April 2nd - April 5th Severe Weather

[Thundersnow12]

Moving on, anyone see the GFS progs for 4/8-9? Consistency is building*, and for once the GFS doesn't even show a thermonuclear cap! (A bit curious as to why not though.)

*Even Dr. No-No, which hasn't been consistent with this system, is trending towards a more interesting soln.

I will take 192hr on the 0z GFS any day. And given its a saturday....

[Stebo]

Pretty hard to ignore. If it wasn't 2011, I'd be jumping out of my skin. As it is, I'm calmly waiting for another bait and switch to a stall-trough-along-west-coast-then-shear-out solution.

Yeah idk what it is about this year that I have been more gun-shy than normal. Hell before I'd be excited even with the current potential.

[baroclinic_instability]

Euro rolling--looks like it has a stronger southern stream. Digging the secondary through UT.

EDIT: Looks similar to the CMC I guess--which eventually looks too slow and strung out.

[Thundersnow12]

I'm quite surprised with this one..

DAY 2 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1258 AM CDT SAT APR 02 2011

VALID 031200Z - 041200Z

...THERE IS A SLGT RISK OF SVR TSTMS SUNDAY AFTERNOON AND NIGHT FROM

THE MIDWEST/LOWER OH VALLEY TO THE SRN PLAINS...

..SYNOPSIS

MODELS REMAIN IN FAIRLY GOOD AGREEMENT SHOWING A FULL LATITUDE

TROUGH AMPLIFYING/DEVELOPING INTO THE CENTRAL U.S. DURING DAY

2...WITH THE 12Z ECMWF/00Z GFS FASTER WITH EWD PROGRESSION THAN THE

WRF-NAM. BY 12Z MONDAY...A POSITIVELY-TILTED TROUGH SHOULD EXTEND

FROM THE UPPER MS VALLEY TO THE SRN HIGH PLAINS. 60-90 METER 500 MB

HEIGHT FALLS ARE EXPECTED FROM OK/KS TO IA/NRN IL DURING THE LATTER

HALF OF THE FORECAST PERIOD. SWLY MIDLEVEL WINDS WILL STRENGTHEN TO

50-60 KT FROM THE SRN ROCKIES TO THE LOWER MO VALLEY AND MIDWEST BY

SUNDAY AFTERNOON...WITH A FURTHER INCREASE SUNDAY NIGHT TO 70-90 KT

FROM THE SRN PLAINS TO LOWER OH VALLEY.

AT THE SURFACE...MODELS HAVE TRENDED NORTH WITH THE INITIAL POSITION

OF LOW PRESSURE AT 12Z SUNDAY...WITH THIS FEATURE LOCATED OVER SERN

SD. THIS LOW WILL TRACK EWD INTO NERN IA BY 04/00Z...AND THEN REACH

THE CENTRAL GREAT LAKES BY 12Z MONDAY. A TRAILING COLD FRONT WILL

ADVANCE SSEWD THROUGH THE CENTRAL AND SRN PLAINS...AND INTERSECT AND

OVERTAKE A DRY LINE FROM ERN KS THROUGH CENTRAL OK TO NRN TX FROM

SUNDAY AFTERNOON TO EARLY MONDAY MORNING. THE NRN EXTENT OF THE

COLD FRONT WILL PROCEED ESEWD THROUGH THE LOWER MO VALLEY REACHING

LOWER MI TO THE OZARKS BY THE END OF THE FORECAST PERIOD.

MEANWHILE...A WARM FRONT WILL LIFT NEWD FROM THE LOWER MO VALLEY

THROUGH THE OH VALLEY TO LOWER GREAT LAKES BY SUNDAY NIGHT.

..SRN PLAINS TO THE MIDWEST/LOWER OH VALLEY

SLY LOW LEVEL WINDS WILL MAINTAIN MOISTURE RETURN FROM THE SRN

PLAINS THROUGH THE LOWER MO TO LOWER OH VALLEY DURING DAY 2...

