Small Craft Advisory 221, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
527 AM AKDT THU MAR 12 2015

.ANALYSIS AND UPPER LEVELS...

ON THE EARLY MORNING WEATHER MAP...A COLD FRONT ASSOCIATED WITH
AN AREA OF LOW PRESSURE OVER EASTERN RUSSIA IS BRINGING SNOW AND
GALE FORCE WINDS TO THE WESTERN ALEUTIANS. LOOKING AT BOTH WATER
VAPOR AND THE DERIVED PERCENT OF NORMAL TOTAL PRECIPITABLE
WATER PRODUCTS...A VERY MOISTURE RICH AIR MASS IS CURRENTLY IN
PLACE AND SHIFTING EASTWARD OVER THE WESTERN ALEUTIANS. OVERNIGHT
OBSERVATIONS AT SHEMYA (PASY) HAVE SHOWN STEADY SNOW WITH VSBY 3
MILES OR LESS ALL NIGHT...HINTING AT DECENT SNOWFALL RATES.
ANOTHER FEATURE OF NOTE ON WATER VAPOR IMAGERY THIS MORNING IS A
TROUGH OF LOW PRESSURE EXTENDING FROM EASTERN RUSSIA TO THE
PACIFIC NORTHWEST COAST OF THE UNITED STATES. OVER THE PAST 6
HOURS...THE TROUGH CONTINUED TO AMPLIFY AND DIG FURTHER SOUTH INTO
THE CENTRAL PACIFIC AS A RIDGE OF HIGH PRESSURE STRENGTHENS ACROSS
THE WEST COAST OF THE UNITED STATES. THE AREA OF HIGH PRESSURE
THAT HAS BEEN DOMINANT ACROSS THE CENTRAL BERING SEA THE PAST FEW
DAYS IS BEING SQUEEZED BETWEEN THE AFOREMENTIONED FRONT OVER THE
WESTERN BERING SEA AND AND THE BROAD AREA OF LOW PRESSURE OVER THE
SOUTHERN HALF OF THE ALASKA MAINLAND. THIS IS FORCING THE HIGH
PRESSURE TO SPLIT IN TWO AND RETREAT INTO THE NORTHERN BERING SEA
AND NORTH PACIFIC.

TOWARD THE GULF COAST...AN AREA OF LOW PRESSURE JUST TO THE WEST
OF THE PANHANDLE HAS BEEN BRINGING RAIN SHOWERS TO THE NORTHEASTERN
GULF COAST AND PANHANDLE OVERNIGHT. SOME CLOUDS ASSOCIATED WITH
THE LOW IN THE EASTERN GULF HAVE MOVED INTO THE COPPER RIVER BASIN
OVERNIGHT BUT FOR THE MOST PART THE ALASKA MAINLAND HAS SEEN
MOSTLY CLEAR SKIES. VISIBLE IMAGERY YESTERDAY EVENING PICKED UP
AN INTERESTING FEATURE THAT IS NOT TOO COMMON TO THE MONTH OF
MARCH. DUE TO THE LACK OF SNOW OVER OVER THE BRISTOL BAY
AREA...ASH FROM THE 1912 ERUPTION OF THE KATMAI ERUPTION HAS BEEN
RESUSPENDED DUE TO STRONG NORTHWESTERLY WINDS. THIS ASH IS BEING
BLOWN TOWARD THE SOUTHERN AND WESTERN PARTS OF KODIAK ISLAND AND
IS RESTRICTING VISIBILITIES. NO ACCUMULATION OF ASH OR DUST IS
EXPECTED.

&&

.MODEL DISCUSSION...

