April 15 Severe Weather Thread

[Srain]

[Thundersnow12]

some of the fcst soundings off the RUC for nw IL/southern WI are def supportive of strong tornadoes, big time low level shear and huge looping hodographs. We stayed overnight in Topeka, on the road now and going to play it by year. Not opposed to chasing but would like to stay in IA/IL given bad terrain further north and crazy fast storm motions.

[janetjanet998]

RUC is rather interesting showing 1500-2000 CAPE from WI down ionto IL and south and HEL increasing to 500 by evening...

also always have to watch just SE the 500mb low in these situations (ie over southern MN)

there will likely be some surprises today with wind fields this strong and at least some instability..just have to pin down where

[Stebo]

...TORNADO WARNING REMAINS IN EFFECT UNTIL 1015 AM CDT FOR

NORTHEASTERN ADAIR...WESTERN WASHINGTON AND SOUTHWESTERN BENTON

COUNTIES...

AT 951 AM CDT...DOPPLER RADAR CONTINUED TO INDICATE A SEVERE

THUNDERSTORM CAPABLE OF PRODUCING A TORNADO LOCATED 6 MILES WEST OF

WESTVILLE...MOVING NORTHEAST AT 35 MPH. DAMAGE HAS BEEN REPORTED

FROM THIS STORM IN CHEROKEE COUNTY.

[wisconsinwx]

Despite the overcast, we're almost up to 70 already. If we can manage partly sunny skies for awhile, 75 and dews in the 60s should be a slam dunk, which is unstable enough for some action one would think.

[Siberian Express]

Despite the overcast, we're almost up to 70 already. If we can manage partly sunny skies for awhile, 75 and dews in the 60s should be a slam dunk, which is unstable enough for some action one would think.

looking at the vis sat, I think a dry slot will probably work its magic in the mod risk area.

[FSMweather]

New rotation trying to develop in Lincoln. Tornado damage being reported in Stilwell & Westville. Tornadoes this morning will develop quickly and be short lived.

http://www.facebook.com/pages/Garrett-Lewis-5NEWS-Weather-Guy/288279856331

[Siberian Express]

MPX estimates initiation around 2 - 3 PM

[janetjanet998]

URGENT - IMMEDIATE BROADCAST REQUESTED

TORNADO WATCH NUMBER 177

NWS STORM PREDICTION CENTER NORMAN OK

1055 AM CDT SUN APR 15 2012

THE NWS STORM PREDICTION CENTER HAS ISSUED A

TORNADO WATCH FOR PORTIONS OF

NORTHERN AND WESTERN ARKANSAS

SOUTHERN MISSOURI

EXTREME EASTERN OKLAHOMA

EFFECTIVE THIS SUNDAY MORNING AND EVENING FROM 1055 AM UNTIL 600

PM CDT.

TORNADOES...HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND

GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE

AREAS.

T

DISCUSSION...A BAND OF THUNDERSTORMS HAS BEEN PROGRESSING SLOWLY EWD

AS CELLS MOVE MORE RAPIDLY NEWD WITHIN THE BAND. SATELLITE IMAGERY

INDICATES AREAS OF THINNING CLOUDS AHEAD OF THE CONVECTION WHICH

WILL PERMIT REGIONS OF ENHANCED HEATING/DESTABILIZATION TO OCCUR

THIS AFTERNOON. LATEST WIND PROFILER AND VAD DATA EXHIBIT VERY

STRONG WINDS /50 KT OR GREATER IN THE 1-2 KM AGL LAYER/ AND

INCREASING WINDS ALOFT...RESULTING IN VERY STRONG SHEAR/SRH THAT

WILL PROMOTE EMBEDDED SUPERCELLS AND OCCASIONAL SMALL SCALE BOW

ECHOES TO DEVELOP. THE THREAT FOR DAMAGING WIND GUSTS AND TORNADOES

IS EXPECTED TO INCREASE THIS AFTERNOON.

