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Good Chance for Svr Tstms on Sunday 8/21/11


Dark Energy

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day1.wind.gif

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE UPPER OH VALLEY AND

MID ATLANTIC STATES INTO NEW ENGLAND...

..SYNOPSIS

AN UPPER TROUGH CURRENTLY EXTENDING SWD THROUGH THE GREAT LAKES AND

ANCHORED BY A VORTEX OVER HUDSON BAY WILL UNDERGO FURTHER

AMPLIFICATION AS A SHORTWAVE TROUGH TRACKS ESEWD FROM THE UPPER

GREAT LAKES TO NY/PA THIS FORECAST PERIOD. AT 12Z SUNDAY...A COLD

FRONT ATTENDANT TO THE PARENT LONGWAVE TROUGH SHOULD EXTEND SWWD

FROM SRN ONTARIO THROUGH THE LOWER OH VALLEY TO CENTRAL AR AND WWD

INTO OK. THIS BOUNDARY WILL PROGRESS E/SEWD MOVING THROUGH MUCH OF

THE NERN AND MID-ATLANTIC STATES...AND EXTEND WSWWD INTO THE CENTRAL

GULF COAST STATES BY 12Z MONDAY.

FARTHER W...AN IMPULSE EMANATING FROM AN UPPER LOW ALONG THE NRN CA

COAST IS EXPECTED TO MOVE INTO WRN/NRN MT THIS AFTERNOON AIDING IN

SOME TSTM DEVELOPMENT OVER THE HIGHER TERRAIN. MEANWHILE...HEIGHT

RISES ARE EXPECTED ACROSS THE NRN HIGH PLAINS...TENDING TO LIMIT

TSTM DEVELOPMENT.

..MID-ATLANTIC STATES TO NEW ENGLAND

00Z NAM/GFS AND 12Z ECMWF AGREE WITH THE TIMING OF THE COLD FRONT

TODAY...REACHING NRN NY TO WRN PA/UPPER OH VALLEY DURING THE

EARLY-MID AFTERNOON. GIVEN THE TIMING OF THE FRONT ALLOWING FOR

SURFACE HEATING/DESTABILIZATION AND THE ARRIVAL OF FORCING ALOFT

DURING THE AFTERNOON/EVENING...THE FORECAST CONFIDENCE REMAINS GOOD

FOR THE DEVELOPMENT OF SEVERE STORMS TODAY INTO TONIGHT ACROSS THE

SLIGHT RISK AREA. SWLY LOW LEVEL WINDS ACROSS THE OH VALLEY TO WRN

PA AND SSWLY LOW LEVEL WINDS IN LEE OF THE CENTRAL APPALACHIANS TO

THE HUDSON VALLEY/NEW ENGLAND WILL EACH SUPPORT MOISTURE ADVECTION

INTO THESE REGIONS. ALTHOUGH MIDLEVEL LAPSE RATES ARE FORECAST TO

BE MODEST /AOB 6.5 C PER KM/ ACROSS THE SLIGHT RISK AREA...SURFACE

HEATING COMBINED WITH THE MOISTURE RETURN WILL RESULT IN MODERATE

INSTABILITY FROM MD/D.C./DELMARVA TO SERN/ERN NY AND SWRN NEW

ENGLAND THIS AFTERNOON. MLCAPE ACROSS THIS CORRIDOR WILL BE UP TO

1500-2000 J/KG WHILE FURTHER W OVER THE UPPER OH VALLEY VALUES WILL

BE UP TO 1000 J/KG.

DIFFLUENT FLOW ALOFT AND HEIGHT FALLS WITH THE APPROACH OF THE UPPER

GREAT LAKES SHORTWAVE TROUGH...AND CONVERGENCE/ASCENT ALONG THE COLD

FRONT AND PRE-FRONTAL/LEE TROUGH EXTENDING FROM VA TO ERN NY WILL

SUPPORT TSTM DEVELOPMENT BY EARLY-MID AFTERNOON IN VICINITY AND

AHEAD OF THESE SURFACE BOUNDARIES. STRENGTHENING WIND FIELDS AND

EFFECTIVE BULK SHEAR OF 40-50 KT COMBINED WITH THE AVAILABLE

INSTABILITY WILL SUPPORT ORGANIZED STORMS. SHEAR VECTORS MORE

NORMAL TO THE LEE TROUGH SUGGEST A GREATER POTENTIAL FOR DISCRETE

STORMS...INCLUDING SUPERCELLS. VERTICALLY VEERING WINDS AND HIGHER

THETAE EXTENDING FROM MD/ERN PA TO SERN NY/SWRN NEW ENGLAND SUPPORT

AN ISOLATED TORNADO THREAT ALONG WITH DAMAGING WINDS AND HAIL.

FARTHER W INTO THE UPPER OH VALLEY...ORGANIZED STRONG TO SEVERE

STORMS WILL BE POSSIBLE BY EARLY-MID AFTERNOON WITH STRONG WIND

GUSTS AND HAIL THE PRIMARY THREATS.

