62 replies to this topic

[LongIslandWthr]

...NERN THROUGH MID ATLANTIC STATES...

MCS CURRENTLY ONGOING COMPLICATES THIS FORECAST SOMEWHAT. FORWARD
PROPAGATING PORTION OF MCS NOW MOVING THROUGH ERN OH IS EXPECTED TO
CONTINUE A WEAKENING TREND INTO THE EARLY MORNING AS IT MOVES EWD
INTO A LESS UNSTABLE AIR MASS. OTHER STORMS ALONG WARM ADVECTION
WING ACROSS SWRN NY WILL SHIFT ENEWD OVERNIGHT INTO CNTRL/ERN NY BY
12Z THURSDAY. BEST DESTABILIZATION POTENTIAL WILL EXIST SOUTH OF
THIS ACTIVITY FROM SERN NY...SRN NEW ENGLAND INTO THE MID ATLANTIC
WHERE STRONGER DIABATIC HEATING OF THE BOUNDARY LAYER WILL
CONTRIBUTE TO MODERATE INSTABILITY /1500-2000 J/KG MLCAPE/. STORMS
ARE EXPECTED TO REDEVELOP AND INTENSIFY ALONG PRE-FRONTAL OUTFLOW
BOUNDARIES...TERRAIN FEATURES AND WARM SECTOR AS THE ATMOSPHERE
DESTABILIZES. A BELT OF WLY DEEP LAYER FLOW WITH 40-50 KT MOSTLY
UNIDIRECTIONAL BULK SHEAR WILL ACCOMPANY THE UPPER TROUGH AND
CONTRIBUTE TO THE POTENTIAL FOR ORGANIZED STORMS INCLUDING
SUPERCELLS AND BOWING SEGMENTS. DAMAGING WIND WILL BE THE MAIN
THREAT...BUT ISOLATED HAIL WILL ALSO BE POSSIBLE ALONG WITH THE
THREAT FOR A COUPLE OF ISOLATED TORNADOES.

[NittanyLion]

Still looking good for a moderate severe outbreak possible later today.

MU CAPE already 1000-2000 and we should get those values at the surface if the sun's out and it mixes out. Lifted Indicies -4 this morning just to the west, with forecasted values to -6 this afternoon, TT forecasted to be near 50, and a SWEAT Index of 325. Midlevel lapse rates up to 6.5 C/km and sfc to 6km wind shear of 50 knots, which puts the main threat today of damaging winds. I wouldn't expect any severe hail today, but some small hail is certainly possible given 20 knts of midlevel storm relative flow and a freezing level of around 13000 feet. Given Bulk Richardson Numbers between 15 and 40 today, along with some storm relative shear of 200, there is the possibility for a few supercells. EHI values also between 1 and 2. But I would favor the southern areas in regards to development of them. And still I wouldn't forecast much in the way of strong tornado development.

Overall, looks like a decent storm threat with damaging winds the prevailing threat, along with some small hail.

[NittanyLion]

HRR favoring initial development of storms in the area around 12noon followed by a broken squall line moving through between 2 and 5PM.

[NittanyLion]

Total forecasted precip:

[NittanyLion]

Mesoscale Discussion just issued, watch likely:


MESOSCALE DISCUSSION 1109
NWS STORM PREDICTION CENTER NORMAN OK
0838 AM CDT THU JUN 24 2010

AREAS AFFECTED...PORTIONS PA...WRN/CENTRAL NY...NWRN NJ...EXTREME
NRN WV...EXTREME SERN OH.

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY

VALID 241338Z - 241515Z

AS NOTED IN 13Z DAY-1 OUTLOOK...DAMAGING WIND THREAT FCST TO
INCREASE ACROSS MID-ATLANTIC REGION THROUGH REMAINDER MORNING HOURS.
IT NOW APPEARS THAT THIS RISK WILL COMMENCE WITH SFC-BASED
EVOLUTION OF INITIALLY ELEVATED COMPLEX OF TSTMS -- NOT YET SVR AS
OF 1315Z BUT STRENGTHENING OVERALL -- THAT DEVELOPED IN PAST HOUR
OVER NERN OH...MOVING EWD 45-50 KT ACROSS NWRN TO N-CENTRAL PA.

