Small Craft Advisory 170, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
440 AM AKST MON FEB 23 2015

.ANALYSIS AND UPPER LEVELS...
AN UPPER LEVEL CLOSED LOW IS POSITIONED OVER THE KAMCHATKA
PENINSULA WITH AN ASSOCIATED TROUGH EXTENDING THROUGH THE BERING
SEA AND INTO THE NORTHERN PACIFIC. AT THE SURFACE THERE IS A WEAK
LOW OVER THE WESTERN TO CENTRAL BERING SEA THIS MORNING. THIS IS
RESULTING IN BROAD SOUTHWESTERLY FLOW THROUGH MAJORITY OF THE GULF
WITH SCATTERED SHOWERY PRECIPITATION. IN THE SOUTHCENTRAL
AREA...THERE IS A WEAK SHORTWAVE WITH THE RADAR IMAGERY SHOWING
NUMEROUS RAIN SHOWERS IN THE COOK INLET...KENAI PENINSULA...
NORTHERN GULF AND PRINCE WILLIAM SOUND REGIONS. AT THE
SURFACE...THE TEMPERATURES ARE BEING REPORTED IN THE LOWER 40S
ALONG THE COAST...THE MID 30S INLAND AND IN UPPER COOK INLET.

THE SOUTHWEST ALASKA REGION HAS A UPPER LEVEL TROUGH LOCATED JUST
SOUTH OF KODIAK EXTENDING THROUGH THE EASTERN BERING SEA. THE
RADAR IMAGERY HAS NUMEROUS RAIN AND SNOW SHOWERS IN THE BRISTOL
BAY AND KUSKOKWIM DELTA REGION MOVING FROM SOUTH TO NORTH. THE 850
MB TEMPERATURES ARE SHOWING COLDER AIR MOVING INTO THE EASTERN
BERING SEA AND INTO THE SOUTHWEST ALASKA REGION. THIS WILL CHANGE
THE PRECIPITATION TO ALL SNOW AS THE TROUGH CONTINUES TO MOVE
THROUGH THE REGION TODAY. IN THE EASTERN GULF OF ALASKA...THERE IS
A SOUTHERLY 120 KNOT MERIDIONAL JET STREAK WHICH WILL CONTINUE TO
BRING MOIST SUBTROPICAL AIR TO THE SOUTHCENTRAL REGION. THIS JET
WILL ALSO CONTINUE TO STRENGTHEN THE AMPLIFIED UPPER LEVEL RIDGE
OVER THE BRITISH COLUMBIA AREA EXTENDING TO THE NORTHWEST INTO THE
YUKON TERRITORY.

