Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 100155
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
455 PM AKST TUE FEB 9 2016

.ANALYSIS AND UPPER LEVELS...
IR/WV SATELLITE SHOWS AN UPPER LEVEL LOW MOVING UP FROM THE
EASTERN PACIFIC TOWARD KODIAK ISLAND WITH ANOTHER BROADER CLOSED
SYSTEM SPINNING IN PLACE JUST SOUTH OF THE EASTERN ALEUTIANS. THE
SYSTEM MOVING TOWARD KODIAK IS A STACKED SYSTEM WITH A DEEP LAYER
OF MOISTURE AROUND THE CENTER OF THE LOW. A FEW SHOWERS ARE
DEVELOPING ACROSS THE GULF AND KENAI PENINSULA AS WEAK DISTURBANCES
PROPAGATE NORTH TOWARD THE MAINLAND...OTHERWISE DRY CONDITIONS
PREVAIL INLAND UNDER PARTLY CLOUDY SKIES. TO THE WEST...A
DEFORMATION ZONE IS SETTING UP ACROSS THE SOUTHERN BERING BETWEEN
LOW PRESSURE SOUTH OF THE CHAIN AND RIDGING TO THE NORTH. RAIN AND
GUSTY WINDS SPREAD ACROSS THE ALASKA PENINSULA TO THE EASTERN
ALEUTIANS.

&&

.MODEL DISCUSSION...

MODEL AGREEMENT IS GOOD THROUGH THE SHORT TERM WITH THE GENERAL
SYNOPTIC PATTERN THROUGH THURSDAY...HOWEVER SURFACE DETAILS WERE
BEST HANDLED BY THE ECMWF AND NAM AND WERE USED TO UPDATE THE
AFTERNOON PACKAGE. THE MAIN CHALLENGE FOR MIDWEEK IS THE STORM
SYSTEM TRACKING TOWARD KODIAK AND THE ALASKA PENINSULA TONIGHT.
GUSTY WINDS ASSOCIATED WITH THIS SYSTEM PEAK TONIGHT AND THEN
SLOWLY DIMINISH ON WEDNESDAY. ANOTHER SURFACE LOW QUICKLY FOLLOWS
A SIMILAR PATH LATE WEDNESDAY.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...

THE FRONTAL SYSTEM ASSOCIATED WITH A LARGE LOW SOUTH OF THE GULF
OF ALASKA IS CURRENTLY LIFTING INTO THE SOUTHERN GULF WHERE
EASTERLY WINDS WILL INCREASE TO STORM FORCE TONIGHT. IN THE
SOUTHWESTERN GULF ALONG KODIAK ISLAND AS WELL AS IN SHELIKOF
STRAIT...NORTHEAST WINDS WILL ALSO INCREASE TO STORMS LATE
TONIGHT AND EARLY WEDNESDAY MORNING. THE FRONT WHICH CURRENTLY
EXTENDS ACROSS THE SOUTHERN GULF AND OVER SOUTHEAST ALASKA WILL
LIFT NORTHWEST ACROSS THE NORTHERN GULF COAST TONIGHT TO BE
STRETCHED OVER KODIAK ISLAND...THE EASTERN KENAI PENINSULA AND
PRINCE WILLIAM SOUND BY WEDNESDAY AFTERNOON.

