Small Craft Advisory 548, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKDT TUE JUL 16 2013

.ANALYSIS AND UPPER LEVELS...
A STACKED LOW IS OVER EASTERN RUSSIA WITH A TROUGH EXTENDING SOUTH
THROUGH THE BERING SEA. RIDGE IS OVER THE MAINLAND BUT GETTING
KNOCKED DOWN FROM LAST WEEKS HIGH AMPLITUDE RIDGE. THIS IS DUE TO A
MODERATE SHORT WAVE TROUGH WITH A 120 KT JET CORE PUSHING THROUGH THE
EASTERN BERING AND ONSHORE THIS AFTERNOON. NESDIS QPE SATELLITE
IMAGERY IS SHOWING SOME PRECIPITATION FALLING OVER THE CENTRAL
ALEUTIANS WITH THE WAVE. RADAR IMAGERY IS STARTING TO CAPTURE SOME
LIGHT PRECIP HITTING THE TOGIAK AREA. OVERALL...WATER VAPOR IMAGERY
DISPLAYS A SERIES OF SHORT WAVE TROUGHS WILL ROTATE OUT OF THE TROUGH
AND FLATTEN THE RIDGE OVER THE MAINLAND.

A WEAK SHORT WAVE MOVED ACROSS SOUTH CENTRAL ALASKA OVERNIGHT WITH
SOME ISOLATED SHOWERS. SOME SHORT WAVE RIDGING OCCURRED BEHIND THIS
FEATURE FOR STRATUS AND FOG THIS MORNING OVER WESTERN ALASKA AND
SOUTH CENTRAL ALASKA.

.MODEL DISCUSSION...
MODELS ARE SURPRISINGLY HANDLING THE PLETHORA OF SHORT WAVE TROUGHS
AND THE TRANSITION OF THE LARGE CLOSED LOW TO AN OPEN WAVE WELL OVER
THE NEXT COUPLE DAYS. THE OPEN WAVE IS A RESULT OF THE POLAR VORTEX
SWITCHING INTO OUR HEMISPHERE THURSDAY. THE FORMER CLOSED LOW WILL
SWING AS A TROUGH ACROSS THE STATE FRIDAY AND SATURDAY. IT IS
ANTICIPATED TO CLOSE AGAIN OVER THE PANHANDLE SUNDAY.

THE STRUCTURE OF THE JET LEVEL WINDS ARE SIMILAR AS WELL WITH THE
TRANSITION. THEREFORE...EXPECT PRECIP TO BE PRETTY CONSTANT OVER
SOUTHWEST ALASKA AND THE EASTERN BERING. NOT UNTIL THE WAVE MOVES
THROUGH THE MAINLAND FRIDAY...WILL CHANCES INCREASE OVER SOUTH
CENTRAL ALASKA. IN THE MEANTIME...SOUTH CENTRAL ALASKA WILL BE A
MOIST AND CONDITIONALLY UNSTABLE AIR MASS WITH ISOLATED TO SCATTERED
SHOWERS.

AT THE SURFACE...THE MOST DOMINANT FEATURE IS THE HIGH PRESSURE IN
THE NORTH PACIFIC AND SOUTHERN GULF OF ALASKA THROUGHOUT THE WEEK. AS
THE UPPER LOW TRANSITIONS FROM THE BERING AND CLOSES OVER THE
PANHANDLE AGAIN THIS WEEKEND...A NORTHERN GULF LOW DEVELOPS FOR SOME
GAPS FLOWS WITH RAINFALL.

CONFIDENCE IS PRETTY HIGH AT THIS POINT THAT THE UPPER LOW WILL PUSH
ACROSS THE STATE AND INTO THE PANHANDLE THIS WEEK. EXACT TIMING OF
MORE STEADY RAIN IS THE QUESTION...NOT WHETHER IT WILL RAIN OVER
SOUTHWEST ALASKA AND LATER THIS WEEK OVER SOUTH CENTRAL.

IN THE MEANTIME...A CLOSED LOW DEVELOPS SOUTH OF THE WESTERN
ALEUTIANS FRIDAY FROM THE REMNANTS OF A LOW IN THE NORTH PACIFIC
INTERACTING WITH THE TROUGH IN THE BERING. THIS LOW HANGS OUT IN
ROUGHLY THE SAME POSITION THROUGH THE WEEKEND.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...
VERY MOIST AND CONDITIONALLY UNSTABLE AIR MASS OVER THE AREA. WITH
THE CONTINUED MOIST SOUTHWEST FLOW AND NO REAL DRYING
EXPECTED...SHOWERS AT TIMES ARE ANTICIPATED THROUGH THE NEXT COUPLE
DAYS. THE ONLY AREA OUT OF THE WAY OF SHOWERS IS THE KODIAK AREA IN A
DRIER WESTERLY FLOW. CHANCES INCREASE FOR RAINFALL WHEN THE TROUGH
MOVES ACROSS THE MAINLAND FRIDAY NIGHT AND SATURDAY.

SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PERIODS OF RAIN WILL START
THIS EVENING OVER THE AREA AS A SERIES OF DISTURBANCES MOVE THROUGH
WESTERN ALASKA IN ADDITION TO THE TROUGH MOVING THROUGH FRIDAY. WITH
THE FIRST WAVE THIS EVENING...SOME MODERATE WINDS ARE EXPECTED IN THE
EASTERN ALEUTIANS TO THE AKPEN THIS EVENING. VERY MOIST LOW LEVELS
WILL LEAD TO FOG AND STRATUS OVER MUCH OF THE AREA OUTSIDE OF MORE
ORGANIZED PRECIP. THE LOW THAT MOVES TO THE WESTERN ALEUTIANS WILL
BRING MODERATE WINDS AND PRECIP TO THAT AREA THURSDAY NIGHT THROUGH
THE WEEKEND. DRIER AIR RETURNS TO SOUTHWEST ALASKA AFTER THE TROUGH
PASSAGE FRIDAY.

.LONG TERM FORECAST...
MODELS PUSH POLAR VORTEX TO THE WESTERN HEMISPHERE AND A RESULTANT
NORTHWEST FLOW WILL BE OVER THE STATE BY FRIDAY AFTERNOON WITH A
CLOSED LOW SOUTH OF THE WESTERN ALEUTIANS. THIS PATTERN WILL REMAIN
THROUGH THE WEEKEND INTO EARLY NEXT WEEK. ULTIMATELY...A RIDGE WILL
RETURN TO THE MAINLAND.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

NELSON JUL 13