April 2nd - April 5th Severe Weather

[OceanStWx]

Its more than region, its time of year, I heard Vortex 2 waited until later because of generally slower storm motions and easier chasing

Slower storm motions and less chance for chaser convergence were definitely considered when deciding to include June rather than April in the operational window.

And it is true that by early June you don't expect 100 knot jet streaks at 500 mb across the Midwest, like you might in early April.

[baroclinic_instability]

This storm looks sick regarding flood potential over the Northern Plains. This storm is essentially an extension of the East Asian Pacific jet plowing across the Pacific following the breakdown of the high latitude blocks. Last time the East Asian Pacific jet took a meander into the plains? Last one I can think of is Octobomb.

[Hoosier]

This storm looks sick regarding flood potential over the Northern Plains. This storm is essentially an extension of the East Asian Pacific jet plowing across the Pacific following the breakdown of the high latitude blocks. Last time the East Asian Pacific jet took a meander into the plains? Last one I can think of is Octobomb.

Funny, I was thinking of the Octobomb earlier but wasn't sure how good of a comparison it was.

[Hoosier]

[baroclinic_instability]

Funny, I was thinking of the Octobomb earlier but wasn't sure how good of a comparison it was.

It does bear some resemblance--although Octobomb was the mother of all jet streaks.

Winter/flood thread started for those interested.

http://www.americanwx.com/bb/index.php/topic/16204-winterflooding-storm-threat-april-3-5/

[Hoosier]

Not trying to make a comparison but it's funny that this potential event is falling on April 3-4.

[Thundersnow12]

The 0z GFS for this coming saturday went back to showing the moisture/instability it was showing the other day with near mid 60 dews along the dryline and a nice area of >1500 j/kg of CAPE.

[Thundersnow12]

Not trying to make a comparison but it's funny that this potential event is falling on April 3-4.

And hopefully the 2nd

[Chicago Storm]

The 0z GFS for this coming saturday went back to showing the moisture/instability it was showing the other day with near mid 60 dews along the dryline and a nice area of >1500 j/kg of CAPE.

Another run that says i'm chasing on Sunday.

[Thundersnow12]

Another run that says i'm chasing on Sunday.

Ya a nice run bringing near mid 60 dews up to the MO/IA/IL intersection.

[Hoosier]

Ya a nice run bringing near mid 60 dews up to the MO/IA/IL intersection.

It's probably not going to handle the surface temps well either if we get a setup like this. If that steep mid level lapse rate environment is in place, then instability could end up being underdone.

[Thundersnow12]

some serious deep moisture return between 96-120hr on the GFS into OK/KS.

[baroclinic_instability]

some serious deep moisture return between 96-120hr on the GFS into OK/KS.

It is all about the wave amplitude and subsequent cross barrier flow. Dry runs have a much lower amplitude initial wave (see Euro 12Z/CMC 12Z). I do see the latest CMC went with a much more amplified wave on the 0Z. GFS suggests a beefy backside jet digging in behind the initial IPV impulse ejecting into the plains--hence the much more impressive moisture return.

[baroclinic_instability]

The new "E-N" rule--Euro-NOGAPS. They both really amplify that PNA ridge and cut off the secondary upper low from the main belt of westerlies.

[SmokeEater]

Can you guys add today, and possibly the next 2 days to the thread title? Looks like possibly a halfway decent event today, with Slight Risks the next 2 days.

DAY 1 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1256 AM CDT TUE MAR 29 2011

VALID 291200Z - 301200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE LOWER MS VALLEY TO

SOUTH CENTRAL TX/LOWER RIO GRANDE VALLEY...

...SYNOPSIS...

SHORTWAVE TROUGH CURRENTLY APPROACHING CO PER WATER VAPOR IMAGERY IS

EXPECTED TO TURN EWD ACROSS THE CENTRAL PLAINS TODAY AND REACH THE

MID MS/LOWER OH VALLEYS BY 12Z WEDNESDAY. MEANWHILE...ZONAL FLOW

WILL PERSIST FROM THE SRN ROCKIES TO THE MIDDLE AND SRN ATLANTIC

COAST. A SHORTWAVE TROUGH...CURRENTLY MOVING ACROSS THE BAJA

REGION...IS EXPECTED TO REACH THE LOWER RIO GRANDE VALLEY BY 30/00Z

AND THE NWRN GULF COAST REGION BY THE END OF THE FORECAST PERIOD.

