530
FXUS61 KGYX 192347
AFDGYX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAY ME
747 PM EDT MON APR 19 2021
SYNOPSIS
A LARGE UPPER LEVEL TROUGH AND SURFACE CYCLONE WILL TRACK
THROUGH NEW ENGLAND ON WEDNESDAY AND WEDNESDAY NIGHT BRINGING
WIDESPREAD RAIN AND SNOW TO THE REGION. THE HIGHEST CHANCE FOR
ACCUMULATING SNOW WILL BE ACROSS THE HIGHER ELEVATIONS AND FAR
NORTH, WHERE SEVERAL INCHES ARE POSSIBLE. GUSTY NORTHWEST WINDS
WILL ALSO BE POSSIBLE AS THE SYSTEM PULLS AWAY TO THE NORTH AND
EAST ON WEDNESDAY NIGHT. HIGH PRESSURE AND MOSTLY TRANQUIL
WEATHER WILL THEN RETURN FOR THE END OF THE WEEK AND EARLY THIS
WEEKEND BEFORE ANOTHER STORM SYSTEM APPROACHES BY SUNDAY.
NEAR TERM /UNTIL 6 AM TUESDAY MORNING/
745PM UPDATE...JUST SOME MINOR TWEAKS TO TEMPERATURES AND SKY
COVER OVER THE NEXT FEW HOURS AS SCATTERED SHOWERS CONTINUE TO
WIND DOWN THIS EVENING. THE REST OF THE GOING FORECAST LOOKS TO
BE ON TRACK.
PREVIOUSLY...
A WEAK UPPER LEVEL WAVE CROSSES THE REGION THIS EVENING AND
TONIGHT WITH DIURNALLY DRIVEN CONVECTIVE SHOWERS THIS AFTERNOON
GRADUALLY WANING AFTER SUNSET. WHILE SHOWERS HAVE HAD A TOUGH
TIME STANDING UP THIS EVENING AN ISOLATED THUNDERSTORM CAN'T BE
RULED OUT ENTIRELY WHICH COULD BRING GUSTY WINDS TO NEAR 30 MPH
AND SMALL HAIL. TONIGHT, THE WAVE MOVES ON WITH NICE CLEARING
BEHIND IT, WHICH COMBINED WITH WEAK HIGH PRESSURE AT THE SURFACE
WILL LEAD TO NICE RADIATIONAL COOLING AND PATCHY VALLEY FOG
TONIGHT WITH LOWS IN THE 30S FOR MOST LOCATIONS.
SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/
ANOTHER UPPER LEVEL WAVE CROSSES TOMORROW AS ATTENDANT LOW
PRESSURE OVER QUEBEC PUSHES A COLD FRONT ACROSS NEW ENGLAND.
THUS ANOTHER ROUND OF RAIN SHOWERS IS EXPECTED TOMORROW, MOSTLY
OVER THE MOUNTAINS CLOSER TO PARENT FORCING. STEEPENING LAPSE
RATES ALOFT WITH THE WAVE MAY PRODUCE ISOLATED THUNDERSHOWERS
DURING THE AFTERNOON AS WELL. OTHERWISE, WINDS WILL INCREASE OUT
OF THE SOUTHWEST IN THE MORNING AND BACK TO THE WEST THROUGH THE
DAY AS THE COLD FRONT CROSSES... WITH WIND GUSTS UP TO AROUND 30
MPH. TEMPERATURES WILL CLIMB TO NEAR 70 OVER THE LOWER
ELEVATIONS, BUT BE MORE SUBDUED IN THE 50S AND LOW-60S OVER THE
MOUNTAINS WHERE RAIN AND CLOUDS ARE EXPECTED.
