Small Craft Advisory 658, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
134 PM AKDT SUN AUG 31 2014

.ANALYSIS AND UPPER LEVELS...
THERE IS A DEEP UPPER LEVEL LOW CENTERED OVER THE ARCTIC OCEAN TO
THE NORTHWEST OF ALASKA. THERE IS AN UPPER LEVEL RIDGE OVER THE
WESTERN BERING SEA. A WEAK SHORT-WAVE TROUGH IS OVER THE
CENTRAL/EASTERN ALEUTIANS AND ALASKA PENINSULA WHICH IS MOVING
TOWARDS THE SOUTH. THERE IS A WEAK SHORT-WAVE TROUGH OVER THE
KUSKOKWIM DELTA AND LOWER KUSKOKWIM VALLEY. THERE IS YET ANOTHER
WEAK TROUGH OVER THE COPPER RIVER BASIN. THERE IS A STRONGER
TROUGH OVER EXTREME NORTHEAST RUSSIA MOVING RAPIDLY WESTWARD.

&&

.MODEL DISCUSSION...
THE NUMERICAL MODELS ARE IN GOOD AGREEMENT THROUGH ABOUT 48
HOURS...THEN BEGIN TO DIVERGE. THE MAIN ARE OF DISAGREEMENT AFTER
48 HOURS IS HOW THE MODELS HANDLE THE ENTRAINMENT OF NORTH PACIFIC
MOISTURE INTO THE ARCTIC JET STREAM OVER ALASKA. THE AMERICAN
MODELS SEEM TO BE A LITTLE FASTER AND MORE AGGRESSIVE WITH
PUSHING THE MOISTURE NORTH (ESPECIALLY THE NAM) WHILE THE ECMWF
AND CANADIAN NH GEM PREFER TO KEEP THE MOISTURE SEPARATED AND A
LITTLE FURTHER SOUTH.

&&

.SHORT TERM FORECAST...

FOR SOUTH CENTRAL ALASKA...THE WEAK TROUGH THAT HAS BEEN OVER THE
COPPER RIVER BASIN THE LAST FEW DAYS WILL FINALLY MOVE EAST LATER
TONIGHT. THIS WILL BE IN RESPONSE TO THE SYSTEM CURRENTLY OVER
NORTHEAST RUSSIA...WHICH WILL PUSH INTO SOUTHWEST ALASKA LATE
TONIGHT AND INTO SOUTH CENTRAL MONDAY NIGHT AND TUESDAY. NOT MUCH
PRECIPITATION IS EXPECTED FROM THIS SYSTEM DUE TO THE WESTERLY
FLOW ALOFT...WITH THE BEST CHANCES OVER THE SUSITNA VALLEY AND
NORTHERN COPPER RIVER BASIN. FLOW ALOFT WILL BACK TO A LITTLE MORE
SOUTHWESTERLY ON WEDNESDAY WHICH MAY SPREAD SOME SHOWERS
SOUTHWARD. ALSO ON WEDNESDAY...MOISTURE OVER THE NORTH PACIFIC
WILL BE DRAWN NORTHEASTWARD TOWARD SOUTHERN ALASKA. AS MENTIONED
IN THE PREVIOUS SECTION...SOME UNCERTAINTY EXISTS AS TO WHERE THIS
MOISTURE WILL GO. THERE IS A CHANCE SOME OF IT WILL GET TO KODIAK
ISLAND...BUT FURTHER NORTHWEST THAN THAT IS UNLIKELY.

FOR SOUTHWEST ALASKA...THE WEAK TROUGH OVER THE LOWER KUSKOKWIM
AND KUSKOKWIM DELTA WILL PROVIDE A CHANCE OF SHOWERS OVERNIGHT.
BETTER CHANCES OF PRECIPITATION WILL PUSH SOUTH AND EAST ON MONDAY
AS THE NEXT STRONGER SYSTEM MOVES ACROSS THE AREA. THE SYSTEM
ITSELF WILL MAINLY MOVE ACROSS THE INTERIOR...SO FURTHER NORTH
AREAS ARE MOST LIKELY TO SEE PRECIPITATION. SOME LINGERING SHOWERS
ARE POSSIBLE THROUGH WEDNESDAY IN THE WESTERLY FLOW ALOFT.

FOR THE BERING SEA/ALEUTIANS...AS THE ALEUTIAN/PENINSULA TROUGH
MOVES SOUTHWARD TONIGHT...THE WESTERN BERING RIDGE WILL PUSH INTO
THE SOUTHERN BERING AND ALEUTIANS. THIS RIDGE WILL BASICALLY
REMAIN IN PLACE THROUGH WEDNESDAY. LOW PRESSURE TO THE NORTH WILL
PROVIDE FAIRLY BREEZY CONDITIONS ACROSS THE NORTHERN BERING...WITH
THE STRONGEST WINDS TONIGHT INTO MONDAY AS THE NORTHEAST RUSSIAN
SYSTEM MOVES OVER THE BERING STRAIT AND INTO MAINLAND ALASKA.

&&

.LONG TERM FORECAST (SEP 4TH - SEP 7TH)...
THE SOUTH CENTRAL MAINLAND AND THE NORTHERN GULF WILL BE UNDER
THE INFLUENCE OF AN UPPER LEVEL RIDGE. THIS WILL BRING A BRIEF
PERIOD OF DRIER CONDITIONS BY MIDWEEK BEFORE AN INCREASE IN CLOUDS
AND PRECIPITATION AS A NORTH PACIFIC LOW TRACKS TOWARDS THE
EASTERN ALEUTIANS HEADING INTO NEXT WEEKEND. AN UPPER LEVEL TROUGH
WILL DROP THROUGH THE NORTHERN AND CENTRAL BERING SEA BY MIDWEEK.
THIS WILL BRING COOLER TEMPERATURES WITH SCATTERED SHOWERS AND
NORTHERLY FLOW TO SOUTHWEST ALASKA HEADING INTO FRIDAY. THE
CENTRAL AND WESTERN BERING SEA WILL HAVE STRATUS AND FOG AS HIGH
PRESSURE BUILDS INTO THE AREA HEADING INTO THE WEEKEND. BY
THURSDAY A NORTH PACIFIC LOW WILL TRACK SOUTH OF EASTERN ALEUTIANS
AND MOVE INTO THE NORTHERN GULF BY SATURDAY. THIS WILL RESULT IN
NORTHEASTERLY WINDS WITH AN INCREASE IN CLOUDS AND PRECIPITATION
ALONG THE STORM PATH GOING INTO THE WEEKEND. A SECOND NORTH
PACIFIC LOW WILL APPROACH THE CENTRAL ALEUTIANS BY SATURDAY
AFTERNOON BRINGING MORE MOISTURE AND PRECIPITATION WITH
NORTHEASTERLY WINDS WHICH WILL SPREAD INTO THE THE CENTRAL BERING
SEA FOR REST OF NEXT WEEKEND.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.
&&

LUDWIG/PLD AUG 14