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Central PA Thread - Summer 2012


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nws afd update doesn't seem so impressed.

They wont jump the gun until more certain that things will come together. No sense in causing alarm by discussing severe potential before certainty over what will actually occur. I am sure they will update often over the course of the afternoon as things develop.

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nws afd update doesn't seem so impressed.

This is what they changed. It's hard to tell if they are less impressed.

-- Changed Discussion --

HOT AND HUMID CONDITIONS WILL RETURN TO CENTRAL PENNSYLVANIA AS A WARM FRONT SURGES JUST TO THE NORTHEAST OF THE COMMONWEALTH THIS AFTERNOON. A SLOW MOVING COLD FRONT APPROACHING THE LOWER GREAT LAKES WILL COMBINE WITH HIGH INSTABILITY...RICH LEVEL MOISTURE... AND MODERATELY STRONG MID-LEVEL WINDS TO PROMOTE THE DEVELOPMENT OF SEVERE THUNDERSTORMS CAPABLE OF PRODUCING WIDESPREAD DAMAGING WINDS TODAY INTO TONIGHT.

-- End Changed Discussion --

&& .NEAR TERM /THROUGH TONIGHT/...

-- Changed Discussion --

REGIONAL RADAR SHOWS DYING QUASI-MCS QUICKLY EXITING OUR EASTERN ZONES...ALONG THE LEADING EDGE OF STRONG 925-850 MB MOISTURE FLUX. THE ATMOSPHERE WILL RE-ADJUST OVER THE NEXT SEVERAL HOURS...AND DEEPENING MIXING WILL HELP TO TRANSPORT A GUSTY WEST SOUTHWEST WIND OF 15-25 KTS DOWN TO THE SFC AS CLEARING SPREADS EAST ACROSS MUCH OF THE CWA FOR THE LATE MORNING THROUGH MID AFTERNOON HOURS. NEAR TERM MODELS INDICATE THE BRUNT OF STRONG TO SEVERE TSRA SPREADING SE ACROSS THE REGION /IN ONE OR MORE BROKEN LINES/ LATE THIS AFTERNOON AND EVENING AS A SFC COLD FRONT EDGES SLOWLY SERWD FROM THE GLAKES. STRONGEST...WSWRLY 0-1KM SHEAR OF 20-25 KTS BECOMES FOCUSED ACROSS THE NW MTNS BETWEEN 19-22Z...AND THEN JUMPS TO OUR EASTERN ZONES EARLY THIS EVENING. IT/S THESE AREAS THAT WILL LIKELY SEE BOUNDARY INTERACTIONS /WITH EITHER PREVIOUS CONVECTION OR THE LEADING EDGE OF THE LAKE ERIE BREEZE/...AND SUPPORT DEVELOPMENT OF THE MORE INTENSE...POSSIBLY ROTATING/DISCRETE SUPERCELLS.

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CTP's MDT forecast is nothing more than a typical summer afternoon writeup.

?

This Afternoon: A chance of showers and thunderstorms. Some storms could be severe, with large hail, damaging winds, gusty winds, and frequent lightning. Partly sunny and hot, with a high near 99. Heat index values as high as 103. Southwest wind 9 to 11 mph, with gusts as high as 23 mph. Chance of precipitation is 30%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms

Tonight: Showers and thunderstorms likely, mainly before 3am. Some storms could be severe, with large hail and damaging winds. Mostly cloudy, with a low around 77. West wind 6 to 9 mph. Chance of precipitation is 60%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

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This is what wunderground is pulling.

Thursday

Partly cloudy with a chance of a thunderstorm and a chance of rain. High of 95F with a heat index of 102F. Winds from the SW at 5 to 15 mph. Chance of rain 50%.

Thursday Night

Partly cloudy with a chance of a thunderstorm and a chance of rain. Low of 77F. Winds from the West at 5 to 10 mph. Chance of rain 40%.

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Latest PBZ AFD text:

&&

.NEAR TERM /THROUGH TONIGHT/...

