Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 132221
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
221 PM AKDT SUN JUL 13 2014

.ANALYSIS AND UPPER LEVELS...

TWO UPPER LEVEL LOW CENTERS ARE SITUATED OVER THE ALASKA REGION.
ONE IS CENTERED OVER THE BEAUFORT SEA WHILE THE OTHER IS OVER THE
EASTERN ALEUTIAN ISLANDS. THERE ARE A COUPLE SHORT WAVE TROUGHS
MOVING NORTH THROUGH SOUTHERN ALASKA THIS MORNING. IN THE
MEANTIME...A RIDGE IS BUILDING INTO THE BERING SEA. THE JET IS
STRONGEST ON THE BACKSIDE OF THE UPPER LOW OVER THE EASTERN
ALEUTIANS. THIS WILL HELP THE LOW RETROGRADE INTO THE NORTH
PACIFIC AND ALLOW THE RIDGE TO BUILD OVER THE ENTIRE BERING SEA
AND STRETCH INTO THE MAINLAND. THE UPPER LOW OVER THE ARCTIC WILL
SHIFT INTO THE CANADIANS ARCHIPELAGO AND BE REPLACE BY ANOTHER
UPPER LEVEL AND SURFACE LOW IN THE CHUKCHI SEA BY WEDNESDAY
AFTERNOON.

AT THE SURFACE...LOW PRESSURE IS SITUATED UNDER THE UPPER LOWS
WITH HIGH PRESSURE OVER THE GULF OF ALASKA AND OVER THE WESTERN
BERING SEA. THE AIR MASS IN BETWEEN THE TWO UPPER LEVEL LOWS IS
UNSTABLE WITH SHOWERS ACROSS MOST OF THE MAINLAND. THERE IS
ENOUGH INSTABILITY FOR ISOLATED THUNDERSTORM ACTIVITY AGAIN TODAY
ALONG THE ALASKA AND TALKEETNA RANGES. A FRONT ASSOCIATED WITH THE
ARCTIC LOW IS PUSHING MORE ORGANIZED RAIN ACTIVITY TO THE WEST
COAST OF NORTHERN ALASKA. THIS FRONT WILL PUSH THROUGH THE
NORTHERN HALF OF THE STATE MONDAY AND BRING COOLER AIR MOSTLY
ALOFT. WE MAY SEE SOME THUNDERSTORM ACTIVITY ALONG THE ALASKA
RANGE. ANOTHER UPPER LEVEL DISTURBANCE MOVES THROUGH NORTHERN
ALASKA WITH MOST RAIN ACTIVITY TO THE NORTH OF THE ALASKA RANGE
AND KUSKOKWIM VALLEY.

&&

.MODEL DISCUSSION...

THE MODELS ARE IN GREAT AGREEMENT THROUGH TUESDAY WITH THE
SYNOPTIC PATTERN. THE MAIN CHALLENGE ARRIVES WITH HOW THE LOW THAT
ENTERS THE CHUKCHI SEA ON WEDNESDAY INTERACTS WITH THE UPPER LOW
OVER THE NORTH PACIFIC. THE ECMWF...GEM...AND GFS ALL DISAGREE ON
THE PUSH OF THE UPPER LEVEL LOW OUT OF THE NORTH PACIFIC INTO THE
GULF OF ALASKA. THE FASTEST OF THE SOLUTIONS IS THE GFS ARRIVING
IN THE GULF ON THURSDAY MORNING. THE SLOWEST IS THE GEM REACHING
THE GULF ON FRIDAY AFTERNOON.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...
THE WEAK UPPER LEVEL DISTURBANCES MOVING NORTH THROUGH
SOUTHCENTRAL ALASKA KEEPING THE AIR MASS UNSTABLE FOR SHOWERS.
WITH DAYTIME HEATING...ISOLATED THUNDERSTORMS ARE POSSIBLE LATER
THIS AFTERNOON AND EARLY EVENING. IN ADDITION...THE LOW SOUTH OF
COLD BAY COMBINED WITH HIGH PRESSURE RIDGING INTO THE NORTHERN
GULF OF ALASKA COAST...THERE IS SOME MODERATE SOUTH TO SOUTHEAST
WINDS IN SOUTHCENTRAL ALASKA THIS AFTERNOON. THESE WINDS SHOULD
CONTINUE INTO THE EVENING. THE FRONT MOVING IN THE WEST COAST OF
NORTHERN ALASKA WILL MOVE THROUGH THE MAINLAND TOMORROW AFTERNOON
STAYING MOSTLY NORTH OF THE ALASKA RANGE. THERE WILL BE SHOWERS
ALONG THE ALASKA RANGE WITH A SLIGHT CHANCE OF THUNDERSTORM
ACTIVITY AS WELL. INSTABILITY REMAINS TUESDAY...ALBEIT LESS...FOR
ISOLATED MOUNTAIN SHOWER ACTIVITY. THESE CONDITIONS WILL CONTINUE
INTO WEDNESDAY. WITH SOME WARMER TEMPERATURES...MONDAY INTO
WEDNESDAY SEA BREEZE CONDITIONS WILL CONTINUE OVER THE AREA BUT
NOT AS STRONG AS TODAYS WINDS.

