Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 310006
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
406 PM AKDT MON MAR 30 2015

.ANALYSIS AND UPPER LEVELS...
A LONG-WAVE TROUGH REMAINS FIRMLY ENTRENCHED ACROSS ALASKA AND
THE NORTH PACIFIC. THE SUBTROPICAL JET IS NEARLY ZONAL JUST SOUTH
OF THE ALEUTIAN CHAIN THEN DIVES SOUTHEASTWARD INTO THE NORTH
PACIFIC. THIS IS RESULTING IN A PERSISTENT STORM TRACK ALONG THE
SOUTHERN TIER OF THE FORECAST AREA. THERE ARE TWO RELATIVELY WEAK
LOWS AFFECTING THE FORECAST AREA...ONE JUST SOUTH OF THE GULF AND
ANOTHER OVER THE FAR WESTERN ALEUTIANS. SATELLITE IMAGERY SHOWS
CONVECTIVE CLOUDS ACROSS MUCH OF THE FORECAST AREA WHICH IS
INDICATIVE OF A GENERALLY UNSTABLE ATMOSPHERE. AS HAS BEEN THE
CASE OVER THE PAST FEW DAYS A SERIES OF UPPER LEVEL WAVES ARE
TRACKING NORTHWESTWARD ACROSS THE GULF AND SOUTHCENTRAL. THE BULK
OF PRECIP HAS BEEN ALONG THE COAST THANKS TO PERSISTENT
DOWN-SLOPING OFF THE COASTAL MOUNTAINS...THOUGH THE LOW LEVEL
SOUTHEASTERLY FLOW IS BEGINNING TO WEAKEN AND BACK TOWARD THE
NORTH.

AS THE UPPER WAVES CONTINUE WESTWARD TO SOUTHWEST ALASKA THEY RUN
INTO SOME WEAK RIDGING WHICH HAS LED TO FORMATION OF A DEFORMATION
BAND. KING SALMON RADAR SHOWS A NORTH-SOUTH ORIENTED BAND OF
PRECIP ALIGNED DIRECTLY OVER KING SALMON. A SEPARATE UPPER LEVEL
WAVE IS LIFTING NORTHWARD ACROSS THE KUSKOKWIM DELTA PRODUCING
AREAS OF LIGHT SNOW.

&&

.MODEL DISCUSSION...
MODELS REMAIN IN VERY GOOD AGREEMENT WITH HANDLING OF LARGE SCALE
FEATURES OVER THE NEXT COUPLE DAYS. THUS FORECAST CONFIDENCE IS
GENERALLY HIGH. WITH MUCH WEAKER FLOW OUTSIDE OF THE MAIN LOW
PRESSURE SYSTEMS THE BIGGEST FORECAST CHALLENGES ARE ON THE LOCAL
SCALE...WITH ELEMENTS SUCH AS FOG AND CLOUD COVER. MODELS DO BEGIN
TO DIVERGE A BIT AS SYSTEM TRACKING SOUTH OF THE ALEUTIANS PASSES
SOUTH OF KODIAK ISLAND TUESDAY NIGHT INTO WEDNESDAY. THEY ALL HINT
AS DEVELOPMENT OF A TRIPLE POINT LOW...BUT DIFFER AS TO WHETHER
THIS BECOMES THE PRIMARY LOW CENTER. IN ANY CASE THESE DIFFERENCES
ONLY AFFECT THE AREA IN THE DIRECT VICINITY OF THE SYSTEM. WITH
A DECENT JET STREAK ALONG THE SOUTH TO EAST SIDE OF THIS SYSTEM
AND GOOD UPPER LEVEL DIFFLUENCE OUT AHEAD OF IT...PREFER THE MORE
AGGRESSIVE TRIPLE POINT DEVELOPMENT AS SEEN IN THE NAM.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (TONIGHT THROUGH WED NIGHT)...

AN AREA OF LOW PRESSURE OVER THE SOUTHERN GULF OF ALASKA WILL
PHASE WITH A LOW PUSHING ACROSS THE ALASKA PENINSULA TONIGHT. RAIN
SHOWER ACTIVITY IS EXPECTED TO CONTINUE ALONG THE NORTHERN GULF
COAST WITH THE ENHANCED LIFT ASSOCIATED WITH THE PHASING LOWS AND
AND UPPER LEVEL SHORTWAVE ROTATING AROUND A PARENT LOW ALSO
LOCATED IN THE SOUTHERN GULF. DOWN-SLOPING HAS BEEN EATING AWAY
AT A MAJORITY OF THE PRECIPITATION THAT HAS TRIED TO MOVE INLAND
DURING THE DAY BUT 00Z RAOB DATA SUPPORTS THE MODEL DATA IN THAT
THE LOW LEVEL FLOW IS WEAKENING AND SHIFTING TO A MORE SOUTHERLY
ORIENTATION. THIS WILL ALLOW AN ISOLATED SHOWER OR TWO TO MOVE
INLAND DURING THE EVENING HOURS IF DEW POINT DEPRESSIONS IN EXCESS
OF 10 DEGREES ARE ABLE TO BE OVERCOME.