[janetjanet998]

AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE LA CROSSE WI

1117 AM CDT SUN APR 15 2012

ATTENTION FOR LATE THIS AFTERNOON...SAY 3-4 PM...IS ON THE DRY-

LINE/PRE-FRONTAL TROUGH. ANTICIPATING CONVECTIVE INITATION ON THIS

TROUGH IN NORTHWEST IOWA INTO SOUTHWEST MINNESOTA...PERHAPS NEAR

OR JUST WEST OF I-35. THIS IS VERY WELL AGREED UPON BY THE 15.12Z

NAM/HRRR AND MANY OTHER HIGH RESOLUTION MODEL RUNS. WITH REALLY

STRONG SHEAR (0-6 KM AT 70-80 KTS...0-3 KM AT 40-50 KT)...

ANTICIPATING INITIAL CELLS TO TURN SUPERCELLULAR RAPIDLY. 0-1 KM

SHEAR RAMPS UP THROUGH THE AFTERNOON...25-30 KT AT 21Z TO 30-35 KT

AT 00Z...WHICH IS FAVORABLE FOR TORNADOES. DEPENDING ON HOW MUCH

INSTABILITY WE CAN DEVELOP...SOME OF THE TORNADOES COULD BECOME

STRONG/VIOLENT. HODOGRAPHS FAVOR RIGHT MOVING SUPERCELLS...WITH

RIGHT MOVING SUPERCELL MOTION AT 50-60 KT. SO STORMS ARE GOING TO

MOVE VERY FAST. CERTAINLY TOO THE STRONG WIND FIELDS NOTED BY THE

BULK SHEAR MEANS DAMAGING WINDS ARE HIGHLY FAVORABLE TOO BY ANY

SHOWER/STORM THAT DEVELOPS. GIVEN THE FACT THAT THE MAIN MID-LEVEL

UPPER JET IS RUNNING PRETTY MUCH THROUGH THE FORECAST AREA...THE

NORTHWEST HALF OF THE FORECAST AREA FROM CHARLES CITY TO LA CROSSE

TO WISCONSIN RAPIDS IS THE MAIN THREAT AREA.

[janetjanet998]

316

ACUS01 KWNS 151629

SWODY1

SPC AC 151627

DAY 1 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1127 AM CDT SUN APR 15 2012

VALID 151630Z - 161200Z

...THERE IS A MDT RISK OF SVR TSTMS OVER NORTH CENTRAL/NERN

IA...SOUTH CENTRAL/SERN MN...AND WRN WI...

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE UPPER MS VALLEY SWD

INTO ERN TX AND LA...

..SYNOPSIS

UPPER TROUGH OVER THE PLAINS IS FORECAST TO LIFT NEWD DURING THE

PERIOD REACHING THE UPPER MS VALLEY BY LATE TONIGHT. ASSOCIATED

SURFACE LOW OVER NERN NEB WILL MOVE TO THE NWRN IA/SWRN MN BORDER

AREA BY THIS EVENING...THEN CONTINUE NEWD ACROSS NRN WI/UPPER MI AND

SRN LAKE SUPERIOR BY 16/12Z. A WARM FRONT CURRENTLY EXTENDING FROM

THE LOW ACROSS EXTREME WRN MN AND SRN WI IS EXPECTED TO GRADUALLY

LIFT NWD...WITH INCREASING MOISTURE /SURFACE DEW POINTS IN THE LOW

60S/ SPREADING NWD INTO SERN MN AND WI. A COLD FRONT TRAILING SWD

FROM THE LOW WILL ADVANCE MORE RAPIDLY ACROSS THE UPPER AND MIDDLE

MS VALLEY TOWARD THE WRN GREAT LAKES DURING THE PERIOD...WITH THE

SRN PART OF THE FRONT STALLING ACROSS ERN AND SRN TX TONIGHT.