MODELS ARE IN RELATIVELY GOOD AGREEMENT THROUGH FRIDAY MORNING
WITH THE AREA OF LOW PRESSURE OVER THE NORTHEASTERN GULF OF
ALASKA AND A SERIES OF LOW CENTERS EXTENDING FROM THE WESTERN
BERING SEA TO THE KAMCHATKA PENINSULA. ON EARLY FRIDAY MORNING...A
DEVELOPING AREA OF LOW PRESSURE IN THE SOUTHERN GULF OF ALASKA
WILL PUSH RAPIDLY NORTH TOWARD CAPE FAIRWEATHER BAY AND MOVE
INLAND FRIDAY AFTERNOON. WHILE THE SYNOPTIC MODELS ALL HAVE A
SIMILAR SOLUTION...THE GFS IS AN OUTLIER AS IT TRIES TO DEVELOP A
MUCH DEEPER LOW WHICH IS DUE IN LARGE PART TO A MUCH STRONGER
UPPER LEVEL JET THAN DEPICTED ON THE NAM/ECMWF. THE OVERALL
IMPACTS OF THE STRONGER LOW ARE MINIMAL AS OUTFLOW WINDS ACROSS
THE GAPS IN SOUTHCENTRAL ALASKA WILL CONTINUE TO BLOW. THINGS GET
A BIT MORE COMPLICATED OVER THE WESTERN BERING SEA FRIDAY
AFTERNOON AS AN AREA OF LOW PRESSURE PUSHES OFF KAMCHATKA AND
PHASES WITH A LOW OVER THE WESTERN BERING SEA. A TRIPLE POINT LOW
IS EXPECTED TO DEVELOP SOUTH OF DUTCH HARBOR AND DEEPEN RAPIDLY ON
SATURDAY WHICH COULD EFFECT HOW MUCH WARM AIR IS ACTUALLY ADVECTED
NORTHWARD. OVERALL...THE ECMWF SOLUTION WAS PREFERRED WITH THE
AFOREMENTIONED MODEL ISSUES.

&&

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

CLEAR AND COLD CONDITIONS WILL CONTINUE TODAY ACROSS MOST OF THE
AREA AS A REINFORCING SHOT OF COLD AIR MOVES IN FROM THE
NORTHWEST. THE LONGWAVE TROUGH ENCOMPASSING THE STATE IS IN THE
PROCESS OF SHARPENING AND TURNING INTO A CLOSED UPPER LOW WHICH
WILL BE IN THE VICINITY OF UPPER COOK INLET BY THIS EVENING. AS
ANTICIPATED...THE INCREASING SOUTHERLY FLOW OVER THE EASTERN GULF
IS ALLOWING DEEP MOISTURE AND CLOUD-COVER TO CREEP BACK INTO THE
FAR EASTERN PORTIONS OF THE COPPER BASIN TODAY. A SURFACE LOW
MOVING NORTHWARD THROUGH THE GULF WILL MAKE LANDFALL NEAR YAKUTAT
THIS AFTERNOON...THOUGH ALL ASSOCIATED PRECIPITATION WILL STAY
EAST OF OUR AREA.

A WEAK LOW WILL FORM JUST OUTSIDE PRINCE WILLIAM SOUND
TONIGHT...WHICH MAY HELP TO SPREAD SOME SHOWER ACTIVITY OR AT
LEAST INCREASING AMOUNTS OF LOW-LEVEL MOISTURE FURTHER WEST TOWARD
PRINCE WILLIAM SOUND AND THE REST OF THE COPPER BASIN BY EARLY
FRIDAY MORNING. THE COOK INLET POPULATION CENTERS LOOK TO REMAIN
RIGHT ON THE PERIPHERY OF THE CLOUDS DURING THIS PERIOD...AND WILL
ALMOST CERTAINLY REMAIN DRY THROUGH THE END OF THE WEEK. AS THE
UPPER LOW BEGINS TO LIFT NORTH/NORTHEAST ON FRIDAY THERE SHOULD BE
ENOUGH DYNAMIC LIFT TO TEAM-UP WITH INCREASING LOW-LEVEL MOISTURE
TO GENERATE SOME LIGHT SNOW IN THE CORDOVA- VALDEZ- GLENNALLEN
CORRIDOR BEFORE YET ANOTHER SHOT OF COLD AIR MOVES IN FROM THE
WEST/SOUTHWEST AND SKIES AGAIN CLEAR.

