Area Forecast Discussion
Issued by NWS Anchorage, AK

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34
000
FXAK68 PAFC 051300
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 AM AKDT SAT SEP 5 2015

.ANALYSIS AND UPPER LEVELS...
THERE IS AN UPPER LEVEL CLOSED LOW JUST NORTH OF THE PRIBILOF
ISLANDS WITH AN ASSOCIATED TROUGH EXTENDING SOUTHWARD THROUGH THE
EASTERN ALEUTIANS. THE SATELLITE LOOP IMAGERY IS SHOWING CYCLONIC
CIRCULATION NEAR SAINT MATTHEW ISLAND AND A LARGE SWATH OF
MOISTURE OVER THE CENTRAL/EASTERN BERING SEA REGION. THE SURFACE
IS REFLECTING A WEAK LOW PRESSURE SYSTEM JUST EAST OF SAINT
MATTHEW ISLAND. THE REST OF THE BERING SEA HAS WEAK SOUTHWESTERLY
FLOW. THE SATELLITE IMAGERY IS SHOWING WIDESPREAD LOW STRATUS
OVER THE BERING SEA AND THE FRONTAL BOUNDARY OVER THE PRIBILOF
ISLANDS THIS MORNING. AS THIS SYNOPTIC FEATURE SWINGS MORE
EASTWARD COMBINED WITH THE COLDER AIR BEHIND THE FRONT WILL HELP
TO POSSIBLY KICKOFF SOME AFTERNOON/EVENING ISOLATED THUNDERSTORMS
IN THE EASTERN BERING SEA. WHILE...THE NORTHERN GULF HAS A WEAK
NORTH PACIFIC LOW LOCATED NEAR MIDDLETON ISLAND AND A 100 KNOT
JET STREAK EXITING THE EASTERN GULF THIS MORNING. THIS IS
PRODUCING SHOWERY PRECIPITATION ALONG THE COASTAL MARINE AREAS.
THE UPPER LEVELS ARE SHOWING A WEAK RIDGE MOVING OVER THE
ANCHORAGE BOWL AREA WITH SURFACE OBSERVATIONS REPORTING LOW
STRATUS THROUGH THE REGION.

&&

.MODEL DISCUSSION...
THE MODELS REMAIN IN GOOD AGREEMENT WITH THE LOW IN THE NORTHERN
GULF AS IT TRACKS TO THE EASTERN GULF THROUGH THE WEEKEND. THE
MODELS ARE PICKING UP THE LOW TRACKING ALONG THE KAMCHATKA
PENINSULA AND THE ASSOCIATED WEATHER MOVING THROUGH THE WESTERN
ALEUTIANS BY SATURDAY AFTERNOON. BY MONDAY THIS SYSTEM TRACKS
INTO THE WESTERN BERING SEA AND THE WPC BEGINS TO BROAD BRUSH THIS
SYSTEM. THE NAM WAS THE PREFERRED MODEL OF CHOICE WITH THE
FORECAST CONFIDENCE REMAINING ABOVE AVERAGE THROUGH REST OF THE
WEEKEND.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE UPPER LEVEL TROUGH OVER THE AREA IS KEEPING SHOWERS OVER THE
NORTH GULF COAST AS WELL AS IN UPPER COOK INLET THIS MORNING. THIS
TROUGH SHOULD MOVE EASTWARD OVER THE COURSE OF THE DAY AND ALLOW
THE SHOWER ACTIVITY TO DIMINISH. THERE REMAINS A LOT OF LOW LEVEL
MOISTURE OVER SOUTHCENTRAL WHICH WILL KEEP LOW LEVEL CLOUDS OVER A
LARGE AMOUNT OF THE AREA THROUGH AT LEAST THE MORNING. THE UPPER
LEVEL LOW TRACK WILL BE OVER THE GULF OF ALASKA THE NEXT FEW DAYS
AND THAT MAY ALLOW THE NORTHERN PARTS OF THE SUSITNA VALLEY AND
COPPER RIVER BASIN TO GET A LITTLE CLEARING ON SUNDAY AS DRIER AIR
NORTH OF THE ALASKA RANGE FILTERS TO THE AREA. THE UPPER LEVEL LOW
MOVING OVER THE GULF ON SUNDAY MORNING THROUGH SUNDAY EVENING HAS
A LOT OF COLD AIR ALOFT ASSOCIATED WITH IT WHICH MAY MAKE THE
ATMOSPHERE UNSTABLE ENOUGH TO KICK OFF SOME THUNDERSTORMS OVER THE
SOUTHERN GULF OFFSHORE AREA.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2...SAT AND
SUN)...A VERY WEAK AREA OF HIGH PRESSURE IS PASSING THROUGH THE
SOUTHWEST THIS MORNING. WHILE THIS IS HELPING TO CUT DOWN ON THE
RAIN ACROSS THE AREA...THERE IS STILL ABUNDANT MOISTURE MAKING FOR
PLENTY OF LOW CLOUDS AND FOG. AN UPPER LEVEL LOW IS READILY
EVIDENT ON SATELLITE OVER THE CENTRAL BERING. IT WILL CONTINUE TO
TRACK RATHER QUICKLY TOWARDS THE ALASKA PENINSULA THROUGH THE DAY.
THIS WILL BRING ANOTHER ROUND OF RAIN TO THE COAST BY THIS EVENING AND
NUMEROUS SHOWERS TO INLAND LOCATIONS OF BRISTOL BAY. THE BRUNT OF
THIS SYSTEM WILL DEFINITELY HIT THE AKPEN...PARTICULARLY THE
BERING SIDE WITH GUSTY NORTHWEST FLOW. WITH SOME DECENT UPPER
LEVEL DYNAMICS...CAN`T RULE OUT EVEN A STRIKE OR TWO OF LIGHTNING
LATE TONIGHT INTO EARLY SUNDAY FOR THE AKPEN.

