Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 020024
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
424 PM AKDT WED JUL 1 2015

.ANALYSIS AND UPPER LEVELS...
THE UPPER LEVEL RIDGE EXTENDS OVER THE NORTHERN AND EASTERN
BERING SEA AND INTO THE NORTH PACIFIC WITH THE UPPER LEVEL LOW
CENTERED IN THE NORTHERN GULF OF ALASKA. THE UPPER LEVEL TROUGH
EXTENDING OUT OF THIS LOW INTO THE INTERIOR OF THE STATE IS THE
FOCUS FOR RAINFALL IN THE SUSITNA VALLEY TODAY. THIS PATTERN IS
ALSO KEEPING RATHER WEAK FLOW ALOFT OVER THE MAJORITY OF THE
MAINLAND PART OF THE STATE. THE SURFACE LOW IS A BIT TO THE
SOUTHEAST OF THE UPPER LEVEL LOW AND IS TRACKING TOWARD YAKUTAT.
THE AREA IN BETWEEN THESE FEATURES REMAINS RATHER UNSTABLE WITH
NUMEROUS SHOWERS...BUT IT IS NOT UNSTABLE ENOUGH FOR
THUNDERSTORMS. SOUTHWEST MAINLAND ALASKA IS MORE UNSTABLE THAN
SOUTHCENTRAL AND THERE IS ENOUGH INSTABILITY TO SUPPORT
THUNDERSTORMS. THE LIMITING FACTOR IS THAT THE ATMOSPHERE IS
CAPPED JUST ABOVE THE 850 MB LEVEL AND THE LFC IS HIGHER THAN
THIS. THEREFORE THE POTENTIAL FOR THUNDERSTORMS DOES EXIST BUT
DEVELOPMENT IS NOT EXPECTED TO BE WIDESPREAD.

&&

.MODEL DISCUSSION...
THE MODELS ARE DOING WELL FOR THE NEXT FEW DAYS ON THE SYNOPTIC
FEATURES. THE BIGGEST MODEL QUESTION IN THE SHORT TERM HAS BEEN
IN THE WAY THE UPPER LEVEL WAVE OVER SOUTHCENTRAL ALASKA IS BEING
HANDLED TONIGHT INTO TOMORROW MORNING. THE RUN TO RUN CONSISTENCY
IN THE MODELS HAS NOT BEEN GREAT WITH THIS FEATURE AND THERE
REMAINS SOME QUESTION AS TO HOW FAR TO THE SOUTH IT WILL BRING
RAINFALL OVERNIGHT AND EARLY TOMORROW MORNING AS IT EVENTUALLY
MOVES EASTWARD INTO THE COPPER RIVER BASIN.

THE MODELS ARE BEGINNING TO SETTLE ON MAKING THE RIDGE OVER
BRISTOL BAY AND THE ALASKA PENINSULA MORE TRANSITORY IN NATURE AS
IT COMES ACROSS THE MAINLAND PART OF THE STATE THURSDAY THROUGH
SATURDAY. THIS WOULD MAKE THE WARM UP IN TEMPERATURES BE RATHER
SHORT LIVED.

&&

.FIRE WEATHER...
FOR SOUTHCENTRAL ALASKA...THE UPPER LEVEL WAVE WILL BRING WETTING
RAINS TO THE SUSITNA VALLEY OVERNIGHT AND POSSIBLY TO THE COPPER
RIVER BASIN TOMORROW. AREAS SOUTH OF THE SUSITNA VALLEY WILL
LIKELY SEE SOME PRECIPITATION BUT NOT WIDESPREAD WETTING RAINS.
THERE WILL BE A WARMING AND DRYING TREND THROUGH FRIDAY BUT THE
NEXT FRONT WILL MOVE INTO SOUTHCENTRAL ALASKA SATURDAY AFTERNOON
BRINGING IN MORE MOISTURE BUT ALSO GUSTY SOUTH TO SOUTHEAST GAP
WINDS.