BENEATH A STRONG EML/CAP. THIS CAP WILL LIMIT TSTM DEVELOPMENT

THROUGH MUCH OF THE DAY...WITH MODELS SUGGESTING TSTM DEVELOPMENT

WILL BE LIKELY ALONG THE COLD FRONT AS IT ADVANCES INTO NRN/CENTRAL

IL...NRN MO AND INTERSECTS THE DRY LINE IN NERN-ERN KS MID-LATE

SUNDAY AFTERNOON. MODERATE INSTABILITY...STRENGTHENING DEEP LAYER

SHEAR AND STEEP LAPSE RATES WILL SUPPORT ORGANIZED SUPERCELLULAR

STORMS PRODUCING A FEW TORNADOES...LARGE HAIL /SOME SIGNIFICANT/ AND

DAMAGING WINDS. A SECONDARY LLJ IS EXPECTED TO INCREASE TO 45-65 KT

FROM OK TO MO/IL SUNDAY EVENING...FURTHER ENHANCING LOW LEVEL SHEAR

FOR AN INCREASED TORNADO THREAT. AS THE COLD FRONT ADVANCES SWD

OVERNIGHT...STRONG WIND FIELDS COUPLED WITH MODERATE INSTABILITY

WILL SUPPORT A SEVERE WEATHER THREAT PERSISTING WELL AFTER

DARK...ESPECIALLY ACROSS MO/NRN AR TO LOWER OH VALLEY.

UNCERTAINTY EXISTS IN THE GUIDANCE FOR WHETHER TSTMS INITIATE SWD

ALONG THE DRY LINE...S OF THE KS BORDER...THROUGH OK TO NRN TX. THE

00Z WRF-NAM/21Z ETAKF MEMBER OF THE SREF/12Z ECMWF DO NOT INITIATE

ACROSS THESE AREAS...WHILE 00Z GFS TO SOME EXTENT AND THE EACH OF

THE 21Z WRF-ARW MEMBERS OF THE SREF SUGGEST STORMS DO FORM INTO OK/N

TX SUNDAY AFTERNOON. DESPITE THESE DIFFERENCES...STEEP MIDLEVEL

LAPSE RATES /8-9 C PER KM/... MODERATE INSTABILITY AND STRENGTHENING

BULK SHEAR TO 50 KT INDICATES A SLIGHT RISK REMAINS WARRANTED WITH

SWD EXTENT. IF STORMS DEVELOP...THEN THE POTENTIAL WILL EXIST FOR

LARGE HAIL...SOME SIGNIFICANT...PRIOR TO THE COLD FRONT REACHING

THIS REGION AND PROGRESSING SWD INTO TX.

[baroclinic_instability]

Hr 72 upper level height field has potential.

[PatrickSumner]

Tell em' SPC!

[Hoosier]

I'm quite surprised with this one..

They talked up the tornado threat more than I would've thought. I'm not really surprised by the 30% hatched though.

[MoeWx]

I'm quite surprised with this one..

DAY 2 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1258 AM CDT SAT APR 02 2011

VALID 031200Z - 041200Z

...THERE IS A SLGT RISK OF SVR TSTMS SUNDAY AFTERNOON AND NIGHT FROM

THE MIDWEST/LOWER OH VALLEY TO THE SRN PLAINS...

..SYNOPSIS

MODELS REMAIN IN FAIRLY GOOD AGREEMENT SHOWING A FULL LATITUDE

TROUGH AMPLIFYING/DEVELOPING INTO THE CENTRAL U.S. DURING DAY

2...WITH THE 12Z ECMWF/00Z GFS FASTER WITH EWD PROGRESSION THAN THE

WRF-NAM. BY 12Z MONDAY...A POSITIVELY-TILTED TROUGH SHOULD EXTEND

FROM THE UPPER MS VALLEY TO THE SRN HIGH PLAINS. 60-90 METER 500 MB

HEIGHT FALLS ARE EXPECTED FROM OK/KS TO IA/NRN IL DURING THE LATTER

HALF OF THE FORECAST PERIOD. SWLY MIDLEVEL WINDS WILL STRENGTHEN TO

50-60 KT FROM THE SRN ROCKIES TO THE LOWER MO VALLEY AND MIDWEST BY

SUNDAY AFTERNOON...WITH A FURTHER INCREASE SUNDAY NIGHT TO 70-90 KT

FROM THE SRN PLAINS TO LOWER OH VALLEY.

