395
FXUS61 KGYX 170426
AFDGYX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAY ME
1126 PM EST WED JAN 16 2019
SYNOPSIS
A COLD FRONT WILL CROSS THE REGION LATE TODAY ACCOMPANIED BY
SCATTERED SNOW SHOWERS AND A FEW MOUNTAIN SNOW SQUALLS. IT WILL
BE 15 TO 20 DEGREES COLDER ON THURSDAY AS ARCTIC HIGH PRESSURE
BUILDS IN. THE NEXT WAVE OF LOW PRESSURE TRACKS ACROSS THE
REGION ON FRIDAY BRINGING WIDESPREAD BUT LIGHT SNOWFALL. A
LARGER STORM WILL BRING WINTRY WEATHER FOR THE SECOND HALF OF
THE UPCOMING WEEKEND. SIGNIFICANT AMOUNTS OF WINTRY
PRECIPITATION ARE LIKELY, BUT THE EXACT TRACK WILL DETERMINE
THOSE PRECIPITATION TYPES.
NEAR TERM /UNTIL 6 AM THURSDAY MORNING/
UPDATE...
HAVE UPDATED THE FORECAST BASED ON CURRENT OBSERVATIONS AND
LATEST RADAR IMAGERY. SCATTERED SNOW SHOWERS AND POSSIBLY A
COUPLE SNOW SQUALLS EXITED THE MOUNTAINS AND FOOTHILLS EARLIER
AND WEAKEND. HAVE ADDED HIGHER WINDS FOR TERRAIN ABOVE 4500
FEET AS MOUNT WASHINGTON CONTINUES TO GUST WELL OVER HURRICANE
FORCE THIS EVENING.
OTHERWISE, ONLY MINOR ADJUSTMENTS MADE TO POPS, TEMPERATURES AND
SKY COVER THIS EVENING.
PREV DISC...
LOW PRESSURE TRACKING THROUGH SOUTHERN QUEBEC IS DRAGGING A
COLD FRONT THROUGH NEW ENGLAND AT PRESENT. THIS HAS TRIGGERED
NUMEROUS SNOW SHOWERS WHICH HAVE RECENTLY SHOWN UP ON REGIONAL
RADAR OVER THE WHITE MOUNTAINS. SNOW SQUALLS ARE STILL INDICATED
FOR THE MOUNTAINS AND FOOTHILLS THE NEXT FEW HOURS, AND HAVE
COVERED THIS THREAT WITH A STATEMENT WHICH CAUTIONS FOR LOCALLY
HEAVY SNOWFALL CAUSING LOW VISIBILITIES FOR THE AFTERNOON
COMMUTE.
THE ARCTIC COLD FRONT MOVES OFFSHORE AROUND 6 PM BRINGING AN END
TO PRECIPITATION. GUSTY NW WINDS WILL FOLLOW FOR A FEW HOURS
ALLOWING MUCH COLDER AND DRIER AIR TO POUR IN FROM THE NORTH.
SKIES CLEAR OUT QUICKLY AND OVERNIGHT LOWS WILL DROP TO NEAR
-10F ACROSS THE NORTH TO THE SINGLE DIGITS SOUTH. A WIND CHILL
ADVISORY REMAINS IN EFFECT FOR AREAS INCLUDING THE NORTHERN
MOUNTAINS OF NH AND MAINE TONIGHT INTO TOMORROW MORNING.
SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY/
WE WILL SEE HIGHS THURSDAY IN THE SINGLE DIGITS NORTH TO TEENS
FOR THE COASTAL PLAIN WITH COLD HIGH PRESSURE DRIFTING FROM WEST
TO EAST. OVER SOUTHERN NH AND ALONG THE IMMEDIATE COAST
READINGS WILL REACH THE LOWER 20S. LOWS FRIDAY NIGHT WON'T BE AS
BRUTALLY COLD AS THE PREVIOUS NIGHT, WITH READINGS AROUND ZERO
ACROSS THE NORTH AND IN THE 10S SOUTH.