..UPPER MS VALLEY REGION

VISIBLE SATELLITE IMAGERY SHOWS AN AREA OF THINNING CLOUDS FROM ERN

NEB AND WRN IA INTO SRN MN...WHICH SHOULD SPREAD NEWD INTO PARTS OF

NERN IA AND CENTRAL/SRN WI THIS AFTERNOON. THIS WILL PROMOTE

DIABATIC HEATING AND...WHEN COUPLED WITH AN INCREASE IN LOW LEVEL

MOISTURE...CONTRIBUTE TO AIR MASS DESTABILIZATION WITH MLCAPE

REACHING 1000-1500 J/KG. DYNAMIC FORCING FOR LARGE SCALE ASCENT IN

ADVANCE OF THE APPROACHING UPPER TROUGH COUPLED WITH LOW LEVEL

CONVERGENCE NEAR THE SURFACE LOW AND ALONG THE FRONTAL BOUNDARIES IS

EXPECTED TO RESULT IN CONVECTIVE INITIATION DURING THE AFTERNOON.

VERY STRONG WIND FIELDS AND ASSOCIATED PRONOUNCED DEEP-LAYER AND

LOW-LEVEL SHEAR WILL SUPPORT ORGANIZED CONVECTIVE STRUCTURES

INCLUDING FAST-MOVING SUPERCELLS. LARGE HAIL...DAMAGING WIND

GUSTS...AND TORNADOES /A FEW POTENTIALLY STRONG/...WILL BE POSSIBLE

WITH THE STRONGER STORMS. THE ACTIVITY WILL SPREAD EWD/NEWD THROUGH

THE EVENING BEFORE STORMS GRADUALLY WEAKEN AFTER 03-06Z.

..MIDDLE MS VALLEY SSWWD INTO ERN TX/NWRN LA

PREFRONTAL BAND OF THUNDERSTORMS FROM SWRN MO INTO CENTRAL TX IS

EXPECTED TO MOVE EWD THIS AFTERNOON AND EVENING...WITH STORMS LIKELY

INTENSIFYING IN RESPONSE TO DIURNAL HEATING AND DESTABILIZATION

/MLCAPE REACHING 1000-2000 J PER KG/. WIND PROFILES EXHIBIT 50+ KT

FLOW BEGINNING IN THE LOWEST 1-2 KM AGL...WITH THE RESULTANT INTENSE

LOW LEVEL SHEAR/SRH AND STRONG DEEP LAYER SHEAR FAVORABLE FOR

EMBEDDED SUPERCELLS AND BOW ECHOES WITHIN THE BAND.

THERE IS POTENTIAL FOR ADDITIONAL STORMS TO DEVELOP FARTHER TO THE

NORTHEAST INTO NERN MO AND IL THIS AFTERNOON AND EVENING AS DIABATIC

HEATING AND LOW LEVEL MOISTENING RESULT IN DESTABILIZATION AND A

WEAKENING OF THE CAP. MODEL GUIDANCE INDICATES THAT THE STRONGEST

LOW LEVEL WINDS WILL TRANSLATE NNEWD INTO THE MIDDLE MS VALLEY THIS

AFTERNOON WITH LOW LEVEL AND DEEP LAYER SHEAR INCREASING WITH TIME.

THIS WILL FAVOR ORGANIZED CONVECTIVE STORMS INCLUDING POTENTIAL FOR

A FEW SUPERCELLS TO DEVELOP...WITH AN ASSOCIATED THREAT FOR DAMAGING

WIND GUSTS...LARGE HAIL...AND A FEW TORNADOES THROUGH THE EVENING

HOURS.

[thunderman]

Yeah, according to the following, discrete supercells would be big trouble tomorrow afternoon/evening...

Pretty ridiculous sounding at Eau Claire at 00z from the NAM:

Is that from wxcaster? Can you send me the link? I haven't been able to access wxcaster soundings since Friday evening from some reason.

[NaoPos]

Tax day outbreak tm? Lol first heard here!

On a more serious note, solid clearing and associated warm punch going on in the target zone:

And. Quite the gradient:

Sent from my iPad HD

[wxmeddler]

Is that from wxcaster? Can you send me the link? I haven't been able to access wxcaster soundings since Friday evening from some reason.

Thunderman:

http://www.wxcaster.com/model_skewt.htm

[Indystorm]

988 low in east central Nebraska. Highest pressure falls at present are in central/east central IA. Will the low move more east rather than progged ne? If so this places southern WI/northern IL at greater risk. Will be interesting to watch and see how things develop this afternoon. 73/60 here IMBY after morning t storms caused power to flicker.