AT THE SURFACE...MODELS HAVE TRENDED NORTH WITH THE INITIAL POSITION

OF LOW PRESSURE AT 12Z SUNDAY...WITH THIS FEATURE LOCATED OVER SERN

SD. THIS LOW WILL TRACK EWD INTO NERN IA BY 04/00Z...AND THEN REACH

THE CENTRAL GREAT LAKES BY 12Z MONDAY. A TRAILING COLD FRONT WILL

ADVANCE SSEWD THROUGH THE CENTRAL AND SRN PLAINS...AND INTERSECT AND

OVERTAKE A DRY LINE FROM ERN KS THROUGH CENTRAL OK TO NRN TX FROM

SUNDAY AFTERNOON TO EARLY MONDAY MORNING. THE NRN EXTENT OF THE

COLD FRONT WILL PROCEED ESEWD THROUGH THE LOWER MO VALLEY REACHING

LOWER MI TO THE OZARKS BY THE END OF THE FORECAST PERIOD.

MEANWHILE...A WARM FRONT WILL LIFT NEWD FROM THE LOWER MO VALLEY

THROUGH THE OH VALLEY TO LOWER GREAT LAKES BY SUNDAY NIGHT.

..SRN PLAINS TO THE MIDWEST/LOWER OH VALLEY

SLY LOW LEVEL WINDS WILL MAINTAIN MOISTURE RETURN FROM THE SRN

PLAINS THROUGH THE LOWER MO TO LOWER OH VALLEY DURING DAY 2...

BENEATH A STRONG EML/CAP. THIS CAP WILL LIMIT TSTM DEVELOPMENT

THROUGH MUCH OF THE DAY...WITH MODELS SUGGESTING TSTM DEVELOPMENT

WILL BE LIKELY ALONG THE COLD FRONT AS IT ADVANCES INTO NRN/CENTRAL

IL...NRN MO AND INTERSECTS THE DRY LINE IN NERN-ERN KS MID-LATE

SUNDAY AFTERNOON. MODERATE INSTABILITY...STRENGTHENING DEEP LAYER

SHEAR AND STEEP LAPSE RATES WILL SUPPORT ORGANIZED SUPERCELLULAR

STORMS PRODUCING A FEW TORNADOES...LARGE HAIL /SOME SIGNIFICANT/ AND

DAMAGING WINDS. A SECONDARY LLJ IS EXPECTED TO INCREASE TO 45-65 KT

FROM OK TO MO/IL SUNDAY EVENING...FURTHER ENHANCING LOW LEVEL SHEAR

FOR AN INCREASED TORNADO THREAT. AS THE COLD FRONT ADVANCES SWD

OVERNIGHT...STRONG WIND FIELDS COUPLED WITH MODERATE INSTABILITY

WILL SUPPORT A SEVERE WEATHER THREAT PERSISTING WELL AFTER

DARK...ESPECIALLY ACROSS MO/NRN AR TO LOWER OH VALLEY.

UNCERTAINTY EXISTS IN THE GUIDANCE FOR WHETHER TSTMS INITIATE SWD

ALONG THE DRY LINE...S OF THE KS BORDER...THROUGH OK TO NRN TX. THE

00Z WRF-NAM/21Z ETAKF MEMBER OF THE SREF/12Z ECMWF DO NOT INITIATE

ACROSS THESE AREAS...WHILE 00Z GFS TO SOME EXTENT AND THE EACH OF

THE 21Z WRF-ARW MEMBERS OF THE SREF SUGGEST STORMS DO FORM INTO OK/N

TX SUNDAY AFTERNOON. DESPITE THESE DIFFERENCES...STEEP MIDLEVEL

LAPSE RATES /8-9 C PER KM/... MODERATE INSTABILITY AND STRENGTHENING

BULK SHEAR TO 50 KT INDICATES A SLIGHT RISK REMAINS WARRANTED WITH

SWD EXTENT. IF STORMS DEVELOP...THEN THE POTENTIAL WILL EXIST FOR

LARGE HAIL...SOME SIGNIFICANT...PRIOR TO THE COLD FRONT REACHING

THIS REGION AND PROGRESSING SWD INTO TX.