THE MAIN CONCERN THIS AFTERNOON AND EVENING WILL BE THE PASSAGE OF

A SQUALL LINE OF SEVERE THUNDERSTORMS WITH DAMAGING WIND, HAIL,

HEAVY RAIN, AND LOTS OF LIGHTNING. SPC CONTINUES TO PROJECT A

MODERATE RISK OF SEVERE THUNDERSTORMS FOR THE ENTIRE UPPER OHIO

VALLEY, WITH WIDESPREAD DAMAGING THUNDERSTORMS THE MOST PROBABLE

SEVERE THUNDERSTORM HAZARD. HPC HAS JOINED IN WITH A SLIGHT RISK

OF EXCESSIVE RAINFALL. RAIN AMOUNTS OF MORE THAN 1.5 INCHES IN

LESS THAN 3 HOURS CAN CAUSE FLASH FLOODING IN URBAN AREAS AND

WHERE DRAINAGE IS POOR.

CONCUR WITH THESE FORECASTS BASED ON RECENT SREF INSTABILITY AND

VERTICAL SHEAR PROFILES.

RECENT SATELLITE DATA SHOWS THE LEADING EDGE OF THICKER CLOUDS

FROM KMFD TO KCVG. ALSO A BAND OF CUMULUS IS DEVELOPING FROM KHLG

TO KLEX. THE FORMER IS MORE LIKELY WHERE THE SQUALL LINE WILL

FORM, BUT THE LATTER HAS TO BE MONITORED ALSO. RECENT HRRR MODEL

OUTPUT, ALONG WITH 00Z WRF-NMM MODEL OUTPUT, SHOWS THE FOLLOWING

TIMING OF SQUALL LINE ONSET.

FRANKLIN PA TO ZANESVILLE OH/ KFKL-KZZV/: 2-4PM.

DUBOIS-PITTSBURGH PA-WHEELING WV/ KDUJ-KPIT-KHLG/: 3-5PM.

INDIANA-MORGANTOWN WV/ KIDI-KMGW/: 4-6PM.

OAKLAND MD/ K2G4/: 6 PM.

CONTINUE TO EXPECT SCATTERED THUNDERSTORMS IN THE WAKE OF THE

SYSTEM.

&&

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just throwing this out there... since we are starting to get up there in # of posts on this thread... would it be worth it to start fresh for the events later? This is the most active we have been here in quite some time and if things do pan out it would be nice to have everything together and not split by needed to start new later on...

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just throwing this out there... since we are starting to get up there in # of posts on this thread... would it be worth it to start fresh for the events later? This is the most active we have been here in quite some time and if things do pan out it would be nice to have everything together and not split by needed to start new later on...

We should be alright...still almost 300 posts until we hit 1,000, and we can always continue past that in this thread until the event is over.

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MESOSCALE DISCUSSION 1600

NWS STORM PREDICTION CENTER NORMAN OK

1126 AM CDT THU JUL 26 2012

AREAS AFFECTED...PORTIONS CENTRAL/SRN INDIANA...OH...NRN KY...NRN

PANHANDLE OF WV...WRN/NRN PA...WRN NY.

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY

VALID 261626Z - 261830Z

PROBABILITY OF WATCH ISSUANCE...95 PERCENT

SUMMARY...RAPID DEVELOPMENT...INTENSIFICATION AND UPSCALE GROWTH OF

TSTMS IS POSSIBLE THROUGH 20Z OVER WRN/NRN PARTS OF THIS DISCUSSION

AREA...INVOF ANY OF SEVERAL BOUNDARIES DESCRIBED BELOW. DAMAGING

GUSTS ARE PRIMARY THREAT...THOUGH OTHER SVR MODES ARE POSSIBLE.

