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Early May (1st-7th) Severe Chances


Stebo

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SPC site not updating for me for some reason

..IL/INDIANA TO ERN OK

SCATTERED TO LOCALLY NUMEROUS TSTMS SHOULD DEVELOP INVOF SFC COLD FRONT DURING AFTERNOON...WHILE CONDITIONAL POTENTIAL FOR SVR CONVECTION EXISTS OVER WARM FRONT. DAMAGING HAIL/GUSTS ARE MAIN SVR THREATS.

LACK OF DEEP-LAYER SHEAR OVER MOST OF THIS CORRIDOR SUGGESTS PREDOMINANTLY MULTICELLULAR MODE...ALTHOUGH BRIEF SUPERCELL STRUCTURES ARE POSSIBLE. WARM SECTOR WILL BE CHARACTERIZED COMMONLY BY MID-UPPER 60S SFC DEW POINTS...WITH POCKETS OF 70S F...BENEATH STEEP MIDLEVEL LAPSE RATES. STG SFC DIABATIC HEATING IS EXPECTED WITH MID-LATE AFTERNOON MLCAPE 3500-5000 J/KG IN MUCH OF OUTLOOK AREA. MOST PROBABLE CORRIDOR FOR SUSTAINED/NOCTURNAL CONVECTION APPEARS TO BE NEAR WARM FRONT OVER PORTIONS INDIANA/OH...SVR POTENTIAL DIMINISHING WITH TIME AND EWD EXTENT.

GIVEN UNCERTAINTIES IN FRONTAL POSITION/TIMING AND DIFFERENCES IN AREAS OF STRONGEST LOW-LEVEL LIFT...SVR OUTLOOK IS KEPT RATHER BROAD-BRUSHED ATTM. HOWEVER...GIVEN LIKELIHOOD OF STG-EXTREME INSTABILITY ACROSS MUCH OF PREFRONTAL CORRIDOR...30% SVR CONCENTRATION EASILY MAY BECOME APPARENT WITHIN THIS AREA IN SUCCEEDING OUTLOOKS. AS IT STANDS...THREAT EXISTS FOR ISOLATED VERY LARGE/DAMAGING HAIL IN EARLY STAGES OF CONVECTIVE REGIME...ALONG WITH SVR HAIL AND GUSTS AS COVERAGE INCREASES ALONG/AHEAD OF FRONT AND COLD POOLS ACCUMULATE.

day2.prob.gif

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Looks like Monday could also get a little interesting in the Ohio Valley.

A couple of the models especially the foreign models are a bit slower and further North with the surface Low for Sunday/Monday. The Euro has been consistent on being slower with with low. This could have huge ramifications on Northern parts of the the outlooks for Sunday and whatever is put out for Monday.

The fastest model with the surface low track right now is the NAM, and we all know how the NAM has done at this range.

Edit: more than half of the 21z SREF runs agree with a slower and further North surface low track too. Some are even tracking it North of 94 in MI. The mean takes it through Toledo however it is being skewed by ETAs which have the low going along the Ohio River (unlikely).

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I'm in Chicago the next 3 days. Bank on several reports within 30 miles of Anderson.

Sent from my ADR6400L 2

haha

Other than the lame speed shear (which should be overcome to some extent by large instability) my other main concern is timing. Sorta rooting for the slower solutions so we don't get caught in between with a better threat west on Sunday and east on Monday.

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DAY 2 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1230 PM CDT SAT MAY 05 2012

VALID 061200Z - 071200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE UPPER

MIDWEST...OZARKS...MID MS VALLEY...SRN PLAINS...CNTRL PLAINS...

