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August 22-31 Severe Weather Thread


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It's the RUC/GFS vs the NAM regarding amount of instability here tomorrow afternoon and evening with the NAM being alot less bullish.

Interesting, the NAM seemed pretty bullish last night. Has its instability decreased, or are the RUC/GFS more impressive with instability than the NAM was even last night?

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0Z NAM shows quite a cap opening tomorrow afternoon/evening, which it did not show yesterday evening...

MKX:

IF THIS SYSTEM CAN EXIT THE REGION AND GIVE THE AREA A FEW HOURS TO

HELP INSTABILITY RECOVER...THERE IS A SHOT AT SEVERE WEATHER BY LATE

AFTERNOON ACROSS THE AREA. DEEP LAYER SHEAR INCREASES TO AROUND 40

KNOTS DURING THE AFTERNOON...WITH 0-1KM SHEAR INCREASING TO AROUND

30 KNOTS WITH A CURVED HODOGRAPH. AROUND 1500 J/KG MEAN LAYER CAPES

EXIST AS WELL...WITH SOME CONVECTIVE INHIBITION. THIS SHOULD BE

OVERCOME AS STRONG SHORTWAVE TROUGH MOVES SOUTHEAST INTO THE REGION

BY 00Z WEDNESDAY. WARM FRONT ALSO APPROACHES THE AREA FROM THE

SOUTHWEST...AND OUTFLOW BOUNDARIES FROM MORNING CONVECTION LINGERING

IN THE AREA. LARGE HAIL...DAMAGING WINDS...TORNADOES AND HEAVY

RAINFALL ARE ALL POSSIBLE GIVEN THE DEGREE OF INSTABILITY/SHEAR/LIFT

AND BOUNDARIES IN THE AREA. SPC DAY 2 SLIGHT RISK ACROSS THE AREA

LOOKS GOOD.

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Day 2 outlook is out

DAY 2 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1210 AM CDT TUE AUG 23 2011

VALID 241200Z - 251200Z

..THERE IS A SLGT RISK OF SVR TSTMS OVER LOWER MI...NERN IL NRN IND...NWRN OH...

..SYNOPSIS

A POTENT SHORTWAVE TROUGH WILL MOVE SEWD ACROSS THE UPPER MS VALLEY AND INTO THE GREAT LAKES OVERNIGHT. AT THE SURFACE...A COLD FRONT WILL EXTEND FROM LOWER MI SWWD ACROSS IL/MO AND INTO NRN OK BY 00Z. SWLY FLOW AHEAD OF THIS FRONT WILL MAINTAIN SUBSTANTIAL BOUNDARY LAYER MOISTURE WITH UPPER 60S TO LOWER 70S DEWPOINTS.

..LOWER MI INTO NERN IL...IND...OH

MORNING CONVECTION WITH PERHAPS A MARGINAL HAIL THREAT WILL QUICKLY MOVE OUT BY MID MORNING...ALLOWING FOR DESTABILIZATION DURING THE DAY. FORCING ALONG THE COLD FRONT AND STRONG FLOW ALOFT SHOULD LEAD TO SCATTERED SEVERE THUNDERSTORMS...INITIALLY AS SUPERCELLS CAPABLE OF VERY LARGE HAIL. SIG HAIL THREAT MAY BE MITIGATED BY THE RELATIVELY SHORT HODOGRAPH LENGTH...BUT MODERATELY STRONG MEAN WIND THROUGH THE COLUMN WILL SUPPORT RAPIDLY MOVING STORMS WITH DAMAGING WINDS. 700 MB WINDS WILL APPROACH 50 KT BY EVENING.

..MID MS VALLEY INTO THE LOWER OH/TN VALLEYS

ELEVATED MORNING STORMS ARE LIKELY IN THIS REGION DRIVEN BY WARM ADVECTION. PRESENCE OF STEEP LAPSE RATES ALOFT AND MARGINAL SHEAR MAY ALLOW A FEW OF THESE STORMS TO CONTAIN MARGINALLY SEVERE HAIL. AFTER THIS ACTIVITY WANES DURING THE LATE MORNING...STRONG INSTABILITY WILL MATERIALIZE WITH A VERY MOIST AND WARM AIR MASS IN PLACE. FORCING WILL BE WEAK INITIALLY BUT WILL INCREASE DURING THE EVENING AS A COLD FRONT MOVES SWD. ALSO...MORE VIGOROUS ACTIVITY TO THE NE MAY BACK BUILD SWWD INTO THE REGION...WITH SOME WIND AND HAIL THREAT.

