Severe threat april 14, Tornado outbreak possible

[janetjanet998]

12z gfs still bombs the low. moisture return not as good as the current system but still ok

DAY 4-8 CONVECTIVE OUTLOOK CORR 1

NWS STORM PREDICTION CENTER NORMAN OK

0410 AM CDT SUN APR 10 2011

VALID 131200Z - 181200Z

CORRECTED OUTLOOK GRAPHIC...DAY 4 LABEL SHOULD BE DAY 5

THE MEDIUM RANGE MODELS BEGIN THE DAY 4 TO 8 PERIOD WITH AN

UPPER-LEVEL RIDGE IN THE ERN STATES AND AN UPPER-LEVEL TROUGH IN THE

ROCKIES WEDNESDAY MORNING/DAY 4. THE MODELS MOVE THIS UPPER-LEVEL

TROUGH EWD INTO THE MS RIVER VALLEY WEDNESDAY NIGHT WITH ANOTHER

TROUGH DEVELOPING FURTHER TO THE WEST IN THE ROCKIES. THE ECMWF AND

GFS ARE SIMILAR WITH THE SECOND UPPER-LEVEL TROUGH...MOVING THE

SYSTEM ACROSS THE GREAT PLAINS ON THURSDAY/DAY 5 BUT THE ECMWF IS

THE SLOWER SOLUTION. THIS WOULD SEEM THE MORE LIKELY SCENARIO WHICH

WOULD SUGGEST NUMEROUS THUNDERSTORMS DEVELOPING THURSDAY EVENING

ALONG THE MOIST AXIS FROM ERN OK AND ERN KS EWD INTO MO AND AR. DUE

TO THE NEGATIVELY-TILT OF THE UPPER-LEVEL TROUGH AND STRONG

LOW-LEVEL JET RESPONSE FORECAST BY THE MODELS...WILL INTRODUCE A

SEVERE THREAT AREA FOR PARTS OF THE SRN AND CNTRL PLAINS EWD INTO

THE OZARKS. A WIDESPREAD SEVERE WEATHER EVENT REMAINS POSSIBLE

ACROSS THIS AREA THURSDAY AFTERNOON AND EVENING.

ON FRIDAY/DAY

6...THE MODELS DIVERGE WITH THE ECMWF DEVELOPING AN UPPER-LEVEL LOW

OVER THE NCNTRL PLAINS AND THE GFS DEVELOPING THE LOW FURTHER EAST

IN THE UPPER MIDWEST. STRONG THUNDERSTORMS WOULD BE POSSIBLE ON THE

ERN SIDE OF THE SYSTEM ALONG A MOIST AXIS IN THE MS VALLEY. ON

SATURDAY/DAY 7...THE UPPER-LEVEL MOVES INTO THE OH VALLEY WITH THE

ECMWF SLOWER. THIS WOULD MOVE THE SEVERE THREAT SATURDAY AFTERNOON

INTO THE ERN STATES. OTHER THAN THE DAY 5 OUTLOOK AREA...CONFIDENCE

IS NOT GREAT ENOUGH TO ADD A THREAT AREA IN THE MS VALLEY OR ERN

STATES.

[KokomoWX]

Dr. Greg Forbes - FRIDAY

Numerical models differ, so the area listed here could subsequently shift a bit. As a strong surface and upper low push eastward, severe thunderstorms and isolated tornadoes in southeast IL, IN, west half OH, west and central KY, west and middle TN, north, central, and southwest GA, AL, MS, LA, west FL panhandle, upper coastal...

[Chinook]

Negatively tilted trough!

Thursday: Oklahoma/Arkansas: 50 knot shear (0-6km) and higher CAPE/moisture: Moderate Risk

Friday: Arkansas/Tennessee/Kentucky/Missouri/Indiana : 50-70 knot shear (0-6km) and higher CAPE/moisture. 0-8km shear of 80 to 100 knots could bring some highly tornadic supercells. Moderate Risk.

[Ed Lizard]

I'm not over impressed by the severe probabilties as much as the nearly perfectly stacked low in Northeast Kansas Thursday evening.

