Small Craft Advisory 300, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
400 PM AKDT FRI APR 5 2013

.MODEL DISCUSSION...
FORECAST MODELS CONTINUE TO HANDLE THE MAJOR UPPER LEVEL LOW FEATURE
DIVING OVER ALASKA FAIRLY WELL. THIS LOW TO REMAIN OVER THE MAINLAND
THROUGH THURSDAY. A RIDGE PUSHES ACROSS THE BERING THURSDAY AND INTO
THE MAINLAND FRIDAY AND SATURDAY OF NEXT WEEK. IN THE MEANTIME...THE
OPERATIONAL GFS HOLDS THE LOW A BIT LONGER IN THE WESTERN MAINLAND
THURSDAY AND FRIDAY THAN THE ECMWF SOLUTION. HOWEVER...THE GFS
ENSEMBLE IS SLIGHTLY FASTER SUGGESTING MORE ENSEMBLE MEMBERS ARE ON
THE TRACK OF THE ECMWF AND HAVE LEANED OUR MEDIUM RANGE FORECAST IN
THIS DIRECTION.

AT THE SURFACE...THE ECMWF AND NAM ARE IN VERY GOOD AGREEMENT WITH
SURFACE LOW CENTERS AND AREAS OVER THE GULF OF ALASKA THROUGH MONDAY.
NOT MUCH DIFFERENCE EXISTS IN THE BERING AND NORTH PACIFIC DUE TO
LITTLE DEVELOPMENT OF SURFACE LOWS ANYHOW. SURFACE WIND AND PRECIP
PATTERNS IN THE MEDIUM RANGE WILL FOLLOW MOSTLY ALONG THE ECMWF
LINES.

.ANALYSIS AND UPPER LEVELS...
AT THE SURFACE...GENERALLY STRONG HIGH PRESSURE OVER THE ARCTIC AND
LOW PRESSURE IN THE NORTH PACIFIC EXTENDING FROM 40N 180 TO 55N 140W.
THIS IS CREATING A STRONG PRESSURE GRADIENT OVER THE BERING AND
SOUTHWEST ALASKA WITH MODERATE NORTHEAST WINDS ACROSS THE REGION. A
WEAK SURFACE TROUGH ASSOCIATED WITH AN UPPER LOW NEAR SHEMYA EXTENDS
FROM UNALASKA BACK TO THE KAMCHATKA PENINSULA WITH RAIN AND SNOW
SHOWERS.
AT UPPER LEVELS...THE ARCTIC UPPER LOW IS ENTERING THE STATE NEAR THE
MACKENZIE RIVER DELTA WITH HIGH PRESSURE OVER THE BERING AND ANOTHER
UPPER LOW NEAR SHEMYA. THE JET STREAM WRAPPING AROUND THE MAIN UPPER
LOW IN MAINLAND ALASKA IS NOT THAT STRONG AT AROUND 40-50 KT.

.SHORT TERM FORECAST...
FOR SOUTH CENTRAL ALASKA...
MOSTLY CLEAR SKIES TO PERSIST THROUGH THE AFTERNOON AND EVENING HOURS
TONIGHT BEFORE THE MOISTURE STARTS TO BUILD WITH SOUTHERLY FLOW ALOFT
TAKING OVER THE WEATHER PATTERN. COLDER AIR FILTERS INTO THE AREA
TONIGHT AND TOMORROW. MOISTURE WILL WRAP IN FROM THE GULF AND
OVERRIDE THE COLD AIR AT THE SURFACE PROVIDING FOR SNOWFALL TO BEGIN
SATURDAY. AS THE UPPER LEVEL SUPPORT INCREASES SATURDAY NIGHT INTO
SUNDAY WITH THE COLD UPPER LOWS PROXIMITY...SNOWFALL INTENSITY WILL
INCREASE. THE INTENSITY AT THIS TIME IS ANTICIPATED TO WANE DURING
THE DAY SUNDAY. HOWEVER...THERE COULD BE FEATURES WITHIN THE FLOW
TAHT COULD EXTEND SNOWFALL THROUGH THE EVENING SUNDAY BEFORE THE FLOW
BACKS TO THE SOUTHEAST. THE PRESSURE GRADIENTS AT THE SURFACE WILL
NOT BE ALL THAT IMPRESSIVE SATURDAY INTO SUNDAY. THEREFORE...THERE IS
NOT MUCH THREAT FOR BLOWING SNOW JUST HEAVY SNOW. HOWEVER...AS THE
UPPER LEVEL LOW SWINGS EAST A BIT SUNDAY SOME NORTHWESTERLY GAP FLOW
WILL DEVELOP THROUGH THE BARREN ISLAND REGION. THE FLOW REMAINS
SOUTHERLY THROUGH MID NEXT WEEK. DEPENDING ON THE EXACT POSITIONS OF
THE SUBSEQUENT SURFACE LOWS IN THIS FLOW...SNOWFALL WILL BE EAST OF
ANCHORAGE OR FILL BACK INTO ANCHORAGE AND MAT-SU VALLEYS. IN THE
MEANTIME...KODIAK WILL BE BREEZY WITH NORTHWEST FLOW SUNDAY THROUGH
MID WEEK AS ANY SURFACE LOW WILL BE EAST OF THE ISLAND AND CREATE A
WEST TO EAST GRADIENT.

