Small Craft Advisory 67, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
440 AM AKST THU JAN 22 2015

.ANALYSIS AND UPPER LEVELS...
CURRENTLY THE SOUTHERN MAINLAND SITS BETWEEN A NUMBER OF FEATURES
ALOFT WHICH WILL ALL CONTRIBUTE TO THE DEVELOPMENT OF ACTIVE
WEATHER OVER THE NEXT FEW DAYS. A DEEP UPPER LEVEL LOW PRESSURE
DIGS SOUTHEASTWARD FROM NORTHWESTERN ALASKA WHILE ANOTHER BROAD
AREA OF LOW PRESSURE ALOFT SPINS SOUTH OF THE ENTIRE ALEUTIAN
CHAIN. A CLOSED HIGH ALOFT SEPARATED THESE FEATURES THE PAST
COUPLE OF DAYS BUT HAS SINCE MIGRATED INTO THE EASTERN BERING SEA
ALLOWING FOR THE AFOREMENTIONED FEATURES TO COLLIDE OVER THE
SOUTHCENTRAL. THE FIRST PIECE OF THE PUZZLE IS AN OCCLUDED FRONT
ASSOCIATED WITH A MATURE SURFACE LOW SOUTH OF THE ALASKA
PENINSULA. THE SECOND IS A POLAR/ARCTIC FRONT ASSOCIATED WITH THE
NORTHWEST ALASKA TROUGH DROPPING SOUTHWARD.

