4/21/07 FCST: OK / KS / TX / NE

[Michael O'Keeffe]

I'm not sure why the WRF has such sucky tds across the region when we have alomst 65F tds on Friday. I'm wondering how the Tds can drop that much over the course of 24 hours. That's why I think the dewpoints are a bit underforecast and there are mid-upper 50s tds across the TX Panhandle and that along with the Caprock will be plenty for at least a tornado or two along with the amount of favorable parameters associated with the system. Like I stated earlier on the Fenruary 28 tornadoes the TDs at Iola were 54F. So anything can happen, I'm still planning on chasing this event.

 

[Jason McKittrick]

yeah, that's what i said last year! Not this time. Don't know what will happen in May. Do know that Sat has a lot of potential, even if it's not a major tor outbreak. I'll be happy with the 60 dews or 58 dews or even 55 dews. Just another detail. I won't be surprised if the lousy moisture doesn't show, but a ridge over the gulf doesn't cause me any undue concern. 24 hours of limited return on Friday looks fine to me. As Karen said, gotta be hopeful.

For everyone on the board that is waiting for the season to magically start when the calender changes to May I would like to point out a couple of things to you. Not to say there have not been any May tornadoes the last couple of year but that despite my good efforts I have not seen a one since 2004. Last year I chased 3 times during the first half of April and got some great video (3 tornadoes). This year I chased twice before April 1 and again more great video (6 tornadoes, yes on 3/28 but not in TX). My point is you need to judge each event on its own merit and not just expect great storm chasing when the calender switches to May. The last several runs of the GFS are hinting that a PNA pattern will develop during the first week of May I sure we all remember what great chase opportunities that pattern produced last May.

As for Saturday I like what I am seeing in this mornings models. Last night I was about to give up but with each new day comes new hope. The models today are trending more toward a good chaseable event.

Both the GFS and NAM have abandon the idea of a closed low jetting out of the Rockies and are now indicating a nice negative tilt open wave trough. However the devil is in the details. There is at least one major difference between the two which has a huge impact on the potential storm types and locations for this event.

The NAM is the best model in terms of a chaseble severe weather event. It ejects the trough over southeast Colorado and brings out an associated 60knt westerly 500mb jet which is juxtaposed with 30-35knt south southeasterly 850mb flow. This yields great directional and speed shear for storms across SW KS south to the South Plaines of TX to work with. Model forecast 3km and 1km SRH's of 300 m^2/s^2 and 150 m^2/s^2 respectively are present across this area along with CAPE's from 1000-2000 J/Kg. Another feature which is present in the NAM is a mid level dry intrusion which the NAM RH fields show overtaking the dryline across the South Plaines late in the day Saturday. As a result if the NAM solution were to verify we should see several supercells across west TX into SW KS late Saturday.

As far as things that could go wrong one has to do with moisture. It is true that it does not take a 70F DP to get great storms at 3500ft. However with DP's around 55 this afternoon along the TX coast will the quality of moisture return be good enough to get low 60 DP's on the cap rock. The event is still three days away that's more than enough time to transport moisture northward into KS and west TX and I am sure that evapotranspiration will also help but if the moisture does not make it onto the cap rock I fear the dynamics and moisture may not meet until sunset and that might not be such a great thing as far as chasing goes. One thing to note however is that both models are indicating low 60 DP's in Amarillo by 7PM Saturday.

The other concern stems from the GFS solution which has the trough over southeast New Mexico late Saturday with the 500mb jet moving through Guadalupe Pass. With this more southerly solution the more favorable super cell kinematics are confined to west TX south of I 40, with more and more unidirectional shear profiles as you go north through KS favoring a more linear storm mode. I suppose this solution would not be so bad for many but its a little to far away for my liking.

Since I have an opportunity to chase in the panhandle this weekend I for one will be rooting for the NAM solution.