FOR SOUTHWEST ALASKA...RELATIVE HUMIDITY VALUES REMAIN ELEVATED
AS A MOIST AND CLOUDY REGIME STAY IN PLACE OVER THE MAINLAND. AS
WEAK RIDGING BUILDS IN ALOFT ALONG WITH A WARMER AIR
MASS...RELATIVE HUMIDITY WILL TREND DOWNWARD THURSDAY INTO FRIDAY
WITH REDUCED CLOUD COVER AS WELL. WHILE MINIMUM VALUES WILL
APPROACH 30 PERCENT IN SOME PLACES WINDS WILL REMAIN LIGHT AS HIGH
PRESSURE IS IN CONTROL OF THE SURFACE.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE UPPER LOW IN THE GULF WILL ASSURE THAT CLOUDY AND MOIST
CONDITIONS WILL PERSIST THROUGH THURSDAY OVER MUCH OF SOUTHCENTRAL
AK. RAIN WILL BE COMMON ALONG THE COAST WITH SHOWERS ON THE LEE
SIDE OF COASTAL MOUNTAIN RANGES. A BAND OF PRECIPITATION ALONG THE
WESTERN FLANK OF THE UPPER LOW WILL SPREAD RAIN OVER INTERIOR
ZONES THROUGH THURSDAY. BY THURSDAY NIGHT THE LOW WILL MOVE EAST
AND PARTIAL CLEARING WILL BEGIN. ON FRIDAY BREAKS IN THE CLOUDS
ALONG THE AK RANGE AND TALKEETNA MOUNTAINS WILL ALLOW ENOUGH
SURFACE HEATING TO TRIGGER SOME THUNDERSTORMS...WHILE THE REST OF
THE REGION WILL BE PARTLY CLOUDY AND WARMER.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE MAINLAND IS STILL SPLIT BETWEEN A COUPLE DIFFERENT REGIMES.
THE GULF OF ALASKA LOW PRESSURE SYSTEM STILL KEEPS THE FAR EASTERN
PORTIONS OF THE SOUTHWEST IN WEAK CYCLONIC FLOW WHILE A WEAK
EXTENSION OF A SEWARD PENINSULA TROUGH BRINGS IN A COOLER AND
CLOUDIER STABLE REGIME TO THE KUSKOKWIM DELTA...ALONG WITH A
DIURNALLY FORCED MARINE LAYER FROM THE BERING SEA. THIS AFTERNOON
AND EVENING WILL BE THE LAST DAY FOR CONVECTIVE SHOWERS OR ANY
CHANCE OF LIGHTNING FROM THE KUSKOKWIM VALLEY THROUGH INTERIOR
BRISTOL BAY...AND THE CHANCE IS LOW. THURSDAY THE ONLY CHANCE OF
SHOWERS WILL REMAIN ALONG THE ALASKA RANGE BUT MOST OF THE
MAINLAND WILL BE DRY THROUGH FRIDAY. THE MARINE LAYER WILL MAKE A
DAILY PUSH THROUGH THE KUSKOKWIM DELTA AS WELL AS SNEAKING UP THE
ALASKA PENINSULA TONIGHT. WINDS WILL REMAIN LIGHT AND TEMPERATURES
AROUND NORMAL FOR THIS TIME OF YEAR.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE STALLED FRONT SITS OVER THE CENTRAL ALEUTIANS. IT WILL MAKE
VERY SLOW PROGRESS EASTWARD UNTIL A SEPARATE DISTURBANCE COMES IN
FROM THE NORTHCENTRAL PACIFIC...ACTING TO ENHANCE THE FRONT AND
BRING RAIN TO THE EASTERN ALEUTIANS AND EVENTUALLY THE ALASKA
PENINSULA...WHILE ELONGATING THE FRONT JUST SOUTH OF THE PRIBILOF
ISLANDS. MARINE LAYER STRATUS ENCOMPASSES MUCH OF THE BERING
SEA...INCREASING SOUTHEASTERLY FLOW WILL ENHANCE THIS CLOUD COVER
OVER THE NEXT COUPLE DAYS WITH AREAS OF DENSE FOG.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
FOR THE START OF THE WEEKEND A RIDGE TRANSITS THE GULF AND SOUTH
CENTRAL SUPPRESSING RAIN EXCEPT FOR ALONG THE MOUNTAIN RANGES OF
THE SUSITNA AND COPPER RIVER VALLEYS WHERE AFTERNOON SHOWERS
DEVELOP ALONG A TROUGH THAT MOVES ACROSS THE INTERIOR. TO THE
WEST...A LOW PRESSURE SYSTEM OVER THE WESTERN ALEUTIAN CHAIN PULLS
A FRONT NORTH FROM THE PACIFIC. THIS FRONT IS EXPECTED TO MOVE TO
THE ALASKA PENINSULA AND SOUTHERN GULF EARLY SATURDAY MORNING. THE
NORTHWARD PROGRESSION STILL REMAINS UNCERTAIN AS MODEL SOLUTIONS
STILL LACK AGREEMENT. THE ALASKA PENINSULA...KODIAK ISLAND AND THE
EASTERN KENAI WILL SEE THE HIGHEST PRECIPITATION AMOUNTS FROM THIS
FRONT DURING THE WEEKEND. MODELS DO AGREE ON BRINGING A SWATH OF
RAIN ACROSS BRISTOL BAY SATURDAY NIGHT AND INTO THE KUSKOKWIM ON
SUNDAY. INCREASED CLOUD COVER CAN BE EXPECTED ACROSS THE REST OF
THE SOUTHERN MAINLAND THIS WEEKEND WITH SCATTERED SHOWERS MAINLY
ALONG THE MOUNTAINS.

OVERALL FORECAST CONFIDENCE DECREASES IN TIME AS MODELS HAVE
STRUGGLED WITH HANDLING THE UPPER TROUGH DEEPENING ACROSS THE
INTERIOR THROUGH THE WEEKEND. THE GFS AND ECMWF WERE USED TO
UPDATE THE WEEKEND FORECAST WITH NO SIGNIFICANT CHANGES MADE
BEYOND MONDAY. THE BEGINNING OF NEXT WEEK MODELS ARE SUGGESTING
THAT A RIDGE AMPLIFIES ACROSS EASTERN ALASKA KEEPING SOUTHCENTRAL
DRY ON MONDAY. LOW PRESSURE IN THE BERING BRINGS ANOTHER
REINFORCING FRONT LATE SUNDAY SPREADING RAIN TO THE SOUTHWEST
MAINLAND AND BERING INTO MONDAY. THIS LOW PRESSURE SYSTEM WILL BE
THE PATTERN TO WATCH NEXT WEEK AS IT MAY BECOME THE DOMINATING
SYSTEM THAT BRINGS A REGULAR PATTERN OF CLOUDS AND RAIN.

&&


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

&&

$$

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


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