Area Forecast Discussion
Issued by NWS Portland, ME

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000
FXUS61 KGYX 020040
AFDGYX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAY ME
840 PM EDT SAT AUG 1 2015

.SYNOPSIS...
A COLD FRONT WILL EXIT THE REGION THIS EVENING AS SCATTERED
SHOWERS AND THUNDERSTORMS COME TO AN END. TEMPERATURES AND
HUMIDITY DROP OFF A LITTLE MORE BEHIND THIS FRONT. SUNDAY SHOULD
BE MAINLY DRY AS HIGH PRESSURE BUILDS ACROSS NEW ENGLAND. WEAK LOW
PRESSURE ALOFT...SITUATED OVER QUEBEC...WILL BRING ANOTHER ROUND
SHOWERS OR STORMS MONDAY AFTERNOON INTO MONDAY NIGHT.

&&
00Z UPDATE...
ASIDE FROM A FEW PATCHY MID LEVEL CLOUDS SKIES HAVE CLEARED ACROSS
THE FORECAST AREA THIS EVENING. CONVECTION BACK TO THE WEST OVER
NORTHERN NEW YORK AND VERMONT STILL HOLDING TOGETHER BUT
DIMINISHING AS IT HEADS EAST. HAVE BUMPED UP POPS IN FAR NORTHWEST
ZONES FOR THE NEXT 3 TO 4 HOURS FOR ANY CELLS WHICH MIGHT SURVIVE
THE TRIP INTO NORTHWEST NEW HAMPSHIRE AND MAINE. ASIDE FROM A FEW
TEMP AND TD TWEAKS...NO OTHER CHANGES PLANNED ATTM.


PREVIOUS DISCUSSION...
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
SURFACE COLD FRONT AND AN UPPER LEVEL SHORT WAVE WILL BE EXITING
TO OUR EAST THIS EVENING. THIS WILL BRING AN END TO ANY REMAINING
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS. AS SKIES BEGIN TO
CLEAR AND WINDS BECOME LIGHT...PATCHY INLAND VALLEY FOG WILL FORM.
LOCALLY...THE VISIBILITY MAY DROP DOWN BELOW A MILE IN SOME
LOCATIONS.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
EXPECT DRY CONDITIONS SUNDAY MORNING WITH RIDGING OCCURRING ALOFT.
HOWEVER...IN THE AFTERNOON...A LARGE SCALE UPPER TROUGH WILL
BEGIN TO APPROACH FROM THE NORTHWEST. WITH CYCLONIC FLOW AND COLD
AIR ALOFT...DIURNALLY DRIVEN CU WILL FORM - MAINLY OVER NORTHERN
AREAS. THERE MAY BE SUFFICIENT MOISTURE FOR A SPRINKLE OR A BRIEF
SHOWER...AGAIN...MAINLY CONFINED TO THE FAR NORTH. HOWEVER...HAVE
KEPT POPS RELATIVELY LOW FOR THE DAY.

A COLD FRONT WILL BEGIN TO APPROACH FROM THE WEST SUNDAY NIGHT.
THE CHANCE FOR SHOWERS WILL BE ON THE INCREASE LATE AT NIGHT ALONG
THE CANADIAN BORDER. THIS TAKES US TO THE LONG TERM PORTION OF THE
DISCUSSION WITH A SLOW MOVING UPPER LEVEL LOW PRESSURE SYSTEM NEAR
THE GREAT LAKES REGION.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
WARM MOIST AIR MOVES BACK INTO THE AREA ON MONDAY AHEAD OF AN
APPROACHING UPPER LEVEL TROUGH. TEMPERATURES ACROSS THE AREA WARM
INTO THE 80S WITH A FEW LOW 90S POSSIBLE IN SOUTHERN NEW
HAMPSHIRE. THE INCREASING MOISTURE AT THE SURFACE WILL GENERATE
INSTABILITY WHILE THE ADVANCING HEAT ALOFT (700 MB) WILL SERVE AS
A CAP TO PREVENT ACCESS TO THAT INSTABILITY UNLESS A FORCING
MECHANISM CAN BE FOUND TO OVERCOME THE CAP. AS THE UPPER TROUGH
GETS CLOSER TO THE AREA LATER IN THE DAY IT WILL BEGIN ERODING THE
CAP AND ALLOW GREATER ACCESS TO THE INSTABILITY IN ADDITION TO
PROVIDING UPPER LEVEL LIFT AND PUSHING A SURFACE COLD FRONT
EASTWARD. AS A RESULT... EXPECT SHOWERS AND THUNDERSTORMS AS THE
TROUGH AND COLD FRONT MOVE THROUGH BUT THIS MAY NOT OCCUR UNTIL
LATE IN THE AFTERNOON AND INTO THE OVERNIGHT MONDAY NIGHT. MODELS
IN PRETTY GOOD AGREEMENT ON HOLDING PRECIPITATION OFF UNTIL LATE
AFTERNOON AT THE EARLIEST. THE NAM IS ACTUALLY THE FASTEST OF ALL
THE MODELS IN SPITE OF ITS NORMAL SLOW BIAS... TRIGGERING STORMS
AROUND MID AFTERNOON.