 

[Kenny Drake]

Okay it now seems the NAM, ECMWF and GFS are in fairly good agreement with location of a 500mb open wave across the eastern sides of the Rockies centered over New Mexico by Saturday evening. I have noticed a fairly large difference in the positioning of the surface low between the NAM and GFS, the NAM having it centered over SW NE while the GFS over the western sides of the ND/SD border. The ECMWF has the surface low in relative agreement with the GFS which has just recently come into agreement with the ECMWF. Given this agreement between the GFS and ECMWF along with ECMWFs consistency in the previous couple of runs I will base my current forecast along these lines. GFS has recently decreased the surface Td's pretty much from the northern plains to the coast showing isolated pockets of 60s but mostly upper 50s. It appears the reasoning behind this relatively lax moisture return given current readings across the southern plains (upper 40s, low 50s) is the origin air mass the LLJ will be advecting being the east coast, with a quick route over the Gulf immediately along the southern coast.
Here is a map of the SST in the Gulf recorded at 1200Z today:
http://marine.rutgers.edu/mrs/show/...ico/sst/noaa/2007/img/070418.108.1205.n15.jpg

Forecast model valid 4-13 through 4-18:
http://www.opc.ncep.noaa.gov/sst/images/gmex/GMex_GoesENH.gif

The surface temperatures near and where the 850 and surface winds will be advecting are less than desired (54-65F). Normally when we have seen the gulf wide open the 850 winds were coming from the western Gulf region where SST's are shown to be in the mid 70s currently.

Maybe I'm just a natural skeptic, but I'd rather be surprised than dissapointed. Given the current surface Td forecasts of upper 50s I'm still not blowing this off. The dewpoints were in the upper 50s during the May 28th event. The main difference between the events of March 28th and the current forecasts for Saturday is the 500mb trough, based off of NWS AMA's analysis of the March 28th event that had the low much deeper and farther west. The AMA sounding at 18Z on the 28th showed a temperature of 70F, with a TD of 57F.

Bringing the forecast for Saturday into this, temperatures near Amarillo seem to be very similar (upper 60s to low 70s) so, upper 50 Tds (about a 12F spread) are definitely doable. Upper level winds will likely be slightly less than the 3-28 event. The surface low if I recall was across NE/SD area which is also relatively similar to this forecasted event. Given all of these assesments based on model output that is 3 days in advance of the forecast day in question I will not pick a target zone but a target area that would extend from central NE southwards into the TX panhandle where surface winds ahead of the dryline are out of the SE. My hope is that models trend towards more of a southerly LLJ across the Gulf. The implications of a LLJ coming out of the SE obviously lead to a much stronger convergence zone up and down the dryline, which may spell disaster for cell isolation. However, the negative side would also be a disaster if the LLJ veered too much and we ended up with SSW surface winds ahead of the dryline northwards all the way to the surface low. It appears the NAM is taking the weaker east coast ridge solution while the GFS and ECMWF are taking the stronger. If models end up overplaying the magnitude or western extent of the east coast ridge then the LLJ would likely become more favorable for deeper moisture advection and less convergence ahead of the dryline/pacific front. For deeper moisture some of the larger scale surface convergence would have to be given up.

 

[Bob Schafer]

I have to laugh a little at the posts made by folks who obviously haven't read any of the previous posts. I'm also laughing at the raging debate over Td's. I don't think I've ever seen eight pages of banter about Td's for one event before.

That said, something on-topic (gasp!):

18Z WRF run has this to offer for 00Z Sunday:

http://www.wxcaster.com/CONUS_MESO-ETA_LCL_GPH_78HR.gif

Broad area of 1000-1200m LCL's from PH's-northward. Love it or hate it. Believe it or don't.

http://grib2.com/nam/CONUS_NAM218_ATMOS_BRF_78HR.gif

You have to like that Derived Radar Reflectivity forecast, even it it does look a tad linear.

 

[Michael O'Keeffe]

I am starting to look at the South Dakota area for Saturday near the TP. Tds in the 60s and SFC temps in the 70s along with CAPE to 3000 j/kg north of I90 also the area of instability is far greater area than the panhandles. I'm quite confident that SD may be the play for Saturday.