ALTHOUGH INSTABILITY SHOULD BE WEAKENING THIS EVENING...A FURTHER

INCREASE IN DEEP LAYER WIND FIELDS INTO THE NERN STATES AND 60-90

METER HEIGHT FALLS ACROSS THIS REGION SHOULD COMPENSATE THE WEAKER

THERMODYNAMICS FOR AT LEAST A CONTINUED THREAT FOR DAMAGING WINDS

INTO PARTS OF NEW ENGLAND. FORECAST SOUNDINGS SUGGEST A TORNADO

CANNOT BE RULED OUT ACROSS SRN NEW ENGLAND AS STRENGTHENING SLY LLJ

SUPPORTS AN INCREASE IN LOW LEVEL HODOGRAPH CURVATURE.

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.SHORT TERM /NOON TODAY THROUGH 6 AM MONDAY/...

UPR LOW SPINNING OVER HUDSON BAY WITH THE JET APPROACHING THE NRN

GREAT LAKES PER WATER VAPOR. H25 U COMPONENT WINDS AND H5 HEIGHT

ANOMALIES WITH THIS SYSTEM ABOUT 2-3 STD/S. 00Z SUITE OF MODELS

CONTINUE TO PROG SCT TSTMS DEVELOPING THIS AFTN ACROSS THE

W...EVOLVING INTO WIDESPREAD TSTMS THIS EVE AND THRU THE OVERNIGHT

AS THE COLD FRONT AND INCREASING DYNAMICS CATCH UP. THIS SOLN HAS

BEEN ACCEPTED FOR THE FCST.

PARAMETERS REMAIN IN PLACE FOR A SEVERE OUTBREAK. 00Z NAM CAME IN

A BIT HIGHER WITH THE BRN...RESULTING IN A TENDENCY TOWARDS

MULTICELLULAR. SYNOPTIC LLVL DIRECTIONAL SHEAR IS

LIMITED...HOWEVER AS STORMS DEVELOP ALLOWING FOR LLVL

INFLOW...EXPECT THIS SHEAR TO BE ENHANCED RESULTING IN AN

ENVIRONMENT MORE SUPPORTIVE OF SUPERCELLS.

ALTHOUGH THERE ISN/T A WARM FRONT INVOF THE CWA WITH THIS

EVENT...EHI STILL IN THE 1-2 RANGE SUPPORTING A TOR POTENTIAL.

INFLOW MAY ENHANCE THESE NUMBERS AS WELL BUT COMPUTATION IS BASED

ON SRH SO CONFIDENCE NOT AS HIGH AS IN THE BRN. ANY OUTFLOW

BOUNDARIES WILL ELEVATE THE SPIN UP RISK...AND AS THE CONVECTION

CONSOLIDATES TONIGHT THE RISK COULD SHIFT TO LI WITH COASTAL

BOUNDARY DEVELOPMENT.

PW/S STILL ON TRACK TO REACH JUST UNDER 2 INCHES SO HVY RAIN HAS

BEEN INCLUDED IN THE FCST. SEE HYDRO SECTION FOR ADDITIONAL INFO.

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Thinking moderate risk ONCE the storms get going and start doing dmg. FWIW. SPC wont issue it until it is already happening.

It would be a low probability and confidence moderate risk for them...because there are still plenty of questions to be answered. But I think there is a small chance that they do issue one today.

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SPC's disco. They are saying the storms to the west should hold together and strengthen some. The cloud cover might cut down on new storms popping up.

DAY 1 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0745 AM CDT SUN AUG 21 2011

...NERN STATES TO MID-ATLANTIC REGION...

BUSY WEATHER DAY ON TAP FOR THE REGION. WATER VAPOR SHOWS

TWO-STREAM FLOW WITH PRIMARY WLYS AND STRONG UPR TROUGH DIGGING

ACROSS THE CNTRL GREAT LAKES. SEPARATE UPR JET WAS MOVING THROUGH

THE MIDWEST WITH A FORMIDABLE SHORTWAVE TROUGH MIGRATING ACROSS THE

MID-OH VLY AND A WEAKER PERTURBATION MOVING INTO THE LWR GREAT LAKES

REGION.

ONGOING TSTM CLUSTERS TIED TO THE LWR GREAT LAKES DISTURBANCE WILL

CONTINUE TO PROGRESS EWD...REACHING CNTRL/ERN NY BY 15-18Z.

DOWNSTREAM AIR MASS HAS BEEN MOISTENING OVERNIGHT AND DAYBREAK SATL

IMAGES SUGGEST MODEST DIABATIC HEATING WILL OCCUR THIS MORNING WITH

MLCAPES 1000-1500 J/KG BY AFTN. EXPECT EXISTING TSTMS TO GROW

STRONGER THIS MORNING WITH ADDITIONAL STORMS DEVELOPING WITHIN THE

INSTABILITY AXIS. THIS WILL RESULT IN BKN-BANDS OF STG-SVR STORMS

THAT TRANSLATE ENE INTO WRN NEW ENGLAND/ERN NY BY MID/LATE AFTN.

