Small Craft Advisory 288, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
448 PM AKDT WED APR 1 2015

.ANALYSIS AND UPPER LEVELS...
IN THE UPPER LEVELS THE MAIN SYNOPTIC FEATURES ARE THE LOW IN THE
GULF OF ALASKA AND ANOTHER LOW JUST OFF THE KAMCHATKA PENINSULA
WITH A RIDGE EXTENDING FROM THE NORTH PACIFIC OVER THE CENTRAL
BERING SEA. THE UPPER LOW OVER THE GULF IS SUPPORTING THE
WEAKENING SURFACE LOW SOUTH OF KODIAK. THIS LOW HAS AN OCCLUDED
FRONT THAT IS WRAPPING NORTH AROUND THE LOW INTO THE NORTH GULF
COAST. AN UPPER TROUGH IS ROTATING ACROSS THE SOUTH CENTRAL REGION
RESULTING IN PERIODS OF RAIN AND SNOW ALONG THE CHUGACH MOUNTAINS
AND RAIN AND SNOW SHOWERS ON THE LEE SIDE OF THE MOUNTAINS ON UP
INTO THE SOUTHERN SUSITNA VALLEY. THE LOW OFF THE KAMCHATKA
PENINSULA HAS A GALE FORCE FRONT PUSHING EAST ALONG THE ALEUTIANS.

&&

.MODEL DISCUSSION...
THE MODELS ARE IS GOOD AGREEMENT THROUGH FRI AFTERNOON.
DIFFERENCES CROP UP WITH THE HANDLING OF THE LOW MOVING INTO THE
WESTERN BERING SEA BEGINNING FRI AFTERNOON ALTHOUGH THE OVERALL
TREND IS IN GOOD GENERAL AGREEMENT.

FOR SOUTH CENTRAL ALASKA AND THE SOUTHERN MAINLAND THE SURFACE AND
UPPER LEVEL TROUGHS ARE ROTATING AROUND THE SURFACE AND UPPER LOW
INTO THE COAST FROM KODIAK EAST AND ACROSS THE CHUGACH AND
TALKEETNA MOUNTAINS. ON THE COASTAL SIDE OF THE MOUNTAINS THE
ASSOCIATED PRECIPITATION WILL BE MORE CONTINUOUS DUE TO THE UP
SLOPE FLOW REGIME WHILE THE LEE WARD SIDE OF THE MOUNTAINS WILL
SEE MORE SHOWERY PRECIPITATION. THE LOW IS EXPECTED TO MOVE TO THE
EAST BRINGING A MORE NORTHERLY AND DRY FLOW PATTERN ACROSS SOUTH
CENTRAL ALASKA BY THU AFTERNOON. THIS WILL USHER IN A RETURN OF
THE OUTFLOW GAP TYPE WINDS THROUGH THE CHUGACH MOUNTAINS, THOUGH
WE CURRENTLY DO NOT ANTICIPATE WIND RISING TO WARNING LEVELS.

A GALE FORCE FRONT IS SPREADING ACROSS THE WESTERN ALEUTIANS AND
WILL ELONGATE TO THE SOUTHEAST WEAKENING AND STALLING ACROSS THE
CENTRAL BERING SEA TO THE EASTERN ALEUTIANS. A SECONDARY OCCLUSION
WILL WRAP AROUND THE SOUTHERN QUADRANT OF THIS LOW INTO THE
WESTERN ALEUTIANS THU EVENING. A LOW WILL FORM ALONG THIS FRONT
AND BECOME THE MAIN LOW MOVING INTO THE CENTRAL BERING SEA AS A
990 MB LOW FRI AFTERNOON.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (TONIGHT THROUGH FRI NIGHT)...

THE MAIN AREA OF LOW PRESSURE RESIDES IN THE NORTH PACIFIC
(FURTHER SOUTH THAN THE MODELS HAD PROGGED YESTERDAY) WITH A
TRIPLE POINT LOW DEVELOPING IN THE WESTERN GULF OF ALASKA. THIS
TRIPLE POINT LOW HAS DELAYED THE ONSET OF WINDS AND PRECIPITATION
TO KODIAK ISLAND. THE REMAINDER OF SOUTHCENTRAL ALASKA HAS SEEN
WIDESPREAD SHOWER ACTIVITY DURING THE DAY DUE IN LARGE PART TO AN
UPPER LEVEL SHORTWAVE TRAVERSING THE AREA. THE 00Z PANC RAOB SHOWS
AN UNSTABLE AIR MASS CURRENTLY IN PLACE WITH SFC TO 3 KM LAPSE
RATES AVERAGING 9 DEGREES CELSIUS/KILOMETER. THE SUN MADE A BRIEF
APPEARANCE EARLY IN THE AFTERNOON AND THIS WAS ENOUGH TO ALLOW FOR
SOME DIURNAL CUMULUS CLOUDS TO DEVELOP. SCATTERED SHOWERS WILL BE
POSSIBLE THROUGH THE EVENING HOURS UNTIL THE SFC LAYER BEGINS TO
STABILIZE AND THE UPPER LEVEL SHORTWAVE BEGINS TO WEAKEN. WINDS
WILL BEGIN TO MAKE IT INTO KODIAK LATE TONIGHT WITH GUSTS TO 30
MPH AFTER MIDNIGHT AND GUSTS TO 45 MPH TOMORROW AFTERNOON. WITH
NORTHEASTERLY WINDS EXPECTED...CLIMATOLOGY FAVORS A MORE SHOWERY
REGIME WITH THE PRECIPITATION VS STRATIFORM PRECIP ASSOCIATED WITH
SOUTHEASTERLY WINDS.