FOR SOUTHWEST ALASKA...COLD AND CLEAR CONDITIONS MAINLY TO PERSIST
THROUGH EARLY NEXT WEEK. THE GRADIENT CURRENTLY PRODUCING MODERATE
NORTH TO NORTHEAST WINDS WILL LESSEN OVER THE MAINLAND TOMORROW AS
THE UPPER LOW MOVES OVERHEAD. NEAR 20 DEGREES BELOW NORMAL TEMPS TO
REMAIN THROUGH MID WEEK WITH LOWS IN THE 10 TO 20 BELOW RANGE. IN THE
NORTHERLY FLOW SOME INSTABILITY SHOWERS WILL PROBABLY DEVELOP ALONG
THE AKPEN STARTING TUESDAY.

FOR ALEUTIANS...THE UPPER LOW NEAR SHEMYA TO REMAIN IN THE AREA
THROUGH SUNDAY WITH SHOWERS AS WELL. THE PRESSURE GRADIENT OVER THE
BERING NOT TO LESSEN THROUGH EARLY NEXT WEEK. THEREFORE...MODERATE
NORTHEAST WINDS TO PERSIST AS WELL. HIGH PRESSURE TO MOVE OVER THE
BERING WEDNESDAY WITH LESSENING WINDS AND SOME INSTABILITY SHOWERS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...WINTER WEATHER ADVISORY ZONE 101 AND 111.
MARINE...GALE WARNING 160 179.
         STORM WARNING 155.
FIRE WEATHER...NONE.

NELSON APR 13

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1125 AM AKDT FRI APR 5 2013

AKZ101-111-125-145-060000-

...SNOW EXPECTED AGAIN IN SOUTH CENTRAL ALASKA THIS WEEKEND...

DESPITE A NUMBER OF DAYS OF SUNNY WEATHER THIS WEEK, WINTER IS NOT
OVER IN SOUTH CENTRAL ALASKA AND SNOW IS EXPECTED AGAIN THIS WEEKEND.

THE SNOW WILL BEGIN TO FLY SATURDAY AFTERNOON...BUT ACCUMULATIONS
WILL BE MINIMAL. THE HEAVIEST PART OF THE EVENT IS ANTICIPATED TO BE
FROM THE EVENING ON SATURDAY INTO SUNDAY. SIGNIFICANT SNOWFALL IS
EXPECTED AND TRAVEL WILL BE IMPACTED SATURDAY NIGHT AND SUNDAY AS A
RESULT.

DUE TO THE WEATHER PATTERN WE FIND OURSELVES IN AFTER THIS
WEEKEND...SNOW IS A POSSIBILITY OVER ANCHORAGE AND THE MAT-SU AREAS
THROUGH WEDNESDAY. SNOW WILL CONTINUE OVER PRINCE WILLIAM SOUND AND
POINTS EAST FOR SURE THROUGH MID NEXT WEEK. HOWEVER...DEPENDING ON
THE EXACT POSITIONING OF THE SURFACE LOWS MONDAY THROUGH
WEDNESDAY...ANCHORAGE AND THE MAT-SU COULD RECEIVE ANYWHERE FROM
LITTLE TO NO SNOWFALL OR SIGNIFICANT SNOWFALL THROUGH THE WEEK.

IN ADDITION...NIGHTTIME TEMPERATURES WILL BE IN THE TEENS THROUGH THE
WEEK.

STAY TUNED TO FURTHER WEATHER STATEMENTS ABOUT WEEKEND SNOW AMOUNTS
AND POTENTIAL SNOW IMPACTS FOR NEXT WEEK.