..MID TO UPPER MS VALLEY

AN UPPER-LEVEL RIDGE WILL BE IN PLACE SUNDAY FROM THE MID-MS VALLEY

NWD INTO THE GREAT LAKES REGION. AT THE SFC...A COLD FRONT WILL MOVE

SEWD ACROSS THE UPPER MIDWEST WITH A BROAD WARM SECTOR IN PLACE

AHEAD OF THE FRONT FROM THE UPPER MS VALLEY EXTENDING SWWD ACROSS

THE OZARKS. AN MCS MAY BE ONGOING NEAR THE FRONT ACROSS PARTS OF THE

REGION SUNDAY MORNING AND OUTFLOW BOUNDARIES ASSOCIATED WITH THE MCS

SHOULD FAVOR CERTAIN AREAS FOR CONVECTIVE INITIATION. AS SFC TEMPS

WARM...NEW CONVECTION SHOULD INITIATE NEAR THOSE BOUNDARIES WHERE

THE AIRMASS HAS BEEN UNDISTURBED. AS STORMS INCREASE IN

COVERAGE...MCS DEVELOPMENT WILL BE POSSIBLE ACROSS THE REGION LATE

SUNDAY AFTERNOON WITH STORMS MOVING SEWD ACROSS THE SLIGHT RISK

AREA.

FORECAST SOUNDINGS ACROSS THE WARM SECTOR IN CNTRL IA...NRN IL AND

NRN MO BY EARLY AFTERNOON HAVE MODERATE INSTABILITY...MLCAPE IN THE

2500 TO 3500 J/KG RANGE WITH 0-6 KM SHEAR OF 30 TO 40 KT. THIS

ENVIRONMENT SHOULD SUPPORT SUPERCELLS AND A THREAT FOR LARGE HAIL

SHOULD EXIST WHERE SUPERCELLS HAVE ACCESS TO STRONG INSTABILITY.

SUPERCELLS SHOULD ALSO HAVE AN ISOLATED TORNADO THREAT.

HOWEVER...FORECAST WIND PROFILES SUGGEST THE DOMINANT STORM MODE IS

QUESTIONABLE. AS WINDS VEER AT LOW-LEVELS AHEAD OF THE APPROACHING

FRONT...LINEAR MULTICELLS MAY DEVELOP WITH A WIND DAMAGE POTENTIAL.

DURING THE LATE AFTERNOON AND EARLY EVENING...A NARROW CORRIDOR WITH

AN ENHANCED SEVERE THREAT COULD EXIST FROM SRN WI SWWD ACROSS NW IL

INTO ERN IA...NRN MO AND FAR ERN KS WHERE THE COMBINATION OF

INSTABILITY/DEEP LAYER SHEAR SHOULD BE MAXIMIZED AND CO-LOCATED WITH

STEEP LAPSE RATES.

day2.gif

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LOT regarding tomorrow..

FORECAST SOUNDINGS INDICATE UPWARDS OF 2000 J/KG OF SURFACE BASED

CAPE AVAILABLE WITH 30-35 KT OF SHEAR...THOUGH THERE ARE SOME

INDICATIONS THAT CAPE VALUES COULD SHOOT UP BEYOND 3000. WITH A LOW

TRACK THAT IS FAVORED TO MOVE ACROSS THE CWA AND INTO NORTHERN

INDIANA...WINDS WILL BE ALLOWED TO BACK TO THE EAST OF THIS FEATURE.

THE NICE VEERING PROFILE TO THE HODOGRAPH YIELDS HELICITY VALUES IN

THE 2 TO 300 M2/S2 RANGE...AND THE THREAT FOR TORNADIC CELLS IN THE

WARM SECTOR AND WITH THE COLD FRONT CANNOT BE LOOKED OVER.

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Thunderstorms moving into western WI are strong, but not quite severe. Severe part of the line to the south could make it into SW WI in a bit.

SWS:

WIZ023>028-052130-

CHIPPEWA-DUNN-EAU CLAIRE-PEPIN-PIERCE-ST. CROIX-

331 PM CDT SAT MAY 5 2012

...THUNDERSTORMS MOVING INTO CHIPPEWA...DUNN...EAU

CLAIRE...PEPIN...PIERCE AND ST. CROIX COUNTIES THROUGH 430 PM CDT...