&&

.MODEL DISCUSSION...
AT FIRST GLANCE GUIDANCE SEEMS IN GREAT AGREEMENT WITH THE
EVOLUTION OF THE UPCOMING PATTERN BUT AS IN MOST CASES...THE DEVIL
IS IN THE DETAILS. THE MAIN DIVISION IN MODEL GUIDANCE IS
GLOBAL/HEMISPHERIC VS. MESOSCALE. THE LOWER RESOLUTION GUIDANCE
PUSHES THE WARM AIR FURTHER INLAND OVER COOK INLET ALOFT WHILE THE
HIGHER RESOLUTION GUIDANCE KEEPS THE WARMER AIR CLOSER TO THE
GULF/SOUND...HOWEVER AT THIS POINT IT DOES NOT LOOK LIKE A THREAT
FOR LIQUID PRECIPITATION NO MATTER WHAT GUIDANCE IS CHOSEN. ALL
THE GUIDANCE LOOKS AT A THREE-PRONGED SYNOPTIC SITUATION. THE
FIRST IS THE OCCLUDED FRONTAL PASSAGE...FOLLOWED BY THE
WESTERLY/SOUTHWESTERLY COLD ADVECTION THEN THE UPPER TROUGH
PASSAGE. ALL GUIDANCE IS IN AGREEMENT WITH THE THE PROGRESSION OF
THESE EVENTS BUT ALL BRING A DIFFERENT FLAVOR IN HOW THINGS ALL
COME TOGETHER. THE MOST LIKELY SCENARIO DEPICTED IS WIDESPREAD
SNOW WITH THE FRONTAL PASSAGE THIS AFTERNOON/EARLY EVENING...THEN
A BREAK LATE EVENING INTO THE OVERNIGHT...FOLLOWED BY
INTENSIFICATION FRIDAY MORNING/AFTERNOON.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
MIDDLE TO HIGH LEVEL CLOUDS WILL STREAM OVERHEAD THIS MORNING AS A
FRONT DECAYS AHEAD OF ANOTHER APPROACHING FRONTAL BOUNDARY.
TEMPERATURES WILL REMAIN NEAR NORMAL VALUES THOUGH SIGNIFICANTLY
COLDER THAT MOST OF THE WINTER. LIGHT SNOW WILL OVERSPREAD THE
MAINLAND FROM SOUTH TO NORTH TODAY...BEGINNING IN THE ANCHORAGE
AREA AROUND 3 PM...GIVE OR TAKE AN HOUR. EXPECT A THREE TO FIVE
HOUR PERIOD OF LIGHT SNOW FROM KENAI THROUGH THE MATANUSKA VALLEY
FOLLOWED BY A PERIOD WHERE SNOW SIGNIFICANTLY TAPERS OR STOPS IN
THE LATE EVENING. AT THIS POINT THE FRONT WILL STALL OVER THE
SUSITNA VALLEY BEFORE MOVING BACK EASTWARD FRIDAY MORNING AND
AFTERNOON. THE HEAVIEST SNOW FOR THE EASTERN COOK INLET REGION
SHOULD FALL LATE FRIDAY MORNING/EARLY AFTERNOON. LIGHT SNOW COULD
CONTINUE TO LINGER THROUGH SATURDAY AFTERNOON BEFORE TAPERING OFF
SATURDAY EVENING. HEAVIER SNOW WILL PUSH INTO THE COPPER RIVER
BASIN ON SATURDAY AND LINGER THROUGH SUNDAY. CONFIDENCE IS HIGH
ON MOST AREAS RECEIVING ACCUMULATING SNOW BUT EXACT AMOUNTS ARE
LOWER CONFIDENCE AS THE POTENTIAL FOR HEAVY BANDED SNOW EXISTS
SOMEWHERE BETWEEN THE CHUGACH AND EASTERN SUSITNA VALLEY. STAY
TUNED TO THE LASTED FORECAST FOR UPDATED INFORMATION.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (TODAY THROUGH SATURDAY)...
OFFSHORE FLOW WILL CONTINUE TO BRING CLEAR SKIES TO MOST THE
SOUTHWEST INTO THIS WEEKEND WITH GUSTY NORTHERLY WINDS FROM THE
KUSKOKWIM DELTA INTO BRISTOL BAY. THIS WILL BRING SOME OF THE
COLDEST WIND CHILLS OF THE SEASON TO THE REGION...HOWEVER THEY
WILL NOT QUITE REACH ADVISORY CRITERIA. EASTERN BRISTOL BAY WILL
ALSO BE CLIPPED BY A ROUND OF ACCUMULATING SNOW FROM THE FRONT
CURRENTLY APPROACHING KODIAK ISLAND. THIS IS EXPECTED TO BEGIN
LATE THIS AFTERNOON AND CONTINUE THROUGH TONIGHT...WITH
ACCUMULATIONS EXPECTED TO BE FAIRLY LIGHT.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (TODAY THROUGH SATURDAY)...
GUSTY NORTHEASTERLY FLOW WILL ALSO CONTINUE THROUGHOUT THE BERING
SEA REGION THROUGH FRIDAY WHEN WINDS WILL BEGIN TO WEAKEN AND TURN
SOUTHERLY IN ADVANCE OF A LOW APPROACHING THE WESTERN ALEUTIANS
FOR THE WEEKEND. THESE GUSTY NORTHERLY FLOW WILL BRING SNOW
SHOWERS TO THE REGION...WITH HEAVY FREEZING SPRAY SPREADING
THROUGHOUT MUCH OF THE BERING TO THE NORTH OF THE PRIBILOFS.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE BIG QUESTION DURING THIS TIME FRAME IS HOW LONG SNOW WILL
CONTINUE ACROSS SOUTHCENTRAL AK. WITH MODELS EACH SHOWING A
SLIGHTLY DIFFERENT STORY...IT IS DIFFICULT TO ADD MORE DETAIL TO
THE FORECAST AT THIS POINT. OVERALL THOUGH...PERIODS OF SNOW CAN
BE EXPECTED FOR SOUTHCENTRAL AK UNTIL THE UPPER TROUGH AXIS MOVES
EAST OF THE AREA \LIKELY LATE SATURDAY OR SOMETIME SUNDAY\ AT
WHICH POINT CONDITIONS SHOULD TURN CLEARER AND COLDER INTO EARLY
NEXT WEEK. SOUTHWEST MAINLAND AREAS SHOULD SEE RELATIVELY BENIGN
BUT COLD CONDITIONS THIS WEEKEND INTO EARLY NEXT WEEK.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...SNOW ADVISORY 101 111 121 141 145.
MARINE...GALE WARNING 120 130 138 150 155 160 165 170 171 172 173
                      174 175 176 177 179 180.
         HEAVY FREEZING SPRAY WARNING 160 165 180 181 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...ML
SOUTHCENTRAL ALASKA...ML
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DEK
LONG TERM...MBS