Small Craft Advisory 238, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
506 AM AKDT TUE MAR 17 2015

.ANALYSIS AND UPPER LEVELS...
THE MAIN UPPER LEVEL FEATURE INFLUENCING THE WEATHER ACROSS THE
REGION THIS MORNING IS A LARGE COMPLEX LOW SOUTH OF DUTCH HARBOR.
THIS LOW IS EMBEDDED IN A LONGWAVE TROUGH THAT EXTENDS THROUGH THE
BERING SEA WELL INTO THE NORTH PACIFIC...WITH AN UPPER RIDGE
LOCATED DOWNSTREAM OVER WESTERN CANADA. WARM AND MOIST SOUTHERLY
FLOW IS IN PLACE OVER MAINLAND ALASKA BETWEEN THESE TWO
FEATURES...WITH A SERIES OF DISTURBANCES TRACKING NORTHWARD
THROUGH THE GULF. ONE OF THESE WAVES IS CURRENTLY EXITING
SOUTHCENTRAL ALASKA AS IT MOVES QUICKLY INTO THE
INTERIOR...LEAVING A MIX OF RAIN AND SNOW SHOWERS AND GUSTY
SOUTHEAST WINDS IN ITS WAKE. MEANWHILE...A FRONT ASSOCIATED WITH
THE LOW SOUTH OF DUTCH HARBOR EXTENDS NORTHEASTWARD INTO THE
BERING...BRINGING RAIN AND STRONG WINDS TO THE EASTERN ALEUTIANS
AND ALASKA PENINSULA AS SNOW SHOWERS SPREAD INTO PORTIONS OF
BRISTOL BAY. BLOWING SNOW CONTINUES TO IMPACT THE PRIBILOF ISLANDS
WITH NORTHERLY GALE FORCE WINDS EXTENDING THROUGH THE CENTRAL
BERING.

&&

.MODEL DISCUSSION...
MODELS ARE IN GOOD OVERALL AGREEMENT WITH RESPECT TO THE SYNOPTIC
PATTERN IN THE SHORT TERM AS THE BROAD LOW REMAINS QUASI
STATIONARY SOUTH OF DUTCH HARBOR FOR THE NEXT SEVERAL DAYS. THERE
ARE SOME DIFFERENCES IN THE HANDLING OF THE NUMEROUS INDIVIDUAL
WAVES TRACKING INTO THE GULF OF ALASKA IN THIS TIME FRAME...BUT
FOR THE MOST PART ALL OF THE GUIDANCE APPEARS TO BE ON THE SAME
PAGE. UTILIZED THE GEM REGIONAL FOR ENHANCED DETAIL IN THE FIRST
24-36 HOURS OF THE FORECAST BEFORE TRANSITIONING TOWARDS A GFS/EC
BLEND INTO THE MIDTERM.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
HIGH PRESSURE WILL BRIEFLY BUILD OVER SOUTHERN ALASKA TODAY. AN
UPPER LOW CURRENTLY OFF THE COAST OF THE PANHANDLE WILL SLIDE
NORTHWEST TODAY INTO THE GULF TODAY. PRECIPITATION FROM THIS
SYSTEM WILL REACH THE GULF COAST AND KODIAK TONIGHT AND MOVE
INLAND ON WEDNESDAY. ONCE AGAIN MOST OF THE PRECIPITATION WILL
CONFINED TO COASTAL AREAS AS THE SOUTHEAST FLOW ALOFT KEEPS THE
DOWN-SLOPE COMPONENT IN PLAY FOR INLAND AREAS. ANOTHER SYSTEM
WILL QUICKLY FOLLOW...MOVING INTO THE NORTHERN GULF ON WEDNESDAY
AND TO THE GULF COAST WEDNESDAY NIGHT. THIS SYSTEM WILL FOLLOW A
VERY SIMILAR TRAJECTORY TO THE FIRST SYSTEM.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
ANOTHER UPPER LEVEL TROUGH OVER THE SOUTHWEST MAINLAND WILL BRING
SNOW FROM WESTERN BRISTOL BAY INTO THE KUSKOKWIM DELTA THIS
MORNING...WITH A FEW INCHES OF ADDITIONAL ACCUMULATION EXPECTED
BY THIS AFTERNOON. WEAK RIDGING ALOFT WILL QUICKLY MOVE IN BEHIND
THIS SNOW...WHICH SHOULD ALLOW FOR RAPID CLEARING OF CLOUDCOVER BY
THIS EVENING IN MOST AREAS. ANOTHER WEAKER SHORTWAVE WILL APPROACH
THE AKPEN ON WEDNESDAY...WHICH SHOULD BRING ANOTHER ROUND OF
LIGHT SNOW TO THE SAME AREAS ON FOR THE AFTERNOON AND EVENING
HOURS.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
SNOW THAT CAN BE SEEN DEVELOPING OVER THE EASTERN BERING SEA ON
SATELLITE IMAGERY IS HEADING WESTWARD TOWARDS THE PRIBILOF
ISLANDS. THIS WILL BEGIN TO CREATE BLIZZARD CONDITIONS BEGINNING
LATER THIS MORNING AND CONTINUE THROUGH THE EARLY EVENING. SHOWERS
WILL THEN DIMINISH BY THIS LATE EVENING...THEN RETURN ON WEDNESDAY
AFTERNOON AS A WEAK UPPER LEVEL TROUGH MOVES INTO THE AREA THESE
SHOWERS HOWEVER ARE EXPECTED TO BE MUCH LIGHTER...AND WITH
DIMINISHING WINDS A RETURN TO BLIZZARD CONDITIONS IS NOT EXPECTED.

