Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 040018
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
418 PM AKDT MON AUG 3 2015

.ANALYSIS AND UPPER LEVELS...
THE VAST ALASKA FORECAST AREA IS UNDER THE INFLUENCE OF A REX
BLOCK-TYPE PATTERN...CHARACTERIZED BY HIGH PRESSURE OVER THE
MAINLAND PORTIONS OF THE STATE AND A VERTICALLY STACKED LOW
PRESSURE SYSTEM SOUTH OF THE ALASKA PENINSULA. AS A RESULT...THE
MAINLAND IS SEEING ANOTHER DAY OF ABUNDANT SUNSHINE AND LIGHT
WINDS. OCEAN TEMPERATURES IN THE GULF ARE NOW APPROACHING OR
EXCEEDING 60 DEGREES FAHRENHEIT...SO IT IS NOT SURPRISING THAT
DEWPOINTS ACROSS SOUTHCENTRAL ALASKA ARE IN THE LOW TO MID 50S AT
MOST LOCATIONS. THIS GENERALLY MOIST AIRMASS IS COMBINING WITH
NEAR-RECORD HIGH TEMPERATURES TO PRODUCE A HOT AND MUGGY (FOR
ALASKA) DAY AGAIN TODAY FOR A GOOD PORTION OF THE AREA. THE UPPER
LEVEL HIGH PRESSURE OVERHEAD WILL REACH PEAK STRENGTH DURING THE
DAY TODAY...WHICH WILL AGAIN SUPPRESS THE DEVELOPMENT OF SHOWERS
AND THUNDERSTORMS THIS AFTERNOON. A LARGE SHIELD OF MARINE
FOG/STRATUS IS COVERING MUCH OF THE CENTRAL AND WESTERN BERING
SEA...AS WELL AS THE NORTHERN GULF. MEANWHILE...UNDER CLEAR SKIES
COMBINED WITH THE HIGH-DEWPOINT AIRMASS (MENTIONED EARLIER)
RADIATIONAL FOG DEVELOPED EARLY THIS MORNING ACROSS THE LOWER
KUSKOKWIM VALLEY AND THE BRISTOL BAY ZONE AND EVEN INTO THE
SUSITNA VALLEY...THOUGH ALL HAS DISSIPATED QUICKLY THIS MORNING IN
THE FACE OF STRONG DIURNAL HEATING.

&&

.MODEL DISCUSSION...
THE MODELS ARE ALL HANDLING THE GRADUAL DEMISE OF THE UPPER HIGH
OVER MAINLAND ALASKA IN A GOOD FASHION OVER THE NEXT 2 DAYS...TO
INCLUDE THE APPROACH OF AN UPPER TROUGH FROM THE ARCTIC DROPPING
INTO THE STATE IN THE WEDNESDAY/WEDNESDAY NIGHT TIME FRAME.
PROBLEMS START TO DEVELOP BY THURSDAY AS THE WAVE CONTINUES TO DIG
SOUTHWARD (OR NOT) ACROSS THE ALASKA RANGE. THE NAM IS THE MOST
AGGRESSIVE IN THIS DIGGING TROUGH SOLUTION THAT WOULD BRING ALMOST
ALL OF THE UPPER LEVEL ENERGY INTO THE NORTHERN GULF BY THURSDAY
NIGHT. MEANWHILE...THE ECMWF CONTINUES TO KEEP THE MAJORITY OF THE
ENERGY NORTH OF THE ALASKA RANGE THROUGH THE END OF THE WEEK.
INTERESTINGLY...THE GFS HAS MADE A MOVEMENT TOWARD THE ECMWF
SOLUTION THIS MORNING...WHICH IS MAKING THE NAM LOOK LIKE MORE AND
MORE OF AN OUTLIER. IN PRACTICAL TERMS...WHILE EVEN THE ECMWF
WOULD SUPPORT INCREASED SHOWER ACTIVITY AND CLOUDINESS ACROSS
SOUTHWEST AND SOUTHCENTRAL ALASKA...THE NAM WOULD LIKELY LEAD TO
THE MORE WIDESPREAD STEADY PERIOD OF RAIN AROUND UPPER COOK INLET
AND THE MAT-SU VALLEYS ON THURSDAY. THE FORECAST TODAY BEGAN WITH
HEAVY NAM INFLUENCE FOR LOCAL TERRAIN-DRIVEN DETAILS...BUT SWITCHED
TO THE SUPERIOR CONSISTENCY OF THE GLOBAL MODELS (ESPECIALLY THE
ECMWF) FOR THE END OF THE WEEK.