SKIES WILL BEGIN TO INCREASE FROM THE SW THURSDAY NIGHT AS A
WEAK AND POORLY ORGANIZED STORM APPROACHES FROM THE MIDWEST. WE
WILL HAVE A VERY COLD AIRMASS IN PLACE THROUGHOUT THE
ATMOSPHERE, AND AS LOW PRESSURE CROSSES THE AREA WIDESPREAD BUT
WEAKLY FORCED SNOWFALL IS EXPECTED FRIDAY BEGINNING BEFORE DAWN
AND ENDING SOMETIME IN THE AFTERNOON AS DRIER AIR IS DRAWN IN
FROM THE SW. SPECIFIC HUMIDITIES ARE LOW INDICATING LOW QPF
AMOUNTS. THIS YIELDS A WIDESPREAD 1-3" SNOWFALL WITH THE HIGHER
AMOUNTS OVER THE MOUNTAINS AND THE MID COAST REGION WHERE THE
SYSTEM BEGINS TO DEEPEN RIGHT BEFORE TAKING OFF IN FAST MOVING
CONVERGENT FLOW ALOFT. TEMPERATURES SHOULD REACH THE LOWER 20S
NORTH TO MID 30S TOWARDS SOUTHERN SECTIONS.
LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/
HIGH IMPACT WEATHER: *** SIGNIFICANT WINTER STORM WILL IMPACT THE
REGION FROM SATURDAY NIGHT INTO SUNDAY. ***
OVERVIEW: CONFIDENCE IS INCREASING FOR A SIGNIFICANT WINTER STORM TO
IMPACT THE REGION OVER THE WEEKEND. SATURDAY WILL START OFF CLEAR
AND COLD OVER NORTHERN NEW ENGLAND AS HIGH PRESSURE EXITS TO THE
EAST. MEANWHILE OUR STORM WILL DEVELOP OVER THE FOUR CORNERS AND
RAPIDLY INTENSIFY AS IT MOVES ACROSS THE SOUTHERN PLAINS. BY 00Z
SUNDAY WE'LL SEE THE FIRST FLAKES MOVING INTO SOUTHERN NEW HAMPSHIRE
AS THE LOW MOVES UP THE OHIO RIVER VALLEY. BY SUNDAY MORNING THE LOW
WILL MOVE OFFSHORE OF DELMARVA WITH SIGNIFICANT SNOWFALL IN THE
NORTHWEST QUADRANT. HEAVY SNOW WILL CONTINUE THROUGH THE DAY ON
SUNDAY BEFORE COMING TO AN END LATE SUNDAY NIGHT.
TRENDS: OVER THE PAST DAY OR SO WE'VE SEEN A CONSISTENT COLDER
TREND IN THE GUIDANCE AS THE LOW CENTER SHIFTS FURTHER OFFSHORE.
AS OF 12Z A SUPER MAJORITY OF ENSEMBLE MEMBERS WOULD KEEP THE
LOW CENTER EAST OF THE MAINE COAST OVER THE GULF OF MAINE
KEEPING OUR REGION IN SNOW.
UPPER LEVEL PATTERN: THIS NOR'EASTER WILL FORM IN A PRETTY CLASSIC
PATTERN ALONG THE EASTERN EDGE OF A DEEPENING 500MB TROUGH. TO OUR
WEST THE WEST CONUS REMAINS UNDER STRONG HIGH PRESSURE WITH THE
RESULT BEING BLOCKED FLOW. THIS ALLOWS OUR STORM TO SOURCE FROM
TWO REGIONS. A SHORT WAVE IN THE NORTHERN STREAM WILL DIVE
SOUTH THROUGH THE CANADIAN PRAIRIES. AS IT DOES THE SOUTHERN
STREAM LOW OVER THE SOUTHERN PLAINS WILL ALSO PHASE WITH THE TWO
SYSTEMS COMBINING TO FOR A VERY ELONGATED LOW PRESSURE ALONG
THE COAST. WHENEVER THERE ARE TWO SYSTEMS TRYING TO ACT IN PHASE
THERE IS ROOM FOR ERROR, AND WITH NEITHER OF THEM ONSHORE YET
THAT IS CERTAINLY THE CASE HERE HOWEVER THE PRESENCE OF AN
UPPER BLOCK OVER ALASKA ALONG WITH WEAKLY BLOCKED FLOW OVER
EUROPE SUPPORTS THE STRENGTHENING EAST COAST TROUGH.
