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8/21 Severe Threat - Obs/Discussion


Kmlwx

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Oh hai

how be things former mid atlantic peoples

Well hey there... long-ish time no see! Things will (hopefully) be awesome this afternoon :whistle:

-----

SPC's Day 1:

Regional: 2% Tor (within Slight Risk boundaries) / 15% wind / 15% hail

Far northern MD is touching the 5% Tor and is in the 30% wind, which extends N+E through E PA and W NJ:

day1otlk_20110821_1200_prt.gif

day1probotlk_20110821_1200_wind_prt.gif

Pertinent Disc:

...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.

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18Z GUIDANCE MAINTAINING THE POTENTIAL FOR A GOOD WIDESPREAD

THUNDERSTORM EVENT. MAX POPS KEPT IN THE LIKELY RANGE GIVEN

DISCRETE CONVECTIVE MODE GIVEN STRAIGHT LINE HODOGRAPH ABOVE 1KM.

70 POPS WERE GIVEN FOR BALT-WASH METRO CONSIDERING LATE AFTERNOON

TIMING AND EXPECTED PRESENCE OF MESOSCALE BOUNDARIES THAT WOULD

INCREASE COVERAGE OF THUNDERSTORMS.

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18Z GUIDANCE MAINTAINING THE POTENTIAL FOR A GOOD WIDESPREAD

THUNDERSTORM EVENT. MAX POPS KEPT IN THE LIKELY RANGE GIVEN

DISCRETE CONVECTIVE MODE GIVEN STRAIGHT LINE HODOGRAPH ABOVE 1KM.

70 POPS WERE GIVEN FOR BALT-WASH METRO CONSIDERING LATE AFTERNOON

TIMING AND EXPECTED PRESENCE OF MESOSCALE BOUNDARIES THAT WOULD

INCREASE COVERAGE OF THUNDERSTORMS.

See post 23 :P

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My apologies for a weenie question, but I thought the nasty weather was to fire up this afternoon. Yet at 7:30 a.m. Baltimore/East is getting a boomer of a storm (heavy rain, C2G lighting.) Will this pop up have an effect on the storms later, possibly making them stronger or weaker?

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My apologies for a weenie question, but I thought the nasty weather was to fire up this afternoon. Yet at 7:30 a.m. Baltimore/East is getting a boomer of a storm (heavy rain, C2G lighting.) Will this pop up have an effect on the storms later, possibly making them stronger or weaker?

shouldn't have too much of an impact.

But damn the echo tops are near 55K feet.

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Upton gung ho for a big event in their CWA. Mentions of supercells. Interesting to note that LWX lacks any mention of supercells in their CWA, surprised as I thought we would see at least for northern portions. Further north in the slight risk area, ALB says if clouds do not significantly hamper instability, severe likely. They are pushing enhanced wording. Mount Holly seems somewhat lackadaisical with the threat.. mentioning high parameters of svr, their afd wanes in comparison to the gung ho upton one however.

Do I think this is a huge event for the books? No. Maybe our most memorable event locally however. But I think there will be a couple supercells this afternoon with plenty of svr reports. Well organized storms elsewhere.. and possibly a pretty awesome line of storms.

Thoughts on a map:

5yhmqp.png

UPTON

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.

