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Friday 2/25 Flood and Heavy Rain Potential


am19psu

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TU drexel hill on the threads. on wind...imo this will be significantly worse between noon and 9 PM Friday...convective gusts of 50-60 knots appear realistic in the lines of remaining midday/aftn instability. everything i am seeing thru the 18z runs from tghe ec/gfs/nam says tstms with svr wind. then i think we will see a few minutes of nw gusts of 45 to 55 kts at many locations along and se of I95 between 4 pm and 7 P as the strong cold front pushes thru with asstd 10mb pres rises in 3 hrs and temps dropping 10-18 degs within an hr. presuming this expectation of convection and momentum transfer is correct...then it will be notably MUCH stronger than last saturday with resultant many trees and wires down with asstd power outages. the rest you can conjecture. this is based on hi wind composites/transfer programs/richardson numbers and internal mxg ht gust transfer tools. liklihood for convection between noon and 5P and I think PHL will have its strong cfp ard 5PM... am going to lower temps susbantially at 7 pm tomorrow. the warmer its is above MOS guidance during midday tomorrow the stronger the wind. wd

Walt, you thinking this will be a true squall/convective line or scattered/broken line?

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At least one positive thing is that there are no leaves on the trees. Therefore, we do not have the leaf canopy to act like a sail and put even more stress on the trees. However, the ground will be wetter with this wind event. The convective aspect of this event looks interesting. If the frontal forcing is real strong, a solid line of convection will probably form and tend to move faster than the cold front itself given the rather robust wind field. Given the shear forecast though, any squall line that is able to form may break into several segments and this is where the intense winds may be transferred down to the surface more efficiently (the convection will probably tend to lean, with height, down wind of the flow given the strong wind field). The mini line segments idea is similar to what was observed in radar data during the late night/early morning strong to severe squall line of November 16-17, 2010.

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For those that didn't see the Day 2 outlook.

DAY 2 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1057 AM CST THU FEB 24 2011

VALID 251200Z - 261200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...

MODELS INDICATE THAT BLOCKING WILL REMAIN PROMINENT WITHIN THE UPPER

PATTERN OVER THE EASTERN PACIFIC...WITH DOWNSTREAM SPLIT FLOW

BROADLY CONFLUENT ACROSS MUCH OF NORTH AMERICA...AND RATHER STRONG

AND GENERALLY ZONAL ACROSS THE U.S. IN PARTICULAR. WITHIN THIS

REGIME A LARGE SHORT WAVE TROUGH AND EMBEDDED CLOSED LOW ARE PROGGED

TO CONTINUE DIGGING NEAR THE PACIFIC COAST FRIDAY...WHILE A

SIGNIFICANT DOWNSTREAM PERTURBATION RAPIDLY ACCELERATES EAST OF THE

OHIO VALLEY INTO THE WESTERN ATLANTIC.

...APPALACHIANS INTO ATLANTIC SEABOARD...

SUBSTANTIAL FURTHER DEEPENING OF THE CYCLONE ASSOCIATED WITH THE

LATTER FEATURE APPEARS PROBABLE AS IT MIGRATES NORTHEAST OF THE

UPPER OHIO VALLEY INTO AREAS OFF THE NORTH ATLANTIC COAST...AND

EVENTUALLY THE CANADIAN MARITIMES. THIS WILL BE ACCOMPANIED BY

FURTHER INTENSIFICATION OF LOW- AND MID-LEVEL WIND FIELDS THROUGH A

BROAD WARM SECTOR OVERSPREADING MUCH OF THE ATLANTIC SEABOARD...WITH

GUIDANCE SUGGESTING STRENGTHENING OF A SOUTHERLY 850 MB JET FROM 70

TO 90 KTS FROM THE LEE OF THE SOUTHERN AND CENTRAL APPALACHIANS INTO

AREAS EAST OF THE MID AND NORTHERN ATLANTIC COAST BY LATE FRIDAY

AFTERNOON.