..JEWELL.. 08/23/2011

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quite the long and nicely written outlook

DAY 1 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1258 AM CDT TUE AUG 23 2011

VALID 231200Z - 241200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE UPPER MS VALLEY INTO

THE MIDWEST AND CENTRAL GREAT LAKES...

...SYNOPSIS...

A SHORTWAVE TROUGH...CURRENTLY MOVING ESEWD ACROSS THE DAKOTAS PER

WATER VAPOR IMAGERY...WILL AMPLIFY TODAY AS IT MAINTAINS AN ESEWD

TRACK THROUGH THE WRN GREAT LAKES BY 24/00Z...AND REACH THE LOWER

GREAT LAKES/UPPER OH VALLEY REGION BY 12Z WEDNESDAY. MEANWHILE...AN

UPSTREAM SHORTWAVE TROUGH...CURRENTLY MOVING EWD INTO BRITISH

COLUMBIA...WILL BEGIN TO AMPLIFY IN LEE OF THE CANADIAN ROCKIES

TODAY...AND UNDERGO FURTHER DEEPENING/AMPLIFICATION TUESDAY NIGHT

REACHING NWRN ONTARIO AND NRN MN BY THE END OF THE PERIOD.

OTHERWISE...A STRONG RIDGE WILL REMAIN ANCHORED ACROSS THE FOUR

CORNERS STATES EXTENDING EWD TO THE LOWER MS VALLEY/CENTRAL GULF

COAST STATES.

IN THE LOW LEVELS...A NNW-SSE ORIENTED WARM FRONT WILL ADVANCE EWD

ACROSS MN...IA...AND MO TODAY REACHING THE MN/WI BORDER TO THE MID

MS VALLEY BY MID-LATE THIS AFTERNOON. BY THIS TIME...A DRY LINE

SHIFTING ESEWD SHOULD INTERSECT THE WARM FRONT OVER EAST

CENTRAL-SERN MN AND EXTEND SWWD INTO CENTRAL NEB. MEANWHILE...A

COLD FRONT ATTENDANT TO THE UPSTREAM AMPLIFYING CANADIAN TROUGH WILL

MOVE ESEWD ACROSS THE NRN PLAINS TODAY...REACHING THE UPPER MS

VALLEY TO CENTRAL NEB BY 12Z WEDNESDAY.

...UPPER AND MID MS VALLEY TO CENTRAL GREAT LAKES...

AT 12Z TODAY...MODELS ARE IN GENERAL AGREEMENT SUGGESTING AT LEAST

ONE MCS SHOULD BE ONGOING OVER PARTS OF SRN MN/NRN IA AND

POTENTIALLY INTO WRN/SWRN WI. MODERATE INSTABILITY AND EFFECTIVE

BULK SHEAR AROUND 35 KT IN THIS REGION INDICATE POTENTIAL FOR SOME

ONGOING SEVERE WEATHER THREAT WITH THIS MCS. ALTHOUGH LOW LEVEL WAA

SHOULD PERSISTENT THROUGH THE MORNING...WEAKENING OF THE SWLY LLJ

INTO ERN IA/SRN WI SUGGESTS THE MCS MAY UNDERGO AT LEAST TEMPORARY

WEAKENING BETWEEN 12-18Z AS THE LLJ WEAKENS. A CONVECTIVE OUTFLOW

BOUNDARY ATTENDANT TO THIS MCS SHOULD EXTEND WWD THROUGH NRN IL AND

THEN NWWD THROUGH NERN IA TO EAST CENTRAL-SERN MN BY MID-LATE

AFTERNOON WHERE IT WILL INTERSECT AND/OR MERGE WITH THE WARM FRONT.