Has me baffled... They really sped this thing up.

[Hoosier]

00z Euro is substantially slower than the 12z run.

[baroclinic_instability]

This storm (both the convective and winter event) is simply baffling--no other way around it. Surprised to see this large shift in the Euro only 48 hours into the forecast.

[Thundersnow12]

They talked up the tornado threat more than I would've thought. I'm not really surprised by the 30% hatched though.

Ya agreed. I don't know much about how well Peters is a forecaster. I'm guessing it will be someone different on the day shift tomorrow with the next day 2.

[Hoosier]

Ya agreed. I don't know much about how well Peters is a forecaster. I'm guessing it will be someone different on the day shift tomorrow with the next day 2.

This run of the Euro has me wondering what the next runs are going to spit out. This run is literally 150-200 miles farther west with the cold front at 12z Mon.

[Thundersnow12]

This run of the Euro has me wondering what the next runs are going to spit out. This run is literally 150-200 miles farther west with the cold front at 12z Mon.

Looks like it has the sfc low just east of DSM at 48hr. 12z runs will be interesting.

[Stebo]

This run of the Euro has me wondering what the next runs are going to spit out. This run is literally 150-200 miles farther west with the cold front at 12z Mon.

Just wait til the Euro comes out and shows apocalypse again.

Not quite apocalypse but certainly more questions than answers.

[snowlover2]

With a 30% hatched area up for Sunday, anyone think with Monday supposed to be the big day that the SPC might pull the trigger on a day 3 moderate or do we see a 30% hatched at most?

[Stebo]

With a 30% hatched area up for Sunday, anyone think with Monday supposed to be the big day that the SPC might pull the trigger on a day 3 moderate or do we see a 30% hatched at most?

30% hatched would be my guess, I really don't think they could pull the trigger on a day 3 Mod right now. If they did they are seeing something I am not.

[PatrickSumner]

Well everyone was downplaying the tornado threat until SPC updated, so maybe they are seeing something we aren't. They are the professionals...

[PatrickSumner]

The EURO is slowing things down...wow

[MoeWx]

This run of the Euro has me wondering what the next runs are going to spit out. This run is literally 150-200 miles farther west with the cold front at 12z Mon.

To me it now looks like two rounds. Euro basically caught on to some serious WAA. Which I guess given how awful the models have been picking them up. Order of 6 - 10°F off the high. This makes perfect sense.

[Stebo]

Looks like a 30 no hatched area outlook

DAY 3 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0237 AM CDT SAT APR 02 2011

VALID 041200Z - 051200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM E TX TO THE CENTRAL GULF

COAST STATES AND NWD THROUGH THE TN/OH VALLEYS...

...E TX TO CENTRAL GULF COAST STATES NWD TO TN/OH VALLEYS...

THE 00Z GFS IS NOW FASTER THAN THE 00Z ECMWF WITH THE PROGRESSION OF

THE CENTRAL PLAINS TROUGH ON MONDAY ACROSS AND E OF THE MS VALLEY

REGION. IN ADDITION TO THESE TIMING DIFFERENCES...THE GFS INDICATED

STRONGER FORCING FOR ASCENT ACROSS THE TN/OH VALLEYS...WHILE THE

ECMWF INDICATED STRONGEST FORCING FOR ASCENT SPREADING ACROSS THE

LOWER MS VALLEY/CENTRAL GULF COAST STATES MONDAY NIGHT WITH A MORE

SWD TRACKING SHORTWAVE TROUGH.

