Historic Tornado Outbreak April 27, 2011

[tornadojay]

Little Rock forecast sounding... pretty impressive parameters.

[baroclinic_instability]

The medium range guidance as of the last 2 days or so has been more suggestive of the potential for the leading day 4 wave to kick out and eject faster. The result is more amplification/deepening potential of the secondary wave day 5+. Euro suggested that yesterday and now the GFS is suggesting that potential.

[thewxmann]

The medium range guidance as of the last 2 days or so has been more suggestive of thje potential for the leading day 4 wave to kick out and eject faster. The result is more amplification/deepening potential of the secondary wave day 5+. Euro suggested to yesterday and now the GFS is now suggesting that potential.

Yep, the models have been hinting at this, overall a weaker Day 1 and stronger Day 2. It'll be interesting to see how this all evolves b/c the solns (well, the GFS one at least), as they are right now, point to WNW flow over the warm sector due to the geometry of the amplifying trough. I don't think I've ever seen that in an April setup (west of the Apps).

[baroclinic_instability]

Day 5 Euro.

[CUmet]

The medium range guidance as of the last 2 days or so has been more suggestive of the potential for the leading day 4 wave to kick out and eject faster. The result is more amplification/deepening potential of the secondary wave day 5+. Euro suggested that yesterday and now the GFS is suggesting that potential.

This is a dangerous scenario the models are suggesting, as this would probably result in a massive tornado outbreak on either/both April 26 or 27. At this point, still being 4-5 days out, this is one of the most impressive synoptic-scale setups for a tornado outbreak that I can remember in recent times.

[hm8]

Dr. Greg Forbes Tue Apr 26. Severe thunderstorms and tornado outbreak in southeast MI, OH,

east and south IN, OH, west and central PA, west and central NY, west MD,

WV, southwest and north VA, DC, TN, KY, north GA, north half AL, north and

central MS, north LA, northeast TX, AR, south MO, southeast and south-central

KS, north and east OK.

[nwohweather]

Ohio looks pretty good for this next outbreak as it will not be linear by the time it gets here but actually fire up in our backyard. I'm startin to like this one

[cyclone77]

Monday's setup looks pretty decent on the new GFS over the south half of Missouri and the southern third of Illinois. Already cleared my schedule for Monday, so I'll be heading south if things continue to look this good.

GFS sounding near the St. Louis area late Monday...

[Stebo]

DAY 3 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0228 AM CDT SAT APR 23 2011

VALID 251200Z - 261200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM ERN PORTIONS OF THE SRN

PLAINS EWD/NEWD INTO THE MID OH AND TN VALLEYS...

...SYNOPSIS...

PROGRESS OF THE LARGE-SCALE UPPER TROUGH WILL SLOW OVER THE CENTRAL

U.S. THIS PERIOD...AS ONE EMBEDDED SHORTER-WAVELENGTH TROUGH EJECTS

NEWD ACROSS THE MO VALLEY INTO THE UPPER MIDWEST/UPPER GREAT LAKES

AND A SECOND DIGS ESEWD OUT OF THE ERN PACIFIC AND INTO THE SRN

ROCKIES BY THE END OF THE PERIOD.

AT THE SURFACE...FRONTAL ZONE WHICH HAS PERSISTED FROM THE

MID-ATLANTIC REGION WSWWD INTO THE SRN PLAINS WILL REMAIN THE FOCUS

FOR SEVERE STORMS THIS PERIOD. HOWEVER...SOME NWD MOVEMENT OF THE

FRONT IS FORECAST THROUGH THE END OF THE PERIOD AS A FRONTAL WAVE

SHIFTS NEWD OUT OF THE SRN PLAINS AND INTO THE UPPER MIDWEST.

...ERN OK/NERN TX ENEWD ACROSS THE LOWER AND MID MS/TN/LOWER AND MID

OH VALLEY REGION...

RELATIVELY WIDESPREAD CONVECTION SHOULD BE ONGOING ACROSS MUCH OF

THE AREA AT THE START OF THE PERIOD...AND SHOULD INCREASE/EXPAND

THROUGH THE AFTERNOON AS AIRMASS DIURNALLY HEATS/DESTABILIZES.

WITH MODERATELY STRONG/VEERING FLOW WITH HEIGHT FORECAST ATOP THE

SURFACE WARM SECTOR...EXPECT ORGANIZED/SUPERCELL STORMS TO AGAIN

BECOME MOST INTENSE THROUGH AFTERNOON AND EVENING -- SIMILAR TO

PRIOR DAYS. ALONG WITH POTENTIAL FOR VERY LARGE HAIL...LOCALLY

DAMAGING WINDS AND A COUPLE OF TORNADOES WILL AGAIN BE POSSIBLE.

