Issued by NWS Albany, NY
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-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --000 FXUS61 KALY 230147 AFDALY AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE ALBANY NY 845 PM EST SUN NOV 22 2009 .SYNOPSIS... HIGH PRESSURE OVER THE CANADIAN MARITIMES THIS EVENING WILL CONTINUE TO DRIFT NORTHEAST TONIGHT...AS A LOW PRESSURE SYSTEM ALONG THE CAROLINA COAST STARTS TO MOVE NORTHEASTWARD. THIS LOW PRESSURE SYSTEM WILL PASS FAR EAST OF CAPE COD ON TUESDAY... RESULTING IN MAINLY LIGHT PRECIPITATION ACROSS MUCH OF OUR REGION MONDAY NIGHT INTO TUESDAY. A SERIES OF MUCH STRONGER STORMS WILL IMPACT OUR REGION LATER IN THE WEEK...RESULTING IN UNSETTLED WEATHER FROM THANKSGIVING THROUGH MUCH OF THE HOLIDAY WEEKEND. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...-- Changed Discussion --SKIES WERE CLEAR ACROSS THE REGION AND WINDS WERE CALM OR NEARLY SO...IDEAL CONDITIONS FOR RADIATIONAL COOLING. TEMPERATURES WERE DROPPING AND IN MANY LOCATIONS WERE WITHIN TWO OR THREE DEGREES OF THE DEWPOINT. HAVE ADJUSTED GRIDS PER LATEST OBS AND TRENDS. HAVE INCREASED THE AREAL EXTENT OF THE VALLEY FOG. GLENS FALLS ALREADY DROPPED BELOW THE IFR THRESHOLD SHORTLY AFTER 8PM ALTHOUGH IT HAD IMPROVED TO MVFR. WE EXPECT THIS IMPROVEMENT WILL BE TEMPORARY. LOWERED TEMPS AND OVERNIGHT LOWS ACROSS THE EASTERN MOHAWK VALLEY AND CAPITAL DISTRICT BASED ON MOST RECENT OBS. THE 00Z ALY SOUNDING SHOWED A RATHER STRONG INVERSION JUST BELOW THE 850 HPA LEVEL WITH A TEMPERATURE OF PLUS 1 AT 880 HPA AND PLUS 6 AT 860. THERE WAS AN ABRUPT DRYING ABOVE THAT LEVEL AS WELL. OVERNIGHT LOWS ARE FORECAST TO RANGE FROM THE LOW 20S IN THE ADIRONDACKS TO THE LOW 30S IN THE HUDSON VALLEY. SKIES WILL BE CLEAR FOR MOST OF THE NIGHT...BUT EXPECT SOME LOW STRATUS MAY FORM IN THE INVERSION OVER THE RIVER VALLEYS AS WELL AS VALLEY FOG. MORE GENERAL CLOUDINESS...WHICH COVERED SOUTHEASTERN NEW ENGLAND...IS EXPECTED TO MOVE IN FROM THE EAST AROUND DAYBREAK.-- End Changed Discussion --&& .SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/... FA WILL BE BRUSHED BY COASTAL LOW MAINLY LATE MONDAY INTO TUESDAY WHICH WILL BE FOLLOWED BY HIGH PRESSURE TUESDAY NIGHT INTO WEDNESDAY. FOR MONDAY EXPECT THAT MID AND HIGH CLOUDS WILL START TO INCREASE QUICKLY MONDAY MORNING FROM SOUTHEAST TO NORTHWEST WITH LOW LEVEL CLOUDS QUICKLY OVERSPREADING SOUTHEAST PORTION OF FA BEFORE 18Z AS GOOD MOISTURE CONVERGENCE H10-H8. FOR MONDAY AFTERNOON WILL BRING CHANCE