LONG TERM /TUESDAY NIGHT THROUGH MONDAY/
OVERVIEW: AN UPPER LEVEL TROUGH AND SURFACE CYCLONE WILL BRING
WIDESPREAD PRECIPITATION IN THE FORM OF RAIN AND SNOW TO THE
REGION WEDNESDAY AND WEDNESDAY NIGHT. GUSTY WINDS WILL ALSO BE
POSSIBLE WEDNESDAY AFTERNOON AND EVENING, ESPECIALLY ALONG THE
COAST. WEAK HIGH PRESSURE WILL KEEP THE WEATHER MOSTLY QUIET FOR
THE END OF THE WEEK AND THE BEGINNING OF THE WEEKEND BEFORE
ANOTHER FRONTAL SYSTEM ARRIVES LATE THIS WEEKEND WITH INCREASED
PRECIPITATION CHANCES RETURNING. HIGH TEMPERATURES WILL
GENERALLY BE AT OR BELOW NORMAL EARLY IN THE PERIOD BEFORE
RETURNING TO ABOVE NORMAL BY THE WEEKEND.
IMPACTS: SLIPPERY TRAVEL CONDITIONS WILL BE POSSIBLE ACROSS THE
NORTH AND HIGHER ELEVATIONS, MAINLY WEDNESDAY NIGHT THROUGH THURSDAY
MORNING DUE TO WET SNOW ACCUMULATIONS. ALONG THE COAST, GUSTY WINDS
MAY BE CAPABLE OF BLOWING AROUND LIGHT WEIGHT UNSECURED OBJECTS ON
WEDNESDAY AND WEDNESDAY NIGHT.
FORECAST DETAILS: AN UPPER LEVEL TROUGH WILL MOVE THROUGH THE UPPER
GREAT LAKES ON WEDNESDAY MORNING BEFORE PASSING THROUGH NORTHERN NEW
ENGLAND ON THURSDAY. A WARM FRONT WILL FORM AND MOVE THROUGH
SOUTHERN NEW HAMPSHIRE BEFORE STALLING ON WEDNESDAY MORNING,
WHICH WILL ALLOW TEMPERATURES TO QUICKLY RISE ACROSS SOUTHERN
LOCATIONS AND PROVIDE SOME CONVECTIVE INSTABILITY. WHILE SEVERE
WEATHER IS UNLIKELY, DID ADD A SLIGHT CHANCE OF THUNDER FOR
THESE LOCATIONS WITHIN THIS FORECAST PACKAGE. DURING THIS SAME
TIME PERIOD, A SURFACE CYCLONE WILL FORM AND MOVE ACROSS THE
OHIO RIVER VALLEY BEFORE QUICKLY MOVING TO THE NORTHEAST. THE
PLACEMENT AND STRENGTH OF THE UPPER LEVEL TROUGH WILL ULTIMATELY
HAVE THE LARGEST IMPACT ON THE TRACK OF THE SURFACE CYCLONE,
WHICH WILL PLAY A LARGE ROLE IN PRECIPITATION TYPES.
DETERMINISTIC AND ENSEMBLE GUIDANCE HAS BEEN TRENDING TO KEEP
THE TROUGH LESS AMPLIFIED, WHICH HAS ALLOWED FOR A EASTWARD
SHIFT IN THE SURFACE CYCLONE. LOOKING MORE CLOSELY, THERE IS
DECENT CLUSTERING WITHIN INDIVIDUAL LOW LOCATION MEMBERS OF THE
ECMWF, CMC, AND GEFS JUST OFFSHORE INTO THE WESTERN GULF OF
MAINE. THE GEFS CONTINUES TO BE THE FURTHEST EAST, WHICH WOULD
FAVOR A COLDER SOLUTION.
THIS EASTWARD TREND IN ENSEMBLE CLUSTERINGS CONTINUES TO INCREASE
CONFIDENCE FOR ACCUMULATING SNOW ACROSS THE MOUNTAINS AND FAR NORTH.