&&

.FIRE WEATHER...
AS MENTIONED ABOVE...WITH RELATIVE HIGH MOISTURE CONTENT IN THE
AIRMASS AROUND THE REGION MOST AREAS WILL NOT APPROACH CRITICAL
THRESHOLDS FOR RELATIVE HUMIDITY DESPITE FULL SUNSHINE. THE DRIEST
AREA WILL BE THE COPPER RIVER BASIN...WHERE ANOTHER DAY OF RH
VALUES IN THE 30 TO 40 RANGE CAN BE EXPECTED...THOUGH LIGHT WINDS
WILL KEEP CONDITIONS WELL OUTSIDE OF ANY CRITICAL THRESHOLDS. NO
THUNDERSTORMS ARE EXPECTED TODAY...BUT AS THE WEEK PROGRESSES AND
THE RIDGE ALOFT WEAKENS SOME DIURNAL THUNDERSTORM ACTIVITY CAN BE
EXPECTED TO DEVELOP AROUND THE ALASKA RANGE AND TALKEETNA MOUNTAINS.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
HIGH PRESSURE ALOFT REMAINS IN CONTROL OF THE FORECAST THIS
AFTERNOON AND EVENING...BUT WILL SLOWLY WEAKEN OVERNIGHT INTO
TUESDAY. TEMPERATURES WILL STILL REMAIN ELEVATED ABOVE
CLIMATOLOGICAL NORMALS WITH A WARM AIR MASS IN PLACE IN THE LOW
LEVELS DESPITE A WEAKENING HIGH ALOFT. TONIGHT...A WEAKENING FRONT
ASSOCIATED WITH A SOUTHWESTERN GULF LOW PRESSURE SYSTEM WILL
SPREAD RAIN OVER KODIAK ISLAND THROUGH TUESDAY BUT WILL FIZZLE OUT
BEFORE IT REACHES THE MAINLAND.

