Small Craft Advisory 276, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
132 PM AKDT THU APR 3 2014

.ANALYSIS AND UPPER LEVELS...AS HAS BEEN WELL ADVERTISED THE PAST
FEW DAYS...THE UPPER LEVELS ARE IN TRANSITION WITH A LARGE UPPER
LEVEL TROUGH/LOW OVER THE BERING SEA AND NORTH PACIFIC SHIFTING
EASTWARD AND BEGINNING TO AFFECT PORTIONS OF MAINLAND ALASKA WHERE
THE DOMINANT BLOCKING RIDGE FROM THE PAST COUPLE WEEKS HAS BEGUN
TO WEAKEN. THE TROUGH IS BROAD AND FAIRLY LOW AMPLITUDE WITH A
NEAR ZONAL UPPER JET WELL SOUTH OF ALASKA WHICH WILL INITIALLY
KEEP THE BULK OF PRECIPITATION ALONG COASTAL AREAS OF THE SOUTHERN
MAINLAND.

&&

.MODEL DISCUSSION...MODELS ARE IN PRETTY GOOD AGREEMENT WITH
HANDLING OF SYNOPTIC SCALE FEATURES...BUT THERE ARE SOME KEY
DIFFERENCES IN THE MESOSCALE. THE NAM LOOKS A LITTLE TOO
AGGRESSIVE WITH UPPER LEVEL SHORT-WAVE CURRENTLY ROUNDING THE
EAST SIDE OF THE TROUGH HEADED TOWARD KODIAK ISLAND. BECAUSE OF
THIS THE NAM IS NOTABLY STRONGER AND FASTER WITH TRIPLE POINT LOW
AND FRONT MOVING ACROSS THE GULF TONIGHT THROUGH FRIDAY NIGHT.
PREFER A SLIGHTLY WEAKER AND SOUTHERLY POSITION AS INDICATED BY
THE REST OF THE SOLUTIONS. THE ULTIMATE TRACK OF THE TRIPLE POINT
LOW IS VERY MUCH IN QUESTION. THIS IS KEY TO DETERMINING WHERE
PRECIPITATION WILL FALL THIS WEEKEND OVER SOUTHCENTRAL. FLOW
BECOMES QUITE CONFUSED AND THERE ARE A LOT OF MODEL VARIATIONS
WITH WEAK FEATURES...SO WILL GENERALLY STICK WITH A BROADBRUSH
APPROACH TO THE PRECIP FORECAST OVER INTERIOR AREAS OF
SOUTHCENTRAL.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...A SERIES OF ELONGATING FRONTAL BOUNDARIES
OVER THE THE GULF WILL CONFINE THE BULK OF PRECIPITATION TO
KODIAK ISLAND AND THE SOUTHERN TO EASTERN KENAI PENINSULA. OVER
THE WEEKEND THE TROUGH MOVING OUT OF THE BERING WILL AMPLIFY AS IT
MOVES TO THE NORTHEAST PACIFIC. MEANWHILE...ANOTHER TROUGH WILL
DROP OUT OF THE ARCTIC INTO NORTHWEST ALASKA. BOTH OF THESE WILL
CONTRIBUTE TO STEERING FLOW BECOMING MORE SOUTHERLY AND DEEPER
MOISTURE MAKING ITS WAY INTO SOUTHCENTRAL. AS MENTIONED IN THE
MODEL DISCUSSION THERE IS QUITE A BIT OF UNCERTAINTY IN THE TRACK
OF WEAK FEATURES ACROSS SOUTHCENTRAL THIS WEEKEND. EVEN
SO...CONDITIONS ARE LOOKING MORE FAVORABLE FOR WIDESPREAD LIGHT
PRECIPITATION ACROSS SOUTHCENTRAL SATURDAY NIGHT AND SUNDAY. LOW
LEVEL THICKNESSES INDICATE PRECIPITATION WOULD FALL MAINLY AS SNOW
INLAND (INCLUDING ANCHORAGE AND THE MAT-SU).

SOUTHWEST ALASKA...AN ELONGATING FRONT OVER SOUTHWEST ALASKA IS
BRINGING WIDELY SCATTERED VERY LIGHT PRECIPITATION TO PORTIONS OF
SOUTHWEST ALASKA TODAY. A STRONGER FRONT OVER THE EASTERN
ALEUTIANS AND SOUTHERN ALASKA PENINSULA WILL MAKE ITS WAY TOWARD
SOUTHWEST TONIGHT AND FRIDAY...BUT WILL STALL EVEN FURTHER SOUTH
THAN THE CURRENT FRONT. THUS...PRECIPITATION WITH THE NEXT FRONT
WILL PRIMARILY AFFECT THE BRISTOL BAY REGION. THE TROUGH DROPPING
OUT OF THE ARCTIC MIGHT PROVIDE ENOUGH LIFT TO PRODUCE SOME SNOW
FURTHER NORTH THIS WEEKEND...BUT ANYTHING THAT DOES FALL WILL BE
LIGHT WITH LITTLE OR NO ACCUMULATION. THERE WILL BE A NOTABLE
COOLING TREND OVER THE WEEKEND WITH THE ARRIVAL OF ARCTIC AIR
BEHIND THE UPPER TROUGH.

BERING SEA/ALEUTIANS...THE LARGE LOW COMPLEX OVER THE BERING AND
ALEUTIANS WILL SHIFT EASTWARD THE NEXT COUPLE DAYS. COLD ADVECTION
ON THE BACK SIDE WILL BRING A PERIOD OF GUSTY NORTHERLIES AND
SNOW SHOWERS. WITH PROGRESSIVE FLOW ALOFT THIS WILL BE SHORT LIVED
AS A TROUGH EXITING ASIA BEGINS TO AFFECT THE ALEUTIANS LATER THIS
WEEKEND.

&&

.LONG TERM FORECAST...FORECAST UNCERTAINTY GROWS SIGNIFICANTLY
EARLY NEXT WEEK WITH INTERACTION OF ARCTIC TROUGH OVER MAINLAND
ALASKA AND NORTHEAST PACIFIC AND GULF OF ALASKA TROUGH. THE
GENERAL SET-UP IS FAVORABLE FOR ACCUMULATING SNOW OVER
SOUTHCENTRAL (INCLUDING THE POPULATION CENTERS)..SO WILL HAVE TO
CLOSELY WATCH THIS OVER THE NEXT COUPLE DAYS. AS THESE TROUGHS
EXIT TO THE EAST MID WEEK A BLOCKING RIDGE WILL SET UP FROM
SIBERIA TO SOUTHWEST ALASKA BRINGING A RETURN TO DRY CONDITIONS
ACROSS MAINLAND ALASKA. THE ARCTIC AIR MASS WHICH MOVES IN WITH
THE UPPER TROUGH WILL RESULT IN BELOW NORMAL TEMPERATURES.
UPSTREAM...A TROUGH WILL SET UP SHOP OVER THE WESTERN ALEUTIANS
AND BERING.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING...119 120 130 131 173 174 175 176 177 178.
         HEAVY FREEZING SPRAY 185.
FIRE WEATHER...NONE.
&&

SEB APR 14