AT 327 PM CDT...WEATHER SERVICE RADAR WAS TRACKING STRONG

THUNDERSTORMS ALONG A LINE EXTENDING FROM EMERALD TO EAU GALLE TO 4

MILES NORTHEAST OF ELLA TO 7 MILES WEST OF BUFFALO. THESE STORMS WERE

MOVING EAST AT 40 MPH.

PEA SIZE HAIL...WINDS UP TO 40 MPH...AND HEAVY DOWNPOURS ARE EXPECTED

WITH THESE STORMS.

* LOCATIONS IN OR NEAR THE PATH OF THESE STORMS INCLUDE...

EAU CLAIRE.

KNAPP.

MENOMONIE.

TAINTER LAKE.

ROCK FALLS.

ELK MOUND.

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re: tornado potential tomorrow, there is definitely some nice veering with height but deep layer shear magnitude seems a bit borderline to me. I guess it's one of those days you wouldn't want to totally sleep on given all the instability.

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Rain through that storm earlier on the way to Rochester,MN....nothing much, but a few very nice cloud to ground lightning...big fat bolts. Foggy now.

La Crosse's update indicates that they still expect the MCS in the Plains to be severe if it makes it through the CWA.

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I'm really confused by the new day 2. A good portion of the Ohio Valley is in a SLIGHT RISK, but no mention of the region in the text...

It's there but it's broad brushed... "mid south to Lake Erie"

..ARKLATEX REGION...MOD-SOUTH TO LE

SCATTERED TO LOCALLY NUMEROUS TSTMS SHOULD DEVELOP THROUGHOUT AFTERNOON INTO EARLY EVENING...ALONG/AHEAD OF SFC COLD FRONT AND NEAR/E OF SFC LOW. POCKET OF RELATIVELY ENHANCED LOW-LEVEL SHEAR IS LIKELY FROM SFC LOW SEWD ALONG WARM FRONT...BENEATH SRN RIM OF FAVORABLE MIDLEVEL FLOW. THEREFORE...POTENTIAL FOR SUPERCELLS MAY EXIST OVER PARTS OF OH AND PERHAPS WRN PA...DEPENDING ON MESOSCALE EWD PROGRESS OF WARM FRONT. WITH FAVORABLY RICH MOISTURE OVER BROAD AREA OF WARM SECTOR...BUOYANCY SHOULD INCREASE WITH SWWD EXTENT FROM OH TO MID-SOUTH REGION...IN KEEPING WITH INCREASES IN MIDLEVEL LAPSE RATES AND SFC HEATING. HOWEVER...DEEP-LAYER WIND PROFILES AND VERTICAL SHEAR WILL BE WEAK...LEADING TO DOMINANT MULTICELL MODE IN LINES AND CLUSTERS. MAIN CONCERNS WILL BE DAMAGING DOWNDRAFT GUSTS AND OCNL HAIL. THREAT SHOULD DECLINE MARKEDLY OVER MOST OF AREA AFTER DARK...THOUGH A FEW COLD-POOL DRIVEN CLUSTERS MAY PERSIST AFTER 06Z WITHIN THIS BROAD SWATH.

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This system went from decent potential to pretty close to bag of crap in 2 days. Tomorrow's risk sounds so conditional per the outlook and with the absolute lack of shear I don't blame them. Going to be a multicell mess tomorrow. The only area that might have a chance at something decent might be the warm front in IL.

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Nice storms moving into the Des Moines area. We are a bit cool and under thick clouds. I think locations along and south of I-80, where it is sunny and will destabilize over the next few hours, have the best shot at seeing strong/severe storms from this line.

Definitely a weak warm front running from Fort Madison to Macomb to Lincoln (see dewpoints in the lower 70s). An hour or two of heating there should build a decent reservoir of CAPE ahead of this line. I'd like to see a little more storm relative flow in the low levels to keep the cold pool from out pacing the storms for a more widespread severe threat, but I don't see any reason why intermittent severe isn't possible.

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