LOW LEVEL WINDS ACROSS E TX/LOWER MS VALLEY ARE EXPECTED TO BACK TO

SLY TODAY IN RESPONSE TO WEAK HEIGHT FALLS AS THE CO TROUGH

PROGRESSES EWD. THIS WILL ALLOW A WARM FRONT TO MOVE NWD INTO SRN

LA BY AFTERNOON WITH THE WRN EXTENT OF THIS BOUNDARY REACHING A

LITTLE FARTHER NWD INTO EAST CENTRAL TX. MEANWHILE...A COLD FRONT

WILL SHIFT S/SEWD THROUGH TX...INTERSECTING THE WARM FRONT OVER EAST

CENTRAL TX BY LATE AFTERNOON WITH THE TRAILING PORTION OF THIS FRONT

EXTENDING SWWD INTO SOUTH CENTRAL TX. THE COLD FRONT WILL PROGRESS

E/SEWD OFF THE TX COAST BY 12Z WEDNESDAY...WITH THE NEWD EXTENSION

STRETCHING INTO SRN MS AND NRN AL.

...ARKLATEX TO SERN TX AND EWD INTO LOWER MS VALLEY...

SLY LOW LEVEL WINDS DEVELOPING ACROSS THIS REGION WILL ALLOW

MOISTURE TO RETURN ACROSS THIS REGION WITH SURFACE DEWPOINTS IN THE

MID-UPPER 60S EXPECTED WITHIN THE WARM SECTOR. THIS COMBINED WITH

SURFACE HEATING BENEATH A PLUME OF STEEP MIDLEVEL LAPSE RATES /7.5-8

C PER KM/ WILL RESULT IN MODERATE INSTABILITY /MLCAPE 1500-2000 J

PER KG/ BY AFTERNOON.

ELEVATED TSTMS...SOME POSSIBLY PRODUCING HAIL...MAY BE ONGOING

ACROSS OK AT 12Z TODAY. LOW LEVEL WAA AND WEAK HEIGHT FALLS FROM

THE ARKLATEX TO SRN AR/WRN MS SHOULD SUPPORT ELEVATED TSTMS

DEVELOPING/SPREADING FROM THE SERN PLAINS THIS MORNING. WEAK

INSTABILITY WITH NWD EXTENT SHOULD LIMIT THE SEVERE WEATHER THREAT.

HOWEVER...STEEP MIDLEVEL LAPSE RATES AND EFFECTIVE BULK SHEAR AROUND

40 KT SUGGEST THE POTENTIAL FOR A FEW ORGANIZED STORMS...WITH HAIL

THE PRIMARY THREAT N OF THE RETREATING WARM FRONT.

MEANWHILE...SURFACE BASED TSTMS ARE EXPECTED TO DEVELOP THIS

AFTERNOON ALONG THE COLD FRONT IN E/SERN TX AND EWD ACROSS THE WARM

SECTOR IN LA TO SWRN MS. FORCING ATTENDANT TO LOW LEVEL WAA AND

LEAD SRN STREAM IMPULSE REACHING THIS REGION BY LATE AFTERNOON WILL

SUPPORT THIS ACTIVITY. MODERATE INSTABILITY AND EFFECTIVE BULK

SHEAR 40-50 KT WILL SUPPORT ORGANIZED /SUPERCELLULAR/ STORMS.

ALTHOUGH LOW LEVEL WINDS WILL TEND TO BE WEAK...VERTICAL VEERING

WINDS SUGGEST A POTENTIAL FOR TORNADOES FROM E TX INTO THE LOWER MS

VALLEY. IN ADDITION...STEEP MIDLEVEL LAPSE RATES WILL SUPPORT A

THREAT FOR HAIL...SOME POSSIBLY VERY LARGE...BUT OVERALL COVERAGE OF

SIGNIFICANT HAIL IS UNCERTAIN AT THIS TIME TO INCLUDE A 10 PERCENT

SIGNIFICANT HAIL CONTOUR.