THE ERN EXTENT OF AN EML/STEEP MIDLEVEL LAPSE RATES /OBSERVED WITH

THE NRN PLAINS 23/00Z SOUNDINGS/ SHOULD BE LOCATED ACROSS THE UPPER

MS VALLEY BY 12Z TODAY...AND ADVANCE EWD TO THE WRN GREAT

LAKES/MIDWEST INTO THE AFTERNOON AND SEWD TO THE MID MS VALLEY LATE

TUESDAY NIGHT. THESE LAPSE RATES WILL BE SPREADING ATOP A QUITE

MOIST WARM SECTOR /SURFACE DEWPOINTS IN THE LOWER 70S AND

PRECIPITABLE WATER VALUES 1.5+ INCH/ BUILDING EWD TODAY...ALONG AND

W THROUGH S OF THE WARM FRONT AND ANY ONGOING EARLY MORNING MCS IN

THE UPPER MS VALLEY. THESE THERMODYNAMICS COMBINED WITH SURFACE

HEATING INVOF AND W-S OF THE AFOREMENTIONED WARM FRONT/CONVECTIVE

OUTFLOW WILL RESULT IN THE STRONGEST INSTABILITY /MLCAPE 3000-4000 J

PER KG/ EXTENDING FROM EAST CENTRAL MN/WRN WI SWD INTO IA AND

ADJACENT NWRN-WRN IL. SIMILAR INSTABILITY VALUES WILL ALSO EXTEND

SWWD INTO THE MID MO VALLEY...THOUGH FORECAST SOUNDINGS INDICATE THE

AIR MASS OVER WRN IA/ERN NEB SHOULD REMAIN CAPPED LIMITING

CONVECTIVE DEVELOPMENT.

FORCING FOR ASCENT ATTENDANT TO THE DAKOTAS SHORTWAVE TROUGH AND

INCREASING LOW LEVEL WAA INVOF OF A RE-STRENGTHENING SWLY LLJ

EXTENDING FROM NRN MO TO SRN WI ARE EXPECTED TO SUPPORT NEW TSTM

DEVELOPMENT ALONG THE WARM FRONT IN EAST CENTRAL-SERN MN INTO ERN IA

AND ALONG THE OUTFLOW BOUNDARY IN NWRN IL. THIS STORM INITIATION

SHOULD OCCUR BY MID-LATE AFTERNOON. SUPERCELLS WILL BE LIKELY WITH

THE FIRST STORMS...GIVEN VERY STRONG INSTABILITY...STEEP MIDLEVEL

LAPSE RATES...EFFECTIVE BULK SHEAR UP TO 40 KT AND ENHANCED LOW

LEVEL SHEAR INVOF THE WARM FRONT/MORNING OUTFLOW BOUNDARY. VERY

LARGE HAIL...SOME EXCEEDING 2 INCH IN DIAMETER...WILL BE POSSIBLE

WITH THE INITIAL ACTIVITY ALONG WITH DAMAGING WINDS. WHILE A

TORNADO THREAT WILL ALSO BE POSSIBLE...THIS THREAT SHOULD INCREASE

INTO THE EARLY EVENING FROM SERN MN/NERN IA TO SRN WI AND NWRN IL AS

A STRENGTHENING LLJ INCREASES THE SIZE OF HODOGRAPH CURVATURE.

AFTER DARK...MODELS SUGGEST STORMS SHOULD GROW UPSCALE INTO ONE OR

TWO MCS SPREADING ESEWD TOWARD LOWER MI AND THE MIDWEST...INCLUDING

THE CHICAGO METRO AREA. LOW LEVEL WAA ALONG THE SWLY LLJ EXTENDING

THROUGH THESE REGIONS TUESDAY NIGHT AND ASCENT ATTENDANT TO THE

SHORTWAVE TROUGH SUPPORT THIS SCENARIO WITH A THE PRIMARY THREATS

BEING HAIL AND STRONG WIND GUSTS.

..PETERS/SMITH.. 08/23/2011

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DTX/GRR both strongly worded AFDs for Wed both mentioning supercells and tornadoes.

DTX

THE SOUTH DAKOTA/MINNESOTA CLUSTER OF THUNDERSTORMS WILL TRAVERSE

EASTWARD TODAY...DIVING SOUTH OF LOWER MICHIGAN LATE THIS

AFTERNOON/EARLY THIS EVENING WHILE DRAMATICALLY WEAKENING. THIS

TRAJECTORY IS SUPPORTED BY THE N TO S ORIENTATION OF THE INSTABILITY

GRADIENT ALONG WITH THE FORECASTED DIRECTION OF THE CORFIDI VECTORS.