THE USUAL GAP WINDS REMAIN ACTIVE...AND WILL CONTINUE TO DO SO
THROUGH THE END OF THE WEEK. SOME LULL IN THE PRESSURE GRADIENT IS
EXPECTED TONIGHT AS A WEAK LOW FORMS ALONG THE COAST AND TRIES TO
WORK ITS WAY BACK WESTWARD TOWARD HINCHINBROOK ENTRANCE.
HOWEVER...REGARDLESS OF HOW FAR WEST THIS FEATURE MOVES...PRESSURE
GRADIENTS WILL AGAIN TIGHTEN BY THE DAYTIME PERIOD FRIDAY AS COLD
AIR SURGES INTO THE AREA AGAIN AND THE SURFACE LOW TURNS BACK INTO
AN ELONGATED COASTAL TROUGH.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
COLD AND DRY CONDITIONS WILL CONTINUE ACROSS SOUTHWEST ALASKA AS A
BROAD UPPER LEVEL TROUGH REMAINS IN PLACE OVER MAINLAND ALASKA.
BREEZY NORTH TO NORTHWEST WINDS WILL KEEP WIND CHILLS NEAR BUT NOT
QUITE TO ADVISORY LEVELS. NORTHWESTERLY FLOW HITTING THE ALASKA
PENINSULA WILL CONTINUE TO GENERATE SNOW SHOWERS WITH STRONG COLD
GUSTS BEING FILTERED THROUGH THE GAPS AND PASSES.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE FRONTAL SYSTEM OVER SHEMYA WILL CONTINUE EAST TO REACH THE
CENTRAL ALEUTIANS THIS AFTERNOON AND EVENING. A FASTER MOVING
SHORTWAVE AND ASSOCIATED SURFACE LOW WILL CATCH UP WITH THE FRONT
THURSDAY NIGHT CAUSING A WAVE TO STRENGTHEN RAPIDLY ALONG IT
INCREASING WINDS OVER THE EASTERN ALEUTIANS ON FRIDAY. THIS FRONT
WILL LIFT NORTH OVER THE BERING FRIDAY NIGHT AS IT SHEARS APART
BUT MAY MAKE IT FAR ENOUGH NORTH TO BRING SNOW AND BLOWING SNOW TO
THE PRIBILOF ISLANDS.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
COLD CONDITIONS WILL PERSIST INTO THE WEEKEND FOR MAINLAND ALASKA
DUE TO THE TROUGHING OVER THE EASTERN PART OF THE STATE.
LOW PRESSURE SOUTH AND WEST OF KODIAK ISLAND THIS WEEKEND INTO
EARLY NEXT WEEK WILL PUSH A SERIES OF WARM FRONTS NORTH ACROSS
THE GULF INTO THE SOUTHERN MAINLAND. TEMPERATURES WILL GRADUALLY
RISE BEHIND EACH WAVE OF MOISTURE...WITH BELOW NORMAL TEMPERATURES
THIS WEEKEND WITH SNOW THE PREDOMINANT PRECIPITATION-TYPE
TRANSITIONING TO ABOVE NORMAL TEMPERATURES AND A SNOW-RAIN MIX
TOWARD THE MONDAY-WEDNESDAY TIME FRAME. THERE IS LOW CONFIDENCE
IN SEEING SOME SNOW ACCUMULATION TOWARD ANCHORAGE IN THE MONDAY
TIME FRAME.

STRONG NORTHERLY FLOW WILL PUSH COLD AIR SOUTH ACROSS THE BERING
SEA THROUGH THE PERIOD WITH SCATTERED TO NUMEROUS SNOW SHOWERS
PREDOMINATING.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES...121 127 129 132 138 150 155 170 172-179 185
         STORMS...130 131
		 HVY FRZG SPRY...120 121 126-132 136-139 141 150 155 160
						 165 179 180 185
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MC
SOUTHCENTRAL ALASKA...AD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR
LONG TERM...CC

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1239 PM AKDT THU MAR 12 2015

AKZ171-130845-
KODIAK ISLAND-
INCLUDING THE CITY OF...KODIAK CITY
1239 PM AKDT THU MAR 12 2015

...RESUSPENDED ASH FROM KATMAI VOLCANO...

STRONG NORTHWEST WINDS ACROSS BRISTOL BAY ARE RESUSPENDING ASH
FROM KATMAI VOLCANO. THESE STRONG WINDS ARE TRANSPORTING SOME OF
THE ASH AND DUST ACROSS SHELIKOF STRAIT INTO KODIAK ISLAND. THIS
ASH IS VISIBLE ON SATELLITE IMAGERY...MAINLY OVER THE SOUTHERN AND
WESTERN END OF THE ISLAND. WINDS ARE EXPECTED TO PERSIST THROUGH
AT LEAST THIS EVENING. NO ACCUMULATION OF ASH OR DUST IS
EXPECTED...BUT LOWER VISIBILITIES IN VICINITY OF THE ASH WILL BE
LIKELY. THIS ASH IS NOT ASSOCIATED WITH AN ACTIVE ERUPTION.