WHILE THIS WILL LIKELY BE ANOTHER ELEVATION DEPENDENT SYSTEM, THERE
IS THE POTENTIAL FOR AT LEAST SOME WET SNOW FLAKES TO MIX IN ACROSS
VALLEY LOCATIONS, ESPECIALLY WEDNESDAY NIGHT AS THE DEPARTING LOW
PULLS DOWN COLDER AIR FROM THE NORTH. ENSEMBLE MEANS SHOW GENERALLY
A 20-30 PERCENT CHANCE FOR AT LEAST ONE INCH OF SNOW AS FAR SOUTH AS
LEWISTON, WITH CATEGORICAL PROBABILITIES ACROSS THE NORTH. THESE
PROBABILITIES THEN DROP OFF RATHER QUICKLY WHEN EXAMINING THE
CHANCES FOR AT LEAST 3 AND 6 INCHES AND THEY BECOME
SIGNIFICANTLY MORE ELEVATION DEPENDENT. IT IS IMPORTANT TO NOTE
THAT THESE ARE BASED ON THE ASSUMPTION OF A 10:1 SNOW TO LIQUID
RATIO, WHERE IN REALITY THEY WILL LIKELY BE LOWER GIVEN
MARGINAL BOUNDARY LAYER TEMPERATURES. AS A RESULT, KEPT BOTH THE
HIGHEST CHANCES FOR SNOW AS WELL AS THE HIGHEST SNOW
ACCUMULATIONS ACROSS THE MOUNTAINS AND ALONG THE INTERNATIONAL
BORDER. AS THE CYCLONE MAKES ITS CLOSEST APPROACH TO THE REGION,
GUSTY WINDS WILL ALSO BE POSSIBLE AS THE PGF INCREASES,
ESPECIALLY ALONG THE COAST WHERE THEY MAY GUST UP TO 35-40 MPH
OR SO. TOTAL QPF LOOKS TO RANGE FROM AROUND ONE THIRD OF AN INCH
TO ONE INCH, WITH LOCALLY HIGHER AMOUNTS POSSIBLE ACROSS THE
WHITE MOUNTAINS.
THE SYSTEM WILL LIKELY SLOW DOWN AND MAYBE EVEN STALL OVER SOUTHERN
QUEBEC AND NOVA SCOTIA ON THURSDAY WITH CYCLONIC FLOW OVERHEAD
ALLOWING FOR CONTINUED CHANCES FOR UPSLOPE SNOW AND RAIN
SHOWERS LIKELY. THURSDAY WILL BE A SIGNIFICANTLY COOLER DAY WITH
HIGH TEMPERATURES ONLY RANGING FROM THE 30S ACROSS THE NORTH TO
THE 40S ELSEWHERE. A FEW LOCATIONS ACROSS THE FAR NORTH MAY
STRUGGLE TO BREAK THE FREEZING MARK. IN ADDITION, GUSTY
NORTHWESTERLY WINDS WILL KEEP WINDCHILL VALUES INTO THE 20S AND
30S FOR MUCH OF THE DAY. UPPER LEVEL RIDING WILL MOVE ACROSS NEW
ENGLAND ON FRIDAY AND SATURDAY, ALLOWING TEMPERATURES TO
MODERATE AND KEEP THE WEATHER MOSTLY BENIGN. SOME UPSLOPE
SHOWERS WILL STILL BE POSSIBLE ACROSS THE FAR NORTH AND
MOUNTAINS THOUGH, ESPECIALLY ON FRIDAY. ANOTHER TROUGH AND AREA
OF LOW PRESSURE MAY TRACK THROUGH THE REGION LATE THIS WEEKEND
AND EARLY NEXT WEEK BRINGING ANOTHER CHANCE FOR WIDESPREAD
PRECIPITATION.
AVIATION /00Z TUESDAY THROUGH SATURDAY/
SHORT TERM...VFR PREVAILS THROUGH TOMORROW WITH A SMALL CHANCE
OF BRIEF MVFR IN -SHRA THIS EVENING AND AGAIN TOMORROW, MOST
LIKELY FOR NORTHERN TERMINALS DURING THE AFTERNOON. PATCHY
VALLEY FOG MAY IMPACT VALLEY SITES LIKE HIE/LEB/CON TONIGHT.
