539
FXUS61 KALY 031943
AFDALY
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ALBANY NY
343 PM EDT MON AUG 3 2020
SYNOPSIS
SCATTERED SHOWERS AND A FEW THUNDERSTORMS IN ADVANCE OF
TROPICAL CYCLONE ISAIAS WILL MOVE ACROSS THE REGION TONIGHT. A
STEADY LIGHT TO MODERATE RAINFALL IS EXPECTED FOR MUCH OF TUESDAY AS
ISAIAS TRACKS TOWARD OUR AREA. ISAIAS WILL THEN MOVE ACROSS THE
REGION LATER TUESDAY AFTERNOON THROUGH TUESDAY EVENING AND BRING
MODERATE TO HEAVY RAINFALL AND GUSTY WINDS. HIGH PRESSURE BUILDS IN
ON WEDNESDAY WITH DRIER WEATHER.
NEAR TERM /UNTIL 6 AM TUESDAY MORNING/
A BRIEF PERIOD OF DRY WEATHER WILL CONTINUE INTO THIS EVENING WITH A
MIX OF SUN AND CLOUDS. HIGHS WILL TOP OUT IN THE MID-70S ACROSS THE
HIGHER ELEVATIONS TO THE MID-80S ACROSS THE VALLEYS.
MEANWHILE, TC ISAIAS WILL CONTINUE TO TRACK NORTHWARD UP THE EAST
COAST, BEING STEERED BY A BERMUDA HIGH ACROSS THE WESTERN ATLANTIC
AND A DEEP UPPER-LEVEL TROUGH ACROSS THE CENTRAL US. MOISTURE HAS
BEGUN TO ADVECT NORTHWARD IN ADVANCE OF ISAIAS ACROSS THE MID-
ATLANTIC STATES.
CLOUDS WILL INCREASE AGAIN LATER THIS EVENING AS THE PRE-STORM
SHOWERS APPROACH AND DEEP LAYER MOISTURE INCREASES. THE FIRST WAVE
OF SHOWERS LOOK TO BEGIN BETWEEN 10PM-MIDNIGHT ACROSS THE MID-HUDSON
VALLEY AND LITCHFIELD COUNTY, CT AND REACH THE ADIRONDACKS, UPPER
HUDSON VALLEY AND SOUTHERN VERMONT BETWEEN 2-4 AM. IT IS WITHIN THIS
FIRST ROUND OF SHOWERS THAT A RUMBLE OF THUNDER CANNOT BE RULED OUT.
FOLLOWING THIS AREA OF SHOWERS, MORE WIDESPREAD RAIN SHOWERS WILL
BEGIN TO DEVELOP. IT IS DURING THIS TIME PERIOD AND INTO TUESDAY
MORNING THAT THE PATTERN IS SOMEWHAT REMINISCENT OF A SOUTHWESTERLY
JET PREDECESSOR RAINFALL EVENT (PRE) PER CSTAR RESEARCH, WHERE
TROPICAL MOISTURE IS ADVECTED POLEWARD OF THE TC AND INTERACTS WITH
ASCENT IN THE RIGHT ENTRANCE REGION OF THE UPPER LEVEL JET. EXPECTED
PLACEMENT OF THIS RAIN IS ACROSS MUCH OF EASTERN NEW YORK INTO FAR
SOUTHWESTERN VERMONT. LESSER ACTIVITY IS LIKELY ACROSS SOUTHEASTERN
VERMONT, THE BERKSHIRES AND LITCHFIELD COUNTY. LOWS TONIGHT WILL
BOTTOM OUT IN THE 60S (WITH SOME UPPER 50S ACROSS PARTS OF THE
ADIRONDACKS).
SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY NIGHT/
TROPICAL CYCLONE ISAIAS WILL AFFECT THE REGION WITH MODERATE TO
HEAVY RAINFALL, GUSTY WINDS AND THE POTENTIAL FOR A TORNADO OR TWO
FROM TUESDAY THROUGH TUESDAY NIGHT. DRIER WEATHER RETURNS ON
WEDNESDAY.