THE PATTERN BEGINS TO SHIFT TUESDAY AFTERNOON/EVENING AS AN AREA
OF LOW PRESSURE MOVES INTO THE WESTERN GULF. A SHORTWAVE PRECEDING
THIS FRONT WILL PUSH ACROSS SOUTHCENTRAL ALASKA AND BRING A DECENT
CHANCE FOR RAIN/SNOW (DEPENDING ON TIMING OF THE PRECIPITATION) TO
ANCHORAGE/KENAI AND THE MAT-SU VALLEY. AS THE LOW MOVES INTO THE
WESTERN GULF...THE PRESSURE GRADIENT WILL BECOME FAVORABLE FOR
SOUTHEASTERLY GAPS (TURNAGAIN ARM...PORTAGE VALLEY AND KNIK RIVER
VALLEY) TO HAVE SOME GUSTY WINDS. HOWEVER...THERE IS STILL SOME
UNCERTAINTY TO THE LOW TRACK WHICH WILL DIRECTLY IMPACT THE
PRESSURE GRADIENT AND WIND GUST STRENGTH.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
LOW STRATUS AND PATCHY FOG WILL BECOME PROMINENT OVER PARTS OF
THE KUSKOKWIM DELTA AND BRISTOL BAY ZONE OVERNIGHT...AS LINGERING
SHOWERS OVER THE MAINLAND TODAY HELPED TO REPLENISH LOW LEVEL
MOISTURE OVER THE AREA. AS THE UPPER LEVEL WAVE OVER THE KUSKOKWIM
DELTA EXITS TO THE NORTH TOMORROW MORNING...PRECIPITATION OVER THE
MAINLAND WILL TAPER OFF THROUGH WEDNESDAY MORNING. WET AND WARMER
CONDITIONS WILL THEN BUILD BACK MAINLY OVER THE ALASKA PENINSULA
WEDNESDAY...AS A GALE FORCE NORTH PACIFIC LOW TRACKS JUST SOUTH OF
KODIAK ISLAND. PRECIPITATION OVER THE BRISTOL BAY ZONE WILL TAPER
OFF BY THURSDAY MORNING...AS THE AFOREMENTIONED LOW TRACKS
FURTHER EASTWARD AND INTO THE GULF OF ALASKA.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
A VERTICALLY STACKED SYSTEM OVER THE WESTERN ALEUTIANS WILL CROSS
INTO THE NORTHERN PACIFIC...BEFORE REFORMING INTO A GALE FORCE
LOW SOUTH OF THE CENTRAL ALEUTIANS OVERNIGHT TONIGHT. THIS SYSTEM
WILL CONTINUE AN EASTWARD TRACK JUST SOUTH OF THE ALEUTIAN
CHAIN...BEFORE TRACKING INTO THE GULF OF ALASKA BY THURSDAY
MORNING. WET AND WINDY CONDITIONS ARE EXPECTED TO ACCOMPANY THIS
SYSTEM AS IT PROGRESSES EASTWARD THROUGH MIDWEEK. AN AREA OF COLD
AIR ADVECTION BEHIND THE PASSING LOW WILL HELP GENERATE SOME
STRONGER GUSTS AND SNOW SHOWERS BEHIND THE SYSTEM...WHICH WILL BE
REINFORCED BY A RIDGE BUILDING INTO THE WESTERN BERING TUESDAY
AFTERNOON. AREAS THAT ARE PRONE TO EXPERIENCING GAP WINDS...SUCH
AS AREAS AROUND THE AKPEN AND EASTERN ALEUTIANS...ARE LIKELY TO
EXPERIENCE STRONGER GAP FLOW AS THIS SYSTEM TRACKS THROUGH THEIR
AREA. A GALE FORCE LOW DROPPING DOWN FROM KAMCHATKA PENINSULA WITH
AN ASSOCIATED WEATHER FRONT WILL BRING THE NEXT ROUND OF
PRECIPITATION TO THE WESTERN ALEUTIANS BY WEDNESDAY. GUSTY
SOUTHERLY WINDS ASSOCIATED WITH THIS SYSTEM WILL BRING IN SOME
WARMER TEMPERATURES FROM THE NORTHERN PACIFIC...CAUSING THE
PRECIPITATION TYPE TO SWITCH OVER TO RAIN AS THE WARM FRONT
PASSES THROUGH THE AREA.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE LATTER PART OF THE WEEK WILL BE CHARACTERIZED FAIRLY QUIET
WEATHER ACROSS THE SOUTHERN MAINLAND. THERE WILL BE A NEAR GALE
FORCE FRONT MOVING UP TOWARD THE NORTHERN GULF THURSDAY BEFORE
WEAKENING LATE THURSDAY INTO FRIDAY. THIS WILL KEEP RAIN AND RAIN
SHOWERS...MAINLY OVER THE WATER BUT WESTERN PRINCE WILLIAM SOUND
COULD SEE NUMEROUS SHOWERS WITH THIS FEATURES. COLDER UPPER LEVEL
TEMPERATURES ALOFT COULD SUPPORT INSTABILITY SHOWERS OVER THE
COASTAL MOUNTAINS WITH INCREASING CYCLONIC FLOW. THIS SYSTEM WILL
WEAKEN IN THE GULF AND MOVE TOWARD THE PANHANDLE FRIDAY. AT THIS
POINT THE PATTERN TURNS MORE AMPLIFIED OUT WEST...BUT IT IS
UNCLEAR HOW MUCH THIS WILL AFFECT THE PATTERN OVER THE MAINLAND.
EXPECT A CONTINUATION OF ABOVE NORMAL TEMPERATURES AND DRIER
CONDITIONS THROUGH EARLY NEXT WEEK.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 173 174.
 HEAVY FREEZING SPRAY 179 185.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...SB
SOUTHCENTRAL ALASKA...MC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP
LONG TERM...ML



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