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April 7th-10th Severe Weather


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Unless the moisture isn't rich enough and there is a shallow non-capping CIN layer. Then, they may be rooted above that.

Yeah that's a good point. I do have some questions regarding the moisture depth for this, so that indeed may turn out to be the case.

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Yeah that's a good point. I do have some questions regarding the moisture depth for this, so that indeed may turn out to be the case.

We're probably about pushing the limit on the models as far as moisture quality/depth this time of year. What we're seeing now would match or exceed some infamous April dates in the past. I'm curious to see how well the models will perform in this regard.

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We're probably about pushing the limit on the models as far as moisture quality/depth this time of year. What we're seeing now would match or exceed some infamous April dates in the past. I'm curious to see how well the models will perform in this regard.

Yeah, the moisture quality/depth for this early in the season for this far north would probably be really good.... if we weren't likely to get quite so warm at the surface.

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Yeah, the moisture quality/depth for this early in the season for this far north would probably be really good.... if we weren't likely to get quite so warm at the surface.

The northward extent is pretty remarkable. To put it in perspective, dewpoints only made it to the low-mid 60's here on 2 well-known April days 9 years apart which won't be mentioned. :whistle:

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The northward extent is pretty remarkable. To put it in perspective, dewpoints only made it to the low-mid 60's here on 2 well-known April days 9 years apart which won't be mentioned. :whistle:

Mention them because my brain is forgetting them.

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30% non hatched for Saturday

day3prob_0730.gif

DAY 3 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0229 AM CDT THU APR 07 2011

VALID 091200Z - 101200Z

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

CENTRAL PLAINS TO THE UPPER MS VALLEY...

...THERE IS A SLGT RISK OF SVR TSTMS FROM PARTS OF THE LOWER OH

VALLEY SEWD TO ERN GA...SC AND WRN/SRN NC...

..ERN PORTION OF CENTRAL PLAINS TO UPPER MS VALLEY

00Z GFS/ECMWF ARE IN BETTER AGREEMENT AS COMPARED TO THE LAST FEW

DAYS SHOWING THE WRN TROUGH BECOMING PROGRESSIVE ON SATURDAY AND

REACHING THE SRN/CENTRAL ROCKIES TO NRN HIGH PLAINS BY 12Z SUNDAY.

A BAND OF STRONG SWLY MID-UPPER LEVEL FLOW IS EXPECTED TO EXTEND

FROM THE SWRN STATES THROUGH THE CENTRAL PLAINS TO THE MID MO RIVER

VALLEY BY SATURDAY AFTERNOON. IN THE LOW LEVELS...LEE CYCLOGENESIS

IS EXPECTED ACROSS ERN CO THROUGH THIS FORECAST PERIOD...WHILE A

SECONDARY SURFACE LOW FORMING OVER NEB /LIKELY ATTENDANT TO A LEAD

IMPULSE/ MOVES INTO SRN MN BY 12Z SUNDAY. STRENGTHENING SLY LOW

LEVEL WINDS ACROSS THE SRN/CENTRAL PLAINS WILL ADVECT MOISTURE

NWD...WHILE A WARM FRONT MOVES FROM THE LOWER MO VALLEY TO THE UPPER

MS VALLEY. THE GREATEST MOISTURE RETURN WILL RESIDE E OF A DRY LINE

EXTENDING FROM THE NEB LOW SWD THROUGH CENTRAL OK TO CENTRAL TX.

A PLUME OF STEEP MIDLEVEL LAPSE RATES EXTENDING NEWD ATOP THE

MOISTURE RETURN WILL SUPPORT MODERATE TO STRONG INSTABILITY...WITH

GENERAL AGREEMENT IN THE MODELS SHOWING CONVECTIVE DEVELOPMENT FROM

MID-LATE AFTERNOON ALONG THE DRY LINE IN NRN OK TO THE MID MO

VALLEY. STRONG EFFECTIVE BULK SHEAR OF 50-70 KT WILL SUPPORT

ORGANIZED SEVERE STORMS. ACTIVITY IS EXPECTED TO DEVELOP/SPREAD

NEWD TOWARD THE UPPER MS VALLEY SATURDAY NIGHT AS THE LLJ VEERS AND

STRENGTHENS TO 60 KT WITH A CONTINUED LIKELIHOOD FOR STRONG TO

SEVERE STORMS.

