Topic: First SVR in tornado alley next weekend 23-25 Feb 2007

[VORTEX]

Hi to all...This is Jim at the east edge of USA's Tornado Alley...Latest model runs are coming together for a negatively tilted system to come though the Midwest Friday into Sunday...Pretty dynamic system..The current SPC guidance has not noted this system as of now....

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On a different note...Go to this website...http://www.interwarn.com/ and download the trial versions of Interwarn and StormLab...I use it when we have a SKYWARN net so that I can pass critical WX info to our mobile intercept spotters and stations across the network...These programs can be downloaded and tried for free...the free trail period is 2 weeks so choose your free download wisely...Since most of you guys are in NZ/AU I thought it would be fun for you guys to get real time warnings and access to the NWS Doppler data suite during a SVR event...HAVE FUN!!!...Also several NWS offices have provided web access to NOAA weather radio for your listening pleasure...Several TV stations go "WALL TO WALL" when there is an active tornado warning or severe WX event in their area and offer free streaming video via the Web..Cheers Jim 

[Jimmy Deguara]

Welcome Jim,

I would not mind some updates as to the potential for tornadoes of this season and the region it may affect. It has been a disastrous start to 2007 with several tornado related deaths.

Time to do some practice forecasting for the upcoming season.

Regards,

Jimmy Deguara

[VORTEX]

Happy Monday...looks like the SPC has picked up on the Possible SVR threat for the coming weekend in the U.S. midwest (http://www.spc.noaa.gov/products/exper/day4-8/)...Most of the local Forecast offices are "SELLING" the SVR threat in their forecast discussions...Here's a snippet of the last AFD for my home forecast office( note this is for the Thursday-Sunday period)......All the best Jim

PRETTY EARLY TO DISCUSS TOO MANY DETAILS REGARDING THIS SYSTEM AND
ITS IMPACTS ON OUR AREA. HAVING SAID THAT THUNDERSTORMS ARE
CERTAINLY JUSTIFIED IN THE GRIDS AND IF THIS WERE A MONTH LATER I
WOULD BE QUITE CONCERNED WITH A POTENTIAL SEVERE WEATHER EVENT.
DESPITE THE TIME OF YEAR...IF THE 12Z GFS IS ANYWHERE EVEN IN THE
BALLPARK OF REALITY THEN WE COULD STILL BE LOOKING AT A POTENTIAL
SEVERE WEATHER EVENT IN THE FRIDAY NIGHT/SATURDAY TIME FRAME. PLENTY
OF TIME FOR THINGS TO CHANGE SINCE THIS IS THE DAY 6-7 TIME FRAME
WE`RE LOOKING AT...BUT THIS IS CERTAINLY A SYSTEM THAT WILL NEED TO
BE WATCHED.
 

[David C]

I wouldnt mind spending the next 5 months over there...when will that early retirement take effect!

Anyway, I just started  peeking at storm track and noticed the usual 'what will '07' be like' thread. There are a few interesting observations there concerning the current / fairly soon to be preceding winter. The drought over the high plains has apparently eased up, the polar jet is nice and low...some comparisons to '03. Statistically, things would have to be odds on as far as bettering last year's nonsense (and wasted plane ticket that is due to expire in 4 weeks <insert 'disgusted' smiley here>).

I am interested Jimmy, have you been in touch with Gene Moore or any of the others that seem to be able to pick out early season patterns? Have there been any comments relating to the early season pattern at all, comparisons to years gone by?

[VORTEX]

Happy Tuesday...looks like the models are coming into fair agreement for a significant severe WX event Friday PM thru Sunday (Sat AM thru Mon in Au) across the eastern 2/3 of the US...Day 1 (today) has a small small Slight Risk area in eastern Arkansas into NW Mississippi...The forecast discussions from the local National Weather Service offices in the affected areas are beginning to use "enhanced wording" to describe the possible severe threat on Fri-Sun period...Attached is the text for the days 4-8 convective outlook...Rumor has it that this will rival the March 12-13 2006 Tornado Outbreak.... All the best..Jim



   DAY 4-8 CONVECTIVE OUTLOOK 
   NWS STORM PREDICTION CENTER NORMAN OK
   0351 AM CST MON FEB 19 2007
   
   VALID 221200Z - 271200Z
   
   MEDIUM RANGE MODELS ARE IN GOOD AGREEMENT CONCERNING THE DEVELOPMENT
   OF A VIGOROUS UPPER-LEVEL TROUGH OVER THE WRN U.S. EARLY IN THE
   PERIOD. AS THE LARGE UPPER-LEVEL TROUGH APPROACHES THE CNTRL U.S.
   FRIDAY...LOW-LEVEL MOISTURE WILL STREAM NWD INTO THE PLAINS AND
   OZARK REGION SETTING THE STAGE FOR A SEVERE WEATHER EVENT FRIDAY
   AFTERNOON AND FRIDAY NIGHT. A LARGE NUMBER OF STRONG THUNDERSTORMS
   WILL LIKELY DEVELOP ACROSS THE MS VALLEY ON SATURDAY AND WIDESPREAD
   SEVERE WEATHER WILL BE POSSIBLE AS THE SYSTEM MOVES INTO THE OH AND
   TN VALLEYS SATURDAY NIGHT. IN ADDITION...THERE IS A POTENTIAL FOR
   SEVERE WEATHER ACROSS NRN FL AND THE SRN PART OF THE ATLANTIC
   SEABOARD SUNDAY AS THE SYSTEM MOVES INTO THE ERN U.S.
   