EACH MODEL SHOWED STRONG BAROCLINICITY AS A COLD FRONT ADVANCES EWD

ACROSS THE OH/TN AND LOWER MS VALLEYS...WITH THE GFS AGAIN FASTER

WITH EWD PROGRESSION SHOWING THE FRONT REACHING THE ERN SEABOARD BY

12Z TUESDAY. DESPITE THE AFOREMENTIONED DIFFERENCES BETWEEN THE GFS

AND ECMWF...THIS TROUGH WILL UNDERGO STRENGTHENING AS IT BECOMES

NEUTRALLY ORIENTED...SUPPORTING INCREASING SWLY MIDLEVEL WINDS

/60-80 KT/ FROM TX/LOWER MS VALLEY TO THE TN/OH VALLEYS...WITH

FURTHER STRENGTHENING /90-100 KT/ MONDAY NIGHT AS THE FLOW BACKS TO

SLY. IN THE LOW LEVELS...A 50-60 KT SSWLY LLJ FROM THE LOWER MS TO

LOWER OH VALLEYS WILL SUPPORT MOISTURE SPREADING NWD ACROSS THE WARM

SECTOR.

TSTMS WILL BE LIKELY AS THE COLD FRONT ENCOUNTERS THE DESTABILIZING

AIR MASS AND FORCING FOR ASCENT INCREASES WITH THE EWD PROGRESSION

OF THE MID-UPPER LEVEL TROUGH. THE GREATEST INSTABILITY IS EXPECTED

FROM THE TN VALLEY SWD. DEEP LAYER SHEAR VECTORS ORIENTED MAINLY

PARALLEL TO THE COLD FRONT SUGGEST A LINEAR STORM MODE WITH BOWING

SEGMENTS LIKELY. HOWEVER...THE STRENGTH OF THE BULK SHEAR /40-55

KT/ MAY SUPPORT EMBEDDED SUPERCELL STRUCTURES WITHIN THE QLCS.

ALTHOUGH INSTABILITY WILL TEND TO BE MARGINAL WITH NWD EXTENT...THE

STRENGTH OF THE DEEP LAYER AND LOW LEVEL SHEAR SHOULD OVERCOME THAT

LIMITING FACTOR AND SUPPORT MAINLY A DAMAGING WIND THREAT ACROSS THE

OH VALLEY.

IF THE ECMWF IS CORRECT...THEN THERE WILL BE A SEVERE WEATHER THREAT

INTO THE LATTER HALF OF THE FORECAST PERIOD FROM THE LOWER MS VALLEY

TO THE CENTRAL GULF COAST STATES.

..PETERS.. 04/02/2011

[thewxmann]

This storm (both the convective and winter event) is simply baffling--no other way around it. Surprised to see this large shift in the Euro only 48 hours into the forecast.

F**** I knew this would happen.

EDIT: Actually it's still not too bad, doesn't completely make it a bad outbreak.

EDIT2: Looking at it more closely, I can only characterize tonight's 0Z run of the Euro as nothing but revolutionary. This is a MUCH stronger southern stream that is able to dig and slow down more than in previous runs. Meanwhile the energy is beginning to come onshore in the Pacific NW. Tomorrow's runs will be crucial.

[Stebo]

Grand Rapids AFD excerpt

PCPN WILL BE MAINLY IN THE FORM OF RAIN SHOWERS EARLY. THUNDER WILL

BECOME MORE LIKELY LATER IN THE DAY ON SUN AND ESPECIALLY SUN NIGHT

AS ELEVATED INSTABILITY MOVES IN OVERHEAD CLOSER TO THE SFC LOW

MOVING IN. AS THE LOW...AND EVENTUALLY THE TRIPLE POINT MOVES JUST

SOUTH OF I-96 SUN NIGHT...IT IS NOT OUT OF THE POSSIBILITY TO SEE

SOME SFC BASED STORMS ACROSS THE AREA. THE RAMIFICATIONS THIS HAS

WILL DICTATE OUR SEVERE CHCS.

THE ELEVATED NATURE OF THE STORMS...AND 2-3K FT STABLE LAYER AT THE

SFC WOULD SUPPORT THE POTENTIAL OF SOME LARGE HAIL WITH SOME OF THE

STORMS. IF WE CAN BREAK INTO THE WARM SECTOR DOWN SOUTH...IT WOULD

NOT BE OUT OF THE QUESTION TO HAVE A WIND AND TORNADO THREAT SNEAK

IN AS BULK SHEAR IS PRETTY GOOD IN THE 50-60 KNOT RANGE DURING THE

TIME OF THE BEST INSTABILITY CENTERED AROUND 06Z. LOW LEVEL HELICITY

VALUES ARE HIGH NEAR THE TRIPLE POINT...AND 0-1KM/0-3KM SHEAR VALUES

ARE SOMEWHAT HIGH ALSO. THIS WILL BE SOMETHING TO KEEP A CLOSE EYE

ON...EVEN WITH IT HAPPENING AT NIGHT.