POPS MAINLY UP TO 190. HIGHS ON MONDAY WILL BE LIMITED BY CLOUDS AND SLOW RECOVERY FROM OVERNIGHT LOWS. EXPECT HIGHS ON MONDAY ONLY IN THE 40S ACROSS THE FA. FOR MONDAY NIGHT INTO TUESDAY THE UNCERTAINTY EXISTS WITH HOW FAR NORTH AND WEST PRECIPITATION SHIELD WILL EXTEND WITH SURFACE LOW PASSING WELL EAST OF CAPE COD ON TUESDAY. FOR NOW WILL GO WITH JUST CHANCE POPS MOST AREAS MONDAY NIGHT INTO TUESDAY...ALTHOUGH WILL INCLUDE LIKELY POPS MONDAY NIGHT ACROSS FAR SOUTHEAST PORTION OF FA. H10-H8 FRONTOGENESIS BARELY REACHES SOUTHEAST PORTION OF FA MONDAY EVENING AND THEN AXIS SLIDES WELL EAST ACROSS FAR SOUTHEAST NEW ENGLAND AND OFF CAPE COD. THIS EVENT LOOKS TO HAVE VERY LITTLE QPF TO WORK WITH ACROSS FA AND ONLY HAVE QPF AMOUNTS MONDAY NIGHT THROUGH TUESDAY FROM LESS THAN A TENTH OF AN INCH FAR NW PORTION OF FA TO JUST OVER A THIRD OF AN INCH FAR SOUTHEAST PORTION. ON MONDAY NIGHT WOULD EXPECT THAT ANY PCPN ACRS WRN ADIRONDACKS WOULD BE IN THE FORM OF SNOW...BUT NOT SURE MOISTURE WILL MAKE IT THAT FAR NORTH AND WEST. FOR NOW HAVE JUST PLACED A FEW TENTHS OF AN INCH OF SNOW ACCUMULATION IN THE GRIDS. EXPECT LOWS MONDAY NIGHT IN THE UPPER 20S TO LOWER 4S0 WITH HIGHS ON TUESDAY IN THE UPPER 40S TO LOWER 50S. FOR TUESDAY NIGHT HIGH PRESSURE EXPECTED TO BUILD ACROSS FA WITH LOWS IN THE UPPER 20S TO MID 30S AND THIS WILL QUICKLY BE FOLLOWED BY INCREASING CLOUDS ON WEDNESDAY AHEAD OF NEXT SYSTEM LIFTING INTO THE UPPER GREAT LAKES LATE IN THE DAY. FOR NOW WILL ONLY INCLUDE SLIGHT CHANCE POPS ACROSS FAR WESTERN ZONES WEDNESDAY AFTERNOON. HIGHS ON WEDNESDAY EXPECTED TO BE IN THE UPPER 40S TO LOWER 50S. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... MUCH OF THE EXTENDED PERIOD WILL BE DOMINATED BY A DEVELOPING TROUGH ACROSS THE EASTERN CONUS AND THE POSSIBILITY OF A PHASED STORM SYSTEM AFFECTING THE NORTHEAST. ON THANKSGIVING EVE INTO THANKSGIVING...A SLOW MOVING CUTOFF TROUGH WILL BE MOVING ACROSS THE GREAT LAKES. AT THE SAME TIME...SFC LOW PRESSURE WILL BE DEVELOPING IN THE SOUTHERN STREAM IN THE VICINITY OF FLORIDA. AHEAD OF THE APPROACHING CUTOFF TROUGH...SOUTHERLY FLOW WILL ALLOW FOR WEAK ISENTROPIC LIFT ACROSS OUR AREA...WHICH MAY ALLOW FOR SOME SHOWERS. WITH 850 HPA TEMPS REMAINING ABOUT 1-5 DEGREES C...THIS SHOULD BE IN THE FORM OF RAIN SHOWERS. THE ACTIVITY WILL BE RATHER SCT DUE TO THE WEAK FORCING...SO WILL KEEP POPS IN THE CHC RANGE. BY THURSDAY NIGHT...HOWEVER...THE FORECAST GETS A BIT MORE INTERESTING...HOWEVER...STILL MUDDLED DUE TO