[MN Transplant]

Tax day outbreak tm? Lol first heard here!

On a more serious note, solid clearing and associated warm punch going on in the target zone:

And. Quite the gradient:

Sent from my iPad HD

Dodge Center and Fairmont, MN sustained from the south at 31mph.

[SquatchinNY]

MN Transplant, whattime do you think supercells will initiate?

[Hoosier]

988 low in east central Nebraska.  Highest pressure falls at present are in central/east central IA.  Will the low move more east rather than progged ne?  If so this places southern WI/northern IL at greater risk.  Will be interesting to watch and see how things develop this afternoon.   73/60 here IMBY.

Gotta watch the trends with that. Quick snapshots can sometimes be misleading.

[wisconsinwx]

988 low in east central Nebraska. Highest pressure falls at present are in central/east central IA. Will the low move more east rather than progged ne? If so this places southern WI/northern IL at greater risk. Will be interesting to watch and see how things develop this afternoon. 73/60 here IMBY after morning t storms caused power to flicker.

Like this image? First model I've seen that painted a complex of storms moving into Milwaukee, especially right around sunset. Most of the other models, if they had anything at all, moved it through well after dark.

http://www.emc.ncep.noaa.gov/mmb/mpyle/spcprod/12/

[Indystorm]

Like this image? First model I've seen that painted a complex of storms moving into Milwaukee, especially right around sunset. Most of the other models, if they had anything at all, moved it through well after dark.

http://www.emc.ncep....yle/spcprod/12/

Ya, although I didn't look at that. Thanks for reminding me. I was basing my hunch on pressure fall and a nice little intense cell rapidly moving ne in the Quincy Illinois area at present.

[Hoosier]

Low level shear ramps up even more after 0z. Questions are will there be enough directional shear and also how fast will surface temps cool?

[SquatchinNY]

HRRR

[wisconsinwx]

Low level shear ramps up even more after 0z. Questions are will there be enough directional shear and also how fast will surface temps cool?

Also a big question is will we get any sunshine at all? Before we were getting peaks of sun/filtered sunshine, but it is completely overcast.

[tornadotony]

Getting real worried about nrn IL. The EMC WRF is a nightmare run for the area, and trends we're seeing seem to suggest that the threat may be higher than SPC is indicating. FYI I'm out chasing nrn IL right now.

[Hoosier]

Also a big question is will we get any sunshine at all?  Before we were getting peaks of sun/filtered sunshine, but it is completely overcast.

I assume there will at least be periods of filtered sun there. Looks like there is some better clearing out west.

[Indystorm]

STP is certainly high for nw and west central IL on ne to Chi town area 00z-3z per current RUC. Of course this is only one parameter dependent on a number of other ingredients coming together.

[MN Transplant]

MN Transplant, whattime do you think supercells will initiate?

Not a severe wx expert, but I told my brother (amateur chaser) to go find something to do in the southern burbs of the twin cities since it may still be a little wait.

[Indystorm]

Getting real worried about nrn IL. The EMC WRF is a nightmare run for the area, and trends we're seeing seem to suggest that the threat may be higher than SPC is indicating. FYI I'm out chasing nrn IL right now.

Good luck Tony, and keep us informed as always. Hope you bag a nader.

[Hoosier]

For anyone who didn't see it, Gino Izzi from LOT had a nice mesoscale update discussing the concerns:

ELEVATED RISK OF SEVERE THUNDERSTORMS EXISTS VERY LATE THIS AFTERNOON AND THROUGH THIS EVENING ACROSS THE CWA.

