Area Forecast Discussion
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000 FXUS61 KPBZ 141726 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 1226 PM EST SUN FEB 14 2016 .SYNOPSIS... MODERATING TEMPERATURES WILL CONTINUE. A MOISTURE-LADEN SYSTEM WILL APPROACH FOR MONDAY NIGHT. A WINTRY MIX WILL BE POSSIBLE IN MANY PLACES. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... LITTLE CHANGE TO THE FORECAST FOR THIS AFTERNOON...WITH MINOR TWEAKS TO SKY COVER AND TEMPERATURES. THE REMAINING WIND CHILL ADVISORY WAS ALLOWED TO EXPIRE. PREVIOUS DISCUSSION... ABUNDANT SUNSHINE WILL START THE DAY BEFORE HIGH CLOUDS START TO FILTER IN FROM THE WEST. SURFACE FLOW WILL SLOWLY TURN SOUTHEAST THROUGH THE DAY WITH SLOW MODERATION IN TEMPERATURES AS A RESULT. THAT SAID...HIGH TEMPERATURES WILL STILL STRUGGLE TO REACH THE UPPER TEENS IN MANY PLACES AS HIGH ALBEDO NEW SNOW COVER AND A WEAK MID FEBRUARY SUN WILL LIKELY HAVE DIFFICULTY OVERCOMING MORNING LOWS NEAR ZERO. && .SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY/... SEVERAL SUCCESSIVE WAVES WILL KEEP THE AREA RATHER UNSETTLED THROUGH EARLY IN THE WEEK. ISENTROPIC ASCENT BEGINS OVER THE AREA ON MONDAY AS A NORTHERN STREAM WAVE MOVES THROUGH THE GREAT LAKES. MODEL QPF IS EXCEEDINGLY LIGHT WITH THIS SYSTEM...HOWEVER GOOD SATURATION IS NOTED IN THE 285-295K LAYER WITH CONDENSATION PRESSURE DEFICITS DROPPING DECIDEDLY BELOW 10 MB FOR MUCH OF THE DAY. THIS COINCIDES WITH A SATURATION OF THE DENDRITIC GROWTH LAYER...HOWEVER BOUNDARY LAYER RH VALUES BELOW IT ARE RATHER ANEMIC. THE RESULT WILL SEEMINGLY BE EFFICIENT SNOW GROWTH WITH ABUNDANT SUBLIMATION IN THE BOUNDARY LAYER. WITH LIGHT QPF...THE NET RESULT SEEMS TO BE GENERAL LIGHT SNOW ON MONDAY WITH FAR LESS THAN AN INCH POSSIBLE MOST EVERYWHERE. ANOTHER DEEPER WAVE RIDES THROUGH THE MIDDLE ATLANTIC MONDAY NIGHT INTO TUESDAY. THE MODEL CONSENSUS HAS SHIFTED DECIDEDLY WEST WITH THE LOW LEVEL REFLECTION OF THIS SYSTEM. MOST GUIDANCE NOW TRACKS THE 850 MB LOW THROUGH EASTERN OHIO OR UP THE NORTHERN PANHANDLE OF WEST VIRGINIA. AS A RESULT...AN ALL SNOW FORECAST SEEMS LIKE AN IMPOSSIBILITY. MODEL SOUNDINGS SUGGEST A PERIOD OF SLEET AND FREEZING RAIN AFTER INITIAL WARM ADVECTION SNOW DEVELOPS...HOWEVER THE DURATION OF TIME THE BOUNDARY LAYER WOULD REMAIN COLD ENOUGH IS FAR FROM CERTAIN. SCREAMING 850 MB FLOW FROM THE SOUTHWEST INTO THE RIDGES AND METRO PITTSBURGH SUGGESTS THE PERIOD OF ICING MAY END UP BEING LOWER IN DURATION THAN ONE WOULD THINK GIVEN WE ARE SITTING AT ZERO DEGREES RIGHT NOW. HOWEVER...GROUND TEMPERATURES ARE LIKELY VERY COLD AND WILL BE VERY COLD AT THE ONSET OF THE EVENT. THUS...FREEZING RAIN WORDING WAS USED IN A FAIRLY HEAVY- HANDED FASHION THROUGH THE FORECAST. GIVEN MODEL WAFFLING AND TRENDS...IT WOULD SEEM MOST AREAS WOULD SEE A COUPLE INCHES OF SNOW...BEFORE SOME ICE...AND MANY AREAS SOUTH OF PITTSBURGH AND EVEN IN THE RIDGES WOULD GO ALL RAIN OVERNIGHT MONDAY NIGHT. GIVEN THAT NONE OF THE PARAMETERS ARE LIKELY TO MEET WARNING CRITERIA IN AND OF THEMSELVES...NO WATCHES HAVE BEEN ISSUED. ADDITIONALLY...GIVEN THAT MODEL TRENDS HAVE BEEN ANYTHING BUT IN UNISON...CONFIDENCE IS NOT ANYWHERE NEAR HIGH ENOUGH TO ISSUED ADVISORIES AT THIS EARLY JUNCTURE. THUS...HWO WORDING HAS BEEN MAINTAINED AND FURTHER SCRUTINY CAN BE GIVEN BY FURTHER SHIFTS WITH REGARD TO SNOW/ICE/RAIN POTENTIAL. FRIES && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... A SECOND WEAK LOW WILL CROSS TUESDAY NIGHT WITH WARM ADVECTION CONTINUING. AGAIN...P-TYPE ISSUES REMAIN WITH RAIN AND SNOW CHANGING TO SNOW WITH COLD ADVECTION WEDNESDAY WITH THE SYSTEMS DEPARTURE. APPEARS ANY PRECIPITATION WITH THIS LOW WILL BE LIGHT. RIDGING AND A WARM UP LOOKS TO TAKE PLACE BY LATE IN THE PERIOD. HEAVY EMPHASIS WAS USED ON THE SUPERBLEND FOR THE LONG TERM. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... SOME BKN MVFR CU HAVE FORMED UP IN A LINE FROM YNG THROUGH BTP TO NEAR LBE...LIKELY FROM LEFTOVER LAKE PLUME MOISTURE. THESE SHOULD BREAK UP OVER THE NEXT FEW HOURS. OTHERWISE...MID AND HI CLOUDS WILL BE INCREASING AHEAD OF THE NEXT STORM SYSTEM. A PERIOD OF LIGHT SNOW IS EXPECTED OVERNIGHT AND INTO MONDAY MORNING. MVFR CIGS ARE LIKELY WITH THE SNOW. VIS COULD DROP BRIEFLY INTO IFR TERRITORY BUT TIMING THAT REMAINS TRICKY. A GENERAL LULL IN PRECIPITATION WILL FOLLOW FOR MIDDAY AND EARLY AFTERNOON. PRECIPITATION THEN INCREASES AGAIN FROM THE SOUTH LATE IN THE DAY...ALONG WITH A WARMER PUSH OF AIR. ADDED A FZRA POSSIBILITY TO THE TAIL END OF THE 30 HOUR PIT TAF. .OUTLOOK.../MONDAY THROUGH FRIDAY/... LOW PRESSURE SYSTEMS WILL BRING WIDESPREAD RESTRICTIONS LATER MONDAY THROUGH WEDNESDAY. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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