STERLING

THE COLD FRONT OVER THE GREAT LAKES EARLY THIS MORNING WILL BUILD

SOUTH AND EAST INTO PENNSYLVANIA AND THE OHIO VALLEY LATER TODAY. A

WARM SOUTHWEST FLOW IS EXPECTED TO CONTINUE AHEAD OF THE FRONT

ACROSS OUR AREA. DESPITE THE FRONT REMAINING TO THE NORTH...A

PRESSURE TROUGH NEAR THE ALLEGHENY HIGHLANDS WILL ACT AS A LIFTING

MECHANISM FOR CONVECTION TO DEVELOP WELL AHEAD OF THE COLD FRONT

THIS AFTERNOON. THE WARM MOIST AIRMASS ALONG WITH SOME SUNSHINE WILL

ALLOW FOR MODERATE AMOUNTS OF INSTABILITY TO DEVELOP LATE THIS

MORNING AND AFTERNOON. NAM/GFS BUFKIT INDICATE ABOUT 1500 J/KG OF

MLCAPE DEVELOPING THROUGHOUT THE DAY. WEAK DEEP LAYER SHEAR PROFILES

WILL STRENGTHEN THROUGHOUT THE DAY AS THE UPPER-LEVEL TROUGH AXIS

SLIDES EASTWARD TOWARD THE OHIO VALLEY. THE COMBINATION OF MODERATE

INSTABILITY AND MODERATE DEEP LAYER SHEAR SUGGESTS THAT STORMS WILL

BE CAPABLE OF PRODUCING DAMAGING WIND GUSTS AND LARGE HAIL THIS

AFTERNOON. THUNDERSTORMS WILL ALSO BE CAPABLE OF PRODUCING LOCALLY

HEAVY RAINFALL AND THIS COULD LEAD TO LOCALIZED FLASH FLOODING THIS

AFTERNOON ESPECIALLY WHERE FLASH FLOOD GUIDANCE IS LOW DUE TO RECENT

RAINFALL. LOWEST FLASH FLOOD GUIDANCE IS ACROSS BALTIMORE AND

WASHINGTON WHERE ONE HOUR FFG VALUES ARE AROUND 1 TO 1.5 INCHES.

SIMILAR VALUES IN FFG EXIST ACROSS PORTIONS OF THE SHENANDOAH VALLEY

AS WELL.

ALBANY

FOR TODAY...THERE IS THE POTENTIAL FOR SOME STRONG TO SEVERE

THUNDERSTORMS ESPECIALLY FROM MID MORNING THROUGH THIS AFTERNOON

AHEAD OF A STRONG COLD FRONT WHICH IS EXPECTED TO DROP SOUTHEAST

FROM THE EASTERN GREAT LAKES THIS MORNING REACHING THE HUDSON

VALLEY LATE IN THE DAY. ML MUCAPES REACH 1000-2500 J/KG THIS

AFTERNOON... H7-H5 LAPSE RATE NOT OVERLY IMPRESSIVE 5.5 TO 6.5

C/KM...0-3 KM HELICITY 100-300 M2/S2 WITH HIGHEST VALUES ON GFS

AND NAM TOWARDS 00Z ACROSS THE SE TWO THIRDS OF THE FA...AND

CYCLONICALLY CURVED H5 JET OF 60 TO 70 KNOTS MOVING INTO FA

INDICATE THAT THE POTENTIAL CERTAINLY EXISTS FOR SEVERE

CONVECTION...HOWEVER HEATING AND INSTABILITY MAY BE SIGNIFICANTLY

INHIBITED BY CLOUD COVER. WILL CONTINUE TO HIGHLIGHT SLIGHT RISK

POTENTIAL IN HWO AND HAVE PLACED ENHANCED WORDING IN THE GRIDS

STARTING AROUND 14Z MENTIONING HEAVY RAIN...SMALL HAIL AND GUSTY

WINDS.

Mount Holly

THE STORM PREDICTION CENTER HAS PLACED ALL OF THE MID

ATLANTIC REGION IN A SLIGHT RISK FOR SEVERE THUNDERSTORMS. WITH

THE LATER TIMING, THERE SHOULD BE AMPLE OPPORTUNITY FOR DAYTIME

HEATING AND DESTABILIZATION, BUT THERE CONTINUES TO BE ENOUGH LOW

LEVEL MOISTURE AROUND. THIS MOISTURE, COUPLED WITH THE DAYTIME

HEATING WILL CAUSE AN INCREASE IN CAPE VALUES. ADDITIONALLY, WITH

INCREASING LL FLOW DURG THE AFTN AND EVENING HOURS, A WIND THREAT

WILL DEVELOP AND CERTAINLY IN THIS TYPE OF REGIME, HAIL CANNOT BE

RULED OUT EITHER.

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Haven't seen that in an HWO before from LWX :unsure:

"STORMS WILL BE CAPABLE OF PRODUCING VERY DAMAGING WIND GUSTS... LARGE HAIL, AND ISOLATED TORNADOES."

June 4 2008 all over again (jk) :arrowhead:

That does sound pretty impressive right there. Where is Ian? Still being a trollministrator over on the main forum?

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