Area Forecast Discussion
Issued by NWS Portland, ME

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299
FXUS61 KGYX 221551
AFDGYX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAY ME
1151 AM EDT FRI MAY 22 2015

.SYNOPSIS...
A COLD FRONT WILL CROSS NEW ENGLAND TODAY...SETTING OFF A FEW
SHOWERS AND ISOLATED THUNDERSTORMS. HIGH PRESSURE THEN BUILDS IN
SATURDAY AND SUNDAY. A WARM FRONT WILL APPROACH NEW ENGLAND ON
MONDAY...AND CROSS THE AREAS MONDAY NIGHT AND TUESDAY....PROVIDING
ANOTHER CHANCE FOR SHOWERS AND STORMS. WARM AND MORE HUMID
CONDITIONS ARE EXPECTED MID TO LATE WEEK.

&&

.NEAR TERM /UNTIL 8 PM THIS EVENING/...

1150 AM...MINOR ADJUSTMENTS TO 1ST PERIOD GRIDS TO INCORPORATE
THE LATEST MESONET AND SATELLITE TRENDS.

PREV DISC...
950 AM...MINOR ADJUSTMENTS TO 1ST PERIOD GRIDS TO INCORPORATE THE
LATEST MESONET.

PREV DISC...
UPDATE...A FEW MINOR CHANGES TO REFLECT CURRENT OBSERVATIONAL
TRENDS. DID INCLUDE SOME SLIGHT CHANCE POP S OF THE MTNS THIS
MORNING...AS A BAND OF VERY LIGHT SHOWERS DRIFTS THRU THE AREA ON
THE NW SIDE OF WEAK COASTAL LOW PRES.

PREVIOUS DISCUSSION...A SEASONABLY STRONG COLD FRONT WILL CROSS
THE FORECAST AREA TODAY...USHERING IN SOME VERY CHILLY AIR. PRIOR
TO ITS ARRIVAL AREAS E OF THE MTNS SHOULD WARM SUFFICIENTLY TO
PROVIDE A LITTLE BIT OF FUEL FOR SHOWERS TO POP UP ALONG THE
FRONT.

MESOSCALE GUIDANCE IS IN EXCELLENT AGREEMENT THAT A BAND OR
CLUSTERS OF SHOWERS WILL DEVELOP QUICKLY ALONG THE MTNS AND RACE
EWD TOWARDS THE COAST...ESPECIALLY ACROSS WRN ME. FARTHER S AND
W...THE AIR MASS WILL BE QUITE DRY AND SOUNDINGS SUGGEST IT WILL
BE DIFFICULT TO SATURATE ENOUGH FOR PCPN. DEEPER MOIST LAYERS WILL
RESIDE ACROSS WRN ME...AND WILL SUPPORT LIKELY POP FOR PARTS OF
THE MIDCOAST. LOW FREEZING LEVELS WILL ALSO SUPPORT PLENTY OF ICE
IN THE CLOUDS...AND CANNOT RULE OUT SOME THUNDER OR SMALL
HAIL/GRAUPEL. STEEP LAPSE RATES WILL RESIDE IN THE BOUNDARY LAYER
THANKS TO THE DRY AIR MASS...SO SOME OF THESE SHOWERS/TSTMS MAY BE
GUSTY.

&&

.SHORT TERM /8 PM THIS EVENING THROUGH 6 PM SATURDAY/...
TONIGHT THE COLD FRONT WILL BRING H8 TEMPS BETWEEN -4 AND -8 C
ACROSS THE FORECAST AREA. THIS IS NEARLY A 3 SIGMA DEPARTURE FROM
NORMAL...AND MODEL GUIDANCE HAS EVEN COOLED A LITTLE FROM LAST
NIGHT. SOUNDING CLIMATOLOGY SUGGESTS THIS COLD SHOT WILL FALL WELL
WITHIN THE LOWEST 10 PERCENT OF OBSERVATIONS FOR THIS TIME OF
YEAR. THIS ALL ADDS UP TO A LOW TEMP FORECAST AT LEAST AS COLD AS
WED NIGHT...AND PROBABLY A FEW DEGREES COOLER.