   ..BROYLES.. 02/19/2007

[nzstorm]

It will be an interesting system to watch and I wonder whether it will end up being a fast moving squall line with perhaps some discrete supercells along the Gulf States.  This winter is a bit different to winter 2006 which was a lot milder.

[VORTEX]

Hi...SPC has placed most of the "HISTORIC TORNADO ALLEY" in a categorical slight risk in their latest Day 3 outlook....This should be upgraded in later outlooks....The way I see it is that supercellular storms will form along and ahead of the dryline...some may produce strong tornadoes..(As early a Friday overnight to Sat morning in NZ/AU)...Then as the cold front catches the dryline the event will change to a broken squall line with discrete supercells and LEWPS...From a climatological stand point it is 4-6 weeks too early for a system of this strength and magnitude...I along with the SPC have a tendency to "oversell" the first severe events of the year...I've wasted gallons of gas and miles of wear on my truck on forecasts just like this...I agree with nzstorm that it has been fun to watch and forecast...It may end up historic or forgotten...Stay tuned and happy Thursday...Jim

[nzstorm]

I see its a moderate risk now for western Ok, sw KS. Strong capping should lead initially to discrete supercells. Looks interesting.

[VORTEX]

Could be a fun chase day....moisture and Diurnal heating are the key now...Synoptic setup is good...hodographs are impressive....LOOKS LIKE A GOOD BUST DAY!!!Hee Hee....seriously the day looks impressive for Friday...Low topped supercells, tornadoes some might be strong....Best bet I see would be bounded by Amarillo Texas east to OKC and south to Wichita Falls....Altus Oklahoma would be right in the "BULLSEYE"...SPC has most of this area "HATCHED"....Happy friday and have a fun weekend....Jim

UPDATE!!!

Forecast Discussion
   SPC AC 230532
   
   DAY 1 CONVECTIVE OUTLOOK 
   NWS STORM PREDICTION CENTER NORMAN OK
   1132 PM CST THU FEB 22 2007
   
   VALID 231200Z - 241200Z
   
   ...THERE IS A MDT RISK OF SVR TSTMS FROM CENTRAL KS...SWD INTO NWRN
   TX...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MDT RISK FROM
   CENTRAL TX INTO SRN NEB...
   
  ...SIGNIFICANT SEVERE WEATHER EPISODE IS POSSIBLE ACROSS MUCH OF THE
   CENTRAL AND SOUTHERN PLAINS LATE FRIDAY INTO SATURDAY MORNING...
   
   A POWERFUL UPPER TROUGH IS MOVING ACROSS CA EARLY THIS MORNING.
   THIS FEATURE WILL SHIFT EAST ACROSS THE CNTRL/SRN ROCKIES LATE
   TODAY...INDUCING LEE CYCLOGENESIS OVER ERN CO/NWRN KS BY EARLY
   EVENING.  PARAMETERS APPEAR TO BE COMING TOGETHER FOR
   WIDESPREAD...POTENTIALLY SIGNIFICANT SEVERE THUNDERSTORMS ACROSS
   MUCH OF KS...OK...INTO NORTH CENTRAL TX AHEAD OF ADVANCING COLD
   FRONT.  DAMAGING WINDS...VERY LARGE HAIL...AND TORNADOES ARE
   
 

[VORTEX]

F.Y.I..SPC thought about "PULLING THE TRIGGER" on a HIGH RISK for this period but wanted to wait on the next soundings and model run (IMO I expect a Public Severe Weather Outlook and a categorical upgrade to HIGH RISK in the next Day 1 issued)....Also looks like a similar pattern next Wednesday and Thursday...
Yum Yum...Jim

[David C]

It really is looking like a potentially significant severe episode starting across the plains Friday (today).
What are everyone's thoughts.

There are quite significant height falls with this upper trough (eg GFS, look at the H5 temperature drop through the evening!) and the windshear is potent. According to SPC helicity values will be 400-600m2s2.  This will support very intense storm scale rotation and impressive SRH values in the inflow layer are favourable for strong tornadoes. SPC concerns lay with surface dewpoints being upper 50s at best, although LCLs will still be quite low, and anticipated cloud cover --  looking at GFS 850mb RH values are 100% so there will a decent stratus deck that will limit insolation over the target area and will tend to stabilise the surface airmass....to some extent.  Either may a bit of cloud cover might not be a bad thing with a weakening cap during the day and with weak forcing along the dryline. Hopefully this will promote a favourable balance for discrete storms until well into the wee hours at which time large scale ascent associated with the upper trough will result in more widespread convection.

So, overall, I get the gut feeling Friday evening will be big.   

It is difficult to finalise a target and it will come down to surface observations and satpics tomorrow. I would be inclined to head to the eastern Texas panhandle somewhere along 83 between Wheeler and Wellington for initiation along the dryline. Moisture return may be better a bit further south, eg around Childress, and GFS hints at more clearing in the stratus there too...we'll see. Once storms develop you'd expect rapid intensification and be prepared to head into western Oklahoma during the dark hours for some significant tornadoes.


time will tell......