SOUTHWEST ALASKA...
UNSTABLE AIR MASS CONTINUES OVER THE SOUTHWEST MAINLAND TODAY AND
THIS EVENING FOR SHOWERS AND ISOLATED TUNDERSTORMS. SOME SHOWERS
TO WORK OVER THE KUSKOKWIM VALLEY AND ALASKA RANGE WITH THE FRONT
MOVING OUT OF THE CHUKCHI SEA MONDAY. THERE MAY BE ENOUGH PUNCH
WITH THE FRONT FOR ISOLATED THUNDERSTORMS AGAIN MONDAY AFTERNOON.
FOG IS A THREAT ALONG THE WEST COAST AND AKPEN TONIGHT AS OFFSHORE
FLOW WEAKENS AND ESPECIALLY TOMORROW NIGHT. HIGH PRESSURE AT THE
SURFACE WILL KEEP WINDS LIGHT.

BERING SEA/ALEUTIANS...
HIGH PRESSURE OVER THE BERING SEA IS BUILDING. THEREFORE...STRATUS
AND FOG WILL BE PRESENT. AS EXPECTED...MOST OF THE EASTERN BERING
HAS BEEN FREE OF CLOUDS WITH DRY OFFSHORE FLOW. THIS FLOW WEAKENS
OVERNIGHT ALLOWING FOG AND STRATUS TO RETURN. WITH THE LOW SOUTH
OF THE EASTERN ALEUTIAN ISLANDS...RAIN WILL BE PRESENT THROUGH THE
EVENING AND INTO THE MORNING HOURS ON MONDAY. MOST SHOWER ACTIVITY
WILL BE GONE TUESDAY BEFORE WE GET INTO THE UNCERTAINTY OF THE
UPPER LOWS PROGRESSION EASTWARD WEDNESDAY AND THURSDAY.

&&

.LONG TERM FORECAST...

THE MAIN FOCUS IN THE LONG TERM FORECAST IS THE UPPER LEVEL LOW
THAT MOVES UP FROM THE NORTH PACIFIC TOWARD THE ALASKA WEDNESDAY
NIGHT. THIS SYSTEM STALLS INITIALLY SOUTH OF THE EASTERN ALEUTIANS
WHILE IT ORGANIZES INTO A STACKED LOW AND THEN PICKS UP MOMENTUM
AS IT MOVES EASTWARD ON THURSDAY. MODELS GREATLY DIFFER IN THE
TRACK OF THIS SYSTEM. THE GFS IS THE FASTEST SOLUTION ON AN
EASTERLY TRACK ALONG THE SOUTHERN GULF OF ALASKA AND THE ECMWF IS
FURTHER NORTH INTO THE NORTHERN GULF BY FRIDAY MORNING. THE LONG
TERM FORECAST WAS CONSERVATIVELY UPDATED WITH THE ECMWF AS THIS
SOLUTION HAD THE BEST RUN TO RUN CONSISTENCY. THIS STORM SYSTEM
WILL BE THE NEXT TO BRING APPRECIABLE RAINFALL AND SHOULD BE
MONITORED AS DETAILS OF THE STRENGTH AND TRACK OF THIS SYSTEM WILL
BECOME MORE RESOLVED IN UPDATED MODEL RUNS.

&&

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

$$

NELSON/HOEPPNER JUL 14



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