THAT BEING SAID...MODEL FORECAST SOUNDINGS INDICATE THE BOUNDARY
LAYER WILL REMAIN AT LEAST PARTIALLY MIXED AS CAA CONTINUES
OVERNIGHT TONIGHT. MAV/MET GUIDANCE CAN OFTEN BE TOO AGGRESSIVE
IN DECOUPLING THE BOUNDARY LAYER...THUS FORECASTING MIN TEMPS TOO
COLD ESPECIALLY DOWNWIND OF THE MTNS. THE LATEST MAV FOR INSTANCE
BRINGS KHIE AND KBML DOWN TO THE UPPER TEENS. TO OFFSET THIS BIAS
I HAVE BLENDED IN SOME 2 M TEMPS FROM REGIONAL SCALE MODEL
GUIDANCE TO PROVIDE AN ELEMENT CAA MIXED LAYER. OVERALL THIS
LOWERED THE PREVIOUS FORECAST A DEGREE OR TWO. THE GRADIENT FLOW
MAY BE ENOUGH TO PRECLUDE FROST FOR MOST AREAS...BUT TEMPS
REGARDLESS LOOK TO FALL BELOW FREEZING FOR A LARGE PORTION OF THE
NRN FORECAST AREA. I EXPANDED THE FREEZE WATCH TO AREAS ON THE
BORDERLINE OF 32 DEGREES TO HIGHLIGHT THE POTENTIAL FOR A COLDER
FORECAST SOLUTION. THIS IS ESPECIALLY TRUE IF RIDGING CAN MOVE IN
FASTER...ALLOWING THE BOUNDARY LAYER TO DECOUPLE. THIS WOULD MOST
LIKELY HAPPEN OVER WRN ZONES...SO THE MOST UNCERTAINTY IN THE
FORECAST LIES IN THOSE AREAS.

IT WILL BE A COOL AND BREEZY DAY SAT IN THE POST-FRONTAL AIR MASS.
WILL HAVE TO KEEP AN EYE ON DEW POINT FORECASTS DURING THE DAY.
MODEL GUIDANCE IS IN THE LOW TO MID 20S...WHILE BUFKIT SOUNDINGS
SHOW THE DEPTH OF MIXED LAYER HINTING AT REALITY BEING CLOSER TO
THE LOW TO MID TEENS. THIS WOULD BRING RH VALUES WELL BELOW 25
PERCENT...AND COUPLED WITH WINDS AND RECENT DRYNESS COULD CAUSE
SOME FIRE DANGER ISSUES.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
500MB PATTERN TRANSITIONS TO BLOCKY SUMMER-LIKE PATTERN NEXT WEEK
AS RIDGING DEVELOPS OVER THE ERN CONUS AND WRN ATLANTIC AND 500MB
JET RETREATS WELL POLEWARD. THIS WILL LEAD TO WARM AND MORE HUMID
CONDITIONS MOVING IN...WITH POTENTIAL FOR SCT TSRA AT TIMES AS WE
ARE ON THE SRN PERIPHERY OF IMPULSES MOVING BY IN THE STRONGER
500 MB TO OUR N.

SUNDAY LOOKS TO BE A SEASONABLY FAIR DAY WITH HIGHS MAINLY IN THE
70S AND A DECENT WEST WIND WILL KEEP THE COOLER MARINE AIR MAINLY
OFFSHORE...EXCEPT MAYBE AT THE BEACHES. SUNDAY NIGHT LOOKS CLEAR
AND MORE MILD THAN PREVIOUS NIGHTS WITH LOWS IN THE MID 40S N...TO
MID 50S S. DECENT WAA BEGINS TO DEVELOP TO OUR WEST ON
MONDAY...AND SHOULD CLOUDS OVERSPREAD WRN ZONES AT LEAST DURING
THE AFTERNOON...BUT THINKING ANY RAIN/SHOWERS WILL HOLD OFF UNTIL
MON NIGHT. THE SW FLOW SHOULD WARM TEMPS INLAND WELL INTO THE
MID-UPPER 70S...BUT WILL COOL THE COAST DOWN...ESPECIALLY THE MID
COAST.