STRONGER FORCING FOR ASCENT IS EXPECTED TO REACH THE NWRN GULF COAST

THIS EVENING AND SPREAD EWD TO THE CENTRAL GULF COAST BY 12Z

WEDNESDAY. THIS WILL INDUCE CYCLOGENESIS OVER SERN TX/SWRN LA WITH

THE LOW REACHING SERN LA/SERN MS REGION BY EARLY WEDNESDAY MORNING.

STRENGTHENING LLJ E OF THE LOW WILL ENHANCE LOW LEVEL SHEAR AND

SUPPORT AN OVERNIGHT TORNADO THREAT ACROSS SRN LA TO SERN MS/SWRN

AL.

...PARTS OF SOUTH CENTRAL TX/LOWER RIO GRANDE VALLEY...

MODELS SUGGEST ISOLATED TSTMS MAY DEVELOP BY LATE AFTERNOON/EARLY

EVENING ACROSS THE SRN EXTENT OF THE COLD FRONT AS IT MOVES INTO

SOUTH CENTRAL TX...ENCOUNTERING A MODERATELY UNSTABLE AIR MASS

/MLCAPE AROUND 2000 J PER KG/. THIS ACTIVITY WILL BE FURTHER

SUPPORTED BY FORCING WITH THE BAJA TROUGH AS IT MOVES ACROSS THIS

REGION. STORMS THAT DEVELOP IN THIS REGION WILL BE CAPABLE OF

PRODUCING LARGE HAIL...SOME VERY LARGE...GIVEN THE DEGREE OF

INSTABILITY...STEEP LAPSE RATES AND EFFECTIVE BULK SHEAR AROUND 50

KT FAVORABLE FOR SUPERCELLS. IN ADDITION...DAMAGING WINDS WILL BE A

THREAT. THIS ACTIVITY WILL SPREAD SWD IN THE EVENING AND THE

DIMINISH AS THE BOUNDARY LAYER STABILIZES WITH THE ONSET OF DIABATIC

COOLING.

..PETERS/COHEN.. 03/29/2011

[Ed Lizard]

BUT OVERALL COVERAGE OF

SIGNIFICANT HAIL IS UNCERTAIN AT THIS TIME TO INCLUDE A 10 PERCENT

SIGNIFICANT HAIL CONTOUR.

Hmmm... but they did include it

[TheWeatherPimp]

From IWX:

SUN-MON...INCREASING CHANCE FOR A STRONG MID LEVEL WAVE AND

ASSOCIATED SFC WAVE TO AFFECT THE GREAT LAKES. AS STATED

ABOVE...PREFERRED A SLOW BIASED GFS SOLUTION ATTM...PLACING THE BULK OF

LARGE SCALE FORCING AND DYNAMICS INTO THE MONDAY PERIOD. HENCE OPTED

FOR 40 POP THERE. OTHERWISE...RETAINED SUN NIGHT POPS FOR WARM

FRONTAL PROCESSES...WITH 30 POPS MON NIGHT GIVEN SYSTEM TIMING

UNCERTAINTY. DID ADD THUNDER GIVEN MID LEVEL LAPSE RATE TRENDS AND

THE STRONG NATURE OF THIS SYSTEM...FURTHER EXEMPLIFIED IN H5

ANOMALIES. AGAIN...THIS SYSTEM BEARS WATCHING DUE TO THE POTENTIAL

FOR A PROLIFIC SEVERE WEATHER EPISODE IF THINGS LINE UP. TOO MUCH

UNCERTAINTY STILL PRESENT IN SYSTEM TRACK/TIMING/AND LL MOISTURE

DETAILS TO WARRANT ANYTHING MORE THAN A PASSIVE MENTION FOR NOW.

WILL CONTINUE TO MONITOR. OTHERWISE...WARMING TEMPS EXPECTED IN THE

PERIOD...GIVEN TRENDS IN ADVECTION FIELDS.

[hm8]

If things pan out, this could be the third year in a row that I'll be on vacation for SEMI's first severe weather of the season

[kab2791]

Meh, highly doubtful especially with a Euro solution.

If things pan out, this could be the third year in a row that I'll be on vacation for SEMI's first severe weather of the season

[Indystorm]

Not trying to make a comparison but it's funny that this potential event is falling on April 3-4.

