000
FXUS61 KGYX 051834
AFDGYX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAY ME
234 PM EDT SUN JUL 5 2009

.SYNOPSIS...
A WEAK RIDGE OF HIGH PRESSURE WILL DISSIPATE TONIGHT.
THIS WILL ALLOW LOW PRESSURE SURFACE AND ALOFT CENTERED NORTH OF
THE GREAT LAKES TO SLIDE SOUTHEAST INTO NEW ENGLAND ON MONDAY. 
WEAK HIGH PRESSURE WILL CROSS THE AREA MONDAY NIGHT. A WEAK COLD
FRONT WILL CROSS NORTHERN NEW ENGLAND TUESDAY AND TUESDAY NIGHT.
AN UPPER LEVEL DISTURBANCE MAY BRING SCATTERED SHOWERS AND
THUNDERSTORMS WEDNESDAY. HIGH PRESSURE WILL BUILD OVER THE REGION
FROM THE GREAT LAKES THURSDAY AND FRIDAY. A COLD FRONT WILL
APPROACH THE AREA SATURDAY.

&&

.NEAR TERM /UNTIL 8 PM THIS EVENING/...
AT 18Z 998 MILLIBAR LOW WAS VICINITY OF PRINCE EDWARD ISLAND WITH
TRAILING SURFACE TROUGH EXTENDING SOUTHWEST THROUGH THE COASTAL
WATERS. A WEAK RIDGE EXTENDED NORTHEAST INTO WESTERN NEW ENGLAND.
CLOUDS AND WINDS DIMINISH AS WE HEAD INTO THE EVENING HOURS AS
WEAK RIDGING SURFACE AND ALOFT SLIDES EASTWARD. 

&&

.SHORT TERM /8 PM THIS EVENING THROUGH 6 PM MONDAY/...BRIEF CLEARING 
UNDER THE RIDGE TONIGHT WITH SEASONABLY COOL TEMPERATURES AS
WINDS GO CALM IN MANY LOCATIONS. LOWS DROP INTO THE 40'S ACROSS
THE NORMALLY COOLER INTERIOR SECTIONS WITH LOWER 50'S ELSEWHERE.
EXPECT WE'LL SEE RADIATION FOG DEVELOP ACROSS MANY INTERIOR
VALLEYS AS WELL. OUR DRY BREAK WILL BE BRIEF AS WATER VAPOR SHOWED
THE EXITING UPPER LOW EAST OF NOVA SCOTIA AND A NEW UPPER LOW
SITUATED NORTH OF THE LAKES. THE UPPER LOW FROM THE LAKES WILL
DROP SOUTHEAST AND REACH THE AREA ON MONDAY. CLOUDS WILL BE ON THE
INCREASE ON MONDAY WITH SCATTERED CONVECTION BREAKING OUT BY
AFTERNOON. THE DEVELOPING ONSHORE FLOW WILL LIKELY LIMIT THE
POTENTIAL FOR CONVECTION AT THE IMMEDIATE COAST WITH HIGHEST
CHANCE POPS CONFINED TO INTERIOR SECTIONS. LOW FREEZING HEIGHTS
WILL INCREASE THE CHANCE FOR HAIL WITH THE STRONGER CELLS. I USED
A MET/MAV BLEND TO INITIALIZE THE SHORT TERM TEMPS WITH SREF FOR
POPS. I SHAVED A FEW DEGREES OFF TEMPS ON MONDAY GIVEN 850
MILLIBAR TEMPS...ONSHORE FLOW...AND INCREASING CLOUD COVER.

&&

.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
A BRIEF BREAK IN THE PATTERN IS IN THE OFFING FOR THE MIDDLE AND
END OF THE UPCOMING WEEK...BUT AFTER THAT THE PERSISTENT NORTHEAST
THROUGH WILL RETURN.

