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05/07/05 FCST:Central Plains

Well, looking at the latest GFS run (12z 4/30/05) I don’t see much to get excited about for most of the week. The large Canadian low is keeping the northern and central plains locked in with frigid northerly winds at least until midweek. Wed. we should see this system spin itself off into the North Atlantic, and southerly winds begin to return to the plains. The southerly winds should bring warm gulf air and moisture to the upper plains by Fri & Sat, with Dp’s possibly reaching 60. It appears there could be a couple of short waves pass through the central plains Wed. & Thur., but they don’t look too exciting at this time. Later in the week, the models have a neg. tilted system moving into the central / northern plains from the northwest. By Sat. morning this system could be tracking along the CO / WY border and provide an area of upper air divergence over central KS & NE, and a mid level Vort Max in ne CO. The surface low located in the corners of CO, WY, & NE should track ne during the day. At this time I don’t see much change in the wind directions from the upper levels down, except a slight backing from sw to south at the surface. This is all a long way out & could change or not develop at all.
 
I wouldn't get too excited over this one until the GFS can maintain this forecast within 120 hrs or less. There seems to be this perpetual southwest trough stuck within the 156-228 hour time frame every run for the past week. I think the GFS has been too eager to kick out these Hudson lows this season which has been making its longrange forecasts pretty useless. But, this thing can't spin up there forever so hopefully soon the GFS will be correct in spitting out a nice shortwave into the plains. I of course would like to see the current forecast pan out since it falls on a weekend.
 
Anyone else believe, as I do, that the southern jet needs to calm down in the spring before the "serious" chase season starts? I've reached that conclusion over the last couple years.
That thing has been howling all spring this year.

You can't see much change at 250mb, but run a 500mb GFS loop.
 
The 0Z and 6Z GFS from today still show this system, though now it is in extreme northern North Dakota and extreme southern Canada (I don't know what province that is located north of North Dakota). It looks rather potent, and I see some moisture finally coming up to that area, TD getting up to around 55 to 60 along the Canadian/US border. One thing that is not there for severe weather development is upper level winds (less than 30 knots at 500mb). As I see it right now, it is still too far for the GFS model which has been pretty bad at verifying items at the long range and odds are is that it will shift dramatically south, dramatically north, or weaken dramatically to like 1009mb (like last week on Friday). On the other hand, I see some good moisture building into the Southern/Central Plains, but where is the storm system for them?
 
Next Weekend

This thread may have to be expanded to include the 6th and 8th if things keep speeding up the way they have according to the GFS in the low levels. The LLJ kicks back in midweek and a very nice longwave tough is going to drape itself across the intermountain west. You've got to love May. Anybody else think it's a coincidence things start looking good right before finals week?
 
I hope this latest run is wrong because I have no desire to drive all the way from south central Tx to North Dakota / Minnesota just to start a chase. I'd maybe go there if already in say Nebraska. What I'm seeing on the GFS doesn't look too organized, and still may be a GFS error / myth. Suffice it to say IMO so far this week doesn't look too good for chasing.

As for someones comment about the need for the southern branch of the jet to settle down....I don't think that is the problem. The southern branch can help do some good stuff such as when you have split jet flow. I think the problem this year has been the timing of the surface and mid level lows compared to when the last strong cold front pushed through and jettisoned all our good moisture far into the Gulf. Too many times we have had the nice sfc and mid low with not much moisture to really crank things up. I guess a better question is why is it out of sync? Right now I'm not sure and would have to evaluate a larger map, but probably has to do with position of blocking lows / highs.

It kind of looks to me that the pattern has now changed and what you're seeing on the 7th is a sign of that; however right now I don't like what I see and I don't necessarily think that the far north ND setup is what the model is changing to. I'm thinking it may be more of a wobble as it restabilizes to a new pattern. Hopefully that new pattern, perhaps coming next week will be something like TX Panhandle, OK, KS and NE. Or, we may have a week or two of 'wobble' before something good sets up again.
 
Wow, have to disagree about the prospects on the new GFS. To me it looks very promising, with the potential to run chasers ragged for an extended period.

It seems to me that you can't take the day to day solutions literally past 120 or so, such as whether or not there's a deep surface low in exactly the right spot on the 168 hour panel. I think you have to look at the medium progs sort of like an abstract painting, where large scale synoptic trends are suggested, where low level flow screaming from the GOM on a daily basis suggests from experience what happens when midlevel westerlies carrying shortwave energy overspread a juiced airmass. Add a dash of climo which suggests that South Dakota is never the place to be the first week of May, and I think the picture becomes clearer.

To keep my post on topic, concerning the prospects on May 7th specifically, I think the Texas Panhandle looks like a strong contender for dryline storms given sufficient recovery from a primed, post high-pressure GOM. Directional shear is impressive and surface temps may actually be a little lower than normal considering the current regime, which could help reduce dewpoint depressions and storm bases in a spot already well elevated. A little early to make specific calls, so I post this mainly to comply with forum rules.
 