 

[Jason A.C. Brock]

March 28 also had some interesting ineractions in the Panhandle that were not see up north. If the differential heating area hadnt occured etc. would the storms in the panhandle have been as impressive? I think so but it would be nice to find some type of an intersecting or close by boundary along with the dryline. You can never find these things till maybe even hours ahead of time. If dewpoints do recover SD may very well be the place to be near the TP. Ill chase the panhandel tho....moisture is more likey to make it at least to this point as well as storms being a little more islolated and a bit of a cap kepping them that way. Atleast initially.
Still way too far off to make any decision. All I know is unless things change dramatically ill be in the Panhadle.
Get out and chase people! I know its not May but I belive the first week of May or the first 5-10 days at least are gonna be very very quite....this week doesnt look like any massive outbreaks but it looks like one thing to me

STORMCHASING:
Storm chasing is broadly defined as the pursuit of any severe weather condition, regardless of motive. A person who chases storms is known as a stormchaser, or simply a chaser. While witnessing a tornado is the biggest objective for many chasers, many chase thunderstorms and delight in seeing cumulonimbus structure, watching a barrage of hail and lightning, and seeing what skyscapes unfold. There are also a smaller number of storm chasers who chase hurricanes.

;-)

On a side note Friday will have a isoalted sup or two.....its just amatter of finding where...NE Colorado....TO Abiliene..... It will be somewhere in there lol.

 

[Bob Schafer]

Look no further!

http://weather.cod.edu/forecast/AVN/OFFAVN/avn_usUS_500_rhum_84.gif

There ya go, everyone! There is clearly a tornado at Lakeview TX based on that anvil you see there.

 

[Jeff Snyder]

I haven't paid much attention to the models given that, until the 0z runs come in tonight, we're still looking >72 hours out. When it comes to specifics such as whether the dewpoint at AMA and DDC will be 54F, 58F, or 62F, I think we all could agree that model forecasts at >72 hours out shouldn't be taken too strictly.

My biggest concern regarding a potential significant tornado event on Saturday is moisture quality and depth. As others have noted, at the elevation of the TX and OK panhandles and western Kansas and Nebraska, lower dewpoints are expected compared to areas farther east (the dewpoint of a surface parcel will decrease naturally as the elevation increases). However, there have also been other events that have looked similar but that have not produced significant severe weather. We can debate Tds to death, but the "Td required" or "Td sufficient" to produce a particular level of severe weather will always vary from situation to situation. The depth of the moisture is important, the degree of turbulent mixing in the boundary layer is important (both by mechanical mixing by strong shear and convective mixing caused by buoyancy as insolation occurs at the surface), and the vertical virtual potential temperature profile is important, amongst many others. I've never liked the use of "magic numbers", so I won't continue any further.

Let's remember that forecasts are the opinions of others. Nobody is a perfect forecaster, nor should anyone think they are a perfect forecaster. As such, let's try to be less critical of each other. Everyone has been burned before. In addition, everyone chases for different reasons -- some chase for the sole purpose of seeing a tornado, while others chase to see any strong convection. It's a personal decision, and I don't think any motive is any more "hardcore" or is any better than another. Let's not try to make ourselves feel more "hardcore" by putting down those who may only want to chase on "big days". Live and let live, as they say.

The strong negative-tilt nature of the trough, which appears to the first such trough of the spring, argues for a very strong ageostrophic response as strong pressure falls occur downstream of the trough and vorticity maximum. The surface reflection and response to the strong disturbance aloft will seen in the backed flow east of the dryline. Depending upon the depth of the southeasterly and south-southeasterly flow, we may be able to mitigate the amount of mixing that occurs in the boundary layer, which may help keep dewpoints from dropping too much through the day (or it may at least help off-set the positive affects from advection). In actuality, I'm increasingly becoming a fan of days with SOME cirrus in the warm sector, since ci may help prevent an "overmixing" of the BL (preventing the BL from becoming too deep, which tends to reduce low-level shear as winds in a well-mixed boundary layer tend to be relatively vertically homogeneous).

With deep-layer shear on the order of 50-60kts out of the west in the OK and TX panhandles, we should see a discrete convective mode preferred (deep-layer shear vector normal to the dryline), largely aided by mid-upper level flow out of the west at the base of the trough. Model performance in the past few days has been quite good, but let's remember that we are still 72 hours before the event. Despite how things look now, we should all know that they can change quickly and unpredictably.