AS THE HIGH PRESSURE WEAKENS ALOFT ON TUESDAY THE REDUCED CAP WILL
BRING THE CHANCE FOR ISOLATED SHOWERS AND THUNDERSTORMS...MAINLY
OVER THE TALKEETNA MOUNTAINS AND ALASKA RANGE. OTHERWISE MOSTLY
CLEAR SKIES AND DRY CONDITIONS WILL PREVAIL. TEMPERATURES ACROSS
THE MAINLAND WILL REMAIN IN THE 70S FOR MOST LOCATIONS THROUGH
WEDNESDAY WITH GENERALLY LIGHT WINDS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
HIGH PRESSURE RIDGING HAS ALLOWED FOR MOST OF THE REGION TO DRY
OUT AND WARM UP THIS AFTERNOON. A LOW SOUTH OF THE ALASKA
PENINSULA WILL SPREAD RAIN OVER THAT AREA THROUGH TONIGHT...WITH
MOST OF THE MOISTURE MOVING EAST BY TOMORROW. HOWEVER...ENOUGH
MOISTURE AND LIFTING FROM THE LOW WILL SUPPORT THE DEVELOPMENT OF
ISOLATED TO SCATTERED RAIN SHOWERS LATE TOMORROW AFTERNOON...WITH
THE POSSIBILITY OF ISOLATED THUNDERSTORMS NEAR THE ALASKA RANGE IN
THE LATE AFTERNOON AND EVENING. SHOWER THREATS WILL CONTINUE
WEDNESDAY AS THE LOW MOVES EAST ACROSS THE EASTERN PORTIONS OF
BRISTOL BAY AND THE LOWER KUSKOKWIM VALLEY. CONTINUED PUSHES OF
MARINE STRATUS AND FOG WILL IMPACT THE KUSKOKWIM DELTA DURING THE
OVERNIGHT AND EARLY MORNING PERIODS...WITH PATCHY FOG ACROSS
VALLEYS IN THE LOWER KUSKOKWIM VALLEY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
HIGH PRESSURE OVER THE BERING CONTINUES TO DOMINATE AS A LOW NEAR
THE ALASKA PENINSULA SUPPORTS RAIN OVER THE EASTERN ALEUTIANS...AND
NEAR GALE FORCE WINDS. THESE WILL DIMINISH TONIGHT...ALONG WITH
RAIN...AS THE LOW MOVES EAST. SHOWERS WILL LINGER OVER THE EASTERN
ALEUTIANS UNDER THE INFLUENCE OF CONTINUED NORTHERLY FLOW. PATCHY
FOG AND MARINE STRATUS WILL BE THE MAIN STORY ELSEWHERE UNDER THE
STABLE HIGH PRESSURE.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
WEDNESDAY NIGHT THROUGH FRIDAY WILL BE A TRANSITIONAL PATTERN AS
TWO LOW PRESSURE SYSTEMS BREAK DOWN THE AMPLIFIED RIDGE OVER THE
BERING. MODELS WERE IN BETTER AGREEMENT WITH THE MID RANGE
FORECAST...HOWEVER THE EC SOLUTION WAS HEAVILY UTILIZED TO MAKE
CHANGES AS IT HAD THE MOST REASONABLE SOLUTION ON THE TRACK OF
THE LOW PRESSURE SYSTEM MOVING UP FROM THE NORTH PACIFIC.

ON WEDNESDAY NIGHT A STRONG SHORTWAVE DIGS SOUTH ACROSS THE
INTERIOR WITH SOME OF THE ENERGY DIVING AROUND THE GULF LOW. RAIN
IS EXPECTED TO DEVELOP ALONG THIS WAVE WEDNESDAY NIGHT WITH
ACTIVITY STARTING ALONG THE ALASKA RANGE TO THE ALEUTIAN RANGE.
RAIN THEN SPREADS SOUTH AND EAST INTO THURSDAY. ON FRIDAY AND
SATURDAY...WEAK RIDGING SETS UP BEHIND THE FRONT KEEPING THE
SOUTHERN MAINLAND DRY...EXCEPT FOR A FEW AFTERNOON SHOWERS ALONG
THE RANGES.

TO THE WEST ON WEDNESDAY NIGHT...A NORTH PACIFIC LOW PRESSURE
SYSTEM PUSHES A FRONT INTO THE WESTERN AND CENTRAL ALEUTIANS.
THIS FRONT MAKES SLOW PROGRESS WITH A BETTER DEVELOPED RAIN BAND
ON THURSDAY. THE FRONT OCCLUDES LATE THURSDAY AND PUSHES ITS
LEADING EDGE INTO THE CENTRAL BERING WITH THE BOUNDARY STRETCHED
OUT TO THE ALASKA PENINSULA BY FRIDAY.

THE BERING LOW STALLS ON SATURDAY AND ORGANIZES INTO A STRONGER
AND FASTER MOVING SYSTEM SATURDAY NIGHT THROUGH MONDAY. THIS
SYSTEM IS EXPECTED TO BRING GUSTY WINDS AND RAIN ACROSS THE
SOUTHERN MAINLAND AND GULF WATERS THROUGH THE BEGINNING OF NEXT
WEEK.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...AD
SOUTHCENTRAL ALASKA...MTL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
LONG TERM...KH



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