INTENSE SPRING CYCLONE WILL LIFT NORTHEAST INTO THE UPPER MISSISSIPPI TONIGHT. REMNANT SQUALL LINE FROM SUNDAY EVENINGS CONVECTION STRETCHES FROM CENTRAL MO SOUTHWEST INTO NE TX...WITH SOME EVIDENCE OF A CONVECTIVE OR CONVECTIVELY ENHANCED VORT OVER NORTH CENTRAL MISSOURI. CIRRUS CANOPY OVER ILLINOIS IS THINNING ALLOWING FOR SOME MODEST HEATING TO TAKE PLACE THIS AFTERNOON WHICH GIVEN THE MODERATELY STEEP LAPSE RATES IN PLACE WILL PROBABLY BE SUFFICIENT FOR MODERATE INSTABILITY TO DEVELOP. HAVE SEEN SOME DEEPEN CU AND WEAK CONVECTIVE DEVELOPMENT OVER EASTERN CWA...LIKELY DRIVEN BY THETA-E ADVECTION AND PROBABLY ROOTED ABOVE THE STILL SOMEWHAT STABLE BOUNDARY LAYER.

STRONG SOUTHERLY WINDS SHOULD CONTINUE TO SUPPLY A STEADY FEED OF NEAR 60F DEWPOINTS INTO THE AREA...WITH THE BIGGER WILDCARDS REGARDING INSTABILITY APPEARING TO BE HOW MUCH CIRRUS ASSOCIATED WITH MO VORT IS ABLE TO RETARD HEATING THIS AFTERNOON. SFC TEMPS HAVE ALREADY WARMED INTO THE LOW/MID 70S AND IT WOULD ONLY TAKE ANOTHER 5-7F OR SO TO REACH CONVECTIVE TEMPS BASED ON KDVN SOUNDING SO SEEMS REASONABLE THAT SUFFICIENT INSTABILITY WITH MLCAPE CLIMBING INTO THE 750-1250 J/KG. GIVEN THE ANTICIPATED GRADUAL DESTABILIZATION AND INCREASING LARGE SCALE ASCENT IN ADVANCE OF THE UPPER LOW...MODEL DEPICTIONS OF CONVECTION OVER MO TENDING TO DEVELOP NORTHWARD INTO NORTHERN ILLINOIS LATE THIS AFTERNOON AND INTO THE EVENING CERTAINLY SEEMS PLAUSIBLE.

DEEP LAYER SHEAR IS ALREADY STRONG (0-6KM IN EXCESS OF 60KT) BUT IS PROGGED TO STRENGTHEN EVEN FURTHER LATE THIS AFTERNOON AND EVENING AS 100KT+ MID LEVEL JET ROTATES NORTHWARD INTO THE REGION AROUND THE UPPER PERIPHERY OF THE EJECTING UPPER LOW. OF GREATER CONCERN IS THE LOW LEVEL SHEAR...WITH 60-70KT LOW LEVEL JET PROGGED TO DEVELOP BETWEEN 00Z-03Z THIS EVENING SENDING 0-1KM SRH VALUES SKYROCKETING TO IN EXCESS 400 M^2/S^2. GIVEN THE MAGNITUDE OF SHEAR...EVEN MODEST INSTABILITY WOULD BE ENOUGH TO SUPPORT SEVERE WEATHER. MOST LIKELY STORM MODE APPEARS TO BE A SQUALL LINE OR AT LEAST LINE SEGMENTS WHICH WOULD POSE A THREAT FOR DAMAGING WINDS AND POSSIBLY BRIEF QLCS TYPE SPIN UP TORNADOES. HOWEVER...STRONG ISALLOBARIC FORCING THIS EVENING SHOULD RESULT IN VERY LITTLE IF ANY DIURNAL COOLING AT SUNSET...MEANING STORMS WOULD HAVE THE POTENTIAL TO REMAIN SURFACE BASED LATER INTO THE EVENING THAN IS TYPICAL. GIVEN THE ANTICIPATED EXTREME SHEAR VALUES...SHOULD ANY DISCRETE SUPERCELLS MANAGE TO FORM THE POTENTIAL FOR A MORE SUBSTANTIAL TORNADO THREAT WOULD CERTAINLY EXISTS THIS EVENING.

IZZI

[RCNYILWX]

STP is certainly high for nw and west central IL on ne to Chi town area 00z-3z per current RUC. Of course this is only one parameter dependent on a number of other ingredients coming together.

That heightens concern if convective mode remains discrete, though with the magnitude of low level and deep layer shear this evening, a squall line or qlcs would have an enhanced tornado threat.