[Calderon]

Negatively tilted trough!

Thursday: Oklahoma/Arkansas: 50 knot shear (0-6km) and higher CAPE/moisture: Moderate Risk

Friday: Arkansas/Tennessee/Kentucky/Missouri/Indiana : 50-70 knot shear (0-6km) and higher CAPE/moisture. 0-8km shear of 80 to 100 knots could bring some highly tornadic supercells. Moderate Risk.

Push that back to Saturday and most people will recognize the date.

[JoMo]

I'm not over impressed by the severe probabilties as much as the nearly perfectly stacked low in Northeast Kansas Thursday evening.

Yep with a raging snowstorm on the GFS.

It'll change as the models get a better handle on it in future model runs.

[Reed Stough]

This one is coming in different than the past couple of storms and to me looks more ominious according the 06Z GFS. What is interesting is the CAPE values are very low compared to what I would expect for a system like this.

So at this point who knows until the day of the event.

[BrentO]

I won't hold my breath since it's monday, but it is mid-april so who knows

Negatively tilted trough!

Thursday: Oklahoma/Arkansas: 50 knot shear (0-6km) and higher CAPE/moisture: Moderate Risk

Friday: Arkansas/Tennessee/Kentucky/Missouri/Indiana : 50-70 knot shear (0-6km) and higher CAPE/moisture. 0-8km shear of 80 to 100 knots could bring some highly tornadic supercells. Moderate Risk.

[Chinook]

I was quite zealous with what I posted yesterday. It is true I probably should have said Illinois. It is likely that one or both days will be a slight risk.

[janetjanet998]

I think on this one we may have to worry about moisture return more then the last system..models return moisture quickly thursday but as we have seen they have been over doing it

[JoMo]

00z NAM kinda spooky for my area, thankfully it's the NAM.

[SEMIweather]

00z NAM kinda spooky for my area, thankfully it's the NAM.

Yeah the NAM definitely paints a good picture for severe weather on Thursday. You've got the low deepening 8mb on Thursday. CINH reduced to zero by late afternoon, 2000-2500 J/kg of CAPE which will definitely allow storms to form. And some backing of the surface winds and low LCLs in Eastern Oklahoma. But, like you said, it's the NAM, so I'd like to see some support from the GFS in a little bit.

[baroclinic_instability]

Last time I saw a potential setup like this was a few years ago. This is far more impressive though--and these bombing lows can be prolific producers of ugly supercells. The strongly backed wind fields in the warm sector and very strong hybrid cold front associated with a deep tropofold can be very efficient at initiating supercells through weak capping layers should they exist. I believe the event was sometime in may 2008/9 along the MO/OK border. Some of the better severe guys here can probably fill in the date better.

[baroclinic_instability]

Here is the event I was referring to. May 10th. Very similar bombing low and somewhat similar upper height config. http://www.meteo.psu.edu/~gadomski/NARR/2008/us0511j3.php

This event is far more impressive synoptically--but that event had much more warm sector instability.

[JoMo]

Last time I saw a potential setup like this was a few years ago. This is far more impressive though--and these bombing lows can be prolific producers of ugly supercells. The strongly backed wind fields in the warm sector and very strong hybrid cold front associated with a deep tropofold can be very efficient at initiating supercells through weak capping layers should they exist. I believe the event was sometime in may 2008/9 along the MO/OK border. Some of the better severe guys here can probably fill in the date better.

May 10th 2008? The day I no longer wanted to see a strong tornado after one was knocking on my door.

Springfield has a write up of it here:

http://www.crh.noaa.gov/sgf/?n=may10,2008description

And the tracks:

http://www.crh.noaa.gov/sgf/?n=may10_2008_tornadoes

[Indystorm]

Well, we were burned with the model forecasts of a possible major tornado outbreak for northern IL this past Sunday right up to the Sat. night NAM deflating expectations, so I'm in a mode to take model runs with a much heavier dose of salt this far out as a result, thank you.

[baroclinic_instability]

May 10th 2008? The day I no longer wanted to see a strong tornado after one was knocking on my door.

