Small Craft Advisory 617, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
200 PM ADT TUE JUL 31 2007

.ANALYSIS AND UPPER LEVELS...
MOST DOMINANT FEATURE IS A BROAD VERTICALLY STACKED LOW PRESSURE
CENTERED IN THE SOUTHWEST BERING SEA NEAR SHEMYA. A FRONT EXTENDING
WELL OUT FROM THIS LOW IS MOVING INLAND. A SECONDARY FRONT IS IN THE
CENTRAL BERING. A WEAK UPPER LEVEL LOW OVER THE MAINLAND LIFTING
SHOWERS OUT OF THE SUSITNA VALLEY. A WEAK UPPER LEVEL AND SURFACE
RIDGE OF HIGH PRESSURE IS BUILDING INTO THE CENTRAL GULF OF ALASKA
FROM THE EAST.

.MODEL DISCUSSION...
MODELS IN DECENT AGREEMENT THROUGH 48 HOURS OF THE MOVEMENT OF UPPER
LEVEL FEATURES. HOWEVER...THE FRONT POSITIONING NOT HANDLED WELL OVER
SOUTHWEST ALASKA. THE MODELS ARE TOO SLOW WITH THE PROGRESSION
ACCORDING TO WATER VAPOR IMAGERY. PAST THIS TIME FRAME...THERE EXISTS
A LARGE DISAGREEMENT OVER THE PROGRESSION AND DEPTH OF THE NEXT LOW
THROUGH THE ALEUTIAN CHAIN THURSDAY ONWARD. GFS DEMONSTRATED A
SIGNIFICANT FLIP FLOP. PREVIOUS 2 GFS RUNS DROVE THE LOW INTO THE
EASTERN BERING AND ABOUT 20 MB DEEPER. CURRENT RUN DRIVES A FAST
MOVING LOW THROUGH THE ALASKA PENINSULA FRIDAY. THIS AGREES WITH THE
ECMWF. ALSO...MOST OF THE 12Z GFS ENSEMBLES AGREE WITH THE
OPERATIONAL RUN.

THE UPPER LEVEL LOW IN THE SOUTHWEST BERING TO SLOWLY PUSH INTO
EASTERN BERING THURSDAY WITH A STRONG SHORT WAVE WORKING UNDERNEATH
AND INTO SOUTHCENTRAL FRIDAY. THE LOW WILL BACK IN THE BERING
SATURDAY THEN EVENTUALLY SWING INTO THE MAINLAND SUNDAY. DRIER
WESTERLY FLOW TO MOVE OVER THE AREA BRIEFLY EARLY NEXT WEEK.

.SHORT TERM FORECAST...

SOUTH CENTRAL ALASKA...
MOIST SOUTHWEST FLOW OVER SOUTH CENTRAL TO REMAIN THROUGH THE
WEEKEND. SHORT WAVE TROUGHS AND RIDGES TO RIP THROUGH WITH THE LARGE
UPPER LOW REMAINING OVER THE BERING. THE FIRST WAVE IS WEDNESDAY
NIGHT INTO THURSDAY. A STRONGER UPPER LEVEL SHORT WAVE TO MOVE UP
INTO THE AREA FRIDAY BRINGING A COPIOUS AMOUNT OF MOISTURE. THE UPPER
LOW MOVES OVER THE AREA SUNDAY WITH CONTINUED MOISTURE. AIDED BY GOOD
JET SUPPORT...PRECIPITATION MAY BE HEAVY AT TIMES FRIDAY AND SUNDAY.
LOW CLOUDS AND PRECIPITATION TO BE THE RULE OVER MUCH OF SOUTH
CENTRAL THROUGH SUNDAY. WINDS WILL PICK UP TO SMALL CRAFT WITH EACH
PASSING WAVE. THE AIR MASS WILL REMAIN CONDITIONALLY UNSTABLE THROUGH
THIS PERIOD WITH SHOWERS MORE PREVALENT OVER THE HIGHER TERRAIN.

SOUTHWEST ALASKA...
A FRONT IS MOVING THROUGH SOUTHWEST ALASKA TONIGHT WITH PLENTY OF
MOISTURE SPREADING OVER THE MAINLAND. A SECONDARY FRONT TO PUSH
INLAND TOMORROW ASSOCIATED WITH AN UPPER LEVEL WAVE. NOT MUCH JET
SUPPORT WITH THESE TWO FEATURES RIGHT...SO PRECIPITATION NOT EXPECTED
TO BE THAT HEAVY. THE BETTER JET SUPPORT IS OVER THE ALASKA PENINSULA
THURSDAY. THE JET SUPPORT LIFTS TO THE MAINLAND THURSDAY NIGHT WITH
PRECIPITATION EXPECTED TO BE HEAVIER OVER BRISTOL BAY AND THE ALASKA
PENINSULA. THE UPPER LOW TO ROTATE INLAND SATURDAY NIGHT WITH GOOD
UPPER LEVEL SUPPORT. A SURFACE LOW TO MOVE OVER BRISTOL BAY AS WELL.
DO EXPECT MODERATE TO HEAVY PRECIPITATION IN THIS AREA AS A RESULT
THROUGH SUNDAY MORNING AT LEAST. OUTSIDE OF TODAY...WINDS WILL BE
LESS THAN SMALL CRAFT CRITERIA.

BERING/ALEUTIAN ISLANDS...
THE STACKED LOW PRESSURE OVER THE WESTERN BERING TO SWING INTO THE
CENTRAL ALEUTIANS WEDNESDAY WITH A STRONG SHORT WAVE IN THE BASE OF
THE LOW. THIS WILL BRING BETTER PRECIPITATION AMOUNTS TO THE CENTRAL
BERING AND ALEUTIANS THEN TO THE EASTERN BERING WEDNESDAY EVENING.
MOST OF THE ACTIVITY WILL BE MORE SCATTERED BEHIND THIS FEATURE
THURSDAY. THE NEXT SURFACE LOW ASSOCIATED WITH THE UPPER LOW TO MOVE
THROUGH THE EASTERN ALEUTIANS THURSDAY NIGHT WITH MODERATE AMOUNTS OF
RAINFALL. THE NEXT SYSTEM TO AFFECT THE AREA BESIDES JUST SCATTERED
SHOWERS WITHIN THE BROAD UPPER LOW TO MOVE TO THE CENTRAL ALEUTIANS
SATURDAY. THIS SYSTEM IS RIDING A STRONG JET MAX. THEREFORE...WE
EXPECT A SYSTEM TO DEVELOP SOUTH OF THE CENTRAL ALEUTIANS WITH
MODERATE AMOUNTS OF PRECIPITATION SPREADING ACROSS THE CENTRAL AND
EASTERN ALEUTIANS SATURDAY AND SATURDAY NIGHT. WINDS OUTSIDE OF TODAY
AND TONIGHT WILL LIKELY BE LESS THAN SMALL CRAFT THROUGH FRIDAY.

.LONG TERM FORECAST...
CONSIDERABLE MODEL UNCERTAINTY IN THE EXTENDED...PARTICULARLY FOR THE
BERING. SOMEWHAT BETTER CONFIDENCE THOUGH FOR THE MAINLAND...WITH WET
SOUTHERLY FLOW GRADUALLY TRANSITIONING TO WESTERLY TOWARD EARLY NEXT
WEEK. WITH POTENTIALLY VERY WET SOUTHWESTERLY FLOW SETTING UP...COOK
INLET UP TO THE SUSITNA VALLEY HAS THE CHANCE OF GETTING MAJOR RAINS
FRIDAY THROUGH SUNDAY.

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

JN JUL 07