DECENT MID-LVL WAA MOVES THROUGH MON NIGHT INTO TUE MORNING...AND
SHOULD PRODUCE A PERIOD OF RAIN OR SOME CONVECTIVE SHOWERS DURING
THIS TIMEFRAME. TDS RISE QUICKLY BEHIND THIS WARM FRONT SHOOTING
UP INTO THE MID 50S TO LOW 60S. WED-FRI WILL BE WARM AND
HUMID...WITH HIGHS GENERALLY RUNNING 80-85 INLAND...AND IN THE 70S
ON THE COAST. SOME WAVES WILL INEVITABLY MOVE OVER THE TOP OF THE
RIDGE...SO THERE WILL BE THE THREAT OF SHRA/TSRA...BUT TIMING
THIS FAR OUT IS A GUESS AT BEST.

&&

.AVIATION /16Z FRIDAY THROUGH TUESDAY/...
SHORT TERM...VFR EXPECTED TO PREVAIL THRU SAT. COLD FRONT CROSSING
THE FORECAST AREA WILL KICK OFF SCATTERED SHOWERS...ESPECIALLY
ACROSS INTERIOR WRN ME. SOME OF THESE SHOWERS MAY CONTAIN SOME
THUNDER...THOUGH THE PROBABILITY IS LOW. AT ALL TERMINALS NW WIND
GUSTS TO 25 KTS ARE POSSIBLE BEHIND THE FRONT. GUSTY WINDS
CONTINUE AGAIN SAT.

LONG TERM...VFR EXPECTED SAT NIGHT THROUGH MONDAY. FLIGHT
RESTRICTIONS ARE EXPECTED MON NIGHT INTO AT LEAST TUE MORNING IS
SHRA AND LOW CLOUDS.

&&

.MARINE...
SHORT TERM...COLD FRONT WILL CROSS THE WATERS TODAY...WITH STRONG
CAA TO FOLLOW BEHIND IT. WINDS WILL GUST ABOVE 25 KTS LATE TONIGHT
INTO SAT MORNING. SEAS WILL BUILD TO NEAR 5 FT ON THE OUTER WATERS
BEFORE SLOWLY DIMINISHING SAT.

LONG TERM...WEST WINDS SUNDAY SHIFT TO SW ON MONDAY...AND WILL
GUST TO AROUND 20 KT BOTH DAYS BUT ARE EXPECTED TO BE SUB-SCA
LVLS. IN GENERAL WINDS WILL REMAIN BLO SCA THROUGH THE MIDDLE OF
NEXT WEEK. SOME SEAS WELL OFFSHORE COULD REACH 5 FT LATE MON AND
TUE.

&&

.FIRE WEATHER...
DRY AIR MASS WILL MOVE INTO THE AREA TODAY. COOLER TEMPERATURES
WILL KEEP RELATIVE HUMIDITY VALUES GENERALLY AROUND 25 PERCENT.
LOWER RELATIVE HUMIDITIES MAY BE POSSIBLE NEAR THE COAST...WHERE
TEMPERATURES MAY CLIMB INTO THE LOWER 70S. AS COLD FRONT CROSSES
THE AREA WINDS WILL BECOME GUSTY FROM THE WEST NORTHWEST. AIR
MASS WILL BECOME WINDIER AND DRIER ON SATURDAY.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...FREEZE WATCH FROM 9 PM EDT THIS EVENING THROUGH SATURDAY
     MORNING FOR MEZ007>009-012-013.
     FIRE WEATHER WATCH FROM SATURDAY AFTERNOON THROUGH SATURDAY
     EVENING FOR MEZ007>009-012>014-018>028.
NH...FREEZE WATCH FROM 9 PM EDT THIS EVENING THROUGH SATURDAY
     MORNING FOR NHZ001>009-011.
     FIRE WEATHER WATCH FROM SATURDAY AFTERNOON THROUGH SATURDAY
     EVENING FOR NHZ004-006>015.
MARINE...SMALL CRAFT ADVISORY FROM 8 PM THIS EVENING TO 11 AM EDT
     SATURDAY FOR ANZ150>154.

&&

$$
ES



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