BOUNDARY LAYER AIR MASS AHEAD OF THIS ACTIVITY IS CHARACTERIZED BY
SFC DEW POINTS MID-UPPER 60S F. HOWEVER...MODIFIED PBZ RAOB SHOWS
SHALLOW MOIST LAYER WITH DRYING ALOFT TO NEAR 800 MB...SUPPORTING
QUICK DIABATIC TRANSITION TO WELL-MIXED SUBCLOUD LAYER IN PRESENCE
OF INCREASING DIABATIC SFC HEATING...IN TURN FAVORING MAINTENANCE TO
SFC OF STG-SVR CONVECTIVE GUSTS GENERATED ALOFT. EXPECT HEATING TO
YIELD FAVORABLE EROSION OF SBCINH/MLCINH NOW INCREASING WITH EWD
EXTENT ACROSS REGION AS WELL. MODIFIED RAOBS AND RUC SOUNDINGS
SUGGEST MLCAPE EXCEEDING 500 J/KG AND APCHG 1000 J/KG IN SOME
LOCALES BY 15Z. KINEMATIC PROFILES ARE FAVORABLE WITH ESSENTIALLY
UNIDIRECTIONAL DEEP-TROPOSPHERIC FLOW...AND STG SPEED SHEAR
CONTRIBUTING TO AROUND 50 KT OF EFFECTIVE SHEAR MAGNITUDE.
DEEP-SHEAR AND MEAN WIND VECTORS WILL TEND TO ALIGN NORMAL TO
MERIDIONAL PORTION OF THIS ACTIVITY AND ANY ADDITIONAL CONVECTION
THAT CAN DEVELOP FARTHER S TOWARD SRN PA BORDER REGION AND NWRN
WV...LATTER AREA BEING IN SRN PERIPHERY OF STRONGEST DCVA ALOFT
RELATED TO EWD-MOVING GREAT LAKES SHORTWAVE TROUGH.

..EDWARDS.. 06/24/2010


ATTN...WFO...OKX...ALY...PHI...BGM...BUF...CTP...LWX...PBZ...
CLE...

LAT...LON 40898070 40947924 41787848 42327806 43017640 43237482
42427400 40997476 40087616 39727833 39598001 39748097
40408095 40898070

[Stormchaser]

Looking very impressive severe wise w/ convective initiation over WPA right now. Storms should organize into bowing segments or possibly even a MCS/unified squall line by this afternoon. MUCAPE's already 1000-2000 J/KG, lifted indices upwards of -4 to -5, mid and low level lapse rates 6-6.5, effective bulk shear conducive w/ unidirectional WLY flow of up to 45-50 kts in EPA. In addition, other parameters which are usually low in this area are fairly impressive: MCS maintenance, derecho composite, etc. Helicity is near 200 m2/s2 so an isolated tornado cannot be ruled out either.

Overall if today busts I'd be surprised; we've got cloud debris thinning w/ what looks to be several hours of intense diurnal heating today, in conjunction w/ favorable mid/upper level dynamics, we should be talking widespread strong convection, with the primary threat being wind damage in bow echos.

[Ehop]

What is the timing of the storms?

[NittanyLion]

NittanyLion, on Jun 24 2010, 07:56 AM, said:

Still looking good for a moderate severe outbreak possible later today.

MU CAPE already 1000-2000 and we should get those values at the surface if the sun's out and it mixes out. Lifted Indicies -4 this morning just to the west, with forecasted values to -6 this afternoon, TT forecasted to be near 50, and a SWEAT Index of 325. Midlevel lapse rates up to 6.5 C/km and sfc to 6km wind shear of 50 knots, which puts the main threat today of damaging winds. I wouldn't expect any severe hail today, but some small hail is certainly possible given 20 knts of midlevel storm relative flow and a freezing level of around 13000 feet. Given Bulk Richardson Numbers between 15 and 40 today, along with some storm relative shear of 200, there is the possibility for a few supercells. EHI values also between 1 and 2. But I would favor the southern areas in regards to development of them. And still I wouldn't forecast much in the way of strong tornado development.