..LOWER OH VALLEY SEWD TO ERN GA/CAROLINAS

GUIDANCE SUGGESTS THE WEAK IMPULSE MOVING ACROSS THE SRN PLAINS ON

FRIDAY SHOULD TRACK SEWD FROM THE MID MS VALLEY WITHIN 40-50 KT NWLY

FLOW ALOFT REACHING THE CAROLINAS BY EARLY EVENING AND THEN MOVING

OFFSHORE. A WEAK SURFACE BOUNDARY EXTENDING FROM MO ESEWD INTO KY

AND OUTFLOW BOUNDARIES LEFT OVER FROM DAY 2 CONVECTION ACROSS PARTS

OF THIS REGION WILL BE THE FOCI FOR NEW TSTMS ON SATURDAY. LOW

LEVEL MOISTURE RETURN ON DAY 2 /FRI/ INTO THESE REGIONS WILL

CONTINUE ON DAY 3 /SAT/ WITH SURFACE DEWPOINTS INTO THE 60S ACROSS

THIS SLIGHT RISK AREA. THIS COMBINED WITH DIABATIC HEATING AND

7-7.5 C/KM MIDLEVEL LAPSE RATES SHOULD RESULT IN MODERATE

INSTABILITY /UP TO 1500-2000 J PER KG/. EFFECTIVE BULK SHEAR AROUND

50 KT WILL SUPPORT ORGANIZED STRONG TO SEVERE STORMS. GIVEN THE

DEGREE OF AVAILABLE INSTABILITY AND SHEAR... HIGHER PROBABILITIES

MAY BE NEEDED IN LATER OUTLOOKS...BUT UNCERTAINTY IN PRIMARY FOCUS

AREAS PRECLUDES THIS INCLUSION AT THIS TIME.

..PETERS.. 04/07/2011

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Looking at things more closely, I really cannot get excited about the Saturday potential. IA is near the crest of the ridge, which historically is a good area for parameters but not so good of an area for convective initiation. I see no dynamic shortwaves or what-not in the vicinity. The cap is by no means negligible, and this is with the model bias of underdoing the cap this far out.

I am, however, confident of initiation along the dry line along KS and srn NE. Models continue to hint at convective initiation along the dry line and the ECM paints a nice lead s/w that hinges upon the warm sector at 0Z. The highly mixed boundary layer would argue against significant tornadic activity, but this may end up being one of the better Plains supercell shows this year thus far. (Friday may end up being a nice 1-2 supercell show too with convective initiation hinted at for days. Again though tornadic potential would be minimal with the well-mixed boundary layer.)

Sunday looks like a squall line day but weak VV's on the GFS, last system's performance with less than ideal wind profiles, and it still being several days out makes this low confidence.

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LOT AFD - IZZI

ATTENTION WILL THEN TURN TO THE HUGE STORM SYSTEM OUT WEST THAT HAS

ME FULL ON METEOROLOGICALLY TINGLY AS ALL GET OUT THIS MORNING

(ABOUT AN 8 ON A SCALE OF 10 TINGLES)! SYSTEM IS ALREADY VERY

IMPRESSIVE LOOKING ON WATER VAPOR IMAGERY OFF THE PAC NW COAST

WITH POCKET OF VERY COLD AIR ALOFT (-37C @ 500MB AT 00Z AT CYZT)

RESULTING IN FAIRLY VIGOROUS CONVECTION WITH NUMEROUS CG LIGHTNING

STRIKES. MODELS HAVE COME INTO BETTER AGREEMENT THIS MORNING ON

DIGGING THIS POWERFUL CLOSED COLD CORE LOW SOUTH INTO SOUTHERN

CALIFORNIA FRIDAY NIGHT...WITH 500MB HEIGHTS PROGGED TO REACH

NEARLY 5 STANDARD DEVIATIONS BELOW AVERAGE (ESSENTIALLY LIKELY

RECORD OR NEAR RECORD LOW 500MB HEIGHTS IF SUCH RECORDS WERE

KEPT). DOWNSTREAM OF THIS ANOMALOUSLY DEEP TROUGH IMPRESSIVE

HEIGHT RISES WITH STRONG UPPER RIDGING EXPECTED OVER

CENTRAL/EASTERN U.S. LIKELY RESULTING IN RECORD/NEAR RECORD WARMTH

OVER PORTIONS OF THE U.S. OUT AHEAD OF THIS SYSTEM WITH H8 TEMPS

PROGGED TO CLIMB TO 2-3 STANDARD DEVIATIONS ABOVE AVERAGE.