DISCUSSION...15Z SFC MESOANALYSIS SHOWS THERMAL GRADIENT ASSOCIATED

WITH DIFFERENTIAL HEATING...AND CORRESPONDING TO DIFFUSE ERN FRINGE

OF THICKER CLOUD COVER ON VIS IMAGERY. THIS ZONE WAS LOCATED FROM

SRN IL AND SWRN INDIANA NEWD OVER W-CENTRAL/NRN OH...THEN ENEWD OVER

NWRN PA...WHERE IT INTERSECTED WARM FRONT EXTENDING ESEWD OVER

S-CENTRAL PA. WARM FRONT IS EXPECTED TO MOVE NEWD ACROSS

CENTRAL/ERN PA THROUGH MID-AFTERNOON. DIFFERENTIAL-HEATING ZONE

WILL MOVE LITTLE AS CLOUDS ERODE WITH EWD EXTENT BUT CONTINUE TO

ADVECT OVER AREA FROM W. VIS IMAGERY ALSO SHOWS MCV MOVING ENEWD

ABOUT 35 KT OVER W-CENTRAL IL...ON TRACK TO REACH NRN INDIANA AROUND

22Z...AND PRECEDED BY MESOSCALE ENHANCEMENTS TO DEEP-LAYER FLOW AND

MIDLEVEL ASCENT. GRAVITY WAVE WAS EVIDENT MOVING SEWD OVER SWRN

PA...OH/WV BORDER AND CENTRAL KY...BEHIND WHICH STRONGEST SFC

HEATING IS OCCURRING FROM NERN OH TO WRN KY.

IN LOW LEVELS...CINH EVIDENT IN 12Z PBZ/ILN RAOBS IS BEING REMOVED

QUICKLY BY STG DIABATIC HEATING AND BOUNDARY-LAYER MIXING...BELOW

PLUME OF ELEVATED MIXED-LAYER AIR THAT CONTRIBUTES STEEP LOW-MIDDLE

LEVEL LAPSE RATES. WITH SFC DEW POINTS COMMONLY 70S F...NET RESULT

WILL BE PRECONVECTIVE MLCAPE STRENGTHENING TO 3500-5000 J/KG RANGE

OVER BROAD SWATH OF WARM SECTOR...BETWEEN WARM FRONT AND

DIFFERENTIAL-HEATING ZONE. SUCH STG-EXTREME BUOYANCY ATOP

WELL-MIXED SUBCLOUD LAYERS...AMIDST NEARLY UNIDIRECTIONAL/WLY-WSWLY

DEEP-LAYER WINDS...SUGGEST POTENTIAL FOR ONE OR MORE

FORWARD-PROPAGATIONAL TSTM CLUSTERS WITH ORGANIZED/AGGREGATE COLD

POOLS ENHANCING SVR WIND RISK. THIS MAY OCCUR WITH DEVELOPMENT NOW

OVER LE AS IT ENCOUNTERS DESTABILIZING AIR MASS NEAR WARM FRONT AND

SRN-SHORE LAKE BREEZE...AS WELL AS SUBSEQUENT DEVELOPMENT INVOF

DIFFERENTIAL-HEATING ZONE AND AHEAD OF MCV OVER PORTIONS INDIANA/OH.

EFFECTIVE SHEAR INCREASES WITH NEWD EXTENT TOWARD AND OVER WARM

FRONT...VALUES REACHING 40-50 KT IN NWRN PA WHERE EFFECTIVE SRH ALSO

IS MAXIMIZED. THIS SUGGESTS RELATIVE MAX IN SUPERCELL/TORNADO RISK

ALSO MAY EXIST INVOF WARM FRONT...SHIFTING EWD/NEWD WITH THAT

BOUNDARY.

