Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 210657 AFDCTP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE STATE COLLEGE PA 257 AM EDT TUE OCT 21 2014 .SYNOPSIS... LOW PRESSURE EVOLVING FROM THE LOWER GREAT LAKES INTO THE MID- ATLANTIC AND NORTHEAST STATES WILL CONTINUE TO BRING COOL AND UNSETTLED WEATHER TO THE REGION THROUGH MID-WEEK. SLOWLY IMPROVING CONDITIONS ARE EXPECTED BY THE END OF THE WEEK WITH MILDER WEATHER BY EARLY NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/... WATER VAPOR IMAGERY SHOWED A PAIR OF SHORTWAVE IMPULSES MOVING THROUGH SRN ONTARIO AND SW PENNSYLVANIA AT 06Z. THE PA IMPULSE WILL SHIFT EWD THRU THE MORNING AND MAINTAIN SHOWER ACTIVITY OVER THE WESTERN ALLEGHENIES...WHICH SHOULD BECOME ENHANCED BY POST FRONTAL NW/UPSLOPE FLOW. LATEST HRRR INDICATES BAND OF SHOWERS WILL EXIT THE ERN LWR SUSQ VALLEY BY 07Z WITH MUCH OF THE SOUTH-CENTRAL AND SOUTHEASTERN PORTIONS OF THE KEYSTONE STATE STAYING MAINLY DRY INTO MID MORNING. ALL GUIDANCE SHOWS THE UPPER LEVEL ENERGY BECOMING BETTERORGANIZED AND EVENTUALLY CLOSING OFF OVER PA BY THIS EVE/00Z. MEANWHILE...SFC LOW CURRENTLY CENTERED JUST NORTH OF BUFFALO NY OVER LAKE ONTARIO WILL TRANSFER ITS ENERGY TO COASTAL DEVELOPMENT NEAR OR JUST OFFSHORE NJ AND THE DELMARVA. DIFFERENCES START TO EMERGE IN THE MODELS BY 22/12Z WITH THE GFS/GEFS MEMBERS BEING WEST OF THE ECMWF/CMC ENSEMBLE MEMBERS. RELATIVELY COOL AIR ALOFT ACCOMPANYING THE EVOLVING UPPER LEVEL LOW WITH MID-LVL LAPSE RATES IN THE 6.5-7.0 C/KM RANGE...AND LG SCALE LIFT GENERATED BY VORT MAXIMA PIVOTING OVER THE REGION SHOULD PROMOTE INCREASED COVERAGE OF SHOWER ACTIVITY BY THE AFTERNOON. HRRR SHOWS BULK OF SHOWERS OVER WRN PA THROUGH 18Z WITH DEVELOPING SHOWERS OVER CENTRAL AND ERN SECTIONS LATER IN THE AFTERNOON. THE MODEL GUIDANCE PROGS WEAK INSTABILITY /CAPES GENERALLY AOB 300 J/KG/ ACROSS THE SOUTH CENTRAL AND SERN ZONES WHICH...WHEN COUPLED WITH THE STEEP MID-LVL LAPSE RATES...MAY PROVE SUFFICIENT FOR A FEW ISOLATED/EMBEDDED LOW-TOPPED TSTMS TO FORM WITHIN A BROADER AREA OF SCT TO NMRS SHOWERS. MAIN CHANGE TO DAY 1 MAX/MIN TEMPS WAS TO RAISE OVERNIGHT LOWS GIVEN PLENTY OF CLOUD COVER AND 5-10KT SUSTAINED N-NW WINDS. && .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... MODEL AND ENSEMBLE GUIDANCE SHOWS THE CLOSED UPPER LOW PIVOTING AND WRAPPING NWWD THROUGH 12Z THURS WITH SFC LOW BECOMING NEARLY STACKED ABOUT 100-200 MILES SSE OF LONG ISLAND. THERE CONTINUES TO BE SOME PLACEMENT ISSUES WITH THE SFC LOW WITH THE 00Z GFS/GEFS AND 21Z SREF ALL REASONABLY WELL CLUSTERED. THE PREVIOUS TWO RUNS OF THE ECMWF ARE SOUTH OF THIS CONSENSUS WITH THE 00Z NAM/CMC TO THE EAST. A SUPERBLEND OF OP/ENS/WPC QPF SHOWS THE HIGHEST POPS OVER THE ERN 1/3 OF THE CWA EARLY WED NEAR POSSIBLE ZONE OF WRAP- AROUND PCPN...BEFORE TRENDING LOWER WED NGT INTO THURS. IT WILL FEEL RATHER RAW WITH PLENTY OF CLOUDS AND A CHILLY/GUSTY NLY WIND. A 50/50 BLEND OF CONSENSUS AND BIAS CORRECTED CONSENSUS GUIDANCE YIELDED SLIGHTLY