Small Craft Advisory 159, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
417 PM AKST THU FEB 19 2015

.ANALYSIS AND UPPER LEVELS...
THE FLOW PATTERN ALOFT LOOKS TO BE TRANSITIONING TO A HIGHER
AMPLITUDE ONE. THE TWO MAIN DRIVERS OF THE FLOW ALOFT ARE A LARGE
AREA OF LOW HEIGHTS CENTERED IN THE NORTHERN PACIFIC SOUTH OF THE
CENTRAL/EASTERN ALEUTIANS AND A BUILDING RIDGE TO THE EAST WHICH
LOOKS LIKE THE REINCARNATION OF THE WESTERN NORTH AMERICA SUPER-
RIDGE. AN OCCLUDED FRONTAL BOUNDARY ASSOCIATED WITH A SHORTWAVE
TROUGH IN THE BERING SEA STRETCHES FROM THE PRIBILOF ISLANDS
TOWARD THE SOUTHWEST MAINLAND BEFORE TURNING SOUTHEAST AND
WEAKENING. THE SOUTHCENTRAL IS MOSTLY DRY BEHIND AN EXITING
SHORTWAVE TROUGH...WITH THE UPPER RIDGE BUILDING IN BEHIND. FOR
THE COMING DAYS IT LOOKS AS IF ATTENTION WILL TURN TO THE ACTIVE
FLOW BETWEEN THESE TWO SYNOPTIC POWERHOUSES. A SHEARING OUT SYSTEM
IS EVIDENT ON SATELLITE ON THE CURRENT FRONT AROUND 50N BUT DOWN
IN THE MID-LATITUDES A STRONGER WAVE IS LURKING.

&&

.MODEL DISCUSSION...
GUIDANCE IS IN GOOD AGREEMENT WITH THE UPCOMING PATTERN ALOFT FROM
A SYNOPTIC PERSPECTIVE. THE CONSENSUS IS THAT THE FIRST UPPER
LEVEL WAVE ALONG THE FRONT WILL CONTINUE TO DEAMPLIFY WHILE THE
NEXT SHORTWAVE TROUGH TO THE SOUTH STRENGTHENS AND CONTINUES THE
FRONTAL SURGE TO THE NORTH. TIMING OF THE FRONT IS PRETTY WELL
AGREED UPON WITH THE FRONT MOVING ONTO THE NORTH GULF COAST LATE
FRIDAY NIGHT INTO SATURDAY MORNING.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAY 1 AND 2)...

WITH THE EXCEPTION OF SOME PATCHY FOG AND LOW STRATUS THAT MAY
DEVELOP AROUND SOUTHCENTRAL OVERNIGHT TONIGHT UNDER WEAK
RIDGING...THE WEATHER IN THE AREA WILL BECOME DOMINATED BY THE
GALE FORCE NORTH PACIFIC FRONT THAT IS BEGINNING TO ENTER THE
SOUTHERN GULF. THIS FRONT WILL BEGIN TO IMPACT KODIAK ISLAND LATE
TONIGHT WITH RAIN AND GUSTY EASTERLY WINDS BEFORE SPREADING INTO
THE NORTHERN GULF BY TOMORROW EVENING. STRONG WARM AIR ADVECTION
ASSOCIATED WITH THIS SYSTEM WILL ALLOW MOST OF THE PRECIPITATION
TO FALL FROM IT IN THE FORM OF RAIN. AREAS SUCH AS THOMPSON PASS
AND THE COPPER RIVER BASIN WILL INITIALLY START OUT WITH WET SNOW
ON LATE FRIDAY NIGHT...BUT BY SATURDAY EVENING EVEN THESE AREAS
WILL BECOME MOSTLY RAIN.