&&

.MODEL DISCUSSION...
THE MODELS WERE IN GOOD AGREEMENT WITH MINOR DIFFERENCES IN THE
DIFFERENT SYNOPTIC FEATURES. THE NAM AND GEM-REG DEPICT A WEAK
LOW IN THE CENTRAL BERING SEA...WHILE THE EC AND GFS SHOW A
TROUGH. THIS FEATURE WILL TRACK NORTHWARD INTO THE KAMCHATKA
PENINSULA BY MONDAY EVENING AND BRING SOUTHWESTERLY FLOW TO
SOUTHWEST ALASKA. BY TUESDAY A NORTH PACIFIC LOW WILL TRACK SOUTH
OF THE EASTERN ALEUTIANS AND THE MODELS ARE STRUGGLING WITH THE
POSITION OF THIS SYSTEM. THE NAM CONTINUES TO BE THE OUTLIER
TRACKING THIS LOW FASTER TO THE NORTHEAST THAN THE OTHER MODELS.
THE PREFERRED MODELS OF CHOICE WERE THE GEM-REG TRANSITIONING TO
THE GFS/ECMWF MODELS BY TUESDAY. THE FORECAST CONFIDENCE REMAINS
AVERAGE STARTING OUT THE WORK WEEK.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
A FINAL SHOT OF MOISTURE WILL PUSH THROUGH SOUTH CENTRAL ALASKA
TODAY AS AN UPPER LEVEL SYSTEM FROM THE SOUTHWEST SLIDES THROUGH
THE AREA. COLDER AIR WILL FOLLOW THIS SYSTEM...CLOSE ENOUGH THAT
SOME SNOW COULD FALL ON THE TAIL END OF THE PRECIPITATION LATER
TODAY IN THE COOK INLET AREAS. PRECIPITATION HAS BEEN HEAVY ENOUGH
THAT THE RAIN HAS TURNED TO SNOW IN VALDEZ AND MUCH OF THE COPPER
RIVER BASIN. BOTH OF THESE AREAS WILL LIKELY TRANSITION BACK AND
FORTH FROM RAIN TO SNOW DEPENDING ON THE INTENSITY OF THE
PRECIPITATION. PRECIPITATION WILL CLEAR ALL OF SOUTH CENTRAL
ALASKA TONIGHT AS AN UPPER LEVEL RIDGE BUILDS IN BEHIND THE
EXITING WEATHER SYSTEM. ANOTHER WEATHER SYSTEM WILL MOVE INTO THE
GULF FROM THE SOUTHWEST LATE TUESDAY AND TUESDAY NIGHT. THE
NUMERICAL MODELS CURRENTLY INDICATE THAT PRECIPITATION FROM THIS
WILL STAY OVER THE GULF...MAYBE JUST CLIPPING SOME GULF COAST
COMMUNITIES TUESDAY NIGHT AND EARLY WEDNESDAY.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
A WEAK COLD FRONT CONTINUES TO PROGRESS THROUGH SOUTHWEST THIS
MORNING...WITH SNOW SHOWERS IMPACTING MOST OF THE REGION. THE
UPPER LEVEL LOW ASSOCIATED WITH THE FRONT WILL MAKE RAPID PROGRESS
TOWARD THE NORTHEAST...WITH DECREASING SHOWERS AND CLEARING SKIES
THROUGH THE DAY. THIS SHOULD ALLOW FOR A RAPID DECREASE IN
TEMPERATURES OVERNIGHT...WITH COOLER (THAN THE PRECEDING
DAYS) TEMPERATURES LINGERING THROUGH TUESDAY. ANOTHER WEAK FRONT
WILL CLIP PARTS OF THE KUSKOKWIM DELTA MONDAY NIGHT AND
TUESDAY...BRINGING WITH IT A THREAT FOR LIGHT SNOW.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
A TROUGH OF LOW PRESSURE ALOFT OVER THE WESTERN BERING SEA WILL
MAKE EASTWARD PROGRESS THROUGH TONIGHT BEFORE IT MOVES INLAND
TUESDAY MORNING. SNOW SHOWERS WILL IMPACT PORTIONS OF THE WESTERN
ALEUTIANS AND PRIBILOF ISLANDS...WITH ACTIVITY WANING FROM WEST TO
EAST. WEAK HIGH PRESSURE WILL KEEP THE CENTRAL AND EASTERN
ALEUTIANS LARGELY DRY THROUGH TUESDAY. A STRONGER MAX GALE FORCE
LOW AND ASSOCIATED FRONT WILL BEGIN IMPACTING THE WESTERN
ALEUTIANS TUESDAY AND TUESDAY NIGHT...WITH MORE WIDESPREAD RAIN
AND SNOW.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
UPPER LEVEL RIDGING WILL BEGIN BUILDING OVER THE EASTERN
ALEUTIANS AND ALASKA PENINSULA ON WEDNESDAY WHILE A LOW PRESSURE
SYSTEM IN THE SOUTHWESTERN GULF TRACKS EAST. A FRONTAL SYSTEM
STRETCHED ACROSS THE WESTERN ALEUTIANS AND BERING WILL LIFT NORTH
WHILE ANOTHER WAVE TO THE SOUTH DEVELOPS AND FOLLOWS IT NORTH OF
UP THE BOUNDARY. THE RIDGE ALOFT WILL CONTINUE TO AMPLIFY
WEDNESDAY NIGHT AND THURSDAY SHIFTING EAST TO BE CENTERED OVER THE
GULF AND MAINLAND ALASKA BRINGING WIDESPREAD DRY WEATHER TO ALL
BUT THE ALEUTIANS.

THE NEXT FRONTAL SYSTEM WILL TRACK NORTH TO THE ALASKA PENINSULA
ON FRIDAY BRINGING A BRIEF RETURN TO WETTER WEATHER. THIS LOW
PRESSURE SYSTEM WILL THEN GET CAUGHT UP BY A FAST MOVING WESTERLY
UPPER LEVEL SHORTWAVE TROUGH OVER NORTHERN ALASKA AND LIFTED
RAPIDLY EAST UP AND OVER THE RIDGE FLATTENING THE RIDGE TO MORE
ZONAL WESTERLY FLOW IN THE PROCESS. WHILE THE SURFACE LOW WILL
STAY CLOSE TO THE GULF COAST THE FRONT WILL SPREAD OVER SOUTHWEST
ALASKA FRIDAY NIGHT...SOUTH CENTRAL ALASKA ON SATURDAY AND THEN
CONTINUE SOUTHEAST INTO THE PANHANDLE SATURDAY NIGHT AND SUNDAY. A
STRONG UPPER LEVEL RIDGE WILL REBUILD RAPIDLY BEHIND THIS
SYSTEM...QUICKLY DRYING CONDITIONS BACK OUT AGAIN AND BRINGING THE
POTENTIAL FOR NORTHERLY OUTFLOW WINDS TO SOUTH CENTRAL ALASKA SUNDAY.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 177 178 411.
HEAVY FREEZING SPRAY 185 411.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...PD
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
LONG TERM...JER