Overall, looks like a decent storm threat with damaging winds the prevailing threat, along with some small hail.

Stormchaser, on Jun 24 2010, 09:11 AM, said:

Looking very impressive severe wise w/ convective initiation over WPA right now. Storms should organize into bowing segments or possibly even a MCS/unified squall line by this afternoon. MUCAPE's already 1000-2000 J/KG, lifted indices upwards of -4 to -5, mid and low level lapse rates 6-6.5, effective bulk shear conducive w/ unidirectional WLY flow of up to 45-50 kts in EPA. In addition, other parameters which are usually low in this area are fairly impressive: MCS maintenance, derecho composite, etc. Helicity is near 200 m2/s2 so an isolated tornado cannot be ruled out either.

Overall if today busts I'd be surprised; we've got cloud debris thinning w/ what looks to be several hours of intense diurnal heating today, in conjunction w/ favorable mid/upper level dynamics, we should be talking widespread strong convection, with the primary threat being wind damage in bow echos.

Good to see that were on the same page, almost identically

[NittanyLion]

Ehop, on Jun 24 2010, 09:12 AM, said:

What is the timing of the storms?

See my post above.

[NittanyLion]

Watch issued just to the northwest now.

[lab94]

ruc for mmu on my bufkit

[lab94]

NittanyLion, on Jun 24 2010, 09:40 AM, said:

Mesoscale Discussion just issued, watch likely:


MESOSCALE DISCUSSION 1109
NWS STORM PREDICTION CENTER NORMAN OK
0838 AM CDT THU JUN 24 2010

AREAS AFFECTED...PORTIONS PA...WRN/CENTRAL NY...NWRN NJ...EXTREME
NRN WV...EXTREME SERN OH.

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY

VALID 241338Z - 241515Z

AS NOTED IN 13Z DAY-1 OUTLOOK...DAMAGING WIND THREAT FCST TO
INCREASE ACROSS MID-ATLANTIC REGION THROUGH REMAINDER MORNING HOURS.
IT NOW APPEARS THAT THIS RISK WILL COMMENCE WITH SFC-BASED
EVOLUTION OF INITIALLY ELEVATED COMPLEX OF TSTMS -- NOT YET SVR AS
OF 1315Z BUT STRENGTHENING OVERALL -- THAT DEVELOPED IN PAST HOUR
OVER NERN OH...MOVING EWD 45-50 KT ACROSS NWRN TO N-CENTRAL PA.

BOUNDARY LAYER AIR MASS AHEAD OF THIS ACTIVITY IS CHARACTERIZED BY
SFC DEW POINTS MID-UPPER 60S F. HOWEVER...MODIFIED PBZ RAOB SHOWS
SHALLOW MOIST LAYER WITH DRYING ALOFT TO NEAR 800 MB...SUPPORTING
QUICK DIABATIC TRANSITION TO WELL-MIXED SUBCLOUD LAYER IN PRESENCE
OF INCREASING DIABATIC SFC HEATING...IN TURN FAVORING MAINTENANCE TO
SFC OF STG-SVR CONVECTIVE GUSTS GENERATED ALOFT. EXPECT HEATING TO
YIELD FAVORABLE EROSION OF SBCINH/MLCINH NOW INCREASING WITH EWD
EXTENT ACROSS REGION AS WELL. MODIFIED RAOBS AND RUC SOUNDINGS
SUGGEST MLCAPE EXCEEDING 500 J/KG AND APCHG 1000 J/KG IN SOME
LOCALES BY 15Z. KINEMATIC PROFILES ARE FAVORABLE WITH ESSENTIALLY
UNIDIRECTIONAL DEEP-TROPOSPHERIC FLOW...AND STG SPEED SHEAR
CONTRIBUTING TO AROUND 50 KT OF EFFECTIVE SHEAR MAGNITUDE.
DEEP-SHEAR AND MEAN WIND VECTORS WILL TEND TO ALIGN NORMAL TO
MERIDIONAL PORTION OF THIS ACTIVITY AND ANY ADDITIONAL CONVECTION
THAT CAN DEVELOP FARTHER S TOWARD SRN PA BORDER REGION AND NWRN
WV...LATTER AREA BEING IN SRN PERIPHERY OF STRONGEST DCVA ALOFT
RELATED TO EWD-MOVING GREAT LAKES SHORTWAVE TROUGH.