WARM FRONTOGENESIS FRIDAY INTO THE WEEKEND WITH SHARPENING

TEMPERATURE GRADIENT ASSOCIATED WITH THE WARM FRONT. WEAK WAVES OF

LOW PRESSURE AND SFC PRESSURE FALLS TO THE NORTHWEST WILL LIKELY

RESULT IN WARM FRONT TRYING TO LIFT NORTHWARD SATURDAY...HOWEVER

EAST WINDS OF THE FRIGID LAKE WATERS WILL LIKELY RETARD ITS

NORTHWARD ADVANCE SATURDAY. VERY LARGE TEMP GRADIENT EXPECTED ACROSS

CWA SATURDAY AFTERNOON WITH TEMPS LIKELY HOLDING IN THE 40S NEAR IL

LAKESHORE WHILE SOUTHERN MOST CWA COULD FLIRT WITH 80F!

STRENGTHENING PRESSURE FALLS TO THE NORTH AHEAD OF DEEPENING LOW

PRESSURE TO OUR NORTHWEST SATURDAY NIGHT SHOULD RESULT IN WARM FRONT

ACCELERATING NORTHWARD AND ENTIRE CWA RIGHT UP TO THE NORTHSHORE

GETTING INTO THE WARM SECTOR. HAVE BUMPED UP HIGHS INTO THE LOWER

80S FOR SUNDAY...AND IF CONVECTIVE DEBRIS ISNT MORE EXTENSIVE EVEN

THOSE FORECAST HIGHS MAY BE CONSERVATIVE. RECORD HIGHS ARE IN THE

LOWER 90S AND EXPECT THAT THEY WILL LIKELY BE OUT OF REACH...

SYNOPTIC SET-UP HEADING INTO THE WEEKEND CONTINUES TO FAVOR

MULTI-DAY AND POTENTIALLY SIGNIFICANT SEVERE WEATHER

OUTBREAK...FIRST OVER THE PLAINS WITH THE THREAT LIKELY TO SPREAD

EAST INTO THE MISSISSIPPI VALLEY BY SUNDAY. ITD BE SILLY TO GET HUNG

UP ON TOO MANY DETAILS THIS FAR OUT...BUT 4+ DAYS OF SOLID RETURN

FLOW FROM THE ALREADY RE-CHARGING GULF OF MEXICO...STRONG/EXTREME

LOW/DEEP LAYER SHEAR ASSOCIATED WITH UNSEASONABLY STRONG/COLD UPPER

LOW...COMBINED WITH THE POTENTIAL FOR A HEALTHY EML ADVECTING OFF

THE HIGHER TERRAIN ALL SCREAM FOR THE POTENTIAL OF

WIDESPREAD/POTENTIALLY SIGNIFICANT MULTI-DAY SEVERE WEATHER EPISODE.

MAGNITUDE AND TYPE OF SEVERE THREAT LOCALLY WILL LIKELY DEPEND

SOMEWHAT ON TIMING OF SYSTEM...WITH CURRENT TIMING LOOKING LIKE

SUNDAY EVENING. MAGNITUDE OF SEVERE THREAT WILL LIKELY BE SOMEWHAT

DIURNALLY DRIVEN WITH SLOWLY WANING...THOUGH GIVEN THE INTENSITY OF

THE SYSTEM...STILL PRESENT SEVERE WEATHER THREAT WELL INTO THE

NIGHT. UPPER LOW IS PROGGED TO BE SLOWLY WEAKENING AS IT MOVES INTO

THE MID-MISSISSIPPI VALLEY SUNDAY NIGHT...HOWEVER COMPACT NATURE OF

THE NEGATIVELY TILTED CLOSED MID LEVEL CIRCULATION KEEPS ME LEARY OF

A POTENTIALLY SIGNIFICANT SEVERE THREAT LINGERING WELL INTO THE

EVENING HOURS SUNDAY.

IZZI

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Not quite as excited about the setup as I was yesterday, but can see both Sat and Sun being MDT risk days. The strengthening LLJ should kick off stuff in the vicinity of IA, though probably late enough where mostly it is elevated in nature. Sunday I can see capping issues until the height falls really come in, which probably results in supercells initially, but may quickly congeal into a line... still could easily be worth of MDT risk though. Obviously much can and probably will change over the next couple of days.

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Could be some significant moisture depth issues on Saturday across the four-state corner region of NE/KS/MO/IA. Looks like the moisture depth there is pretty shallow to begin with, and an EML surge in the wake of a mid level s/w causes it to mix out big time during the heat of the day. A strengthening synoptic LLJ looks to help replenish some of that in the late afternoon, but it's hard to tell whether that will be enough.

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