Don't scare me. The current parameters are frightening enough.

[Thundersnow12]

DAY 4-8 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0355 AM CDT TUE MAR 29 2011

VALID 011200Z - 061200Z

...DISCUSSION...

MODEL CONSENSUS IS THAT PATTERN WILL REMAIN PROGRESSIVE IN THE 4-8

PERIOD WITH THE NEXT IN A SERIES OF SIGNIFICANT SHORTWAVE TROUGHS

LIKELY MOVING INTO THE PLAINS DAY 6-7. IT IS CERTAINLY POSSIBLE THAT

A SIGNIFICANT SEVERE EVENT COULD EVOLVE OVER THE PLAINS BY DAY

6-7...SPREADING INTO THE LOWER MS VALLEY AND SERN STATES DAY 7-8 AS

MOISTURE RETURNS NWD THROUGH PRE-FRONTAL WARM SECTOR.

HOWEVER...CONSIDERABLE RUN TO RUN INCONSISTENCIES EXIST WITH THE

DETERMINISTIC MODELS AND ENSEMBLE MEMBERS ARE DISPERSIVE BEYOND DAY

5 REGARDING AMPLITUDE AND TRAJECTORY OF THE SHORTWAVE TROUGH. AT

THIS TIME PREDICTABILITY REMAINS LOW...BUT PORTIONS OF THE PLAINS

INTO THE SERN STATES WILL PROBABLY NEED TO BE INCLUDED IN A RISK

AREA IN LATER OUTLOOKS FOR DAY 6-7.

..DIAL.. 03/29/2011

[Indystorm]

Low goes south and is much weaker on the 12z GFS. Wait for the next model runs.

[AtticaFanatica]

Slower storm motions and less chance for chaser convergence were definitely considered when deciding to include June rather than April in the operational window.

And it is true that by early June you don't expect 100 knot jet streaks at 500 mb across the Midwest, like you might in early April.

Right, and in 2010, the project started in the first week of May because that's the peak in violent tornadoes according to climatology.

[Jim Martin]

Plenty of cape available for storms.

Plenty of moisture available also. However...

The cap could be an issue. A strong cap is shown here.

[Ed Lizard]

Right, and in 2010, the project started in the first week of May because that's the peak in violent tornadoes according to climatology.

First week in May is different than the whole month, but I had heard April has fewer, but more violent tornadoes than May.

[AtticaFanatica]

First week in May is different than the whole month, but I had heard April has fewer, but more violent tornadoes than May.

Yeah, the last week of April and first week of May are the peak for violent tornadoes, but also for storm motion, which obviously is bad for chasing and worse for research chasing.

[Thundersnow12]

If it wasn't for the cap on sunday, the 12z GFS is hinting at an interesting setup with dew points in the upper 60's and more instability than previous runs.

[Hoosier]

Day 4-8 outlook mentions a risk area probably being needed later.

[brettjrob]

If it wasn't for the cap on sunday, the 12z GFS is hinting at an interesting setup with dew points in the upper 60's and more instability than previous runs.

The change in the evolution of the H5 pattern for this weekend over the past 2-4 runs is astounding, and a testament to how abysmal the models have been so far this year. The trough is now supposed to dig a lot more into the Desert SW, bringing a legitimate SW flow pattern that I could actually see producing significant severe (unlike the NW flow, positive-tilt crap shown on earlier runs). Unfortunately, the timing isn't quite right, as this run also hangs the trough back farther W for Sunday. If we could get the digging but also speed things up by about 12 hours, I imagine the cap wouldn't be such a showstopper. In fact, the 12z Mon H5 prog looks nearly classic to me.

Normally, I'd be discouraged about the prospects of a solution speeding up by 12 hours this close to the event. But this year, I don't think a 24-hour timing and/or 500-mile spatial change is at all out of the question for a 108-hour forecast.

[David Reimer]

The GFS also looks quite interesting for overnight Sunday into Monday. The 12Z GFS has 2,500 J/Kg of SBCAPE over OK at 6 AM Monday with a weak cap by afternoon/evening. I've already made the arrangements in my work schedule so I can be available to chase that day. Should the cap break on Saturday, then that has the potential to be an interesting caprock day.