THE REFIRING OF THE VEERED LOW LEVEL JET IS EXPECTED TO INITIATE AN

ADDITIONAL CLUSTER OF CONVECTION NEAR LAKE MICHIGAN/FAR WESTERN

LOWER MICHIGAN RIGHT AT THE START OF THE PERIOD. THIS ACTIVITY IS

EXPECTED TO ARRIVE AT THE GATES OF THE CWA ROUGHLY AT/AROUND 2Z THIS

EVENING. CONVECTIVE VIGOR WILL NOT BE THAT STRONG...WITH INSTABILITY

RELEGATED TO MOIST ADIABATIC LAPSE RATES. BY FAR...THE MAIN THREAT

TONIGHT WILL BE HEAVY RAINFALL POTENTIAL FROM BOTH...TORRENTIAL

RAINFALL RATES IN CONVECTION (HIGH FORECASTED VALUES OF OMEGA IN THE

WARM CLOUD PORTION OF THE COLUMN/AND PWATS OF 1.9 INCHES) AND

POTENTIAL TRAINING OF INDIVIDUAL CONVECTIVE ELEMENTS. A BIG NEGATIVE

GOING FOR TONIGHT WILL BE QUICK STORM MOTION...LIKELY GREATER THAN

40 MPH. NEVERTHELESS...DECIDED IT PRUDENT TO MENTION POSSIBLE HEAVY

RAINFALL IN THE ZONES/POINT AND CLICK.

LATENT HEAT BOMB IN THE MIDLEVELS ALONG WITH SUBSIDENCE IN THE WAKE

OF OVERNIGHT CONVECTION WILL BRING A QUIET PERIOD WEDNESDAY MORNING.

A STOUT CAPPING INVERSION IN THE 900-800MB LAYER ON WEDNESDAY WILL

ALLOW CAPES TO BUILD SUBSTANTIALLY THROUGHOUT THE DAY. EXPECTATIONS

ARE FOR A THINNING OR EXIT OF HIGH CLOUD/CONVECTIVE DEBRIS DURING

THE AFTERNOON. THIS WILL ONLY HELP THINGS DESTABILIZE. PEERING

THROUGH A FEW ANIMATIONS OF BUFKIT SOUNDINGS FOR VARIOUS DATA POINTS

SUGGESTS THAT THE CAP WILL HOLD TIGHT UNTIL IMMEDIATELY PRECEDING THE

STRONG COLD FRONT. A ROUGH THETA E PLAN VIEW ANALYSIS SUGGESTS IT

WILL TAKE UNTIL THE 850MB RIBBON OF ENHANCED THETA E SLIDES INTO

PLACE. THIS SWATH OF HIGHER MOISTURE CONTENT IS EXPECTED TO BE

ROUGHLY 75-100 MILES IN ADVANCE OF THE SURFACE COLD FRONT. THIS PUTS

SPECIFIC TIMING OF THE SEVERE RISK FOR PRIMARILY 00-06Z THURSDAY.

THE WIND PROFILE LOOKS TO BE RELATIVELY OMINOUS...35 KNOTS AT

900MB...50 KNOTS AT 700MB AND GREATER THAN 20 KNOTS IN THE 0 TO.5KM

LAYER. THE HIGH AMOUNT OF SHEAR WILL SUPPORT SPEEDY SUPERCELLS EARLY

IN THE CONVECTIVE LIFE CYCLE...TRANSITIONING TO DYNAMIC BOW ECHO

STRUCTURES AS THE CELLS MATURE AND CONVECTIVE COLD POOLS

PROLIFERATE. THE NAM PROFILE MAY BE A LITTLE HOT ON THE

DEWPOINTS...BUT DEWPOINTS SHOULD STILL BE IN THE NEIGHBORHOOD OF 70

DEGREES F DURING THE EVENING. GIVEN INSTABILITY/SHEAR BALANCE

EXPECTATIONS ARE FOR A WIDESPREAD SEVERE RISK ACROSS SOUTHEASTERN

MICHIGAN WITH DAMAGING WINDGUSTS...LARGE HAIL...AND TORNADOES ALL

POSSIBLE.

A VERY STABLE SURFACE ANTICYCLONE WILL DRIVE THE REGIONS WEATHER FOR

THE END OF THE WEEK AND MUCH OF THE WEEKEND. WILL LEAVE THE CHANCE

FOR PRECIPITATION ON SATURDAY...BUT 23.00Z NWP SUITE HAS COME IN MUCH

MUCH DRIER WITH THE WEAK COLD FRONTAL FEATURE THAT WILL SLIDE

THROUGH. HIGH TEMPERATURES DURING THIS END OF THE LONG TERM PERIOD

SHOULD PREDOMINATELY REMAIN IN THE 70S.