PTYPE: OVER THE PAST FEW DAYS PTYPE HAS BEEN A CONCERN WITH THIS
SYSTEM BUT IT GRADUALLY BECOMING LESS SO AS THE COLDER TREND APPEARS
TO BE WINNING. THE KEY HERE IS REALLY THAT NORTHERN STREAM SHORT
WAVE WILL PROVIDE THE FORCING TO KEEP THE WARMER AIR OFFSHORE.
TRYING NOT TO FLIP FLOP TOO HARD HAVE OPTED TO LEAVE SOME MIXED
SLEET AND FREEZING RAIN IN PLACE ALONG THE COAST BUT FEEL THAT
AN ALL SNOW SOLUTION IS BECOMING MORE AND MORE LIKELY. A BIT OF
FREEZING DRIZZLE IS ALSO POSSIBLE ON THE BACKSIDE IN THE DRY
SLOT BUT OVERALL WE ARE LOOKING AT A SNOWSTORM WITH A CHANCE FOR
SOME MIX ALONG THE COAST NOT A WIDESPREAD ICING EVENT.
SNOW AMOUNTS: IF YOU'VE BEEN WAITING FOR WINTER, HERE IT IS.
POTENTIAL FOR VERY HEAVY SNOW ACCUMULATION /WIDESPREAD DOUBLE
DIGIT SNOWFALL/ CONTINUES TO INCREASE. WITH 1-1.5" OF LIQUID
PRECIPITATION, EVEN A MODEST 10:1 SNOW RATIO EASILY ACHIEVES
THAT OBJECTIVE. IN FACT HIGHER SNOW RATIOS ARE QUITE POSSIBLE,
PARTICULARLY IN THE INTERIOR. FORECAST SOUNDINGS SHOW STRONG
UPWARD MOTION IN THE SNOW GROWTH ZONE ON SUNDAY MORNING ACROSS
SOUTHERN MAINE AND EXPECT A REGION OF SNOWFALL RATES OVER 1"/HR
THROUGH SUNDAY. IT'S FAR TOO EARLY TO PIN DOWN ANY MESOSCALE
EFFECTS OTHER THAN TO MENTION THAT STRONG SNOW BANDS ARE LIKELY
WITH THIS KIND OF STRONG DYNAMIC STORM AND ANY AREAS THAT REMAIN
UNDER SNOWBANDS MAY SEE CLOSER TO 2"/HR RATES.
WIND: A LOOK AT THE PRESSURE GRADIENT AND RAPID STRENGTHENING
OF THE SYSTEM SAYS THAT STRONG WINDS ARE LIKELY WITH THIS
SYSTEM. THE TRICK WILL BE GETTING THEM DOWN TO THE SURFACE AS A
MORE STABLE COLD LAYER OVER LAND MAY LIMIT THE MIXING SOMEWHAT.
HOWEVER ALONG THE COAST LINE AND CERTAINLY OVER THE COASTAL
WATERS STRONGER GUSTS ARE LIKELY.
MONDAY AND BEYOND: A VERY COLD AIRMASS WILL MOVE IN BEHIND THE STORM
WITH THE POTENTIAL FOR BELOW ZERO TEMPERATURES DOWN TO THE COAST.
AVIATION /06Z THURSDAY THROUGH MONDAY/
SHORT TERM /THROUGH THURSDAY/...VARIABLE CEILINGS ACROSS THE
AREA WITH IMPROVEMENT TO MOSTLY VFR DECKS WITH THE OCCASIONAL
MVFR. CLEARING AND IMPROVEMENT WILL CONTINUE AS A COLD FRONT
PUSHES OFFSHORE TONIGHT. GUSTY WNW WINDS WILL DEVELOP THIS
AFTERNOON AND EVENING BEFORE DIMINISHING OVERNIGHT. WINDS BECOME
LIGHT AND VARIABLE THURSDAY AS HIGH PRESSURE BUILDS IN WITH
PREVAILING VFR.