SUNDAY`S FORECAST WILL FEATURE THAT LOW PULLING AWAY FROM THE AREA
QUICKLY AS IT MOVES INTO THE GULF OF AK. IT WILL LEAVE WIDESPREAD
NORTHWEST FLOW IN ITS WAKE. WITHOUT ANY SIGNIFICANT DRYING IN THE
LOW LEVELS...MOST OF THE AREA WILL BE SUSCEPTIBLE TO SHOWERS
SUNDAY AFTERNOON. THE MOST FAVORABLE LOCATIONS TO SEE SHOWER
DEVELOPMENT WILL BE ON NORTHWEST FACING TERRAIN AND THE BERING
SIDE OF THE AKPEN.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2...SAT AND
SUN)...ONE UPPER LEVEL LOW WILL MOVE THROUGH THE EASTERN BERING
TODAY WHILE A NEW LOW WILL PUSH A WARM FRONT INTO THE WESTERN
ALEUTIANS. IN BETWEEN THESE TWO SYSTEMS IS A WEAK RIDGE MAKING FOR
RELATIVELY QUIET WEATHER AND LIGHT WINDS. THE SYSTEM OVER THE
EASTERN BERING IS ADDRESSED IN THE MARINE PORTION OF THIS
DISCUSSION. THE SYSTEM WAY OUT WEST WILL SLING A WARM FRONT
THROUGH SHEMYA TODAY. SMALL CRAFT WINDS AND RAIN WILL ACCOMPANY
THE FRONT. THE LOW ITSELF WILL "STALL" OVER THE EXTREME WESTERN
BERING ON SUNDAY. THE WESTERN ALEUTIANS WILL SEE WINDS SHIFT
AROUND TO THE WEST AND INCREASE UP TO ABOUT 40 MPH...BUT UNTIL
THE LOW STARTS TO MOVE EAST EARLY NEXT WEEK...THESE WINDS SHOULD
REMAIN CONFINED WAY OUT THERE.