LOWER DAYTIME HIGHS AND WARMER OVERNIGHT LOWS. THIS MAKES SENSE GIVEN THE OVERALL PATTERN. && .LONG TERM /THURSDAY THROUGH MONDAY/... THE POSITION OF THE STORM WILL KEEP LOTS OF MARITIME AIR FLOWING IN FROM THE NORTH/EAST AND KEEP POPS PRETTY HIGH ON WED...BUT SOME IMPROVEMENT IS POSSIBLE ON THURSDAY. THE HIGHEST POPS WILL GENERALLY BE IN THE NRN HALF - ESP THE NE. BUT THE MOISTURE WILL WRAP AROUND THE STORM COMPLETELY AT TIMES. THUS...A MOIST UPSLOPE FLOW IN THE WRN MTNS WILL KEEP PLENTY OF CLOUDS IN PLACE WITH SHOWER CHCS HIGH THERE AS WELL DURING MID-WEEK. AS A SURFACE LOW DEVELOPS UNDER THE UPPER SYSTEM OFF THE NJ/NY COAST...NORTHERLY LOW LEVEL FLOW WILL INCREASE AND BRING A PERIOD OF BREEZY CONDITIONS WED INTO THU...AND POSS EVEN INTO FRI. EVENTUALLY...SFC HIGH PRESSURE AND CONCURRENT UPPER RIDGING SHOULD LEAD TO A DRY WEEKEND WITH WESTERLY FLOW AND MILDER TEMPERATURES ON SAT. THERE COULD BE A WEAK AND DRY FRONT DROP ACROSS THE GREAT LAKES AND MID-ATLANTIC ON SUNDAY...WHICH MAY PRODUCE WIDELY SCT SHOWERS...BUT IT IS NOT WORTH A POP AT THIS POINT. TEMPS MAY THEN DIP A FEW DEGS FROM SAT-SUN. OTHERWISE... GENERALLY ZONAL FLOW LOOKS TO BE THE RULE AT THE LONGEST OF RANGES IN THE LOCAL FORECAST WITH CHANCE FOR JUST WEAK WAVES TO IMPACT CENTRAL PA. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... LOW PRESSURE APPROACHING FROM THE GRT LKS WILL BRING DETERIORATING FLYING CONDS TO CENTRAL PA TONIGHT IN THE FORM OF LOWERING CIGS AND SHOWERS. MAIN CONCERN OVERNIGHT WILL BE DEVELOPING LOW CIGS AT KBFD. MDLS SUGGEST AN INCREASINGLY MOIST SOUTHERLY FLOW ASCENDING THE NW MTNS WILL CAUSE CIGS TO FALL INTO THE IFR RANGE AT KBFD OVERNIGHT. ELSEWHERE...NO WORSE THAN MVFR CONDS EXPECTED OVERNIGHT. AS COLD FRONT PUSHES THRU TUE AM...WIND WILL SHIFT FROM SOUTHERLY TO NWRLY. THE RESULTING UPSLOPE FLOW OVR THE LAUREL HIGHLANDS WILL PLACE KJST AT RISK FOR IFR CIGS BTWN 11Z-15Z. EXPECT RISING CIGS EVERYWHERE BY AFTN...AS MODEST DIURNAL WARMING OCCURS WITHIN THE SFC TO 1KM LAYER. BY AFTN...MDL SOUNDINGS AND MOS GUIDANCE SUPPORT MVFR CIGS AT KBFD/KJST...WITH PREDOMINATELY VFR CONDS FURTHER EAST. HOWEVER...COOL TEMPS ALOFT WILL CREATE AN UNSTABLE ENVIRONMENT THAT WILL LEAD TO NUMEROUS PM SHRA AND EVEN A POSS TSRA. ANY OF THESE SHRA/TSRA COULD PRODUCE A BRIEF DIP TO IFR VSBY. SCT SHOWERS OF DIMINISHING INTENSITY WILL CONTINUE TO AFFECT THE REGION TUE NIGHT...AS SLOW MOVING LOW PRES SYSTEM MOVES THRU THE AREA. HOWEVER...BIGGEST AVIATION CONCERN WILL BE THE POTENTIAL OF LOW CIGS REDEVELOPING TUE NIGHT AT KBFD/KJST...THE RESULT OF RADIATIONAL COOLING OF THE SFC-1KM LAYER AND UPSLOPE FLOW. DOWNSLOPING NW FLOW SHOULD YIELD MUCH MORE FAVORABLE CONDS FURTHER EAST. OUTLOOK... WED-FRI...LOW CIGS POSS W MTNS...MAINLY AT NIGHT/EARLY AM. SAT...NO SIG WX EXPECTED. && .CTP WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...STEINBUGL NEAR TERM...STEINBUGL SHORT TERM...STEINBUGL LONG TERM...RXR AVIATION...FITZGERALD

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