SOUTHWEST WINDS GUST TO NEAR 25 KTS TOMORROW BEFORE BACKING TO
THE WEST LATE IN THE DAY.
LONG TERM...MVFR/IFR CONDITIONS LIKELY ON WEDNESDAY AND WEDNESDAY
NIGHT DUE TO LOW CEILINGS, GUSTY WINDS, AND WIDESPREAD
PRECIPITATION. THERE WILL BE THE POTENTIAL FOR AN ISOLATED
THUNDERSTORM, ESPECIALLY ACROSS SOUTHERN NEW HAMPSHIRE TERMINALS
SUCH AS KMHT. ACROSS NORTHERN TERMINALS, RAIN WILL LIKELY MIX WITH
OR CHANGE TO HEAVY WET SNOW ON WEDNESDAY NIGHT. MVFR/VFR CONDITIONS
POSSIBLE ON THURSDAY ACROSS SOUTHERN TERMINALS AS PRECIPITATION
GRADUALLY ENDS BUT ACROSS NORTHERN AND MOUNTAIN TERMINALS UPSLOPE
SHOWERS OF RAIN AND SNOW WILL LIKELY CONTINUE. NORTHWESTERLY WINDS
MAY GUST UP TO 35 KTS, ESPECIALLY ALONG THE COAST AND HIGHER
ELEVATIONS.
MARINE
SHORT TERM...QUIET OVER THE WATERS THROUGH TONIGHT, THEN SOUTH
WINDS INCREASE DURING THE DAY TOMORROW GUSTING TO NEAR 25 KTS.
SEAS WILL LIKEWISE INCREASE TO 3-5 FT BY TOMORROW NIGHT.
LONG TERM...SCA CONDITIONS LIKELY LATE WEDNESDAY AND WEDNESDAY
NIGHT AS SOUTHERLY WINDS BECOME MORE WESTERLY AND GUST UP TO 25 KTS
AS SEAS BUILD TO 4-6 FEET. GALE CONDITIONS ARE THEN POSSIBLE ON
THURSDAY BEHIND A SURFACE CYCLONE AS WESTERLY WINDS GUST UP TO 40
KTS WITH SEAS OF 4-7 FEET. WIDESPREAD RAIN IS EXPECTED WEDNESDAY AND
WEDNESDAY NIGHT WITH AN ISOLATED THUNDERSTORM ALSO POSSIBLE.
FIRE WEATHER
A BRIEF PERIOD OF ELEVATED FIRE WEATHER DANGER IS EXPECTED
TOMORROW AS A DRY SOUTHWEST WIND DEVELOPS AHEAD OF A CROSSING
WAVE. DURING MID- TO LATE-MORNING, WE'LL MIX OUT THROUGH THE LOW
LEVELS AND LEAD TO HUMIDITY DROPPING TO 25-30 PERCENT FOR MUCH
OF THE LOWER ELEVATIONS COINCIDING WITH WIND GUSTS AROUND 25-30
MPH. FURTHER NORTH AND INTO WESTERN MAINE, RAIN AND CLOUDS WILL
KEEP HUMIDITY HIGHER WITH LOWER FIRE WEATHER DANGER. HUMIDITY
WILL RECOVER NICELY TOMORROW NIGHT, THEN WETTING RAINS ARE
POSSIBLE FOR MUCH OF THE REGION WEDNESDAY INTO WEDNESDAY NIGHT.
GYX WATCHES/WARNINGS/ADVISORIES
ME...NONE.
NH...NONE.
MARINE...NONE.
SYNOPSIS...CASEY/TUBBS
NEAR TERM...CASEY/WATSON
SHORT TERM...CASEY
LONG TERM...TUBBS
AVIATION...CASEY/TUBBS
MARINE...CASEY/TUBBS
FIRE WEATHER...
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