EVENING CONVECTION SHOULD DIE OFF MONDAY NIGHT WITH THE LOSS OF
DAYTIME HEATING AND ITS ATTENDANT INSTABILITY. HOWEVER...THE 
PROXIMITY OF THE CLOSED MID LEVEL LOW TO THE WEST AND IT COLD
POOL WILL NECESSITATE CARRYING SCATTERED SHOWERS FOR MUCH OF MONDAY
NIGHT. DEPENDING ON HOW MUCH SHOWER COVERAGE THERE IS MONDAY
AFTERNOON AND EVENING...PATCHY DENSE FOG MAY BE A PROBLEM IN
SHELTERED LOCATIONS. FOR THE MOST PART...A BLEND OF MOS NUMBERS
WAS USED FOR LOW. 

THE CLOSED MID LEVEL LOW TRUNDLES EAST TUESDAY. COLD MID LEVEL
TEMPERATURES (BETWEEN MINUS 15 AND MINUS 20 C) WILL RESULT IN THE
DEVELOPMENT OF CONVECTION AGAIN TUESDAY AFTERNOON. THE STRENGTH OF
THE CONVECTION WILL BE DICTATED BY THE AMOUNT OF HEATING THAT
OCCURS. THE 1200 UTC NAM SUGGESTS THAT STRATUS MAY BE A PROBLEM
FOR CENTRAL MAINE...AND GIVEN THE SYNOPTIC SETUP...THIS LOOKS
REASONABLE.

FURTHER WEST...THE LOW LEVEL FLOW DOES NOT SUPPORT MUCH IN THE WAY
OF STRATUS. HOWEVER...SYNOPTIC LAYERED CLOUDINESS AHEAD OF THE
CLOSED MID LEVEL SYSTEM COULD SLOW HEATING. NOT MUCH CONFIDENCE IN
THE SKY FORECAST FOR TUESDAY...AND THIS WILL HAVE A DIRECT IMPACT
ON THE AMOUNT OF CONVECTION THAT DEVELOPS.

SHOULD CONVECTION DEVELOP...THERE IS THE POTENTIAL FOR STRONGER
UPDRAFTS TO DEVELOP DUE TO STEEPENING MID LEVEL LAPSE RATES DUE TO
COLD MID LEVEL TEMPERATURES. IN ADDITION...WET BULB ZERO VALUES
SHOULD MAKE HAIL THE MAIN CONVECTIVE THREAT. BULK SHEAR INCREASES
AHEAD OF THE 120 KNOT JET LATE TUESDAY AFTERNOON...BUT THE COLD
FRONT APPEARS TO LAG...WHICH COULD MEAN LITTLE FOCUS FOR CONVECTION.

WILL STICK CLOSE TO THE MOS BLEND FOR HIGHS TUESDAY. THIS SI DUE
MAINLY TO THE LOWER THAN AVERAGE CONFIDENCE IN THE AMOUNT OF SUN
WE WILL SEE.

WITH THE MID LEVEL CLOSED LOW TRYING TO OPEN UP AND CROSS THE
FORECAST AREA TUESDAY NIGHT...NOT SURE THAT THE CONVECTION WILL
DIE OFF IN THE NORMAL DIURNAL FASHION. FOR THIS REASON...MAY NEED
TO CARRY A CHANCE OF SHOWERS FOR MUCH OF THE NIGHT. USED A BLEND
OF MOS NUMBERS FOR LOW.

THERE IS SOME MODEL DIFFERENCE IN JUST HOW FAST THE THE MID LEVEL
SYSTEM OPENS AND MOVES OUT. THIS WILL HAVE DIRECT BEARING ON THE
AMOUNT OF CLOUDINESS AND CONVECTIVE POTENTIAL. AS IT STANDS NOW...
THE SLOWER 1200 UTC GFS SUGGESTS THAT COLD MID LEVEL TEMPERATURES
WILL RESULT IN STEEP MID LEVEL LAPSE RATES. INSTABILITY MAY END OF
BEING THE LIMITING FACTOR...BUT ENOUGH UNCERTAINTY REMAINS TO
INCLUDE A MENTION OF SHOWERS AND THUNDERSTORMS FOR WEDNESDAY.