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DISCUSSION...15Z SFC MESOANALYSIS SHOWS THERMAL GRADIENT ASSOCIATED

WITH DIFFERENTIAL HEATING...AND CORRESPONDING TO DIFFUSE ERN FRINGE

OF THICKER CLOUD COVER ON VIS IMAGERY. THIS ZONE WAS LOCATED FROM

SRN IL AND SWRN INDIANA NEWD OVER W-CENTRAL/NRN OH...THEN ENEWD OVER

NWRN PA...WHERE IT INTERSECTED WARM FRONT EXTENDING ESEWD OVER

S-CENTRAL PA. WARM FRONT IS EXPECTED TO MOVE NEWD ACROSS

CENTRAL/ERN PA THROUGH MID-AFTERNOON. DIFFERENTIAL-HEATING ZONE

WILL MOVE LITTLE AS CLOUDS ERODE WITH EWD EXTENT BUT CONTINUE TO

ADVECT OVER AREA FROM W. VIS IMAGERY ALSO SHOWS MCV MOVING ENEWD

ABOUT 35 KT OVER W-CENTRAL IL...ON TRACK TO REACH NRN INDIANA AROUND

22Z...AND PRECEDED BY MESOSCALE ENHANCEMENTS TO DEEP-LAYER FLOW AND

MIDLEVEL ASCENT. GRAVITY WAVE WAS EVIDENT MOVING SEWD OVER SWRN

PA...OH/WV BORDER AND CENTRAL KY...BEHIND WHICH STRONGEST SFC

HEATING IS OCCURRING FROM NERN OH TO WRN KY.

gravity waves are one of those phenomenons that are really cool to see show up on satellite... look interesting and good to see when looking for severe weather :-)

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SURFACE LOW PRESSURE WILL TRACK EAST-NORTHEASTWARD FROM THE LOWER

GREAT LAKES REGION INTO THE NORTHEAST...WHILE A COLD FRONT TRAILS

SOUTHWESTWARD FROM THE LOW TO THE SOUTHERN PLAINS. HOT AND HUMID

CONDITIONS AHEAD OF THE FRONT WILL ALLOW NUMEROUS CLUSTERS AND BANDS

OF THUNDERSTORMS TO ERUPT BY MID AFTERNOON FROM INTERIOR SOUTHERN

NEW ENGLAND SOUTHWESTWARD TO THE OHIO VALLEY AND FARTHER SOUTHWEST

INTO THE SOUTHERN PLAINS. STORMS ARE EXPECTED TO PERSIST INTO THE

EVENING HOURS.

IN ASSOCIATION WITH AN UPPER-LEVEL STORM SYSTEM...THE STRONGEST

WINDS ALOFT WILL BE FOUND FROM INDIANA AND OHIO ACROSS

PENNSYLVANIA...SOUTHERN NEW YORK...AND INTO SOUTHWESTERN

MASSACHUSETTS AND CONNECTICUT. A MODERATE RISK AREA COVERS THESE

REGIONS...WHERE WIDESPREAD DAMAGING WINDS ARE EXPECTED. A THREAT FOR

SIGNIFICANTLY SEVERE WINDS WILL ALSO EXIST. ADDITIONALLY...ONE OR

TWO TORNADOES WILL BE POSSIBLE THIS AFTERNOON AND EVENING ACROSS

PARTS OF SOUTHERN NEW YORK AND NORTHERN PENNSYLVANIA INTO

SOUTHWESTERN MASSACHUSETTS...CONNECTICUT...AND NORTHERN NEW JERSEY.

Also 88 here dew point 77 :o Heat index 99

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CTP's new HWO

THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON

INTO TONIGHT. A WARM FRONT WILL LIFT NORTHEAST OF THE SUSQUEHANNA

VALLEY THIS AFTERNOON...FOLLOWED BY AN APPROACHING COLD FRONT

THAT WILL REACH THE LOWER GREAT LAKES BY THIS EVENING.

ONE OR MORE...FAST MOVING LINES OF SEVERE THUNDERSTORMS WILL FORM

AHEAD OF THE COLD FRONT AND MOVE INTO THE REGION THIS EVENING.

ADDITIONAL...SUPER-CELL THUNDERSTORMS SHOULD FORM ACROSS CENTRAL

PENNSYLVANIA...PRECEDING THE MORE EXTENSIVE LINES OF

THUNDERSTORMS.

THE MAIN SEVERE WEATHER THREAT IS EXPECTED TO BE IN THE FORM OF

DAMAGING WINDS AND LARGE HAIL. HOWEVER...A FEW ISOLATED TORNADOES

CANNOT BE RULED OUT.

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