Small Craft Advisory 92, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
431 AM AKST THU JAN 29 2015

.ANALYSIS AND UPPER LEVELS...
HIGH PRESSURE CONTINUES TO DOMINATE MOST OF THE SOUTHERN
MAINLAND...PRODUCING CLEAR SKIES AND COLD TEMPERATURES FOR MOST
INTERIOR LOCATIONS. A WEAK SURFACE LOW CAN ALSO BE SEEN MOVING
THROUGH THE NORTHWESTERN GULF ON RECENT ASCAT IMAGERY. THE
PRESSURE GRADIENT BETWEEN THIS AND THE MAINLAND RIDGING IS KEEPING
GAP WINDS ALONG THE NORTH GULF COAST THROUGH THE NIGHT SLIGHTLY
STRONGER THAN WHAT WAS INITIALLY FORECAST. THIS WEAK LOW IS
DRIFTING TO THE SOUTHWEST AS IT WEAKENS...WHICH SHOULD HELP
DIMINISH THESE GAP WINDS OVER THE COURSE OF THIS MORNING. A SHARP
AND DRY SHORTWAVE IS PRESENT IN WATER VAPOR IMAGERY RIDING OVER
THE SURFACE RIDGING...AND STRETCHES FROM THE SOUTHWEST MAINLAND
INTO THE CENTRAL BERING. VERY DEEP AND DRY CONDITIONS ASSOCIATED
WITH THE SURFACE RIDGING IS PREVENTING THE INSTABILITY FROM THIS
FEATURE TO PRODUCE ANY PRECIPITATION. THE NORTH PACIFIC COMPLEX
LOW IS NOW MOVING WELL SOUTH OF THE EASTERN ALEUTIANS...HOWEVER A
TIGHT PRESSURE GRADIENT BETWEEN THIS AND HIGH PRESSURE MOVING
THROUGH THE WESTERN ALEUTIANS CONTINUES TO BRING GALE FORCE WINDS
FROM THE PRIBILOF ISLANDS TO THE EASTERN ALEUTIANS.

&&

.MODEL DISCUSSION...
AS HAS BEEN THE CASE OVER THE PAST FEW DAYS...SYNOPTIC AGREEMENT
REMAINS VERY GOOD FOR THE FIRST 3 DAYS OF THE FORECAST...BUT THE
DEVIL REMAINS IN THE DETAILS. THE MOST SIGNIFICANT OF WHICH
INVOLVES THE TRACK AND INTENSITY OF A SHORTWAVE CURRENTLY ENTERING
THE SOUTHERN GULF AS IT MOVES OVER THE NORTH GULF COAST THIS
EVENING. THE NAM IS THE MOST AGGRESSIVE WITH THIS FEATURE...AND
IS SLIGHTLY FURTHER WEST THAN THE GFS AND IN SOME RESPECTS THE EC.
AS A RESULT IT IS ALSO A SIGNIFICANT OUTLIER IN BRINGING MUCH MORE
SNOW FROM THE ANCHORAGE BOWL TO THE MATANUSKA VALLEY THIS
EVENING THAT COULD CONTINUE INTO FRIDAY MORNING. WHILE THIS IS A
POSSIBLE SCENARIO...THE GFS WAS THE PREFERRED TRACK FOR THIS
WAVE...AS IT WAS MORE CONSISTENT WITH THE CURRENT FORECAST BY
BRINGING A BRIEF ROUND OF ACCUMULATING SNOW TO SOUTHCENTRAL THIS
EVENING. LATER ON IN THE FORECAST THERE IS SOME MINOR DISAGREEMENT
WITH BOTH THE TRACK OF A NORTH PACIFIC LOW APPROACHING THE GULF
AND ANOTHER WEAKER LOW THAT WILL CLIP THE WESTERN ALEUTIANS LATE
FRIDAY...BUT THESE ARE FAIRLY MINOR AND WILL HAVE LITTLE IMPACT ON
FORECAST CONFIDENCE.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
A FRONTAL SYSTEM WILL SLIDE NORTHWESTWARD ACROSS SOUTH CENTRAL
ALASKA TODAY AND TONIGHT. THIS SYSTEM IS NOT VERY STRONG AND
PRECIPITATION AMOUNTS ARE EXPECTED TO BE LIGHT. WITH WEAK
GRADIENTS AND WEAK MID/UPPER WINDS...THERE WILL NOT REALLY BE ANY
DOWN-SLOPE ISSUES AND SOME PRECIPITATION WILL MAKE IT TO MANY
INLAND AREAS. THE WESTWARD EXTENT OF PRECIPITATION WILL REACH
ABOUT TO TALKEETNA LATE TONIGHT...THEN BEGIN TO RETREAT EASTWARD.
THE SYSTEM WILL RAPIDLY DISSIPATE ON FRIDAY AS THE POSITIVELY
TILTED BERING RIDGE PUSHES INTO THE AREA FRIDAY AND FRIDAY NIGHT.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
AS HIGH PRESSURE BUILDS OVER THE BERING SEA AND SOUTHWEST
MAINLAND...CLEAR AND COLD CONDITIONS WILL CONTINUE THROUGH THE END
OF THE WEEK. THE STRONGEST WINDS WILL GENERALLY BE ALONG THE COAST
DURING THIS PERIOD.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
HIGH PRESSURE WILL CONTINUE TO BUILD OVER THE BERING SEA THROUGH
FRIDAY...WHILE THE LOW SOUTH OF THE ALEUTIANS MOVES SOUTHWARD.
THIS WILL BRING MAINLY DRY AND SUNNY CONDITIONS TO THE ALEUTIANS
AND BERING SEA. ANOTHER LOW WILL MOVE NORTHWARD INTO THE WESTERN
BERING SEA ON FRIDAY...BRINGING SOME STRONGER WINDS TO THE WESTERN
ALEUTIANS.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
FORECAST THINKING REMAINS LARGELY UNCHANGED FOR THIS WEEKEND INTO
THE MIDDLE OF NEXT WEEK AS A DRY OFFSHORE FLOW PATTERN DOMINATES
THE MAINLAND WITH HIGH PRESSURE OVERHEAD AND A BROAD NORTH PACIFIC
LOW WELL SOUTH OF THE ALASKA PENINSULA. THIS WILL KEEP ANY
PRECIPITATION LARGELY CONFINED TO THE SOUTHERN GULF AND KODIAK
ISLAND...WHILE A FAVORABLE PRESSURE GRADIENT AND VERY COLD AIR
DRAINING OUT OF THE COPPER RIVER BASIN WILL COMBINE TO PRODUCE
STRONG GAP WINDS THROUGH FAVORED AREAS ALONG THE NORTH GULF COAST
WELL INTO NEXT WEEK. MEANWHILE...TEMPERATURES WILL CONTINUE TO
GRADUALLY MODERATE TO NEAR NORMAL VALUES BY THE WEEKEND. MODELS
HAVE STARTED TO KEY IN ON AN ARCTIC TROUGH DIGGING THROUGH THE
SOUTHWEST MAINLAND BY MIDWEEK...BRINGING SOME COLDER TEMPERATURES
AND PRECIPITATION BACK TO THE SOUTHERN MAINLAND.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WIND CHILL ADVISORY 131.
MARINE...GALE WARNING 127 155 165 170 172 173 174 175 176 179 180.
         HEAVY FRZ SPRAY 160 180.
FIRE WEATHER...NONE.

&&

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