ATTM...THE FORECAST AMOUNT OF CONVECTION ONGOING THROUGH THE END OF

DAY 2 AND INTO DAY 3 RESULTS IN UNCERTAINTY WITH RESPECT TO PRECISE

LOCATION AND DEGREE OF MORE CONCENTRATED CONVECTIVE/SEVERE THREATS.

HOWEVER...THREAT APPEARS SUBSTANTIAL ENOUGH ACROSS THE ARKLATEX

REGION TO WARRANT CONTINUATION OF PROBABILITIES REFLECTIVE OF A

FAIRLY ACTIVE SEVERE THREAT.

Sounds like they wanted to go Mod but too many question marks at this junction to go mod.

[Stebo]

DAY 4-8 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0350 AM CDT SAT APR 23 2011

VALID 261200Z - 011200Z

...DISCUSSION...

SUBSTANTIAL SEVERE WEATHER POTENTIAL IS EXPECTED TO SHIFT SLOWLY EWD

ACROSS THE ERN U.S. DAYS 4-6 /TUE. 4-26 THROUGH THU. 4-28/...AS A

LARGE UPPER TROUGH PROGRESSES FROM THE CENTRAL U.S. DAY 4 ACROSS THE

MS VALLEY DAY 5...AND THEN ON EWD THROUGH DAYS 6/7. MODEL

DIFFERENCES WITH RESPECT TO TIMING OF THIS FEATURE BEGIN TO EMERGE

DAY 5...BUT BECOME INCREASINGLY PRONOUNCED THROUGH DAYS 6 AND 7 AS

THE TROUGH APPROACHES THE E COAST STATES/ERN ATLANTIC.

THE PRIMARY SEVERE THREAT DAY 4 IS PROGGED FROM E TX NEWD ACROSS THE

ARKLATEX INTO THE MID MS VALLEY...AS A SHORT-WAVE TROUGH DIGS ESEWD

INTO THIS REGION...WITHIN THE LARGER-SCALE TROUGH. UNSTABLE AIRMASS

COMBINED WITH THE ENERGETIC SHORT-WAVE FEATURE AND ASSOCIATED/STRONG

FLOW FIELD SUGGESTS WIDESPREAD SEVERE WEATHER POTENTIAL -- INCLUDING

RISKS FOR LARGE HAIL...DAMAGING WINDS...AND ISOLATED TORNADOES.

THE THREAT SHOULD SHIFT E OF THE MS VALLEY INTO THE MID

SOUTH/SOUTHEAST DAY 5...AS THE SHORT-WAVE FEATURE TAKES ON A NEUTRAL

TO EVEN NEGATIVE TILT AS IT CROSSES THIS REGION. AGAIN -- AMPLY

UNSTABLE AIRMASS COMBINED WITH THE STRENGTH OF THE UPPER SYSTEM AND

ASSOCIATED FLOW FIELD SUGGESTS WIDESPREAD SEVERE WEATHER CAN BE

EXPECTED...INCLUDING THE POTENTIAL FOR TORNADOES.

AS MODELS BEGIN DIVERGING SOMEWHAT WITH RESPECT TO TIMING AND

SMALLER-SCALE DETAILS...DEGREE OF THREAT SHIFTING ACROSS THE

APPALACHIANS LATE DAY 5 AND INTO DAY 6 BECOMES LESS CERTAIN. WHILE

SEVERE WEATHER WILL BE LIKELY WITH THE FRONT EXPECTED TO REACH THE

ATLANTIC COAST BY THE END OF THE PERIOD...WILL REFRAIN FROM

HIGHLIGHTING A THREAT AREA THIS FORECAST.

WITH THE FRONT LIKELY OFFSHORE BY THE START OF DAY 7... SEVERE

WEATHER POTENTIAL ACROSS THE U.S. APPEARS LESS

WIDESPREAD/SIGNIFICANT AND MUCH MORE UNCERTAIN THROUGH THE END OF

THE PERIOD.

[Stebo]

Some 03 SREF images

Sunday

Monday

Nothing particularly high yet but a persistent area over E OK/AR/MO region for right now.

[TimChgo9]

Forecast for us is "thunderstorms likely" for Monday and Tuesday, 70% chance both days, but the SPC doesn't have risk area near us, so I am assuming it's just going to be more heavy rain,. We cloud over on Sunday, and we look to stay that way for at least 3 days, going into Wednesday. The low looks to go right over N IL, or slightly south. It looks like some high pressure up in Canada is keeping this thing from moving farther north and putting us in the "cloudy/rainy" cycle through at least Wednesday. At least the temps will be a bit more pleasant, in the lower 60's.

All the same, this weather is getting annoying, so far it's been 3-4 or more days of clouds and rain, a day or so of sun, and then back to the same thing.

[tornadotony]

09z SREF already popping a 50 area in nrn MS at 00z Wed, 87h out...

[janetjanet998]

12z gfs

holy moly

[tornadotony]

12z gfs

holy moly

Bloodbath.

