Area Forecast Discussion
Issued by NWS Buffalo, NY

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000 FXUS61 KBUF 191946 AFDBUF AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BUFFALO NY 346 PM EDT SUN APR 19 2015 .SYNOPSIS... A COMPLEX STORM SYSTEM EVOLVING OVER THE MIDWEST WILL PUSH A WARM FRONT NORTHWARDS ACROSS OUR REGION TONIGHT AND EARLY MONDAY...AND THIS WILL RESULT IN ANOTHER SOAKING RAIN ALONG WITH SOME GUSTY WINDS. AFTER A SIX HOUR BREAK IN THE UNSETTLED WEATHER MONDAY AFTERNOON...A COLD FRONT WILL USHER MORE SHOWERS AND POSSIBLE THUNDERSTORMS THROUGH THE AREA MONDAY NIGHT. && .NEAR TERM /THROUGH MONDAY/... A LARGE EXPANSE OF QUIET WEATHER CURRENTLY STRETCHING ACROSS THE NORTHEAST CONUS...AS THE FORCING ASSOCIATED APPROACHING MID LEVEL WAVE AND STRONG WARM FRONT STILL WELL OFF TO OUR WEST AND SOUTH. THE ARRIVAL OF DEEP LAYER SOUTH/SOUTHEAST FLOW WILL ADVECT A SLUG OF MOISTURE NORTHWARD IN THE REGION EARLY TONIGHT. PRIMARY CORRIDOR OF ISENTROPIC ASCENT WILL LIFT FROM SOUTH TO NORTH ACROSS THE REGION FROM 03Z TO 15Z MONDAY BENEATH INCREASING DIVERGENT FLOW ALOFT. LOW LEVEL JET FORCING WILL BE CONSIDERABLE DURING A GOOD PORTION OF THIS TIME FRAME AS A 60-80 KNOT LOW LEVEL JET IMPINGES ON THE EASTERN GREAT LAKES. STRONG MOISTURE TRANSPORT CENTERED WITHIN A DEEP 10K FEET WARM CLOUD LAYER WILL LEND ITSELF TO HIGHLY EFFICIENT HYDROMETEOR PRODUCTION AND SEVERAL HOURS OF MODERATE RAIN WITH EMBEDDED HEAVIER SHOWERS. GUIDANCE CONSENSUS INDICATES A GENERAL RAINFALL MAXIMUM OF A HALF TO THREE QUARTERS OF AN INCH. THIS RAINFALL WILL LIKELY HAVE LITTLE IMPACT OTHER TO CAUSE SOME MINOR TO MODERATE RISES ON THE SMALL AREA TRIBUTARIES AND SOME PONDING ON AREA ROADS. THE PRIMARY CONCERN FOR TONIGHT WILL BE THE STRONG WINDS THAT WILL BE PRODUCED ACROSS THE HIGHER TERRAIN OF THE SOUTHERN TIER...AND ESPECIALLY THE DOWNSLOPE WINDS ALONG THE LAKE PLAIN OF CHAUTAUQUA AND SOUTHERN ERIE COUNTIES. LOCAL RESEARCH HAS SHOWN THAT A STRONG SOUTHEASTERLY LOW LEVEL JET COMBINED WITH A FAIRLY STRONG LOW LEVEL INVERSION NEAR THE TOP OF THE CHAUTAUQUA RIDGE AND A FAIRLY STABLE LAYER TO THE SURFACE WILL OFTEN PRODUCE VERY STRONG SURFACE WINDS ALONG THE NEW YORK THRUWAY ACROSS CHAUTAUQUA COUNTY AND SOUTHERN ERIE COUNTY. THE MOST DRAMATIC DOWNSLOPE WINDS HAVE BEEN OBSERVED DURING RAINFREE CONDITIONS...SO IT REMAINS UNCERTAIN IF TONIGHTS RAINS WILL PLAY A ROLE IN DAMPENING THIS RISK. WHAT IS KNOWN IS THAT EXCEPTIONALLY STRONG 850 MB WINDS WITH A CLIMATOLOGICAL RETURN INTERVAL OF ONCE IN MORE THAN A 30 YEAR PERIOD WILL BE IN PLACE...AND THIS WILL MOST CERTAINLY PRODUCE STRONG WIND GUSTS IN EXCESS OF 35 KNOTS...WITH GUSTS IN EXCESS OF 40 KNOTS MORE THAN POSSIBLE. WILL MAINTAIN THE WIND ADVISORY CURRENTLY IN PLACE FOR THE SOUTHERN TIER TO COVER THE STRONG WINDS THAT SHOULD BE FOUND ALONG LAKE ERIE AND ALSO ACROSS THE HIGHER TERRAIN. THIS WIND THREAT SHOULD DIMINISH TOWARD DAYBREAK. A STRONG WIND THREAT MAY ALSO DEVELOP EAST OF LAKE ONTARIO DOWN THE BLACK RIVER