LONG TERM...SATURDAY WILL BEGIN VFR AS HIGH PRESSURE DEPARTS. CLOUDS
WILL RAPIDLY ENCROACH AND DESCEND THROUGH THE AFTERNOON DROPPING TO
MVFR BY SUNSET. SNOW WILL TAKE HOLD IN THE EARLY MORNING HOURS OF
SUNDAY WILL ALL LOCATIONS EXPECTING LIFR IN HEAVY SNOW THROUGH THE
DAY ON SUNDAY. SOME MVFR SNOW SHOWERS WILL REMAIN THROUGH THE
MOUNTAINS ON MONDAY WITH A STEADY NORTHWESTERLY WIND THROUGHOUT
THE REGION AS COLD AIR MOVES INTO THE AREA.
MARINE
SHORT TERM /THROUGH THURSDAY/...WINDS REMAIN GUSTY IN
ASSOCIATION WITH A COLD FRONTAL PASSAGE THIS AFTERNOON AND
EVENING. GALES REMAIN IN PLACE FOR ALL AREAS BUT CASCO BAY WHERE
A SMALL CRAFT ADVISORY IS IN EFFECT. A FREEZING SPRAY ADVISORY
HAS BEEN ISSUED FOR THE CENTRAL AND EASTERN OUTER WATERS AS WELL
AS PENOBSCOT BAY OVERNIGHT AND INTO THURSDAY MORNING WHERE
MODERATE FREEZING SPRAY WILL OCCUR.
LONG TERM... A COASTAL LOW WILL RAPIDLY INTENSIFY AND MOVE
THROUGH THE GULF OF MAINE FROM SATURDAY NIGHT INTO SUNDAY WITH
STORM FORCE WINDS POSSIBLE ON THE OUTER WATERS AND GALES LIKELY
IN THE BAYS. WAVES WILL BUILD TO 10-20FT. HAVE INCREASED BOTH
THE WIND GUSTS AND WAVE HEIGHT AS THE RELATIVELY WARMER WATER
TEMPERATURES WILL ALLOW FOR UNSTABLE CONDITIONS NEAR THE SURFACE
OVER THE WATERS AND GOOD MIXING.
TIDES/COASTAL FLOODING
HIGH ASTRONOMICAL TIDES WILL COMBINE WITH AN APPROACHING STORM
WITH STRONG NORTHEASTERLY WINDS AND BUILDING WAVES DURING THE
DAY ON SUNDAY. THE TIMING OF THE PEAK WINDS/WAVES WILL BE
CRUCIAL TO THIS FORECAST AND MAY VARY FROM MODEL RUN TO MODEL
RUN.
THE ASTRONOMICAL HIGH TIDE IN PORTLAND WILL BE NEAR 10 AM ON
SUNDAY AT 11.1 FEET. LEANED HEAVILY TOWARDS THE ESTOFS MODEL
WHICH IS MORE ROBUST IN TERMS OF STORM SURGE LEVELS AT AROUND
1.3 FEET. THIS VALUE MAY BE HIGHER, BUT ALSO ARRIVE AFTER HIGH
TIDE. IN ANY CASE, THIS EVENT WILL LIKELY PRODUCE MINOR COASTAL
FLOODING AND SPLASH-OVER AROUND THE TIME OF HIGH TIDE WITH
POCKETS OF MODERATE FLOODING POSSIBLE FROM PORTLAND AND POINTS
SOUTH TO HAMPTON HARBOR SUNDAY MORNING. LONG PERIOD SWELLS ARE
FORECAST TO ARRIVE SUNDAY NIGHT INTO MONDAY, SO THIS WILL NEED
TO BE MONITORED FOR A CONTINUED POSSIBILITY FOR SOME SPLASH-
OVER.
GYX WATCHES/WARNINGS/ADVISORIES
ME...WIND CHILL ADVISORY UNTIL 10 AM EST THURSDAY FOR MEZ007>009.
NH...WIND CHILL ADVISORY UNTIL 10 AM EST THURSDAY FOR NHZ001-002.
MARINE...SMALL CRAFT ADVISORY UNTIL 7 AM EST THURSDAY FOR ANZ153.
FREEZING SPRAY ADVISORY UNTIL 11 AM EST THURSDAY FOR
ANZ150>152.
GALE WARNING UNTIL 7 AM EST THURSDAY FOR ANZ150>152-154.
JC
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