SOME MODEL INCONSISTENCIES. THE LARGE UPPER TROUGH OVER THE GREAT LAKES BEGINS TO SHIFT EASTWARD TOWARDS THE UPPER OHIO VALLEY AND TAKES ON A MORE NEGATIVE TILT AT 500 HPA. MEANWHILE...SFC PRESSURE BEGIN TO RAPIDLY DEEPEN OFF THE COAST OF NJ...WITH SURPRISINGLY GOOD AGREEMENT BETWEEN THE 12 UTC GFS/ECMWF AND MANY MEMBERS OF THE 12 UTC GEFS AS WELL. WITH THIS SFC/UPPER LEVEL SETUP...A STEADY PERIOD OF PRECIPITATION IS LIKELY ACROSS THE REGION FOR SOMETIME THURSDAY NIGHT INTO FRIDAY. WITH THE AIRMASS STARTING OUT NOT AWFULLY COLD AT ALL...PRECIP TYPE WILL LARGELY BE ELEVATION DEPENDENT FOR THIS PORTION OF THE STORM. SOME COLDER AIR WILL BE DRAWN INTO THE SYSTEM THROUGH THE DAY ON FRIDAY...BUT AT THIS POINT...MUCH OF THE PRECIP IN THE VALLEYS LOOKS TO BE A COLD RAIN...WITH A RAIN/SNOW MIX ACROSS THE HIGHER ELEVATIONS...AS SFC TEMPS WILL REMAIN IN THE LOWER 30S ACROSS THE HIGHER TERRAIN TO THE LOW 40S IN THE VALLEYS. BY LATE FRIDAY...THE LOW PRESSURE WILL LIKELY BE SOMEWHERE NEAR THE COAST OF MAINE OR EVEN SLIGHTLY INLAND ACROSS NORTHERN NEW ENGLAND. HOWEVER...COLDER AIR WILL BE RUSHING IN ON THE WESTERN SIDE OF THE SYSTEM...AND 850 HPA TEMPS WILL PLUNGE TO 0 TO -4 DEGREES C. THIS MAY ALLOW FOR SOME LINGERING SNOW SHOWERS DUE TO THE UPPER TROUGH OVERHEAD...EVEN ACROSS THE VALLEYS. SOME STEADY SNOW MAY CONTINUE ACROSS THE DACKS DUE TO A DEFORMATION BAND...ALTHOUGH THIS WILL ULTIMATELY DEPEND OF THE EXACT TRACK OF BOTH THE 500 HPA LOW AND SFC SYSTEM. IN ADDITION...THE STRONG PRESSURE GRADIENT WILL ALLOW FOR GUSTY NORTHWESTERLY WINDS...ESP ACROSS THE HIGHER TERRAIN AND CHANNELED VALLEY LOCATIONS. BY SATURDAY...LINGERING RAIN OR SNOW SHOWERS ARE POSSIBLE DUE TO THE CYCLONIC FLOW AROUND THE LARGE UPPER TROUGH ACROSS THE NORTHEAST. PRECIP TYPE WILL LARGELY BE ELEVATION AND DIURNAL DEPENDENT...ALTHOUGH MAX TEMPS WILL BE LUCKY TO HIT THE 40 DEGREE MARK...EVEN IN THE VALLEYS. IT/S IMPORTANT TO NOTE THAT DESPITE SOME SIMILARITIES IN THE MODELS...THERE IS STILL A GREAT DEAL OF UNCERTAINTY WITH THIS SYSTEM. THE 12 UTC GGEM SHOWS NO PHASING...AS WELL AS A FEW GEFS MEMBERS AS WELL. CONFIDENCE WILL BE INCREASED...HOWEVER...IF SUBSEQUENT MODEL RUNS CONTINUE TO SHOW A SIMILAR SETUP TO TODAY/S MODEL SUITE. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... SKIES HAVE CLEARED ACROSS THE HUDSON VALLEY TERMINALS THIS EVE ALLOWING FOR TEMPS TO DROP RAPIDLY. WITH T/TD SPREADS LOW AT KALB/KGFL...AND WITH LIGHT TO CALM WINDS FORECASTED FOR MUCH OF THE NIGHT...WOULD EXPECT A PERIOD OF RADIATIONAL FOG AT BOTH TERMINALS. BASED ON WHAT OCCURRED LAST NIGHT...WOULD EXPECT IFR FOG AT KGFL AS EARLY AS 03Z...AND DEF FROM 06Z UNTIL SUNRISE. KALB IS A BIT TRICKIER...AS WOULD EXPECT MVFR FOG THERE AS EARLY AS 05Z...AND DEF AFTER 07Z...BUT AM NOT CONFIDENT THAT IFR FOG WILL DEVELOP AT ALL. IF IT DOES OCCUR...IT WOULD PROBABLY BE JUST AN HOUR OR TWO BEFORE SUNRISE...AND THE 06Z TAF ISSUANCE SHOULD HAVE A BETTER HANDLE ON THIS AT THAT POINT. MEANWHILE...KPOU EXPERIENCED LOW CLOUDS THROUGH THE LATE AFTN...SO T/TD SPREAD NOT QUITE AS LARGE THERE. IN ADDITION...SOME LOW CLOUDS MAY DEVELOP THERE LATE TONIGHT DUE TO AN UPPER LOW OVER NJ...SO WILL ONLY EXPECT MVFR FOG AT WORST THERE FOR A BRIEF PERIOD BEFORE SUNRISE. ON MONDAY...THE MAIN AVIATION CONCERNS WILL BE AT KPOU...WHERE LOW STRATUS WILL CONTINUE TO DEVELOP THROUGH THE MORNING HOURS...AS THE UPPER LEVEL LOW REMAINS NEARBY THE REGION. THIS WILL LIKELY LEAD TO MVFR CIGS THERE. THIS STRATUS WILL ATTEMPT TO MOVE UP THE HUDSON VALLEY...WHICH COULD EVEN LEAD TO MVFR CIGS AT KALB FOR THE MON AFTN HOURS. KGFL SHOULD BE FAR ENOUGH NORTH TO REMAIN VFR ALL DAY. IN ADDITION...SOME RAIN SHOWERS MAY BEGIN TO AFFECT KPOU BY THE MID AFTN...WHICH COULD POTENTIALLY DROP VSBYS TO MVFR LEVELS THERE AS WELL. WINDS WILL BE NEARLY CALM OVERNIGHT. ON MONDAY...A LIGHT EAST TO NORTHEAST SFC WIND OCCUR AT ALL TERMINALS...AT SPEEDS GENERALLY 5 KTS OR LESS. OUTLOOK... MON NIGHT-TUE...VFR-MVFR...CHC OF RAIN, MAINLY KPOU. WED...VFR...CHC OF SHOWERS. THU-FRI...MVFR/IFR...RAIN POSSIBLE LATE THU THROUGH FRI. && .HYDROLOGY... WITH DRY CONDITIONS EXPECTED TO LAST AT LEAST INTO MONDAY RIVERS WILL CONTINUE RECEDE THROUGH MONDAY. THE NEXT THREAT OF PRECIPITATION WILL BE LATE MONDAY INTO TUESDAY. EXPECT TOTAL QPF AMOUNTS TO BE FAIRLY LIGHT WITH LESS THAN A TENTH OF AN INCH OF QPF ACROSS NW ZONES TO A LITTLE OVER A THIRD OF AN INCH FAR SOUTHEAST ZONES. THIS EVENT SHOULD HAVE VERY LITTLE IMPACT ON RIVERS AND STREAMS. FURTHER OUT AN UNSETTLED PERIOD OF WEATHER THURSDAY INTO THE WEEKEND COULD RESULT IN SIGNIFICANT PRECIPITATION AMOUNTS. FOR DETAILS ON SPECIFIC AREA RIVERS AND LAKES...INCLUDING OBSERVED AND FORECAST RIVER STAGES AND LAKE ELEVATIONS...PLEASE VISIT THE ADVANCED HYDROLOGIC PREDICTION SERVICE /AHPS/ GRAPHS ON OUR WEBSITE. && .ALY WATCHES/WARNINGS/ADVISORIES... CT...NONE. NY...NONE. MA...NONE. VT...NONE. && $$ SYNOPSIS...11 NEAR TERM...RCK SHORT TERM...11 LONG TERM...FRUGIS AVIATION...FRUGIS HYDROLOGY...11