EARLY TUESDAY MORNING, THE LATEST NHC FORECAST PROJECTS ISAIAS TO BE
LOCATED INLAND ACROSS EASTERN VIRGINIA AND WILL CONTINUE ON A
NORTHEASTERLY TRACK TOWARD EASTERN NEW YORK LATER TUESDAY AFTERNOON
INTO TUESDAY EVENING AND THEN INTO SOUTHERN QUEBEC BY EARLY
WEDNESDAY. ISAIAS IS EXPECTED TO HOLD TROPICAL STORM INTENSITY AS IT
PASSES ACROSS THE REGION WITH THE POTENTIAL FOR A SLOW TRANSITION TO
AN EXTRATROPICAL CYCLONE AS IT DOES SO.
MODERATE TO HEAVY RAINFALL WILL BE THE PRIMARY THREAT WITH ISAIAS.
TUESDAY WILL BEGIN WITH CONTINUED LIGHT TO MODERATE RAINFALL WITH
THE GREATEST CORRIDOR BEING ACROSS MUCH OF EASTERN NEW YORK INTO
SOUTHWESTERN VERMONT WITH LESS COVERAGE ACROSS SOUTHEASTERN VERMONT,
BERKSHIRE COUNTY AND LITCHFIELD COUNTY. AS ISAIAS PASSES THROUGH
LATER TUESDAY AFTERNOON INTO TUESDAY EVENING, A 3- TO 6-HOUR PERIOD
OF HEAVY RAINFALL IS EXPECTED (ESPECIALLY JUST TO THE WEST OF THE
LOW TRACK). THIS RAINFALL WILL BE AIDED BY STRONG LOW TO MID-LEVEL
FRONTOGENESIS AND A JUICY AIRMASS (WITH PRECIPITABLE WATER VALUES OF
1.75 TO 2.25 INCHES). RAINFALL RATES OF 1-2 INCHES PER HOUR WILL BE
POSSIBLE. TOTAL RAINFALL OF 2-4 INCHES IS EXPECTED WITH LOCALLY
HIGHER AMOUNTS (ESPECIALLY IN THE UPSLOPE-FAVORED LOCATIONS). LESSER
AMOUNTS ARE EXPECTED IN HERKIMER COUNTY, WHICH IS EXPECTED TO BE ON
THE WESTERN EDGE OF THE HEAVIER RAIN (GENERAL 1-2 INCHES). THE FLASH
FLOOD WATCH WILL REMAIN IN EFFECT FOR ALL OF THE FORECAST AREA
OUTSIDE OF HERKIMER COUNTY. THE GREATEST FLOODING CONCERNS WILL BE
IN LOW-LYING AND URBAN AREAS.
WIND WILL ALSO BE AN IMPACT WITH WIND GUSTS UP TO 50 MPH POSSIBLE.
THIS WOULD MOST LIKELY OCCUR IN HEAVIER PERIODS OF RAIN OR
CONVECTIVE ELEMENTS AS THE INTENSITY OF THE RAIN COULD AID IN
TRANSPORTING STRONG LOW-LEVEL WINDS (50-60 KT AT 850 HPA) DOWN TO
THE SURFACE. WITH THIS POTENTIAL, A WIND ADVISORY HAS BEEN ISSUED
FOR THE EASTERN CATSKILLS, HUDSON VALLEY AND SOUTHERN VERMONT VALID
LATE TUESDAY AFTERNOON THROUGH TUESDAY EVENING. A TROPICAL STORM
WARNING IS IN EFFECT FOR BERKSHIRE AND LITCHFIELD COUNTIES TO
ACCOUNT FOR THE WIND THREAT AS WELL.
THE FINAL IMPACT FROM ISAIAS WILL BE THE THREAT FOR ISOLATED
TORNADOES ON ITS NORTHEASTERN QUADRANT. AT THIS TIME, THIS INCLUDES
AREAS SOUTH AND EAST OF THE CAPITAL DISTRICT AS PER THE LATEST
OUTLOOK FROM THE SPC.
WITH THE COMBINATION OF THE CLOUDS AND RAIN, HIGH TEMPERATURES WILL
ONLY REACH THE UPPER 60S ACROSS THE HIGHER ELEVATIONS TO THE LOW TO
MID-70S IN THE VALLEYS.