STRONGEST DIVERGENCE ALOFT ASSOCIATED WITH A COUPLED MID/UPPER JET

STRUCTURE IS PROGGED TO RAPIDLY SHIFT NORTHEAST OF THE CENTRAL

APPALACHIANS/UPPER OHIO VALLEY AND LOWER GREAT LAKES REGION...ALONG

AND NORTH OF THE SURFACE WARM FRONT...EARLY IN THE DAY. AS THIS

OCCURS...A WEAKENING PRE-COLD FRONTAL CONVECTIVE BAND NEAR THE

APPALACHIANS AT THE OUTSET OF THE FORECAST PERIOD PROBABLY WILL

WEAKEN FURTHER AS IT ADVANCES TOWARD THE ATLANTIC COAST. THIS BAND

APPEARS LIKELY TO PROGRESS ACROSS MID ATLANTIC COASTAL AREAS FIRST

AROUND MIDDAY...THEN LATER IN THE AFTERNOON ACROSS SOUTHERN ATLANTIC

AND NORTHEASTERN GULF COASTAL AREAS.

CLEARING IN THE WAKE OF THIS INITIAL BAND MAY ALLOW A WINDOW OF

OPPORTUNITY FOR PRE-FRONTAL SURFACE HEATING AND RENEWED CONVECTIVE

DEVELOPMENT DURING THE AFTERNOON FROM THE LEE OF THE CENTRAL

APPALACHIANS INTO THE NORTHERN MID ATLANTIC COAST...AIDED BY A

SECONDARY ZONE OF FORCING ASSOCIATED WITH THE PASSAGE OF THE

MID-LEVEL TROUGH AXIS. HOWEVER...SOMEWHAT MODEST BOUNDARY LAYER

MOISTENING AND WEAK LAPSE RATES WITHIN/ABOVE THE WARM SECTOR MAY BE

PROBLEMATIC WITH RESPECT TO DESTABILIZATION. IT IS NOT EVEN CLEAR

THAT THERMODYNAMIC PROFILES WILL BECOME SUPPORTIVE OF CONVECTION

CAPABLE OF PRODUCING LIGHTNING...AND THUNDERSTORM PROBABILITIES

ALONG AND EAST OF THE APPALACHIANS IN GENERAL MAY NOT BE MUCH ABOVE

THE MINIMUM 10 PERCENT THRESHOLD FOR A THUNDER OUTLOOK.

REGARDLESS...GIVEN THE LARGE MAGNITUDE OF THE LOW-LEVEL AND DEEP

LAYER MEAN FLOW FIELDS...ANY WARM SECTOR CONVECTIVE DEVELOPMENT MAY

BE CAPABLE OF CONTRIBUTING TO THE DOWNWARD TRANSFER OF HIGHER

MOMENTUM AIR TO THE SURFACE. CONVECTIVE ENHANCEMENT OF SURFACE

GUSTS TO SIGNIFICANTLY DAMAGING SPEEDS SEEMS LIKELY TO REMAIN RATHER

SPARSE IN COVERAGE...SO SEVERE PROBABILITIES BELOW SLIGHT RISK

LEVELS HAVE BEEN MAINTAINED. BUT...THE THREAT AREA HAS BEEN

EXPANDED TO ENCOMPASS MUCH OF THE ATLANTIC SEABOARD.

..KERR.. 02/24/2011

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I am unsure of thunderstorms this afternoon, they are still indicating storms this afternoon, I am prepaired camera wise today. So if anything does form I will be ready to film.

There may be convective elements, however there may end up being little to no lightning. Plenty of wind not that far above the surface, but we will have to see regarding any instability. Temperatures and dew points however increasing quite a bit now across central/southern Delaware toward far southern New Jersey.

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There may be convective elements, however there may end up being little to no lightning. Plenty of wind not that far above the surface, but we will have to see regarding any instability. Temperatures and dew points however increasing quite a bit now across central/southern Delaware toward far southern New Jersey.

Thank you Mike. This year i am gonna try my best on not freaking or flipping out, people gotta bare with me as things go on. Cant help my passion that can litterally take over my emotions and such.

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Very abrupt appearance of fog in the Franklin Township area of Somerset - within the past few minutes. It's not heavy, but to have it suddenly appear during a rainstorm is interesting. Warm air I suppose? Ground is still frozen under an inch or so.

Yeah, the warmer and more moist air coming north over the lingering cooler air right at the surface is allowing for some fog to develop.

FYI...SPC has now put a good part of the area in a slight risk in their updated day 1 outlook.