So again, my primary area of interest is in the OK and TX panhandle region. I'm not confiden

 

[Ray Walker]

Well I may be missing something because im no expert on reading models but from what im looking at on the lates GFS is not very promising for saturday. It shows the low to be even further north, across south dakota and not as strong. Also it shows most of the upper jet energy remaining out to the west at 18z. Also the moisture content is only proged to be in the low 50s. All this is not promissing from what im looking at. Any thoughts, is it me? Do you think this is just one of the famous GFS model bounces or is the system just starting to fizzel?

 

[Mike Hollingshead]

May as well wait on the new data that will be updating now. NAM should be out by 10pm or so and GFS should be starting to update by 10:30.

 

[Matt Hines]

No matter what...1) There will be storms...2) Some will be severe...3) There will be a few tornadoes...Bottom line...There will be a chase on Sat.

 

[Mikey Gribble]

I would agree that there will be some severe storms Matt, but I wouldn't make the statement yet that there will be tornadoes.
I like chasing a non-tornadic supercell just as much as the next guy, but I'm not going to drive 6 hours to do it. If it's within 2 hours of home that is when I consider going out without a reasonable chance of tornadoes. I have to be selective though because obviously I can't chase everything with precipitation, so I typically make my decision based on whether or not there is a decent chance of tornadoes. I still log 20,000 plus miles a year chasing, so at this time in my life that criteria is not too strict for me. I am getting all the chasing in that I want.
If I lived in the panhandle, this would be a definite chase day for me (even if dewpoints were in the low 50's). If the moisture return isn't good you still have the chance of an isolated tornado or two. I haven't paid much attention yet because of the lack of tornado potential, but if I were going to chase, as of now I would target the far northern part of the TX panhandle (not even looking at the northern half of the target).

 

[Matt Hines]

Just trying to lighten the mood a little. I do think that there will be a few tornadoes though...Heck, we had 7 yesterday in West Texas...and yes, they were landspouts, but still are "tornadoes." IF, the models continue to show the sheer they have now, I do think there will be some spin-ups.

 

[Brandon Clement]

Thank you! This is what I always say. There is so much said about seeing tornadoes...personally I'm happy to see nature's power unleashed in a variety of ways, whether it be hail or wind etc. I'm really happy to be on the Plains now in the hopes of seeing a few LP supercells sometime...those tend to be nice to photograph...even if it's just a wall cloud.

AJL

Sounds good when you live in Norman. I have the same concerns as many others on this board....dews. Yes, their have been many events that produced tornadoes with td's in the 50's. However, the tds in the 50's is not ideal, certainly not with temps forecasted to be in the mid 70's yielding a big spread. I know this is still a ways out and a lot could change but over the past few years models have certainly overestimated td's far more often than they have underestimated them. So before I drive 1300 miles while gas prices are creeping towards $3 a gallon I want a lot of confidence in the setups.

I do love the Tx panhandle and playing the dryline but the last thing I want to do is drive all night, spend $300 in gas, be in position by noon and then hope td's creep up all day. I have done this several times and more times than not I am looking at high blue skies by late afternoon with all the moisture mixing out or chasing after high based thunderstorms all day. Don't get me wrong, I love the structures but I don't stay up all night, drop a few hundred bucks, drive over a 1000 miles and eat junk for two days for structure.

Lets just hope the L drops back farther south and the moisture is not even a question by Friday afternoon. If that is the case then I will be there, if not, lets hope this is just the start of the season and not the end like last year.

 

[BrandonWhittington]

Lots of people are worried about the amount of moisture there will be and deep it will be able to go. As of right now at 11:00 pm, dewpoints are already reaching 50 degrees in the southern TX Panhandle....I dont know if I'm missing something that others are seeing, but moisture is the last of my worries. This year so far, tornadoes have formed when dewpoints have been in the mid 50s, and the tornadoes have been large.....Throw the dryline in the whole mess and it looks to be a very interesting day on SAT.