AS THIS SYSTEM DEPARTS, A FEW LINGERING SHOWERS ARE POSSIBLE ON
WEDNESDAY MORNING, MAINLY ACROSS THE ADIRONDACKS, THEN A DRIER AND
LESS HUMID AIR MASS MOVES INTO THE REGION AS SURFACE HIGH PRESSURE
BUILDS IN FROM THE WEST. HIGHS ON WEDNESDAY WILL REACH THE 70S TO
LOWER 80S WITH LOWS WEDNESDAY NIGHT MAINLY IN THE 50S.
LONG TERM /THURSDAY THROUGH MONDAY/
A QUIESCENT WEATHER PATTERN IN THE WAKE OF TC ISAIAS IS ON TAB FOR
THE LONG-TERM PERIOD. THE PRIMARY DRIVER OF OUR SENSIBLE WEATHER
OVER EASTERN NEW YORK AND WESTERN NEW ENGLAND WILL BE A SURFACE HIGH
PRESSURE SYSTEM. THIS WILL BRING PLENTY OF SUBSIDENCE AND ABUNDANT
SUNSHINE OVER THE AREA THROUGH MUCH OF THE PERIOD.
THERE'S A LOW GRADE RISK (20% POPS) FOR SHOWERS AND STORMS OVER THE
AREA ON MONDAY AS MID TO UPPER ENERGY APPROACHES FROM THE WEST. THE
AREA ON MONDAY SHOULD REMAIN RAIN-FREE. THE BETTER CHANCE FOR
PRECIPITATION WILL BE ON TUESDAY AS THE MID TO UPPER ENERGY IS
PROGGED TO BE IN CLOSER IN PROXIMITY TO THE FA.
SURFACE TEMPERATURES DURING THE EXTENDED WILL GRADUALLY TREND
HIGHER/WARMER GOING FROM CLOSER TO SEASONABLE LEVELS TO SLIGHTLY
ABOVE AVERAGE. THIS WILL LARGELY BE DUE TO THE FACT THAT HIGHER
HEIGHTS WILL BE BUILDING OVER THE FA AS WE MOVE FORWARD IN TIME.
HIGH TEMPERATURES IN THE UPPER 70S TO LOWER 80S IS EXPECTED IN THE
VALLEYS (COOLER HIGHER ELEVATIONS) AT THE ONSET OF THIS PERIOD
INCREASING TO THE MID 80S LATE IN THE PERIOD. LOW TEMPERATURES WILL
START OFF IN THE UPPER 50S TO LOWER 60S ACROSS THE VALLEYS AT THE
START OF THE EXTENDED INCREASING INTO THE MID TO UPPER 60S LATE
(COOLER HIGHER ELEVATIONS). HUMIDITY LEVELS WILL ALSO BE ON THE
INCREASE DURING THIS TIME FRAME.
AVIATION /20Z MONDAY THROUGH SATURDAY/
MAIN WEATHER CONCERNS FOR THE TERMINALS THROUGH THE TAF PERIOD
SURROUNDS THE IMPENDING IMPACTS FROM TROPICAL CYCLONE ISAIAS.
CURRENT SATELLITE IMAGERY DEPICTS SCT-BKN VFR MID STRATO-CU MIXED IN
WITH SOME HIGH CIRRO-STRATUS CLOUDS OVER EASTERN NEW YORK AND
WESTERN NEW ENGLAND. AHEAD OF TC ISAIAS, CLOUD LEVELS WILL
GRADUALLY LOWER AS THE AFTERNOON AND EVENING WEARS ON.
RAIN WITH SOME EMBEDDED THUNDER WILL DEVELOP TONIGHT OVER THE AREA
FROM SOUTH TO NORTH BEGINNING BETWEEN THE HOURS OF 01Z-06Z. ANY
SHOWERS OR STORMS WILL HAVE THE POTENTIAL TO BRING CIGS/VSBYS
DOWN TO MVFR LEVELS.
WINDS THIS AFTERNOON INTO THIS EVENING WILL BE OUT OF THE WEST-
SOUTHWEST AND 5-10 KTS. TONIGHT, WINDS WILL BECOME LIGHT AND
VARIABLE BEFORE SHIFTING OUT OF THE SOUTH-SOUTHEAST 5-10 KTS BY
TUESDAY MORNING.
OUTLOOK...
TUESDAY NIGHT: HIGH OPERATIONAL IMPACT. WINDY WITH GUSTS TO 39 KTS. DEFINITE SHRA...RA...TSRA.
WEDNESDAY: NO OPERATIONAL IMPACT. NO SIG WX.