LOWER-AMPLITUDE WAVE MIGRATING EWD FROM THE MID-OH VLY WILL BE

INSTRUMENTAL IN INSTIGATING MORE STORMS FROM ERN PA SWD INTO

NRN/CNTRL VA. STRONGER THERMAL BUOYANCY WILL EXIST HERE AS SATL

SHOWS POTENTIAL FOR STRONG HEATING AMID COMPARATIVELY MORE MOIST

BOUNDARY LAYER.

VERTICAL SHEAR...WHILE SOMEWHAT WEAK THIS MORNING...WILL BE

INCREASING AS 40-60 KT WNW MID-LVL FLOW/STEEPER MID-LVL LAPSE RATES

ARRIVE THIS AFTN PER UPSTREAM RAOBS. THIS WILL RESULT IN MULTICELLS

AND A FEW SUPERCELLS CAPABLE OF DMGG WINDS AND LARGE HAIL. ISOLD

TORNADOES CANNOT BE RULED OUT...ESPECIALLY FROM NRN VA/MD NWD WHERE

FCST HODOGRAPHS SHOW STRONGEST 0-1KM SHEAR VCNTY LEE TROUGH/WEAK SFC

LOW.

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Real shame I've been sunny the whole day here and it probably still won't be enough to get a nice storm where I am.....seabreeze blowsss haha

Where exactly are you located on LI? I think theres a goo chance of strong strongs for LI tonight. They may be below severe, which is not certain, as I think the coastal boundaries could help to enhance things, but there could be activity all the way out east tonight with the front.

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http://www.spc.noaa.gov/products/md/md2030.html

MESOSCALE DISCUSSION 2030

NWS STORM PREDICTION CENTER NORMAN OK

1054 AM CDT SUN AUG 21 2011

AREAS AFFECTED...PARTS OF NRN VA...THE DELMARVA...SRN AND ERN

PA...NJ...INTO THE LWR HUDSON VALLEY

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY

VALID 211554Z - 211800Z

TRENDS ARE BEING MONITORED FOR AN INCREASING SEVERE THREAT THAT

COULD REQUIRE ONE OR MORE WATCHES DURING THE 17-19Z TIME FRAME.

BENEATH DIFLUENT UPPER FLOW DOWNSTREAM OF A VIGOROUS SHORT WAVE

TROUGH NOW TURNING EASTWARD THROUGH THE GREAT LAKES REGION...

SCATTERED THUNDERSTORM ACTIVITY IS ONGOING THROUGH MUCH OF THE

NORTHEAST. ASSOCIATED CLOUD COVER AND PRECIPITATION ARE SLOWING

BOUNDARY LAYER DESTABILIZATION IN BROAD POCKETS...COMPLICATING THE

SEVERE WEATHER POTENTIAL...WITH SOUTHWESTERLY DEEP LAYER MEAN FLOW

AND SHEAR STILL SOMEWHAT MODEST ACROSS MUCH OF THE REGION.

IT DOES APPEAR ONE AREA OF FORCING FOR ASCENT ASSOCIATED WITH A

SMALLER SCALE IMPULSE/WEAK AREA OF MID-LEVEL HEIGHT FALLS IS

BEGINNING TO SHIFT EAST NORTHEAST OF THE CENTRAL APPALACHIANS. THIS

COULD SUPPORT INCREASING STORM DEVELOPMENT WITHIN THE NEXT FEW HOURS

ACROSS NORTHERN VIRGINIA INTO PARTS OF SOUTH CENTRAL/ SOUTHEAST

PENNSYLVANIA...WHERE STRONGEST SURFACE HEATING IS OCCURRING. LATEST

RUC GUIDANCE SUGGESTS INHIBITION FOR MOIST BOUNDARY LAYER PARCELS

CHARACTERIZED BY 70F+ SURFACE DEW POINTS IS DIMINISHING...AND MIXED

LAYER CAPE COULD EXCEED 2000 J/KG TOWARD THE 18-20Z.

THEREAFTER...THE SEVERE WEATHER POTENTIAL...INCLUDING THE RISK FOR

ISOLATED SUPERCELLS AND ORGANIZED STORM CLUSTERS...APPEARS LIKELY TO

GRADUALLY INCREASE THROUGH THE REMAINDER OF THE AFTERNOON. THIS

PROBABLY WILL INCLUDE AREAS FROM THE LEE OF THE LOWER GREAT LAKES

EASTWARD INTO NEW ENGLAND...BUT IT REMAINS UNCLEAR WHETHER THE

THREAT WILL BECOME WIDESPREAD...OR REMAIN RELATIVELY LOCALIZED

ACROSS THESE AREAS.

..KERR.. 08/21/2011

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Where exactly are you located on LI? I think theres a goo chance of strong strongs for LI tonight. They may be below severe, which is not certain, as I think the coastal boundaries could help to enhance things, but there could be activity all the way out east tonight with the front.

I live in southwest suffolk county near the south shore. the front really prolly is my only hope as the single cell storms I usually miss anyway

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