I have to agree with Amos on this one. It looks like a possible tx panhandle dryline day with the dryline close to the tx/nm border. The temps will be close to our below normal and the 700mb temps are up so getting through the cap is the only big issue but that will just keep the storms more isolated anyway. I see a true red box day finally for the southern plains. Now if the models will just stay consistent.
 
Jared - awesome mammatus! And they are so close to the ground as well.

As for Friday, I almost think we could have a split event with South Dakota and Western Oklahoma as the most active areas. The surface low passes on the NE/SD border at 0Z Sunday (12Z GFS) and good moisture pooling in the warm sector combined with cold air aloft (700 mb freezing isotherm is on the US-Canada border) will provide plenty of CAPE for updrafts that can get going. Speed and directional shear are there with a deep LLJ out of the SW at 30+ knots and decent 500 flow. Weak midlevel flow with big instability means HP supercells though which is no good IMO.

Oklahoma may be a different story because we have basically all the things I mentioned for NE/SD except a strong surface low. The forcing in this case will be convergence along the dryline along with significant midlevel vorticity advection in advance of a shortwave. Stronger flow at 500 mb will also allow storms to be more classic in nature. I really like the shear in this area as well and think that if the event verifies Western Oklahoma/the Texas Panhandle will see a significant outbreak.

Of course, this is all based off of the 132 hour forecast from the 12Z GFS. Things are more than likely to change with the next couple of runs.
 
I'm optimistic with the relatively decent run-to-run consistency of the GFS after this thread was created on Saturday. 5 runs later and we're still looking at a potentially active day with a progged negatively-tilted midlevel shortwave ejecting into the high plains.

This morning's GFS paints a promising picture for the Texas panhandle with excellent dynamics and such. I'm interested to see how this forecast evolves, especially once it enters the NAM's forecast period.

Of course, ask anyone in the region of interest their opinion of chasing this weekend, and they'll probably ask you to get back to them once it stops snowing.
 
I know this is waay out there and for the Plains, but Davenport's lastest discussion might open up hope here for us around this time:

ITS EARLY OF COURSE...
BUT CURRENTLY PROGGED SIGNALS ARE SUGGESTING A SET UP WITH UPPER
DYNAMICS AND INCREASING LLJ MOISTURE FEED TO PRODUCE SOME STRONG/
SIGNIFICANT STORMS IN THE MIDWEST FOR THE SECOND HALF OF THE WEEKEND
AND INTO EARLY NEXT WEEK

Temps are supposed to be returning to the 70s and possibly 80s, dewpoints so far are nice as well.
 
This system is taking shape nicely now. Good directional shear from sfc to 500mb, although fairly unidirectional from 500mb and up. However that is enough directional low level shear to get things cranking in west tx. And another thing, we might actually get some real gulf moisture to work with this system. Southerly flow seems to get moving late wed. into thurs, so will have decent moisture to work with. This will give us around 2000 J/KG Cape.

NWS forecast discussion in AMA wording seems encourageing for chasers:
AND AT THIS POINT IT
APPEARS THAT THE DRY LINE WILL SET UP IN EASTERN NM. DEEP UPPER LOW
WILL BE SWEEPING TOWARD THE PANHANDLES SATURDAY MORNING SO THE
ENVIRONMENT SHOULD BE PRIMED FOR THUNDERSTORMS.
:D :D :D

EDIT: Hmmm....snow and possible tornados in west tx...how fun!!!
 
A handful of posts have been removed from this thread due to their lack of actually FORECASTING. General comments about this system (including cheers that its happening and boos that its 30 degrees) can be thrown into a TALK thread regarding this particular date. Please remember the TARGET AREA guidlines before making a post.

Thanks,
Tony
 
:?

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
 
Bill,

I think she's talking about trajectories... Sure, we may be having southerly flow in the plains, but if the central/northern/easter Gulf is seeing northerly-northeasterly-easterly winds, then chances are, it's just continental air being recycled off the US coast, into the Gulf, and back into the plains. It can modify, yes, but it's origins are still from the dry land, so moisture depth is usually an issue. Heck, we've dealt with modified continental air all season, and it where it's gotten us... You've basically been screwed unless you chased the 40 Tds under the mid-level low in KS earlier this spring... I personally don't think we're going to have enough moisture into the plains for this FCST day, and I think the following day will be a close call as well... It looks like we finally get low-mid 60s into the Plains for Sunday, right in time for finals... Even with that, however, I don't think 63-65 Tds in the southern plains with this kind of setup is really going to yield too much, but I'm getting ahead of myself a bit...
 
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
 
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.
 
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
 
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.
 
:?

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
 
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!
 
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
 
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.
 
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.
 
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....
 
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