Small Craft Advisory 77, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
400 PM AKST WED JAN 23 2013

.ANALYSIS AND UPPER LEVELS...A WEAK UPPER LEVEL RIDGE IS CENTERED
NEAR THE BERING STRAIT AND EXTENDS OVER THE INTERIOR OF THE STATE AS
WELL AS INTO THE ARCTIC. A WEAK UPPER LEVEL LOW IS CENTERED SOUTH OF
THE ALASKA PENINSULA WITH A TROUGH EXTENDING TO THE NORTH GULF COAST.
AN UPPER LEVEL TROUGH IS ENTERING THE NORTHEAST CORNER OF THE STATE
AND WILL DROP INTO THE INTERIOR OVERNIGHT AND REACH THE ALASKA RANGE
LATER IN THE DAY TOMORROW. THIS TROUGH WILL BECOME FOCUS FOR SOME
SNOW IN THE SUSITNA VALLEY AND COPPER RIVER BASIN TOMORROW INTO
TOMORROW NIGHT.
THE JET STREAM REMAINS WELL TO THE SOUTH OF THE FORECAST AREA.

AT THE SURFACE THE HIGH IS CENTERED WELL INTO THE ARCTIC NEAR 80N BUT
THE RIDGE EXTENDS INTO THE CENTRAL BERING SEA AND THEN INTO THE NORTH
PACIFIC. THERE ARE TWO SURFACE LOWS THAT ARE INTERCONNECTED. THE
FIRST IS IN THE WESTERN GULF OF ALASKA WHICH IS WEAKENING AS IT IS
BEING PULLED INTO A SLIGHTLY STRONGER LOW THAT IS SOUTH OF THE ALASKA
PENINSULA. ANOTHER LOW TO NOTE IS A 970 MB LOW SOUTH OF ATTU AND
MOVING NORTHWARD. THIS STORM WILL IMPACT THE WESTERN AND CENTRAL
ALEUTIANS TOMORROW INTO FRIDAY.

.MODEL DISCUSSION...MODELS ARE IN VERY NICE AGREEMENT TODAY WITH THE
MODEL SOLUTIONS ALL IN AGREEMENT WITH THE MAJOR FEATURES OVER THE
NEXT FEW DAYS. SOME UNCERTAINTY DOES BEGIN TO CREEP IN ON SATURDAY IN
THE ALEUTIAN ISLANDS AND SOUTHERN BERING SEA AS THE GFS MODEL IS A
LITTLE SLOWER IN MOVING THE LOW NEAR ATTU WESTWARD AND THERE IS A
DIFFERENCE IN TIMING IN REGARDS TO A LOW HEADING OUT OF THE PACIFIC
TOWARD DUTCH HARBOR. THE GOOD NEWS IS THAT ALL THE MODELS DO AVE THIS
FEATURE AND IT IS LIKELY THAT SUCCESSIVE MODEL RUNS WILL SEE
CONVERGENCE TOWARD A COMMON SOLUTION.
CONFIDENCE IN THE MODELS RAPIDLY DECREASES THROUGH THE WEEKEND AS
THERE IS A LARGE DIVERGENCE BETWEEN THE ECMWF AND GFS MODELS BY
SUNDAY.

.SHORT TERM FORECAST...THE LOW IN THE WESTERN GULF IS WEAKENING BUT
IS STILL BRINGING SOME SNOW ALONG A DIFFUSE FRONTAL BOUNDARY THAT
STRETCHES OUT OF THE LOW AND THEN UP COOK INLET AND INTO THE COPPER
RIVER BASIN. THE SNOW ASSOCIATED WITH THIS SYSTEM WILL MAINLY BE
LIGHT THROUGH THIS EVENING AND THEN WILL CUT OFF FROM EAST TO WEST.
RAIN ALONG THE GULF COAST WILL ALSO END FROM EAST TO WEST OVERNIGHT.
AREAS FROM THE WESTERN KENAI PENINSULA THROUGH MATANUSKA VALLEY ARE
MAINLY SHELTERED FROM THE PRECIPITATION BY THE DOWN SLOPE OFF THE
KENAI AND CHUGACH MOUNTAINS. THIS DOWN SLOPE IS A BIG DEAL IN THE
ANCHORAGE AREA AS THE TEMPERATURE PROFILE ALOFT IS CONDUCIVE FOR
FREEZING RAIN BUT THE PRECIPITATION IS NOT MAKING IT INTO THE AREA.
THE BIG WEATHER FEATURE IN SOUTH CENTRAL ALASKA TOMORROW INTO FRIDAY
WILL BE THE UPPER LEVEL TROUGH MOVING IN FROM THE NORTH IN
CONJUNCTION WITH AN INVERTED TROUGH THAT DEVELOPS INTO A MESO-SCALE
LOW OVER NORTHERN COOK INLET LATE THURSDAY. THIS COMBINATION OF LIFT
AND AVAILABLE MOISTURE WILL BRING SNOW ALONG THE ALASKA RANGE BY
EARLY THURSDAY...WHICH WILL MOVE SOUTHWARD AS THE DAY PROGRESSES.
THIS SNOW WILL LIKELY MAKE IN INTO THE ANCHORAGE AREA AFTER MIDNIGHT
THURSDAY NIGHT AND PERSIST THROUGH FRIDAY MORNING. SINCE THE MAIN
ENERGY IS WEAKENING AS THIS TROUGH MOVES SOUTHWARD THERE MAY NOT BE
MUCH PRECIPITATION THAT FALLS OVER THE WESTERN KENAI PENINSULA WITH
THIS SYSTEM.

SOUTHWEST MAINLAND ALASKA IS MOSTLY BEING INFLUENCED BY THE RIDGE IN
THE BERING SEA AND SOME CLOUDS OVERRUNNING THE RIDGE FROM THE
WEAKENING FRONT OVER SOUTH CENTRAL ALASKA. THE PART OF THE BRISTOL
BAY ZONE FROM KING SALMON AND NORTHEASTWARD MAY SEE SOME LIGHT SNOW
THURSDAY NIGHT WITH THE UPPER LEVEL WAVE BUT NOTHING SIGNIFICANT IS
EXPECTED. THE KUSKOKWIM DELTA WILL CONTINUE TO SEE SOME NORTH TO
NORTHEAST WINDS AND COLDER TEMPERATURES.
THE WESTERN ALEUTIANS WILL SEE SOME RAIN AND STRONG WINDS MOVE INTO
THE AREA THURSDAY AS THE LOW APPROACHES THE AREA FROM THE SOUTH.

.LONG TERM FORECAST...THE LONG TERM FORECAST PROBLEMS CONTINUE AND
THEREFORE CREATE LOW CONFIDENCE IN THE PARTICULARS OF THE EXTENDED
FORECASTS. WHAT DOES LOOK LIKELY IS FOR SOME MODERATE SOUTHERLY UPPER
LEVEL FLOW TO MOVE OVER SOUTHWEST AND SOUTH CENTRAL ALASKA EARLY NEXT
WEEK. THIS SHOULD MODERATE THE TEMPERATURES ONCE AGAIN AFTER A CHILLY
WEEKEND. THE EXTENT OF THIS WARM UP IS YET TO BE DETERMINED.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE 175. STORM 176. HEAVY FREEZING SPRAY 185.
FIRE WEATHER...NONE.

JAN 13