&&

.MARINE...ONE OF THE MORE INTERESTING ASPECTS TO THE FORECAST
TODAY WILL BE THE POSSIBILITY OF SOME THUNDERSTORMS OVER THE
WATERS. AN UPPER LEVEL LOW WILL BRING SOME TEMPERATURES AS LOW AS
-28C ALOFT THROUGH THE AREA LATER TODAY. AS THESE PASS OVER
PROGRESSIVELY WARMER SEA SURFACE TEMPERATURES APPROACHING THE
ALASKA PENINSULA...THIS SHOULD MAKE FOR SOME RATHER UNSTABLE LAPSE
RATES. THERE WILL ALSO BE A JET FINGER HELPING TO "FERRY" THIS LOW
TO THE SOUTHEAST. THIS JET FINGER WILL ADD SOME UPPER LEVEL
DIVERGENCE WHICH WILL ONLY SERVE TO ADD MORE UPWARD VERTICAL
MOTION TO THE COLUMN. IF THUNDERSTORMS SHOULD DEVELOP...MARINERS
CAN EXPECT GUSTY WINDS...LOCALLY HIGHER WAVES...AND THE
POSSIBILITY OF SOME SMALL HAIL. THESE STORMS SHOULD CONTINUE INTO
SUNDAY MORNING TRACKING FROM THE PRIBILOF ISLANDS DOWN TOWARDS THE
WESTERN SIDE OF KODIAK. CONFIDENCE IN THUNDERSTORM DEVELOPMENT IS
MODERATE AT THIS TIME. BUT IF THINGS DO GET GOING...THERE WOULD BE
HIGH CONFIDENCE IN IT HOLDING TOGETHER AS IT TRACKS SOUTHEAST.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
AN UPPER LEVEL LOW OVER THE ALASKA PENINSULA WILL TRACK FURTHER
EASTWARD INTO THE GULF...WITH WEAK RIDGING BRIEFLY DEVELOPING OVER
THE EASTERN BERING AND SOUTHWEST COAST IN ITS WAKE. THIS
TRANSITION WILL DIMINISH SHOWERS AND KEEP NEAR NORMAL TEMPERATURES
OVER THE SOUTHERN MAINLAND THROUGH MONDAY MORNING. MODELS CONTINUE
TO STRUGGLE WITH ANOTHER UPPER LEVEL LOW QUICKLY TRACKING INTO THE
BERING SEA FROM THE WEST AND EVENTUALLY JOINING FORCES WITH AN
ARCTIC TROUGH DIGGING OVER THE EASTERN BERING BY TUESDAY...BEFORE
TRACKING FURTHER INLAND BY MIDWEEK. THE 12Z ECMWF...WHICH IS THE
PREFERRED MODEL FOR THIS FORECAST PACKAGE...DEPICTS A MUCH BROADER
TROUGH OVER THE BERING...WHICH EVENTUALLY SWINGS OVER TO THE GULF
LATER NEXT WEEK. BY THE END OF THE WEEK AND INTO THE WEEKEND...THE
ECMWF SHOWS THE UPPER LOW REMAINING STATIONARY OVER THE WESTERN
MAINLAND...AS A NORTH PACIFIC LOW TRACKS UP ALONG THE ALASKA
PENINSULA FRIDAY NIGHT AND INTO THE GULF COAST BY SATURDAY. THE
NET RESULT WILL BE AN INCREASE OF WET AND WINDY CONDITIONS OVER
PARTS OF THE SOUTHERN MAINLAND THROUGH THE END OF THE WEEK...AND A
SURGE OF COLDER AIR FILTERING IN OVER MUCH OF THE BERING AND
ALEUTIANS BEHIND THE TROUGH. HOWEVER...HOW FAR EAST INTO THE
SOUTHERN MAINLAND THIS COLDER AIR WILL PUSH INTO...AND WHEN/WHERE
THE BULK OF THE PRECIPITATION WILL END UP IS STILL IN
QUESTION...AS MODELS CONTINUE TO STRUGGLE WITH THE TIMING AND
STRENGTH OF THE ABOVE MENTIONED SYSTEMS. THUS LEAVING A LOT OF
UNCERTAINTY AND LOWER CONFIDENCE IN THE LONG RANGE FORECAST.

&&


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

&&

$$

SYNOPSIS AND MODEL DISCUSSION...PD
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MO
LONG TERM...TP



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.