EASTERLY WINDS WILL INCREASE THROUGH TURNAGAIN ARM DURING THE DAY
TOMORROW AS THE FRONT ENTERS THE NORTHERN GULF...WITH RAIN SHOWERS
OVER SOUTHCENTRAL LIKELY HOLDING OFF UNTIL LATE FRIDAY NIGHT
BEFORE BECOMING STEADY RAIN ON SATURDAY. THERE IS AN OUTSIDE
CHANCE THAT A FEW ISOLATED AREAS OF FREEZING RAIN MAY DEVELOP
FROM THE ANCHORAGE BOWL NORTHWARD INTO THE SUSITNA VALLEY AS THE
RAIN SHOWERS BEGIN ON FRIDAY EVENING...HOWEVER WITH TEMPERATURES
WARMING THROUGHOUT FRIDAY NIGHT THESE SHOULD NOT BE LONG LIVED OR
WIDESPREAD. RAIN THEN LOOKS TO CONTINUE FOR MUCH OF THE WEEKEND AS
THE FRONT STALLS OVER THE GULF COAST AND MOST OF MAINLAND ALASKA
REMAIN UNDER DEEP AND MOIST SOUTHERLY FLOW.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE FRONT OVER THE EASTERN BERING/BRISTOL BAY WILL PUSH INLAND
TONIGHT. EXPECT PRECIPITATION TO SPREAD FROM SOUTH TO NORTH IN
MOST AREAS EXCEPT FOR THE AREA DOWNWIND OF THE ALEUTIAN RANGE
WHICH SHOULD REMAIN DOWNSLOPED AND DRY. MIXED PRECIPITATION TYPE
WILL BE AN ISSUE AS WARM AIR ACCOMPANIES THE FRONT JUST OFF THE
SURFACE. WIDESPREAD FREEZING RAIN IS NOT EXPECTED BUT THERE IS THE
POSSIBILITY WHEN A TRANSITION FROM SNOW TO RAIN OCCURS OVER THE
KUSKOKWIM DELTA. THE FRONT WILL CLEAR TOMORROW BEFORE ANOTHER WAVE
SPREADS A NEW FRONT OVER THE MAINLAND FROM THE SOUTHEAST TOMORROW
AFTERNOON INTO SATURDAY BRINGING ANOTHER ROUND OF RAIN AS WELL AS
GUSTY SOUTHEASTERLY WINDS.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE MOST ACTIVE WEATHER THROUGH SATURDAY WILL REMAIN CENTERED
OVER THE SOUTHEASTERN PORTION OF THE BERING FROM THE ALASKA
PENINSULA AND EASTERN ALEUTIANS TO THE PRIBILOF ISLANDS AS THE
FRONT PUSHES NORTHWARD THROUGH THE AREA TONIGHT AND THEN A NORTH
PACIFIC LOW FOLLOWS CLOSELY ON ITS HEELS FOR FRIDAY. THIS SYSTEM
WILL CROSS THE AKPEN FRIDAY AFTERNOON AND THEN TRACK ALONG THE
COAST TO NEAR THE BERING STRAIT BY SATURDAY NIGHT...PROVIDING
ANOTHER ROUND OF GUSTY WINDS AND PRECIPITATION FOR THE AREA.
PRECIPITATION TYPE WILL BE MOSTLY RAIN FROM DUTCH HARBOR TO COLD
BAY AND A MIX OF RAIN AND SNOW CLOSER TO THE PRIBILOFS. FARTHER
WEST...THE CENTRAL AND WESTERN BERING WILL REMAIN IN A RELATIVELY
BENIGN SHOWERY REGIME BENEATH BROAD CYCLONIC FLOW ALOFT.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
BROAD SOUTHERLY FLOW WILL REMAIN ENTRENCHED OVER THE MAINLAND
THROUGH MONDAY ON THE WESTERN PERIPHERY OF A HIGHLY AMPLIFIED
UPPER LEVEL RIDGE OVER THE NORTHEAST PACIFIC. THIS WILL KEEP
WIDESPREAD RAIN AND ABOVE NORMAL TEMPERATURES OVER MUCH OF THE
REGION...WITH THE HEAVIEST RAIN FOCUSED ALONG THE GULF COAST AND
MORE SHOWERY CONDITIONS INLAND. THE RIDGE THEN SHOWS SIGNS OF
BREAKING DOWN BY THE MIDDLE OF NEXT WEEK...USHERING IN A MUCH MORE
PROGRESSIVE PATTERN AS FLOW TRANSITIONS FROM THE SOUTH MORE
TOWARDS THE SOUTHWEST. CONFIDENCE IN THE SPECIFIC DETAILS REMAINS
LOW AS MODEL SPREAD INCREASES WITH THE BREAKDOWN OF THE RIDGE...
HOWEVER TEMPERATURES CAN GENERALLY BE EXPECTED TO GRADUALLY
MODERATE CLOSER TO NORMAL VALUES AS THE PATTER BEGINS TO CHANGE.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORMS 130 131 138
         GALES 119 120 132 136 137 139 150 160 175 176 177 180
         HEAVY FREEZING SPRAY 185
FIRE WEATHER...NONE.

&&

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