Heavy Freezing Spray Warning 151, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
145 PM AKDT FRI MAR 30 2012

.ANALYSIS AND UPPER LEVELS...A COMPLEX AREA OF LOW PRESSURE IS
CENTERED OVER THE SOUTHERN GULF OF ALASKA. AN INVERTED TROF EXTENDS
NORTH AND EAST FROM THIS FEATURE INTO SOUTHCENTRAL ALASKA AND THE
SOUTHERN YUKON TERRITORY. MUCH COLDER AIR IS ENTRENCHED NORTH OF THE
ALASKA RANGE AND OUT WEST ON THE BACKSIDE OF THE BROAD CYCLONIC
CIRCULATION. AN IMPRESSIVE LOOKING SHORTWAVE SOUTH OF THE CENTRAL
ALEUTIANS IS RACING EAST TOWARD THE NE PACIFIC. THIS FEATURE IS FAR
ENOUGH SOUTH THAT IT WILL HAVE NO IMPACT ON OUR DOMAIN.

.MODEL DISCUSSION...THIS HAS BEEN AN EXCELLENT WEEK FOR THE MODEL
DISCUSSIONS AS THE MODELS CONTINUE TO BE IN EXCELLENT AGREEMENT. ONE
CHANGE FROM THE PREVIOUS FORECAST IS OUR GROWING CONFIDENCE IN A
LIGHT RAIN AND SNOW EVENT SETTING UP FOR SOUTHCENTRAL OVER THE
WEEKEND. THE MODELS HAVE BEEN HINTING AT THIS POSSIBILITY BUT NOW
SEEM TO BE REALLY HONED IN ON A PROLONGED PERIOD OF LIGHT
PRECIPITATION.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...
INTERESTING PATTERN SETTING UP FOR THE WEEKEND THAT SHOULD BRING
PRECIPITATION TO MOST OF SOUTHCENTRAL. COLD AIR WRAPPING AROUND THE
BROAD CYCLONIC FLOW IS EVIDENT ON SATELLITE WITH THE CONVECTIVE
SIGNATURE SHOWING UP NEAR THE PANHANDLE. THE LEADING EDGE OF THE
COOLER AIR IS A SHORTWAVE THAT IS ENHANCING THE PRECIPITATION AS IT
APPROACHES PRINCE WILLIAM SOUND. THIS WAVE SHOULD MOVE ALONG THE
NORTH GULF COAST AND THEN BEND SOUTHWEST TOWARD KODIAK TONIGHT. A BIT
OF A COL WILL DEVELOP TO THE NORTH OF THIS WAVE OVER SOUTHCENTRAL
INTERIOR IN THE WAKE OF THE DEPARTING SHORTWAVE. THE WEAK FLOW ALOFT
...ABUNDANT LOW LEVEL MOISTURE...AND SURFACE TROF WILL ALL WORK
TOGETHER TO BRING SOUTHCENTRAL LIGHT PRECIPITATION.

PRECIP TYPE WILL BE A CHALLENGE AS THE CURRENT AIRMASS IS VERY WARM
WHILE THE COLD AIR ADVECTING INLAND WILL BE SLOW AND RELATIVELY WEAK.
AT THIS TIME ANTICIPATE THE OVERNIGHT HOURS WILL BE THE BEST
OPPORTUNITY FOR ACCUMULATING SNOWFALL BUT AGAIN GIVEN THE LACK OF ANY
ORGANIZED AREA OF LIFT...DO NOT EXPECT SIGNIFICANT ACCUMULATION.
AFTERNOON HIGH TEMPERATURES WILL STILL REACH THE MID TO UPPER 30S
WHICH WILL LIKELY RESULT IN A MIX OF RAIN AND SNOW DURING THE DAY.

THE ON-AND-OFF PRECIPITATION AND OVERALL CLOUDY CONDITIONS WILL LAST
THROUGH SUNDAY MORNING WHEN AN EASTERLY WAVE MOVES OUT OF SOUTHWEST
YUKON TERRITORY AND ACROSS SOUTHCENTRAL. BY SUNDAY
AFTERNOON...EXPECTING SKIES TO IMPROVE AND TEMPERATURES NEAR
CLIMATOLOGICAL NORMAL FOR THIS TIME OF YEAR.

SOUTHWEST ALASKA AND ALEUTIANS...
AS EXPECTED THE PRECIPITATION OVER SOUTHWEST ALASKA HAS DIMINISHED
OVER THE LAST 24 HOURS. ABUNDANT LOW LEVEL MOISTURE PERSISTS IN THIS
REGION AND AS THE GRADIENT CONTINUES TO WEAKEN...EXPECTING WIDESPREAD
FOG TO DEVELOP TONIGHT. SNOW SHOWERS WILL BE LIMITED TO THE ALASKA
PENINSULA WHILE THE INTERIOR...ESPECIALLY THE LOWER
ELEVATIONS...RADIATE OUT WITH FOG DEVELOPING LATE THIS EVENING OR
EARLY SATURDAY MORNING.

A STRONG TEMPERATURE INVERSION WILL DELAY THE LOW STRATUS AND FOG
FROM SCATTERING OUT SO THIS COULD BE A PERSISTENT ISSUE THROUGH
SUNDAY FOR MUCH OF BRISTOL BAY AND THE KUSKOKWIM VALLEY. SUNDAY
AFTERNOON...A COLDER AIRMASS BEGINS TO ADVECT OVER THE REGION
DROPPING TEMPERATURES BELOW NORMAL AGAIN AT THE START OF NEXT WEEK.
BY MID WEEK AN UPPER RIDGE MOVES THROUGH THE REGION AHEAD OF A WARM
FRONT THAT WILL BRING MILDER WEATHER BACK TO SOUTHWEST AK BY
WEDNESDAY.

ALEUTIANS AND BERING SEA...
VERY BENIGN WEATHER OVER THE ALEUTIANS WITH ONLY COLD ADVECTION SNOW
SHOWERS AND SOME LOCALLY GUSTY WINDS ALONG THE ALASKA PENINSULA. THE
NORTHWEST FLOW WILL CONTINUE TO DIMINISH OVER THE NEXT 24 HOURS WITH
SNOW SHOWERS PERSISTING UNTIL LATE IN THE WEEKEND WHEN AN AREA OF
HIGH PRESSURE BUILDS FROM THE WEST. THIS TRANSIENT RIDGE WILL SHIFT
FROM WEST TO EAST EARLY NEXT WEEK AS A SERIES OF LOW PRESSURE SYSTEMS
AND ASSOCIATED FRONTAL BOUNDARIES DEVELOP AND BEGIN IMPACTING THE
WESTERN ALEUTIANS.

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

AB MAR 12