Springfield has a write up of it here:

http://www.crh.noaa....2008description

And the tracks:

http://www.crh.noaa...._2008_tornadoes

Yah that is the exact one--I just beat you to it after finally getting the date right The similarities are pretty freakish in a lot of ways.

I remember that one vividly since I was forecasting it.

[SEMIweather]

The GFS also comes in w/ favorable severe parameters on Thursday; not as much CAPE as the NAM but I'm fairly certain it is way underdoing surface temps in the warm sector and therefore CAPE is also underdone.

With what the models are showing and just the overall setup of a surface low deepening fairly rapidly on Thursday I'd be pretty surprised if I didn't see a 30% risk area somewhere around Eastern OK/Western AR extending northward to SE Kansas/SW Missouri tomorrow morning in the Day 3 Outlook.

[JoMo]

Yah that is the exact one--I just beat you to it after finally getting the date right The similarities are pretty freakish in a lot of ways.

I remember that one vividly since I was forecasting it.

I remember it vividly because it's the first time I've ever been scared when it came to weather.

I said at about 3:30 PM that "i have a bad feeling about this" on the old Eastern board. Then about 2 hours later an EF4 tracks just south of me.

It was weird because the dewpoints were around 52 earlier in the day and we had elevated storms move across at about 11:30 AM. This alone made me a bit uneasy because I know they laid out boundaries. Dewpoints continued to rise and were at about 66 when the tornado came through.

[Thundersnow12]

This is an interesting little setup we got for thursday..

deepening sfc low throughout the day pulling up moisture with a dryline setting up in eastern KS/eastern OK. A decent instability/theta-e axis up into the sfc low with very impressive low-level lapse rates.

A good looking jet cutting right over the dryline at 0z causing CI all along it with nice looking shear and good hodograph just north of the Joplin area.

something to watch.

[tornadotony]

The similarities to Picher are somewhat haunting, but with how rare that setup was (in terms of strength and severe weather event performance) and how bad the models have blown chunks this year, I'll believe it when I see it.

[JoMo]

Also, This was the May 10th 2008.. "what went wrong by the NWS" write up, since 21 or so people died in that tornado. Basically a lack of communication by Tulsa and Springfield. A rain-wrapped right turning tornado which saved Joplin and probably kept the death toll a lot lower than it would have been.

One of the more interesting things was 75-125 cars fleeing Picher, OK 10 mins before the tornado hit, and the NWS said they did the right thing.

Just have to scroll past the html tags and stuff.

Link to the story

[SEMIweather]

Also, This was the May 10th 2008.. "what went wrong by the NWS" write up, since 21 or so people died in that tornado. Basically a lack of communication by Tulsa and Springfield. A rain-wrapped right turning tornado which saved Joplin and probably kept the death toll a lot lower than it would have been.

One of the more interesting things was 75-125 cars fleeing Picher, OK 10 mins before the tornado hit, and the NWS said they did the right thing.

Just have to scroll past the html tags and stuff.

Link to the story

That was a very interesting article, thanks for sharing.

[brettjrob]

What's funny is I immediately thought of Picher tonight after looking at the 00z NAM, and I hadn't even come to AmWx yet. Like Tony, though, I'm just cautiously interested at this point. I wouldn't be shocked to see the system speed up by 12 hours and/or moisture return end up 5-10 F lower than forecast, either of which could all but eliminate the sig svr potential.

[JoMo]

Euro came in farther south but SPC Day 3.

[baroclinic_instability]

NAM is showing classic full self development cyclogenesis with some Shapiro-Keyser type development and a potential sting jet. NAM verbatim is mixing down 70+ knots in parts of western Colorado. I mentioned it in the winter thread too--storms like this with a potentially deep tropofold and an overall slow moving but rapidly deepening cyclone owing to the intense moist latent heat effects/self development are the NAM's bread and butter with its non-hydro package mesoscale model traits. I disagree with Brett-jrob-I don't see this potentially speeding up significantly but stalling owing to the type of cyclogenesis. Not booking anything though--and I am cautious like Brettjrob--but for different reasons. If anything the weak scenarios would potentially be more GFS like--but still ominous. NAM would be a potential significant event. These bombing lows can't be overlooked for severe threats--they almost always are more impressive than the severe parameters may suggest.