OVER THE ALEUTIANS...RAIN THAT IS CURRENTLY FALLING FROM UNALASKA
EASTWARD WILL BECOME ACCUMULATING SNOW OVER THE CENTRAL ALEUTIANS
AS COLDER AIR WORKS SOUTHWARD BEHIND THE LOW BEGINNING THIS
EVENING. THE HEAVIEST SNOWFALL IS EXPECTED WEST OF ATKA WHERE
TEMPERATURES WILL STAY COOLER...THOUGH ADVISORY LEVEL SNOWFALL IS
NOT EXPECTED AT THIS TIME. TEMPERATURES WILL ALSO REMAIN IN THE
LOW TO MID 30S...WHICH WILL LIMIT ANY BLOWING SNOW CONCERNS FROM
MATERIALIZING WITH STRONG NORTHERLY WINDS. THIS SNOWFALL WILL THEN
DIMINISH ON WEDNESDAY MORNING AS THE UPPER LEVEL LOW SLOWLY MOVES
TO THE SOUTH...WHICH WILL BRING A SLIGHTLY DRIER TREND TO MUCH OF
THE REGION WITH DIMINISHING WINDS.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
MODELS SUPPORT THE IDEA THAT THE BROAD CYCLONIC JET SUPPORTING A
CUT-OFF UPPER LOW OVER THE AKPEN AND EASTERN ALEUTIANS WILL BUCKLE
THIS WEEKEND. THIS WILL ALLOW THE LOW TO MOVE SOUTHEAST INTO THE
PACIFIC. SURFACE FEATURES ARE NOT WELL HANDLED BY OPERATIONAL
MODELS AND WPC GUIDANCE ATTEMPTS TO CONSOLIDATE THE CONFUSION INTO
A REASONABLE SOLUTION BY USING A FAIR AMOUNT OF EC ENSEMBLE.

THE SURFACE LOW OVER DUTCH HARBOR WILL DISSIPATE...A WAVE MOVING
ALONG THE EASTERN FLANK OF THE UPPER LOW WILL MOVE INTO THE
EASTERN BERING SAT THROUGH SUN...AND A NEW NORTH PACIFIC FRONT
WILL SKIRT THE ALEUTIANS EARLY NEXT WEEK. THIS WILL BRING SOME RAIN
AND SNOW TO GULF COASTAL LOCATIONS WITH LESSER AMOUNTS INLAND...AND
RAIN AND SNOW SHOWERS TO THE ALEUTIANS THROUGH MONDAY. THE
FORECAST BRIEFLY UTILIZES THE EC AND GFS IN THE MID TERM WHICH
TRANSITIONS INTO THE WPC SOLUTION FOR THE LONG TERM.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...BLIZZARD WARNING 195.
MARINE...STORM WARNING 173 174.
         GALE WARNING 119 120 130 131 132 138 139 150 155 165
                      170 172 175 176 177 179 412 413 414.
         HEAVY FREEZING SPRAY 179 185 412 414.
FIRE WEATHER...NONE.

&&

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