading into the upper 50's for dewpoints. The latest 0Z GFS run doesn't show any precipitation in the area to go run-after, hopefully I am proven wrong.

Most likely, I will be following the system that will be heading in the Northern Plains states during the day Saturday. Each run of the NAM has deepend the upper level system, now dropping it to 994mb, centered in eastern South Dakota. Dewpoints will be much higher in the area of the northern Plains states, along with instability factors in place which will be better supportive of severe thunderstorm development. However, upper level winds are lacking a little compared to the favored Panhandle/W OK region, but 30-40 knot winds in the 500mb level as far north as Watertown, SD is a little encouraging. I am more tempted to follow this setup on Saturday than the setup in the southern Plains, but I will see what my chase partner for the weekend thinks about the situation.

Graphic on my opinion of risk area can be found on the My Chase Forecasts link below.

 

[Kurt Silvey]

Well Saturday appears to be shaping up with a possibility of two different areas of interest. The models have a 995 mb low setting up INVOF the Black Hills Sat. morning with a warm front extending estwrd and a cold front to the sw. a well defined dryline sets up from the Mexico to central SD. Low-level moisture should move northward through the central and eastern plains Fri. through Sunday, with a pooling in estrn SD. With upper and mid lvl winds from the w / sw and low lvl s / sw (se / s in SD) there would seam to be a lack of directional shear, but the overall consensus is that it will be enough to provide severe activity. There appears to be a central KS dryline play setting up in the afternoon, but I am leaning towards se SD. The models show a dryline punch coming through late in the afternoon ahead of the Low, with temps into the upper 70’s , Dp > 60, ML cape => 2500 and a LI of ~ 10c. Will have to take a closer look at both of these areas tomorrow.

 

[Adam Atkins]

5/7/05 W OK

Severe storm potential looks very good from the new 0z NAM. A moderately strong, diffluent shortwave will move through the S Plains later in the afternoon which should be enough to provide some synoptic scale lift and break the cap, which will be a factor the next week or so. Good, not great, low-level shear on the order of 200 m2/s2 of helicity will be sufficient for long-lived rotating storms. I'm afraid tornadic storms will be few and far between the farther south you chase due to LCL's in the stratosphere. You can't rule out an isolated storm that forms a nice RFD and sucks some cooler, buoyant air in can lower its base and put out a tornado, especially if there are outflow boundaries, which proved to be a key player on April 21 in SE KS, not to mention many, many other cases. (Breath) That's a long sentence. About time we get to chase on the pancake THAT IS western Oklahoma.

 

[Ben Prusia]

Looks like there will be two different distinct areas of severe weather that will break out during the day on Saturday.

Area 1 (SD-NE-MN): The 0Z NAM has a nice looking upper level system of 994mb centered in eastern South Dakota. Moisture should be plentiful in the area with dewpoints running into the lower 60's. Instability, however, is higher in this area than in area 2. 500mb winds, though a tad lower than area 2, still should be able to sustain severe thunderstorm and supercell development, just might be some HP situation going on in that area.

Area 2 (OK-KS): The 0Z NAM shows the dryline situation really well in western Oklahoma running into the fringes of south central Kansas. Lifted Index value of -8 will be found in this area, along with area 1, both well suited for tornadoes. Instability values will run you with a wide swath of up to 3000 J/Kg in the area, with a peak near the Oklahoma/Kansas state line around an area west of Kiowa, Kansas. Granted, we will have some nice 500mb winds in this area, in the 40-50 knot range which is much better than area 1 to try and get some LP's into the game. The northern most area of area 2 could stand the best chance for tornadoes as LCL's will be the lowest in the area, and the LCL will increase the further south.

If I had to choose right now the best area for storm development, I would choose area 2. Graphic is up in the "My Chase Forecasts" link below for this forecast.

 

[Chris C Sanner]

Haha, a funny quote from the OUN AFD:

WELCOME TO SPRINGTIME IN THE
SOUTHERN PLAINS...FINALLY.

But also another random thought from OUN:

FOR SUNDAY... CURRENT
THINKING IS THAT THERE WILL BE ENOUGH RECOVERY TIME DURING THE DAY
SUNDAY FOR MORE SVR WX SUN AFTN AND EVENING AS STORMS FIRE ALONG
DRYLINE/COLD FRONT ACROSS WESTERN OK/N TX AND THEN MARCH EAST

They do not mention Sat in this afternoon's AFD, but I'm getting mildly excited for this weekend. Right now, if we can somehow figure out a way to lower LCLs, maybe by some magic or something similar, we will be in business. I like the cape bullseye in N. Oklahoma, but greatest SRH is a bit E. of the Dryline at 0z. I'm going to be interested to see how this plays out. But weekend chase + Oklahoma + Western Section + May + Lack of anything of note in the state really = TONS OF CHASERS. I plan to join the circus this weekend, both Sat and Sun, who's in?