[CUmet]

This has a legitimate shot at being the outbreak of the year, and this is not hyperbole by any means. At least the areal coverage of this event will be much larger than the April 15-16 event, and frankly all of the parameters are more impressive all across the board. There's still some time for some details to change, but the models have been amazingly consistent over the past several days in showing the same general synoptic solution.

[Hoosier]

Bloodbath.

Outbreak of the century?

[tornadotony]

Outbreak of the century?

I was thinking more like millennium.

[JoMo]

Yeah, hoping for more of a south trend with that system as I think the warm front will probably be just south of here on the 12z GFS. That's nasty looking.

[VAwxman]

Not that I need to repeat what some other great severe wx posters have already mentioned here, but the setup as shown by the GFS is as alarming as any I have seen on modeling in a long time. The LLJ is well out in front of the trailing cold front, and the upper level 500 mb jet punches squarely into the warm sector as opposed to staying near / parallel to the incoming cold front. The 250 mb jet structure is also ideal, as some areas are in both the right rear quad of the departing disturbance, and the left front quad of the stronger incoming one. Also, the GFS shows capping weakening by the evening over AR into western TN, which would spell trouble given storm mode could easily be supercellular / tornadic that far ahead of the front. Will be interesting to say the least to monitor future runs and see how this trends.

[baroclinic_instability]

09z SREF already popping a 50 area in nrn MS at 00z Wed, 87h out...

Yeah that is amazing for SREF at 87 hours.

[beneficii]

Not that I need to repeat what some other great severe wx posters have already mentioned here, but the setup as shown by the GFS is as alarming as any I have seen on modeling in a long time. The LLJ is well out in front of the trailing cold front, and the upper level 500 mb jet punches squarely into the warm sector as opposed to staying near / parallel to the incoming cold front. The 250 mb jet structure is also ideal, as some areas are in both the right rear quad of the departing disturbance, and the left front quad of the stronger incoming one. Also, the GFS shows capping weakening by the evening over AR into western TN, which would spell trouble given storm mode could easily be supercellular / tornadic that far ahead of the front. Will be interesting to say the least to monitor future runs and see how this trends.

On what evening?

[VAwxman]

On what evening?

Oops. Forgot to mention the day... Was looking at Tuesday evening.

[beneficii]

Oops. Forgot to mention the day... Was looking at Tuesday evening.

Thank you. It looked to me like West Tennessee might be spared given the timing and the lack of precipitation on Tuesday evening on the 12z GFS, but it may be that there is convective precipitation that is not picked up by the model.

[TheWeatherPimp]

Obviously one of the biggest questions is how far North does the warm front and low pressure make it on Tuesday and Wednesday.

[VAwxman]

Thank you. It looked to me like West Tennessee might be spared given the timing and the lack of precipitation on Tuesday evening on the 12z GFS, but it may be that there is convective precipitation that is not picked up by the model.

Yeah I tend to ignore where model QPF is and just focus more on where the parameters look strongest. Obvioulsly 78-84 hours out, much can change though.

[baroclinic_instability]

Not that I need to repeat what some other great severe wx posters have already mentioned here, but the setup as shown by the GFS is as alarming as any I have seen on modeling in a long time. The LLJ is well out in front of the trailing cold front, and the upper level 500 mb jet punches squarely into the warm sector as opposed to staying near / parallel to the incoming cold front. The 250 mb jet structure is also ideal, as some areas are in both the right rear quad of the departing disturbance, and the left front quad of the stronger incoming one. Also, the GFS shows capping weakening by the evening over AR into western TN, which would spell trouble given storm mode could easily be supercellular / tornadic that far ahead of the front. Will be interesting to say the least to monitor future runs and see how this trends.

Euro Day 4 has a much more menacing look than the GFS as it ejects a much more E-W consolidated PV anomaly over the warm sector which would incite more vigorous lower tropospheric cyclogenesis than the GFS.

The Euro is showing the potential for positive feedback as well as by day 5 the low is bent back much farther W than the GFS. Still too far out for details--but potential threats can be considered. It is worth mentioning the globals will also not be very indicative yet of feedback potential over a deep low troposphere exhibiting very low static stability/static instability. NAM/SREF/RGEM will catch that potential much better--similar to the 14th through the 17th outbreak (but mainly to the 14th when that intense anomaly ejected over the plains and the rapid tropospheric deep intensification that followed).

Day5 850/SLP.

[Macintosh]

Now, I'm looking at the track of the low on the 12z GFS. Looks like it passes just a tad north of STL. Where can we expect the highest tornado probability?

[TheWeatherPimp]

12z Euro is very ominous with a very large and broad warm sector

[ATL_Militarypolice]

Are there free Euro maps where I can view surface dew-points/temps? I went to Plymouth State Weather Page and went to contoured model maps, but I couldn't get it to view.