DTX's excerpt (not quite as bold)

WITH THE BETTER AGREEMENT OF THE MODELS...IT DOES LOOK LIKE THE MOST

LIKELY TIME FRAME FOR THUNDERSTORMS WILL BE ON SUNDAY

NIGHT...POSSIBLY LINGERING INTO MONDAY MORNING(MAINLY IN THE SOUTH).

ELEVATED INSTABILITY DOES DEVELOP AND LIFT AT LEAST AS FAR NORTH AS

THE I-69 CORRIDOR ON SUNDAY NIGHT IN A HIGHLY SHEARED ENVIRONMENT.

CURRENTLY MODELS ARE KEEPING ANY BETTER SURFACE BASED CONVECTION

JUST SOUTH OF THE STATE LINE. SCATTERED TO NUMEROUS THUNDERSTORMS

ARE EXPECTED SUNDAY NIGHT WITH THE POTENTIAL FOR THESE THUNDERSTORMS

TO BE FAIRLY STRONG. SMALL HAIL WILL BE POSSIBLE ON SUNDAY NIGHT AND

EVEN AN ISOLATED SEVERE STORM(HAIL) IS NOT OUT OF THE QUESTION. SPC

KEEPS THE SLIGHT RISK AREA JUST SOUTH OF THE STATE AND THIS

PLACEMENT LOOKS ON TRACK. WILL LEAVE THE LIKELY POPS IN THE

FORECAST FOR MONDAY FOR NOW GIVEN SOME LINGERING UNCERTAINTY IN

THE EVOLUTION OF THE CONVECTION...ALTHOUGH THERE IS A CHANCE THAT

PRECIPITATION WILL PUSH EAST OF THE AREA BY MONDAY AFTERNOON AS

THE DRY SLOT IS WRAPPED UP INTO THE SYSTEM.

[Stebo]

The differences between the GFS 06z and the Euro are like night and day with respect to the speed of the system. One of these models is going to have to blink.

[weathergy]

Seems morning debris will limit the potential for SEMI. Typical.

[Thundersnow12]

The 12z NAM is breaking the CAP in northeast MO, eastern IA into northern IL by 0z with CAPE values between 1500-2500 j/kg and 40-50kts of shear which is more than enough for supercells. The tornado threat might be limited given the veered low-level flow in the warm sector and ahead of the cold front so if anything is going to spin nicely it will be near the warm front.

[Thundersnow12]

popping a 30 now..

[Indystorm]

Yep, was just going to post that Quad City area east along I-80 looks prime...dews up to mid 60's...low level helicity better east of the metro...200-250...increasing eastward to Chi town...LI of -7 to -8 from ne MO on northeastward. Could get interesting. Lots of good flat chasing/spotting territory in that area.

[OceanStWx]

popping a 30 now..

12z NAM is showing 0-3km CAPE in excess of 100 J/kg coincident with that area now.

[csnavywx]

The 12z NAM is breaking the CAP in northeast MO, eastern IA into northern IL by 0z with CAPE values between 1500-2500 j/kg and 40-50kts of shear which is more than enough for supercells. The tornado threat might be limited given the veered low-level flow in the warm sector and ahead of the cold front so if anything is going to spin nicely it will be near the warm front.

Wouldn't count it out with a plume of very steep low level lapse rates working their way up Sunday afternoon into the evening. Ideal for some vort stretching and strong spin-ups, especially in new cells.

[cyclone77]

Not much else to add to what you guys all mentioned. Looks pretty good over west-central and north-central Illinois later tomorrow. The target area may actually end up pretty close to here, but will have to see how it trends tomorrow. Will definitely be out chasing this one.