VALLEY. MODEL SOUNDINGS ARE NOT QUITE AS IMPRESSIVE HERE AS THEY ARE FARTHER TO THE WEST...AS THE LOW LEVEL JET IS NOT QUITE AS STRONG...BUT THIS AREA BEARS WATCHING NONETHELESS. THE SOUTHEASTERLY FLOW WILL ALSO HELP TO HOLD TEMPERATURES UP TONIGHT. OVERNIGHT LOWS SHOULD RANGE FROM THE UPPER 40S TO NEAR 50 OVER THE FAR WESTERN COUNTIES TO THE LOWER 40S EAST OF LAKE ONTARIO. THESE VALUES WILL BE SOME 10 DEGREES ABOVE NORMAL. RAIN WILL DIMINISH IN COVERAGE FROM WEST TO EAST DURING MONDAY AS THE WING OF STRONG ISENTROPIC ASCENT AND A SIZEABLE PERCENTAGE OF MID LEVEL MOISTURE PUSHES OFF TO THE NORTHEAST AND AREA EMERGES INTO THE WARM SECTOR IN WAKE OF THE WARM FRONTAL PASSAGE. HOWEVER...INCREASINGLY CYCLONIC FLOW WILL BE SPREADING INTO WESTERN NEW YORK DURING THE AFTERNOON AND THE ABUNDANCE OF REMNANT LOW LEVEL MOISTURE WILL BE ACCOMPANIED BY STEEPENING LAPSE RATES AS THE THERMAL RIDGE PUSHES NORTHWARD. AS A RESULT...EXPECT THAT THERE WILL BE AN ADDITIONAL THREAT OF SCATTERED SHOWERS AND POSSIBLE THUNDERSTORMS DEVELOPING DURING THE AFTERNOON AHEAD OF APPROACHING MID LEVEL TROUGH AXIS AND ASSOCIATED SURFACE COLD FRONT. && .SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/... MONDAY NIGHT A COLD FRONT WILL WORK ITS WAY ACROSS THE REGION WITH SHOWERS AND SCATTERED THUNDERSTORMS ALONG IT. INSTABILITY WILL REMAIN MARGINAL...WITH DAYTIME INSOLATION LINGERING SEVERAL HUNDRED J/KG OF CAPE ACROSS THE REGION. THIS INSTABILITY IN ADDITION TO UPLIFT ALONG THE COLD FRONT MAY BE ENOUGH TO TRIGGER A FEW THUNDERSTORMS MONDAY EVENING AND WILL INCLUDE THIS CHANCE IN THE FORECAST. WINDS WILL REMAIN GUSTY MONDAY EVENING...NEAR 35 MPH EAST OF LAKE ONTARIO EARLY ON A SOUTHEAST FLOW...AND THEN LATER PICKING UP TO 35 TO 40 MPH EAST OF LAKE ERIE BEHIND THE COLD FRONT. TUESDAY AND WEDNESDAY...A BROAD UPPER LEVEL CLOSED LOW WILL SLOWLY SPIRAL EASTWARD ACROSS SOUTHERN ONTARIO CANADA...WITH ITS CENTER REMAINING JUST TO THE NORTH OF THE GREAT LAKES. AS POCKETS OF VORTICITY STREAM AROUND THIS UPPER LEVEL LOW...THEY WILL TRIGGER SCATTERED SHOWERS...WITH ACTIVITY LIKELY TO PEAK IN COVERAGE DURING THE AFTERNOON HOURS. WILL CONTINUE WITH CHANCE POPS THROUGH THE REMAINDER OF THE TIME PERIOD...WITH LIKELY ALL AREAS TO RECEIVE AT LEAST SOME RAINFALL OVER THIS 2-DAY STRETCH. THOUGH THE UPPER LEVEL LOW...AND THE CORE OF THE COLD AIR REMAINS JUST TO OUR NORTH...MID LEVEL LAPSE RATES WILL INCREASE TO 8-9 C/KM. THESE LAPSE RATES IN ADDITIONAL TO DAYTIME INSOLATION MAY TRIGGER A FEW RUMBLES OF THUNDER...ACROSS WESTERN NEW YORK ON TUESDAY AND EAST OF LAKE ONTARIO ON WEDNESDAY. CONFIDENCE REMAINS TOO LOW AT THIS POINT IN TIME TO INCLUDE THUNDERSTORMS IN THE FORECAST. FOLLOWING THE PASSAGE OF THE COLD FRONT...THE RECENT NICE STRETCH OF WARMTH WILL BE ERASED WITH HIGHS TUESDAY AND WEDNESDAY IN THE 40S...AND NIGHTTIME LOWS DROPPING BACK INTO THE 30S. THESE DAYTIME READINGS WILL AVERAGE 10 DEGREES OR SO BELOW NORMAL. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... AN UPPER LEVEL LOW WILL SLOWLY SPIRAL ACROSS THE GREAT LAKES AND TOWARDS THE NORTHEAST THIS TIME PERIOD. UNDER THIS LOW PRESSURE EXPECT CLOUDY DAYS WITH SCATTERED RAIN SHOWERS FOR THURSDAY AND FRIDAY. THOUGH THE UPPER LEVEL LOW WILL ADVANCE EASTWARD FOR NEXT WEEKEND...THERE WILL BE VORT MAXES ROTATING AROUND THE FEATURE SUCH THAT A CHANCE FOR RAIN SHOWERS WILL CONTINUE TO BE POSSIBLE... ESPECIALLY ACROSS EASTERN ZONES WHICH WILL LIE CLOSER TO THE UPPER LEVEL LOW. SHOWER CHANCES WILL AGAIN BE GREATEST IN THE AFTERNOON HOURS WITH DAYTIME HEATING...WITH FEWER SHOWERS TO BE FOUND BY NIGHT. THERE MAY EVEN BE SOME WET SNOW MIXING IN AT NIGHT ACROSS THE REGION. DAYTIME AIR TEMPERATURES WILL AVERAGE 5 TO 10 DEGREES BELOW NORMAL TO START THIS PERIOD. THEN AS THE UPPER LEVEL LOW SLOWLY PUSHES EASTWARD SOME MODERATION IN THE AIR TEMPERATURES ARE EXPECTED FROM WEST TO EAST. && .AVIATION /20Z SUNDAY THROUGH FRIDAY/... HIGH PRESSURE OVER EASTERN CANADA WILL KEEP FAIR VFR CONDITIONS IN PLACE ACROSS ALL OF WESTERN AND NORTH CENTRAL NEW YORK THROUGH THE AFTERNOON. CONDITIONS WILL DETERIORATE TONIGHT THOUGH AS A COMPLEX STORM SYSTEM OVER THE MID WEST WILL ADVANCE TO THE UPPER GREAT LAKES. AN ASSOCIATED WARM FRONT WILL PUSH NORTH ACROSS THE WESTERN COUNTIES IN THE PROCESS...WITH LOWERING CIGS AND WIDESPREAD RAIN LEADING TO MVFR CONDITIONS. IFR CONDITIONS WILL BE POSSIBLE ACROSS THE HIGHER TERRAIN OF THE SRN TIER. THE GREATEST CONCERN TONIGHT THOUGH WILL COME FROM A VERY STRONG LOW LEVEL JET THAT WILL PRODUCE GUSTY WINDS ACROSS THE HIGHER TERRAIN OF THE SOUTHERN TIER AND ALSO ALONG THE LAKE PLAIN OF CHAUTAUQUA AND SOUTHERN ERIE COUNTIES. SFC WINDS AT KJHW AND KJHW MAY GUST TO 40 KNOTS WHILE WINDS AT 3K FT WILL RANGE FROM 60-80 KTS. WHILE THE CORE OF THE HIGHLY ANOMALOUS LOW LEVEL JET MAY BE TOO HIGH TO PRODUCE TRUE LOW LEVEL WIND SHEAR PROBLEMS...IT IS CERTAINLY WORTH MENTIONING IN THIS DISCUSSION. OUTLOOK... MONDAY...AREAS OF MVFR WITH OCCASIONAL SHOWERS AND STRONG GUSTY WINDS. TUESDAY THROUGH FRIDAY...VFR/MVFR WITH SCATTERED SHOWERS. && .MARINE... HIGH PRESSURE OVER EASTERN CANADA WILL DRIFT EAST AND GIVE WAY TO A DEEPENING...COMPLEX STORM SYSTEM OVER THE MIDWEST. THIS WILL LEAD TO A TIGHTENING OF THE SURFACE PRESSURE GRADIENT OVER THE LOWER GREAT LAKES TONIGHT...WITH FRESHENING OFFSHORE WINDS OF 20 TO 30 KNOTS SUPPORTING SMALL CRAFT ADVISORIES FOR ALL OF THE NEW YORK NEARSHORE WATERS THROUGH MONDAY. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...WIND ADVISORY FROM 8 PM THIS EVENING TO 8 AM EDT MONDAY FOR NYZ012-019>021-085. MARINE...SMALL CRAFT ADVISORY FROM 8 PM THIS EVENING TO NOON EDT MONDAY FOR LEZ040-041. SMALL CRAFT ADVISORY FROM 11 PM THIS EVENING TO 11 AM EDT MONDAY FOR LEZ020. SMALL CRAFT ADVISORY UNTIL 8 PM EDT MONDAY FOR LOZ042- 043. SMALL CRAFT ADVISORY FROM 8 PM THIS EVENING TO 11 PM EDT MONDAY FOR LOZ044-045. && $$ SYNOPSIS...TMA NEAR TERM...TMA SHORT TERM...THOMAS LONG TERM...THOMAS AVIATION...TMA MARINE...TMA

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