Small Craft Advisory 253, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
430 PM AKDT WED MAR 20 2013

.ANALYSIS AND UPPER LEVELS...
THE UPPER LEVEL PATTERN OVER MAINLAND ALASKA THIS AFTERNOON IS
CHARACTERIZED BY NORTHWESTERLY FLOW BETWEEN AN ELONGATED AREA OF LOW
PRESSURE CENTERED OVER THE ARCTIC COAST AND A NEGATIVELY TILTED RIDGE
OVER THE BERING. THE RIDGE HAS BEEN BEGUN TO BREAK DOWN AS IT IS
IMPACTED BY THE WESTWARD PROGRESSION OF THIS LOW AS WELL AS ANOTHER
UPPER LOW PUSHING EASTWARD FROM THE KAMCHATKA PENINSULA...SIGNALING A
COMING PATTERN CHANGE FOR THE LATER PART OF THE WEEK.
MEANWHILE...PREDOMINANTLY CLEAR SKIES PREVAIL ACROSS MUCH OF SOUTHERN
ALASKA...WITH A WEAK DISTURBANCE BRINGING SOME LIGHT SNOW TO PORTIONS
OF THE SOUTHWESTERN MAINLAND. A SURFACE LOW PERSISTS OVER THE
NORTHEASTERN GULF OF ALASKA...CONTINUING TO SUPPORT STRONG GAP WINDS
THROUGH FAVORED COASTAL AREAS.

.MODEL DISCUSSION...
MODELS REMAIN IN REASONABLE AGREEMENT THROUGH THE SHORT TERM AND THEN
BEGIN TO DIVERGE THEREAFTER. THE BERING RIDGE WILL CONTINUE TO ERODE
AS THE UPPER LOW OVER THE ARCTIC COAST DROPS OVER THE NORTHWESTERN
MAINLAND THROUGH FRIDAY...WITH THE KAMCHATKA LOW TRAVERSING THE
BERING AND REACHING THE SOUTHWEST COAST THURSDAY NIGHT THEN MOVING
INLAND ON FRIDAY.

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...
GENERALLY QUIET CONDITIONS WILL CONTINUE THROUGH THE DAY ON THURSDAY
AS NORTHWESTERLY OFFSHORE FLOW PERSISTS OVER THE AREA. THE SURFACE
LOW OVER THE GULF WILL SLOWLY WEAKEN AND MOVE AWAY FROM THE
AREA...ALLOWING GAP WINDS TO SUBSIDE BY THURSDAY MORNING AS THE
SURFACE PRESSURE GRADIENT WEAKENS. PRECIPITATION WILL RETURN TO THE
AREA LATE THURSDAY NIGHT INTO FRIDAY AS THE AFOREMENTIONED BERING LOW
MOVES INLAND AND BRINGS WIDESPREAD SNOW TO SOUTHCENTRAL AK INCLUDING
THE ANCHORAGE BOWL.

SOUTHWEST ALASKA...
SNOW WILL OVERSPREAD THE SOUTHWEST MAINLAND FROM WEST TO EAST
THURSDAY NIGHT INTO FRIDAY MORNING AS THE BERING LOW MOVES OVER THE
KUSKOKWIM DELTA ON THURSDAY EVENING. AREAS OF BLOWING SNOW WILL BE
POSSIBLE ALONG THE COAST AS GUSTY SOUTHEASTERLY WINDS ACCOMPANY THE
ARRIVAL OF THE SYSTEM.

ALEUTIANS/BERING SEA...
THE KAMCHATKA LOW WILL TRAVERSE THE BERING ON THURSDAY BRINGING SNOW
TO THE PRIBILOFS. THE BULK OF THE PRECIPITATION ASSOCIATED WITH THIS
SYSTEM LOOKS TO REMAIN NORTH OF THE ALEUTIAN CHAIN. HOWEVER...ANOTHER
LOW WILL ENTER THE WESTERN BERING ON FRIDAY WITH AN ASSOCIATED FRONT
WELL OUT AHEAD OF THAT SYSTEM SPREADING RAIN AND SNOW ALONG WITH
GUSTY WINDS ACROSS THE CHAIN FROM WEST TO EAST IN THE THURSDAY TO
FRIDAY NIGHT TIMEFRAME.

.LONG TERM FORECAST...
SOUTHERN ALASKA WILL TRANSITION TO A MORE PROGRESSIVE PATTERN BY THE
END OF THE WEEK...WITH NUMEROUS SYSTEMS KEEPING A CHANCE FOR
PRECIPITATION IN THE FORECAST INTO THE EXTENDED TERM.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE WARNING 130 132 175 176 185
         HEAVY FREEZING SPRAY 121 126 127 128 129 130 138
FIRE WEATHER...NONE

CB MAR 13