Small Craft Advisory 24, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
345 AM AKST TUE JAN 7 2014

.ANALYSIS AND UPPER LEVELS...

THE UPPER LEVEL FLOW PATTERN IS DOMINATED BY A BLOCKING HIGH OVER
NORTHEAST SIBERIA AND THE SIBERIAN SEA...WITH A MODERATE 160 KT NORTH
PACIFIC JET STREAM CENTERED ALONG 40N. NUMEROUS WEAK WAVES EJECTING
OFF THE PACIFIC JET ARE INTERACTING WITH THE SEMI-PERMANENT NORTHEAST
PACIFIC RIDGE AXIS...WITH THESE FEATURES TRACKING INTO THE BERING SEA
AND GULF OF ALASKA. TWO OF THESE LOWS ARE EVIDENT ON SATELLITE
IMAGERY THIS MORNING...WITH ONE TRACKING INTO THE BERING SEA NEAR
DUTCH HARBOR...AND ANOTHER TRACKING NORTH TOWARD THE ALASKA
PENINSULA. OVER MAINLAND ALASKA...WEAK SHORTWAVE RIDGING IS BUILDING
AHEAD OF THE AFOREMENTIONED LOWS.

WITH TIME...THESE WEAK LOWS WILL TRACK EAST OVER SOUTHERN
ALASKA...WITH CONTINUED PERSISTENT LOW PRESSURE OVER THE BERING SEA.
THE GENERAL STORM TRACK WILL REMAIN SHUNTED SOUTH OF THE REGION
HEADING INTO THE WEEKEND.

.MODEL DISCUSSION...

THE NUMERICAL GUIDANCE IS IN EXCELLENT AGREEMENT WITH THE LARGE SCALE
SYNOPTIC PATTERN THROUGH THE WEEKEND. THEY DO DIFFER AS EARLY AS THIS
MORNING WITH WEAK NORTH PACIFIC LOWS THAT ARE TRACKING INTO THE
EASTERN BERING AND GULF...BUT THE OVERALL IMPACTS ARE NOT
SIGNIFICANT. THE NAM AND GFS WERE LARGELY DISCARDED EARLY WITH A LOW
TRACKING INTO THE GULF OF ALASKA AND EASTERN BERING...WITH THE ECMWF
FAVORED WITH THIS FEATURE. OTHERWISE...A GENERAL ECMWF AND GFS BLEND
WAS FAVORED THEREAFTER AS THE FLOW PATTERN REMAINS LARGELY DOMINATED
BY LOW AMPLITUDE WAVE FEATURES BREAKING OFF THE PACIFIC JET
STREAM...WHICH ARE RELATIVELY DIFFICULT TO TIME BEYOND 36 HOURS.

.SHORT TERM FORECAST...

SOUTHCENTRAL...
AN INCREASE IN MID-LEVEL CLOUDS WAS OBSERVED OVERNIGHT AS SUBTROPICAL
AIR WAS ADVECTED NORTH DUE IN LARGE PART TO A LARGE SURFACE LOW OVER
THE EASTERN BERING SEA. AN ASSOCIATED WARM FRONT WILL MOVE SLOWLY
ACROSS KODIAK ISLAND AND INTO THE GULF WHERE IT WILL STALL THROUGH
MOST OF THE DAY TODAY. THIS WILL KEEP SOME SCATTERED RAIN SHOWERS
ACROSS KODIAK ISLAND AND PARTS OF THE GULF COAST. A WEAK LOW WILL
DEVELOP TOWARD WEDNESDAY MORNING WHICH WILL ASSIST IN PUSHING THE
FRONT NORTH TOWARD THE GULF COAST WEDNESDAY MORNING WHERE IT WILL
FALL APART DURING THE DAY ON WEDNESDAY. THE GULF COAST WILL SEE
NUMEROUS RAIN SHOWERS WHILE SUFFICIENT DOWNSLOPE FLOW SHOULD KEEP
ANCHORAGE...THE MATANUSKA VALLEY AND THE WESTERN KENAI MAINLY ON THE
DRY SIDE. A GRADUAL COOL DOWN WILL BE OBSERVED DURING THE WEEK...WITH
TEMPERATURES RETURNING TO NEAR NORMAL VALUES FOR THIS TIME OF THE
YEAR.

SOUTHWEST...
GUSTY SOUTHEAST WINDS WILL KEEP MUCH OF SOUTHWEST DRY WITH ONLY
ISOLATED TO SCATTERED RAIN AND SNOW SHOWERS TODAY. ANOTHER WEAK LOW
WILL TRACK INTO THE AREA DURING THE OVERNIGHT...WITH MORE RAIN AND
SNOW SHOWERS DEVELOPING ACROSS COASTAL LOCATIONS. INLAND AREAS WILL
SEE MUCH SPOTTIER PRECIPITATION UNTIL A FRONT SWEEPS THROUGH THE
REGION.

BERING SEA AND ALEUTIANS...
RAIN SHOWERS...MIXED WITH A FEW SNOW SHOWERS OVER THE WESTERN
CHAIN...WILL CONTINUE THROUGH THE WEEKEND AS A SERIES OF LOWS TRACKS
OVER THE ALEUTIANS. NO SIGNIFICANT STORMS ARE ANTICIPATED THROUGH
SATURDAY.

.LONG TERM FORECAST...

FRIDAY AND BEYOND...TEMPERATURES WILL BE MODERATING BACK TO NEAR
NORMAL...AND THEN BELOW NORMAL BY THE WEEKEND AS AN EXTENSION OF THE
POLAR VORTEX SLIDES INTO SOUTHCENTRAL AND SOUTHWEST ALASKA. WITH
COLDER AIR IN PLACE AND WEAK SYSTEMS TRANSLATING THROUGH THE
FLOW...LIGHT SNOW SHOWERS WILL BE POSSIBLE ACROSS MOST OF SOUTHERN
ALASKA THROUGH THE WEEKEND...BUT THE MAIN STORM TRACK WILL REMAIN
SOUTH OF THE REGION. ALL THE GLOBAL GUIDANCE INCLUDING THE
GFS...ECMWF...GEFS...AND ECMWFENS STRONGLY HINT AT A POWERFUL PACIFIC
JET STREAM...ASSOCIATED WITH INCREASED WPAC TROPICAL CONVECTION...
BUCKLING TUESDAY INTO WEDNESDAY NEXT WEEK...WHICH WILL AMPLIFY THE
NORTHEAST PACIFIC RIDGE. SUCH A PATTERN WOULD SUPPORT ANOTHER CHINOOK
LIKE WARM UP ACROSS MUCH OF SOUTHERN ALASKA...WITH INCREASED
STORMINESS OVER THE BERING SEA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE 172 177 178 185.
FIRE WEATHER...NONE.

AHSENMACHER/CLAY JAN 14