WITH THE INSTABILITY PRESENT (1000 OR MORE CAPE) ON TUESDAY THERE
WILL ALSO BE A SUBSTANTIAL AMOUNT OF WIND SHEAR. MID LEVEL WINDS
WILL BE OUT OF THE SOUTHWEST AT ABOUT 45 OR 50 KT WHILE SURFACE
WINDS ARE LIGHT OUT OF THE SOUTH. THIS WOULD BE PLENTY SUFFICIENT
FOR SUPERCELLS OR A MORE ORGANIZED DAMAGING WIND THREAT. THIS IS
IN AGREEMENT WITH THE STORM PREDICTION CENTER`S OUTLOOK FOR MONDAY
ALSO. HAVE INCLUDED DAMAGING WINDS WITH THE THUNDERSTORMS ON
MONDAY TO HIGHLIGHT THIS THREAT WHICH WILL BE GREATEST OVER NEW
HAMPSHIRE AND FAR WESTERN MAINE.

UPPER LEVEL TROUGH AXIS AND SURFACE FRONTAL BOUNDARY SHOULD CLEAR
THE AREA BY EARLY TUESDAY MORNING... HOWEVER SOME INSTABILITY
STILL EXISTS BEHIND IT AND AN ISOLATED SHOWER OR STORM CANNOT BE
RULED OUT AS THE PRIMARY UPPER LOW AND TROUGH AXIS MOVE ACROSS THE
AREA.

COOL HIGH PRESSURE BUILDS IN FROM THE WEST AND NORTHWEST WEDNESDAY
THROUGH FRIDAY. EXPECT A LITTLE COOLER TEMPERATURES... ALTHOUGH AN
OFFSHORE WIND WILL STILL ALLOW COASTAL AREAS TO GET INTO THE UPPER
70S AND LOW 80S.

THE NEXT UPPER TROUGH WILL MOVE THROUGH THE GREAT LAKES ON
SATURDAY AND TRIGGER CYCLOGENESIS OFF THE MID ATLANTIC COAST INTO
SUNDAY. AN AREA OF RAIN WILL LIKELY FORM AND TRACK THROUGH
SOUTHERN NEW ENGLAND AND POSSIBLY INTO SOUTHERN PARTS OF MAINE AND
NEW HAMPSHIRE BUT SEEMS MORE LIKELY TO STAY JUST SOUTH OF OUR AREA
AT THIS POINT.

&&

.AVIATION /01Z SUNDAY THROUGH THURSDAY/...
SHORT TERM...ISOLATED SHOWERS AND THUNDERSTORMS WILL CONTINUE NEAR
OR OVER THE TAF SITES INTO EARLY THIS EVENING. OTHERWISE CLEARING
WITH PATCHY INLAND FOG DEVELOPING.  WINDS WILL BE LIGHT.

ON SUNDAY...DIURNALLY DRIVEN CU FIELDS WILL DEVELOP DURING THE
DAY. ANY SHOWER ACTIVITY SHOULD BE LIGHT AND MAINLY CONFINED TO
THE NORTH.  MAINLY VFR CONDITIONS.

LONG TERM...EARLY MORNING MARINE FOG OR LOW CLOUDS IS POSSIBLE
ALONG THE MAINE COASTLINE MONDAY MORNING. SHOULD SEE VFR
CONDITIONS AREAWIDE BY LATE MORNING. SHOWERS AND THUNDERSTORMS
CROSS THE AREA FROM WEST TO EAST LATE AFTERNOON THROUGH THE
OVERNIGHT HOURS. THEN EXPECT VFR CONDITIONS OUTSIDE OF NOCTURNAL
FOG IN THE NEW HAMPSHIRE VALLEYS FOR THE REST OF THE WORK WEEK.

&&

.MARINE...
SHORT TERM...EXPECT WAVES AND WINDS TO REMAIN BELOW SMALL CRAFT
LEVELS THROUGH SUNDAY. HOWEVER...SEAS WILL BEGIN TO INCREASE
LATE SUNDAY NIGHT IN AHEAD OF AN APPROACHING COLD FRONT.

LONG TERM...SOUTHERLY FLOW ON MONDAY SHOULD STAY BELOW ADVISORY
LEVELS BUT WAVE HEIGHTS COULD EVENTUALLY BUILD TO AROUND 5 FEET
ESPECIALLY OVER EASTERN WATERS. A COLD FRONT MOVES WEST TO EAST
ACROSS THE GULF OF MAINE ON TUESDAY WITH LIGHTER WINDS BEHIND IT.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...NONE.
NH...NONE.
MARINE...NONE.

&&

$$


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