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While I gear up for possible severe weather later today, I checked out the New York State Thruway camera at the Rochester, NY exit. This is what I saw just a few minutes ago... ;)

Wow, this is one time I'm glad we're not getting that here. I have to be in Hazleton at 3:00PM to photograph a wedding. It would have been a disaster for the bride and groom if I couldn't get there.

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DAY 1 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0658 AM CST FRI FEB 25 2011

VALID 251300Z - 261200Z

...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON OVER PORTIONS OF

THE MID ATLANTIC STATES...

...MID ATLANTIC STATES...

INTENSE FORCING FOR ASCENT /I.E. 500-MB HEIGHT FALLS OF 150-200 M

PER 12-HR/ WILL OVERSPREAD REGION TODAY IN ADVANCE OF WELL-DEFINED

VORTICITY MAXIMUM AND ASSOCIATED 80-100 KT MIDLEVEL JET STREAK NOW

OVER THE OH VALLEY. ATTENDANT SURFACE LOW ANALYZED OVER NRN WV AS

OF 12Z WILL CONCURRENTLY DEVELOP ENEWD THROUGH SRN/CNTRL PA THIS

MORNING TO OFF THE NJ COAST BY LATE AFTERNOON. TRAILING COLD FRONT

WILL ACCORDINGLY SURGE EWD THROUGH THE PIEDMONT AND COASTAL PLAIN

AND OFFSHORE BY EVENING.

A VERY STRONG SWLY LOW-LEVEL WIND FIELD /50-70 KT AT AROUND 1 KM

AGL/ HAS DEVELOPED E OF THE APPALACHIANS THIS MORNING WHICH HAS

HASTENED THE NWD TRANSPORT OF AN INCREASINGLY WARM AND MOIST AIR

MASS THROUGH THE CNTRL/ERN CAROLINAS INTO THE TIDEWATER

REGION...ALONG AND S OF RETREATING WARM/WEDGE FRONT. WARM CONVEYOR

BELT CLOUDS AND PRECIPITATION MANIFEST WITHIN THIS HIGH MOMENTUM AIR

STREAM ARE EXPECTED TO TEMPER DAYTIME HEATING AND RESULTANT AIR MASS

DESTABILIZATION AHEAD OF COLD FRONT THROUGH MOST OF THE MORNING.

HOWEVER...BY 17-19Z LATEST MODEL GUIDANCE SUGGESTS THAT A NARROW

CORRIDOR OF WEAK INSTABILITY /SBCAPE VALUES AROUND 500 J PER KG/

WILL DEVELOP AHEAD OF COLD FRONT AS IT SHIFTS E OF THE BLUE RIDGE.

25/00Z 4-KM ARW/NMM AND SEVERAL OF THE MORE RECENT EXPERIMENTAL HRRR

SIMULATED REFLECTIVITY FORECASTS SUGGEST THE DEVELOPMENT OF DISCRETE

STORMS ALONG THE COLD FRONT FROM PORTIONS OF SERN PA/NJ SWD THROUGH

PARTS OF ERN VA...CNTRL/ERN MD AND DE. GIVEN THE VERY STRONG SHEAR

EVIDENT IN 12Z OBSERVED AND MODEL FORECAST SOUNDINGS...THE POTENTIAL

WILL EXIST FOR LOW-TOPPED SUPERCELLS WITH A RISK FOR DAMAGING WIND

GUSTS AND PERHAPS A TORNADO OR TWO. THE COLD FRONT AND ANY

ASSOCIATED SEVERE WEATHER THREAT SHOULD MOVE OFFSHORE BY LATE

AFTERNOON OR THIS EVENING.

..MEAD/HURLBUT.. 02/25/2011

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Yeah, the warmer and more moist air coming north over the lingering cooler air right at the surface is allowing for some fog to develop.

FYI...SPC has now put a good part of the area in a slight risk in their updated day 1 outlook.

Already having power issues around here, and haven't hardly seen any wind yet. Had 2 activated CO2 alarms, within 5 minutes of each other, on the same street, due to the power outage. Not a good sign for later.

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Already having power issues around here, and haven't hardly seen any wind yet. Had 2 activated CO2 alarms, within 5 minutes of each other, on the same street, due to the power outage. Not a good sign for later.

Interesting, although did see that ACY had a peak gust to 40 mph about an hour ago. We continue to toss out some SPS's to cover the increasing gusty southerly wind this morning. Thanks for the info!

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