GRR

WE EXPECT THE EVENING STORMS TO SHIFT EAST OF THE CWFA BY DAYBREAK

WED MORNING AS THE WAVE AND LLJ SHIFT EAST OF THE AREA. THE WARM

FRONT IS EXPECTED TO PUSH THROUGH THE CWFA...PUTTING THE AREA IN THE

WARM SECTOR WED MORNING. WE EXPECT TEMPS TO WARM QUICKLY WITH SUN

EXPECTED TO BREAK OUT. THE FRONT WILL APPROACH THE NRN SECTION OF

THE CWFA JUST AFTER 18Z...HOWEVER FCST SOUNDINGS SHOW THAT MOST IF

NOT ALL THE AREA SHOULD BE CAPPED AROUND 3-5K FEET. THIS SHOULD HELP

THE AREA WARM WELL INTO THE 80S AND APPROACH 90.

SUNSHINE WILL HELP INSTABILITY BUILD QUITE WELL WITH SFC BASED LI/S

EXPECTED TO DROP TO -7C OR SO AND ML CAPES EXPECTED TO INCREASE TO

OVER 2K J/KG ACROSS THE CWFA. THE HIGHEST INSTABILITY WILL BE FOUND

ACROSS THE SE WHERE NO LAKE INFLUENCE WILL BE FELT AND WHERE THE

FRONT WILL MOVE THROUGH LATER. MODELS ARE ALL INDICATING THAT

CONVECTION WILL NOT FIRE UNTIL VERY LATE IN THE AFTERNOON WHEN THE

CAP BECOMES ERODED BY THE INCOMING UPPER LOW AND ASSOCIATED COLD

POOL ALOFT. BY THIS TIME...THE FRONT SHOULD BE NEAR A LINE ROUGHLY

FROM THE NE CORNER OF THE CWFA TO THE SW CORNER. DEEP LAYER SHEAR

VALUES OF 40-50 KNOTS ALONG WITH THE INSTABILITY AND STRONG

CONVERGENCE ALONG THE FRONT WILL ALLOW FOR STORMS TO EXPLODE ONCE

THEY GO. WE COULD SEE SUPERCELLS DEVELOP INITIALLY WITH ALL OF THE

INSTABILITY AND SHEAR. DAMAGING WINDS...LARGE HAIL...AND ISOLATED

TORNADOES WILL ALL BE POSSIBLE ACROSS THE SE PORTION OF THE CWFA

BEFORE THE FRONT EXITS LATER IN THE EVENING.

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Red sky at morning, sailor take warning :-)

Beautiful sunrise although still very cool this morning among the corn and lowlands on 47 down to Huntley.

Time to really put evapotranspiration to work. Let's keep this morning's MCS north of the border while we're at it. I get the feeling the ofb placement will determine a lot later today, as described by SPC, et. al.

Chistorm - will be done in Elmhurst and heading back nw by 18z.

edit: mcs staying north of the border ain't gonna happen. let's move it on through and out.

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Red sky at morning, sailor take warning :-)

Beautiful sunrise although still very cool this morning among the corn and lowlands on 47 down to Huntley.

Time to really put evapotranspiration to work. Let's keep this morning's MCS north of the border while we're at it. I get the feeling the ofb placement will determine a lot later today, as described by SPC, et. al.

Chistorm - will be done in Elmhurst and heading back nw by 18z.

edit: mcs staying north of the border ain't gonna happen. let's move it on through and out.

heating was never progged to be all that crazy today as it was and with this large MCS in the vicinity I just don't see anything widespread happening this afternoon.

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heating was never progged to be all that crazy today as it was and with this large MCS in the vicinity I just don't see anything widespread happening this afternoon.

I think the bigger factor in causing the thunderstorm activity this afternoon would not be the cape but the shear and helicity numbers, which should still be relatively high.

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line really crapping the bed (expectedly) as it encounters stable environment over NE Illinois and we should be feeling the effects of the large debris field and cold pool well into the afternoon. This afternoon is pretty murky.

the HRRR has been consisten in big storms firing around 21z in northwest IL and pushing them southeast following the instability but id rather see what things look like around noon.

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line really crapping the bed (expectedly) as it encounters stable environment over NE Illinois and we should be feeling the effects of the large debris field and cold pool well into the afternoon. This afternoon is pretty murky.

Can't say I'm surprised either, but is it too much to ask for some rain? Right now I'd settle for a nice moderate to heavy rain for a couple hours, but it looks like even that will be crapping out.

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