AS THE LOW PUSHES EAST ON THURSDAY...AN OUTFLOW TYPE REGIME WILL
SET UP ACROSS SOUTHCENTRAL ALASKA. GUSTY WINDS WILL BE SEEN NEAR
WHITTIER AND THROUGH THOMPSON PASS AND THE OUTFLOW WINDS SHOULD
PREVENT SEA BREEZES FROM IMPACTING SEWARD AND VALDEZ. THIS WILL
LEAD TO MUCH WARMER TEMPERATURES...WITH HIGHS EXCEEDING 50 DEGREES
IN SEWARD AND IN THE MID TO UPPER 40S IN VALDEZ. THURSDAY LOOKS TO
BE THE WARMEST DAY ACROSS MUCH OF SOUTHCENTRAL ALASKA AS SKIES
BEGIN TO CLEAR. BY FRIDAY...COLDER AIR ALOFT WILL FILTER IN AND
PUT A CAP ON AFTERNOON HIGH TEMPERATURES. CLEARING SKIES WILL BE
SEEN THROUGH THE WEEKEND...MAKING FOR A GREAT WEEKEND TO GET OUT
AND ABOUT.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...

SHOWERS ALONG THE NORTH SIDE OF THE ALASKA PENINSULA WILL TAPER OFF
TO SCATTERED COVERAGE OVERNIGHT AND TO ISOLATED THROUGH THE DAY
TOMORROW AS THE RIDGE ALOFT OVER THE BERING SHIFTS EAST. WHILE
THIS PROGRESSION OF THE RIDGE WILL BRING DRY CONDITIONS TO MOST
AREAS...LOW STRATUS AND FOG WILL ALSO BECOME A CONCERN FOLLOWING
THE RIDGE AXIS EAST THROUGH THE END OF THE WEEK. NORTHWESTERLY
FLOW BETWEEN COLD HIGH PRESSURE OVER THE BERING AND THE BROAD LOW
IN THE GULF WILL BRING WINDY CONDITIONS TO THE GAPS AND PASSES
THROUGH THE ALASKA PENINSULA TONIGHT AND THURSDAY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...

THE FRONTAL SYSTEM OVER THE WESTERN ALEUTIANS WILL SLIDE EAST
TONIGHT AS THE PARENT LOW LIFTS NORTH WEAKENING THE FRONT
SOMEWHAT. A SECOND WAVE TO THE SOUTH WILL LIFT NORTH THURSDAY
MORNING TIGHTENING THE PRESSURE GRADIENT OVER THE CENTRAL
ALEUTIANS. THE NEXT LOW WILL TRACK OVER THE WESTERN ALEUTIANS
THURSDAY NIGHT AND THEN RAPIDLY DEEPEN AS IT MOVE INTO THE BERING
FRIDAY.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE WEEKEND WILL BEGIN WITH QUIET WEATHER...LIGHT WINDS AND MOSTLY
CLEAR SKIES FOR THE SOUTHCENTRAL. THERE IS A LINGERING CHANCE FOR
SNOW SHOWERS...MAINLY IN THE COPPER RIVER BASIN AS A COLD UPPER
DISTURBANCE MOVE OVERHEAD. AS THAT SYSTEM EXITS...A STRONG UPPER
LOW AND FRONTAL BOUNDARY MOVES INTO THE GULF...BUT THIS SYSTEM
SHOULD STAY FAR ENOUGH SOUTH TO NOT AFFECT THE SOUTHCENTRAL SAVE
FOR SOME MIDDLE AND HIGH CLOUDS. FURTHER INTO NEXT WEEK DETAIL ARE
STILL A BIT MURKY...BUT IT DOES APPEAR AS IF A STRONGER LOW
PRESSURE SYSTEM DEVELOPS IN THE BERING SEA...THIS WILL EVENTUALLY
SEND A FRONTAL BOUNDARY OVER THE NORTH GULF COAST...FOLLOWED BY
SOME UNSEASONABLY COLD AIR OVER MUCH OF THE AREA.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SA
SOUTHCENTRAL ALASKA...MMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JER
LONG TERM...MTL