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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