[baroclinic_instability]

SPC rarely if ever mentions the NAM in the day 3 outlooks since it is almost always useless.

FORECAST SOUNDINGS BY EARLY EVENING ACROSS ERN OK...WRN AR AND SERN KS SHOW LOOPED HODOGRAPHS WITH 0-3 KM STORM RELATIVE HELICITIES IN THE 400 TO 450 M2/S2 RANGE. THE LOW-LEVEL SHEAR SHOULD INCREASE BY EARLY EVENING AS THE LOW-LEVEL JET STRENGTHENS...SUPPORTING A TORNADO THREAT WITH THE MORE DOMINANT SUPERCELL STORMS. IN ADDITION...MODERATE INSTABILITY...STEEP MID-LEVEL LAPSE RATES AND 500 MB TEMPS OF -14 TO -16 C SHOULD BE FAVORABLE FOR LARGE HAIL. A THREAT FOR VERY LARGE HAIL...>= 2 INCHES IN DIAMETER...WILL ALSO BE POSSIBLE WITH THE BETTER ORGANIZED SUPERCELLS. THE SEVERE THREAT SHOULD EXTEND AS FAR NORTH AS KANSAS CITY WHERE THE NAM SHOWS A 995 MB SFC LOW JUST TO THE EAST OF THE UPPER-LEVEL LOW. BACKED SELY WINDS AHEAD OF THE SFC LOW AND STRONG LOW-LEVEL SHEAR SHOULD ALSO BE SUFFICIENT FOR A TORNADO THREAT IN NE KS AND WRN MO WHERE COLD TEMPS ALOFT WILL ALSO MAKE LARGE HAIL POSSIBLE AS WELL.

[janetjanet998]

SPC rarely if ever mentions the NAM in the day 3 outlooks since it is almost always useless.

FORECAST SOUNDINGS BY EARLY EVENING ACROSS ERN OK...WRN AR AND SERN KS SHOW LOOPED HODOGRAPHS WITH 0-3 KM STORM RELATIVE HELICITIES IN THE 400 TO 450 M2/S2 RANGE. THE LOW-LEVEL SHEAR SHOULD INCREASE BY EARLY EVENING AS THE LOW-LEVEL JET STRENGTHENS...SUPPORTING A TORNADO THREAT WITH THE MORE DOMINANT SUPERCELL STORMS. IN ADDITION...MODERATE INSTABILITY...STEEP MID-LEVEL LAPSE RATES AND 500 MB TEMPS OF -14 TO -16 C SHOULD BE FAVORABLE FOR LARGE HAIL. A THREAT FOR VERY LARGE HAIL...>= 2 INCHES IN DIAMETER...WILL ALSO BE POSSIBLE WITH THE BETTER ORGANIZED SUPERCELLS. THE SEVERE THREAT SHOULD EXTEND AS FAR NORTH AS KANSAS CITY WHERE THE NAM SHOWS A 995 MB SFC LOW JUST TO THE EAST OF THE UPPER-LEVEL LOW. BACKED SELY WINDS AHEAD OF THE SFC LOW AND STRONG LOW-LEVEL SHEAR SHOULD ALSO BE SUFFICIENT FOR A TORNADO THREAT IN NE KS AND WRN MO WHERE COLD TEMPS ALOFT WILL ALSO MAKE LARGE HAIL POSSIBLE AS WELL.

often in these cases when you have a bombing surface low and the 500mb low starts to close off you can get arcs of low topped supercells in a "wedge" shaped warm sector.

temps/dewpoints do not need to be that great 65/53 in some cases for starters near the low

The storms will form near the low first and then develop more south with time..there may be several spokes of them..with the first being more tornadic

I do believe SPC is hinting at just that

[SEMIweather]

The 12z NAM continues to show a favorable setup in Eastern KS and Oklahoma on Thursday.

[janetjanet998]

friday looks good too on the NAM

if fact may be a long, almost continuous event