WEDNESDAY NIGHT: NO OPERATIONAL IMPACT. NO SIG WX.
THURSDAY: NO OPERATIONAL IMPACT. NO SIG WX.
THURSDAY NIGHT: NO OPERATIONAL IMPACT. NO SIG WX.
FRIDAY: LOW OPERATIONAL IMPACT. NO SIG WX.
FRIDAY NIGHT: NO OPERATIONAL IMPACT. NO SIG WX.
SATURDAY: LOW OPERATIONAL IMPACT. SLIGHT CHANCE OF SHRA...TSRA.
FIRE WEATHER
SHOWERS WILL RETURN TO THE REGION TONIGHT AND CONTINUE THROUGH
TUESDAY AFTERNOON. HEAVY RAIN ASSOCIATED WITH TROPICAL CYCLONE
ISAIAS WILL MOVE ACROSS THE AREA LATE TUESDAY AFTERNOON THROUGH
TUESDAY EVENING BEFORE ENDING LATE TUESDAY NIGHT. RH VALUES WILL
REMAIN HIGH THROUGH TOMORROW.
HYDROLOGY
PERIODS OF RAIN ASSOCIATED WITH THE NORTHWARD PROGRESSION OF TC
ISAIAS IS EXPECTED MONDAY NIGHT THROUGH TUESDAY NIGHT. THE
HEAVIEST RAINFALL LOOKS TO OCCUR LATE TUESDAY AFTERNOON THROUGH
TUESDAY EVENING AS THE STORM MAKES ITS CLOSEST APPROACH. QPF OF
2-4" IS EXPECTED, WITH LOCALLY HIGHER AMOUNTS UP TO 6" POSSIBLE.
HERE, RAINFALL RATES COULD EXCEED AN INCH PER HOUR, AND THERE
COULD BE 2-4" IN A 3- HOUR PERIOD BETWEEN 18Z TUESDAY AND 06Z
WEDNESDAY.
THE HEAVY RAINFALL RATES HAVE THE POTENTIAL TO CAUSE FLASH FLOODING
IN URBAN, POOR DRAINAGE AND LOW LYING AREAS. SMALLER STREAMS AND
CREEKS MAY ALSO FLOOD THEIR BANKS DUE TO THE HEAVY RAINFALL
RATES. A FLASH FLOOD WATCH REMAINS IN EFFECT FOR THE ENTIRE HSA
EXCEPT FOR HERKIMER COUNTY.
THE ALY HYDRO SERVICE AREA CONTINUES TO BE IN ABNORMALLY DRY TO
MODERATE DROUGHT CONDITIONS /D0 TO D1/ BASED ON THE LATEST US
DROUGHT MONITOR. THE LATEST MMEFS GUIDANCE CONTINUES TO SHOW LOW
PROBABILITIES FOR WIDESPREAD RIVER FLOODING.
DRIER WEATHER WILL RETURN INTO THE MID WEEK PERIOD.
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...FLASH FLOOD WATCH FROM TUESDAY MORNING THROUGH WEDNESDAY
MORNING FOR CTZ001-013.
TROPICAL STORM WARNING FOR CTZ001-013.
NY...FLASH FLOOD WATCH FROM TUESDAY MORNING THROUGH WEDNESDAY
MORNING FOR NYZ033-039>043-047>054-058>061-063>066-
082>084.
WIND ADVISORY FROM 2 PM TUESDAY TO 1 AM EDT WEDNESDAY FOR
NYZ041-043-047>054-058>061-063>066-083-084.
MA...FLASH FLOOD WATCH FROM TUESDAY MORNING THROUGH WEDNESDAY
MORNING FOR MAZ001-025.
TROPICAL STORM WARNING FOR MAZ001-025.
VT...FLASH FLOOD WATCH FROM TUESDAY MORNING THROUGH WEDNESDAY
MORNING FOR VTZ013>015.
WIND ADVISORY FROM 2 PM TUESDAY TO 1 AM EDT WEDNESDAY FOR
VTZ013>015.
SYNOPSIS...RATHBUN
NEAR TERM...RATHBUN
SHORT TERM...RATHBUN
LONG TERM...EVBUOMA
AVIATION...EVBUOMA
FIRE WEATHER...RATHBUN
HYDROLOGY...THOMPSON/RATHBUN
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