THE INITIAL IMPACT OF THIS FRONT WILL BE TO INCREASE NORTH TO
NORTHEASTERLY WINDS THROUGH TERRAIN GAPS ALONG THE NORTHERN GULF
SUBSTANTIALLY TONIGHT WITH AREAS OF BLOWING SNOW DEVELOPING
THROUGH THOMPSON PASS BY LATE THIS EVENING. SNOW WILL SPREAD OVER
THOMPSON PASS AND THE VALDEZ AREA MID MORNING WEDNESDAY AND TO THE
MOUNTAINS OF THE EASTERN KENAI PENINSULA WEDNESDAY AFTERNOON. AT
LOWER ELEVATIONS ALONG THE COAST PRECIPITATION WILL PRIMARILY BE
RAIN WHILE NORTH AND EAST OF THE CHUGACH MOUNTAINS WILL BE HEAVILY
RAIN SHADOWED. ANOTHER FRONTAL WAVE ASSOCIATED WITH AN ADDITIONAL
SURFACE LOW ROTATING TOWARDS THE SOUTHERN GULF WILL SWING FROM
EAST TO WEST ACROSS THE GULF AND GULF COAST WEDNESDAY THROUGH
WEDNESDAY NIGHT FOLLOWED BY A THIRD WAVE ENTERING THE EASTERN GULF
ON THURSDAY.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
AS THE STORM FORCE LOW TRACKS CLOSER TO THE EASTERN ALEUTIANS FROM
THE PACIFIC SIDE TONIGHT...THIS WILL RESULT IN GUSTY NORTHEASTERLY
FLOW THROUGH SOUTHWEST MAINLAND ALASKA. THE STRONGEST WINDS WILL
BE ALONG THE WESTERN CAPES AND THE ALASKA PENINSULA BEFORE
DIMINISHING AS THE GRADIENT WEAKENS BY WEDNESDAY NIGHT. LIGHT
PRECIPITATION WILL SPILL-OVER FROM THE SOUTHWESTERN GULF ACROSS
THE ALASKA PENINSULA AND THE ALEUTIAN RANGE AS THE LOW PRESSURE
SYSTEM CONTINUES TO MOVE WESTWARD SOUTH OF THE ALEUTIAN CHAIN.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE STORM FORCE LOW SOUTH OF DUTCH HARBOR WILL CONTINUE TO WEAKEN
AS IT MOVES FARTHER SOUTH INTO THE NORTH PACIFIC. THIS WILL ALLOW
THE WINDS TO DIMINISH TO SMALL CRAFT ADVISORY THRESHOLDS THROUGH
THE CENTRAL ALEUTIANS TONIGHT. THE NEXT STORM FORCE LOW WILL
TRACK SOUTH OF THE EASTERN ALEUTIANS BY WEDNESDAY MORNING. THIS
WILL BRING STRONG GALE FORCE NORTHEASTERLY WINDS ALONG THE EASTERN
ALEUTIANS BY LATE TONIGHT EXTENDING THROUGH WEDNESDAY AFTERNOON.
THEREFORE...LOOK FOR WARMER TEMPERATURES FOR THE EASTERN CHAIN
WITH THE BULK OF THE PRECIPITATION FALLING AS RAIN. THE REST OF
THE BERING SEA WILL REMAIN WITH THE NORTHEASTERLY FLOW WITH COLDER
TEMPERATURES AS YOU GO FARTHER NORTH TOWARD THE BERING STRAIT. THE
PRECIPITATION WILL BE A WINTRY MIX FOR THE CENTRAL ALEUTIAN/BERING
SEA. WHILE THE WESTERN ALEUTIANS AND THE NORTHERN BERING SEA WILL
BE UNDER A SHOWERY WEATHER REGIME WITH ALL PRECIPITATION FALLING
AS SNOW THROUGH THE MIDWEEK.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...

NUMERICAL MODELS CONTINUE TO BE IN GOOD AGREEMENT THROUGH THE
BEGINNING OF NEXT WEEK WITH THE OVERALL PROGRESSION OF THE
LONGWAVE PATTERN OVER THE BERING SEA AND NORTH PACIFIC. THE
AMPLIFIED LONGWAVE TROUGH SITUATED OVER THE BERING SEA AND NORTH
PACIFIC WILL SLOWLY PROPAGATE EASTWARD AND SWITCH FROM A NEGATIVE
TILT TO A POSITIVE TILT AS THE JET ENERGY TRANSITIONS FROM THE
ENTRANCE REGION OF THE TROUGH TO THE EXIT REGION. AS THIS
HAPPENS...SEVERAL UPPER LEVEL DISTURBANCES AND ASSOCIATED SURFACE
FEATURES WILL IMPACT THE GULF OF ALASKA AND SOUTHCENTRAL ALASKA.
SEVERAL FRONTS WILL IMPACT MAINLY THE NORTHERN GULF COAST WHICH
WILL KEEP RAINFALL CHANCES PRETTY HIGH AS RAIN UPSLOPES ALONG THE
MOUNTAINS. WITH NOT A LOT OF UPPER LEVEL SUPPORT THESE FRONT
SHOULD FALL APART ALONG THE COASTAL MOUNTAINS AND LEAVE MUCH OF
INTERIOR SOUTHCENTRAL ON THE DRY SIDE. SOUTHWEST ALASKA AND THE
BERING SEA WILL BE ON THE SHOWERY SIDE WITH NO STRONG FEATURES
EXPECTED UNTIL LATE MONDAY INTO TUESDAY WHEN MODELS START HINTING
AT A DECENT LOW PRESSURE SYSTEM REPLACING THE SLOWLY DEPARTING
UPPER LEVEL TROUGH. THE REASON FOR THE SHOWERY REGIME IS DUE IN
LARGE PART TO THE BROAD CYCLONIC FLOW ASSOCIATED WITH THE LONGWAVE
TROUGH. THE AMPLITUDE OF THE LONGWAVE TROUGH IS SUCH THAT IT IS
PREVENTING ANY LOW PRESSURE SYSTEMS FROM THE NORTH PACIFIC TO BE
ABLE TO RE-CURVE INTO THE BERING SEA. TEMPERATURES LOOKS TO
REMAIN WELL ABOVE NORMAL FOR MUCH OF SOUTHERN ALASKA THROUGH THE
WEEKEND BEFORE SOME COLD AIR ADVECTION IS EXPECTED ON THE BACK
SIDE OF THE UPPER LEVEL TROUGH ON TUESDAY.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 119 120 127 130 131 139 160 165 180.
  STORM STORM 132 138 150.
 HEAVY FREEZING SPRAY 160 180 185.

&&
$$


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