..EDWARDS.. 06/24/2010


ATTN...WFO...OKX...ALY...PHI...BGM...BUF...CTP...LWX...PBZ...
CLE...

LAT...LON 40898070 40947924 41787848 42327806 43017640 43237482
42427400 40997476 40087616 39727833 39598001 39748097
40408095 40898070

[Stormchaser]

NittanyLion, on Jun 24 2010, 10:19 AM, said:

Good to see that were on the same page, almost identically

Mike, don't want to jinx it, but this looks like our best threat of the year so far. Pretty impressive thermodynamic parameters and we're not even 12 noon yet. MUCAPES approaching 2500 J/KG in NJ w/ LI's up to -6.

That complex in PA may serve as a cold pool for downstream T-storm explosion.

[LongIslandWthr]

NWS STORM PREDICTION CENTER NORMAN OK
1116 AM CDT THU JUN 24 2010

AREAS AFFECTED...PORTIONS CENTRAL/SRN VT...CENTRAL/SRN NH...SWRN
MAINE...MA...CT...RI...SERN NY INCLUDING LONG ISLAND...NJ...PA
EXCEPT FAR NORTHWESTERN...CENTRAL/NRN MD INCLUDING
PANHANDLE...DE...DC...NRN VA...EXTREME ERN WV INCLUDING PANHANDLE.

CONCERNING...SEVERE THUNDERSTORM WATCH 404...

VALID 241616Z - 241745Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 404
CONTINUES.

SVR POTENTIAL CONTINUES FOR EXISTING WW...PRIMARILY FOR DAMAGING
WIND...AS BOUNDARY LAYER CONTINUES TO MIX/DESTABILIZE MAINLY AHEAD
OF PA CONVECTIVE BAND. ADDITIONALLY...NEW WW PROBABLY WILL BE
REQUIRED WITHIN THE HOUR SEWD TOWARD ATLANTIC COAST FROM PORTIONS
SRN NEW ENGLAND SWWD OVER COASTAL MID-ATLANTIC REGION. AREAS
FARTHER N ACROSS CENTRAL-ERN NEW ENGLAND WILL BE MONITORED FOR
POSSIBLE WW AS WELL. SEVERE POTENTIAL NEAR COASTAL NEW ENGLAND AND
SWRN MAINE IS MORE CONDITIONAL DUE TO RELATIVELY LIMITED
INSTABILITY...BUT ALSO MAY INCREASE WITH TIME.

ALTHOUGH SUBSTANTIAL SFC DOWNSLOPING COMPONENT IS EVIDENT IN
IMMEDIATE LEE OF MOUNTAINS AND VIS IMAGERY SHOWS BILLOW CLOUDS AND
LINGERING STABLE AIR E OF MOUNTAINS FROM SERN NY INTO MD...THIS AIR
MASS SHOULD DESTABILIZE DIABATICALLY SUFFICIENTLY TO SUPPORT TSTM
POTENTIAL THROUGH AT LEAST 21Z. MODIFIED RAOBS AND RUC SOUNDINGS
INDICATE SFC DEW POINTS NOW ANALYZED FROM UPPER 60S TO MID 70S F
WILL SUPPORT MLCAPE INCREASING TO 1000-2000 J/KG RANGE WITH
WEAKENING CINH. DEEP-LAYER VERTICAL WIND PROFILES WILL CONTINUE TO
INCREASE WITH NWD EXTENT ACROSS THIS REGION...WHILE ABUNDANCE OF
LOW-LEVEL MOISTURE GENERALLY INCREASES SWD...MOST FAVORABLE
JUXTAPOSITION BEING IN CORRIDOR COVERING CENTRAL/ERN PORTIONS WW 404
SEWD TO COAST THROUGH MID-AFTERNOON. AS MID-UPPER SHORTWAVE
TROUGH...WITH RELATED HEIGHT GRADIENT ENHANCEMENT AND DCVA ALOFT
APCH...PRIND EFFECTIVE SHEAR SHOULD STRENGTHEN TO AROUND 50 KT SWD
ACROSS NJ AS ALREADY IS APPARENT OVER PORTIONS CENTRAL NEW ENGLAND
INTO ERN PA.