THE EXITING TROUGH WILL BE REPLACED BY MID LEVEL RIDGING FOR 
THURSDAY AND FRIDAY. AT THIS POINT...PLANNING TO KEEP THE
FORECAST DRY AS TEMPERATURE WARM TO CLOSER TO NORMAL FOR JULY.
HOWEVER...THE RIDGING SHOULD BE SHORT LIVED AS SHORT WAVE ENERGY
COMING SHORE ON THE CALIFORNIA COAST RIDES UP OVER THE FOUR
CORNERS RIDGE. AS THE SHORT WAVES RIDES DOWN THE FRONT OF THE
RIDGE NEXT WEEKEND...THE SPECTER OF YET ANOTHER CLOSED LOW LOOMS.
WILL HAVE TO CARRY SHOWERS AND POSSIBLY THUNDERSTORMS FOR NEXT
WEEKEND DUE TO THE TROUGHING.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
SHORT TERM /THROUGH 23Z MONDAY/...VFR WITH POCKETS OF IFR IN FOG AND
STRATUS ACROSS INTERIOR VALLEYS AFT 06Z. VFR ON MONDAY...WITH SCT
MVFR IN MAINLY AFTERNOON SHOWERS AND THUNDERSTORMS.

LONG TERM...WITH A CLOSED MID LEVEL SYSTEM TO THE WEST OF THE
AREA...WOULD EXPECT EVENING CONVECTION TO DIE OFF MONDAY EVENING.
HOWEVER...IN ITS WAKE...IFR/LIFR CONDITIONS ARE POSSIBLE IN FOG.
THE MOST LIKELY TERMINALS TO BE AFFECTED ARE KLEB AND KCON.

THERE IS SOME MODEL DISAGREEMENT ON THE IMPACT OF STRATUS LAT
MONDAY NIGHT AND TUESDAY NIGHT. WITH A LIGHT ONSHORE FLOW...KAUG
AND KPWM STAND THE BEST CHANCE OF SEEING LIFR CONDITIONS IN
STRATUS AHEAD OF A QUASI WARM FRONT. FURTHER WEST...THE MARINE
INFLUENCE SHOULD BE LESS...AND STRATUS IN NOT EXPECTED.

MORE CONVECTION IS LIKELY TUESDAY AND TUESDAY NIGHT...WITH LOCAL
MVFR CONDITIONS IN SHOWERS AND THUNDERSTORMS. MAINLY VFR CONDITIONS
ARE EXPECTED WEDNESDAY THROUGH FRIDAY WITH SURFACE HIGH PRESSURE
BUILDING OVER THE AREA FROM THE GREAT LAKES.


&&

.MARINE...
SHORT TERM /THROUGH MONDAY/...WESTERLY WINDS DIMINISH BY EVENING
AS GRADIENT RELAXES BEHIND THE SURFACE TROUGH. NO FLAGS EXPECTED.

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
FOR THE MOST PART...EXPECTING SUN SMALL CRAFT CONDITIONS THROUGH
THE PERIOD. THERE COULD BE A PERIOD TUESDAY AFTERNOON AND TUESDAY
EVENING WHEN WINDS COULD APPROACH SMALL CRAFT LEVELS AHEAD OF A
SURFACE COLD FRONT.

MODEL SOUNDINGS SUGGEST THAT COLD AIR ADVECTION JUST BEHIND THE
FRONT TUESDAY EVENING COULD RESULT IN GUSTS TO 20 KNOTS. AT THIS
DISTANCE...THAT APPEARS UNLIKELY AS THERE APPEARS BE A LAG BETWEEN
THE FRONTAL PASSAGE AND START OF THE COLD AIR ADVECTION.

THE FRONT WILL EITHER CROSS THE WATERS (OR MORE LIKELY) WASH OUT
FOR WEDNESDAY. AFTER THIS...SURFACE HIGH PRESSURE WILL BUILD
TOWARD THE WATERS WEDNESDAY AND THURSDAY. THE GRADIENT SHOULD
ALLOW SEA BREEZE CIRCULATIONS TO DEVELOP EACH AFTERNOON...WITH
WIND GUSTS NEAR 20 KNOTS IN THE LATE AFTERNOON AND EARLY EVENING
AT C MAN STATIONS.

&&

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

&&

$$