..EDWARDS.. 06/24/2010


ATTN...WFO...GYX...BOX...BTV...OKX...ALY...PHI...BGM...CTP...
LWX...PBZ...RLX...

LAT...LON 40478061 41727775 43697387 44187177 43737085 43477036
43137067 42897081 42707080 42697074 42717058 42617057
42577061 42527085 42407100 42317102 42267090 42217073
42097066 41997067 41927054 41797053 41737033 41787008
41847000 41967004 42037012 42047019 41997023 42097029
42117020 42047002 41866989 41716991 41547001 41387005
41276995 41257004 41267020 41297029 41347049 41297082
41457087 41427110 41477121 41477135 41397149 41137154
41017189 40707300 40597374 40537397 40437398 40177398
39677412 39427441 38607741 38438013 390

[LongIslandWthr]

SEL6
0-250000-

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 406
NWS STORM PREDICTION CENTER NORMAN OK
1230 PM EDT THU JUN 24 2010

THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

SOUTHERN CONNECTICUT
DISTRICT OF COLUMBIA
DELAWARE
MUCH OF MARYLAND
NEW JERSEY
SOUTHEASTERN NEW YORK
EASTERN PENNSYLVANIA
NORTHERN AND CENTRAL VIRGINIA
THE EASTERN WEST VIRGINIA PANHANDLE
COASTAL WATERS

EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM 1230 PM UNTIL
800 PM EDT.

WIDESPREAD DAMAGING WINDS
ISOLATED WIND GUSTS TO 70 MPH POSSIBLE
WIDELY SCATTERED LARGE HAIL TO 1.5 INCHES IN DIAMETER
ISOLATED TORNADOES

THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 140
STATUTE MILES EAST AND WEST OF A LINE FROM 45 MILES SOUTH
SOUTHEAST OF ELKINS WEST VIRGINIA TO 20 MILES NORTH NORTHEAST OF
BLOCK ISLAND RHODE ISLAND. FOR A COMPLETE DEPICTION OF THE WATCH
SEE THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU6).

REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE
FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY
DO PRODUCE TORNADOES.

OTHER WATCH INFORMATION...CONTINUE...WW 404...WW 405...

DISCUSSION...TSTMS EXPECTED TO CONTINUE INCREASING ALONG DIFFUSE
COLD FRONT NOW BISECTING PA. OTHER STORMS MAY FORM AHEAD OF FRONT
ALONG LEE TROUGH. STRENGTH OF DEEP UNIDIRECTIONAL WIND FIELD AND
CONTINUED LOW LVL DESTABILIZATION LIKELY WILL LEAD TO INCREASED
POTENTIAL FOR DMGG WIND GUSTS AS STORMS...INCLUDING A FEW
SUPERCELLS...ORGANIZE INTO SHORT LINE/BANDS.

AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
TO 1.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60
KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM
MOTION VECTOR 24045.


...CORFIDI

[shark253]

NYC is under a Severe Thunderstorm Watch and hopefully I can get a good drenching. It has been quite dry. Also, i could use a nice thunderstorm over the city.

[icehater]

Not much in the way of lightning so far.

http://www.weather.com/maps/maptype/severe...m=36hr_svrWatch

[NittanyLion]

Storms should start to strengthen now as they enter the very unstable air (LI's upward of -7 now).

Wind gust to 45mph at Mount Pocono with lightning reported.

[NYBrit]

We're under a severe thunder watch here.

[NittanyLion]

Pretty good line segment up near the throughway, I would estimate gusts 35-50mph off of radar in that line.

Actually surprised there's not more going on right now, but there does seem to be a very long squall line developing and strengthening from Kentucky right up into PA that should move towards the area, especially southern areas.