Small Craft Advisory 50, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
200 PM AKST SUN JAN 17 2010

.ANALYSIS AND UPPER LEVELS...
A BROAD POLAR UPPER LEVEL TROUGH CONTINUES TO SLOWLY DIG SOUTHWARD
ACROSS WESTERN ALASKA AND THE EAST BERING SEA. A CLOSED UPPER LEVEL
LOW IS EMBEDDED WITHIN THIS TROUGH OF LOW PRESSURE 200 MILES SOUTH OF
THE ALASKA PENINSULA. THIS TROUGH IS FLANKED BY RIDGES OF HIGH
PRESSURE ON EITHER SIDE...ONE OVER CENTRAL BRITISH COLUMBIA AND
ANOTHER BUILDING OVER THE WESTERN ALEUTIANS.

AT THE SURFACE...TWO DISTINCT LOW PRESSURE SYSTEMS RESIDE UNDER THE
GULF OF ALASKA LOW. ONE 965 MB LOW 50 MILES EAST OF KODIAK IS
BRINGING SHOWERS TO MUCH OF THE NORTHERN GULF AND PRINCE WILLIAM
SOUND. THE SECOND 967 MB LOW IS POSITIONED 300 MILES SOUTH OF SAND
POINT. A BROAD TROUGH TRAILS BEHIND THE LATTER LOW...EXTENDING
WESTWARD ALONG THE 50N PARALLEL TO 160E LONGITUDE. COLD AIR CONTINUES
TO FILTER SOUTHWARD ACROSS THE ALEUTIANS AND WESTERN ALASKA IN THE
WAKE OF THIS TROUGH. TWO SHORTWAVES WITH EMBEDDED LOW PRESSURE
SYSTEMS ARE ROTATING AROUND THE OUTSKIRTS OF THIS COMPLEX...WITH THE
NEAREST LOW RACING NORTHWARD NEAR THE SOUTHERN TIP OF THE ALASKA
PANHANDLE. THE SECOND LOW 400 MILES TO THE SOUTHWEST FOLLOWS QUICKLY
ON THE HEELS OF THE FIRST...AND IS POISED TO ROTATE INTO THE GULF OF
ALASKA ON MONDAY.

.MODEL DISCUSSION...
IN STARK CONTRAST TO YESTERDAY...THE MODELS NOW HAVE A MUCH BETTER
HANDLE ON THE GULF LOW. THOUGH THERE ARE SLIGHT DIFFERENCES IN THE
EXACT TRACK OF THE LOW. THE NAM AND GFS TAKE THE LOW NORTHWESTWARD
INTO COOK INLET WHILE THE EUROPEAN TRACKS THE LOW NORTH OVER THE
KENAI PENINSULA. THE GFS ALSO MAINTAINS A RESIDUAL OPEN WAVE TROUGH
OVER SOUTH CENTRAL ALASKA INTO TUESDAY WHILE THE OTHER MODELS QUICKLY
DISSIPATE THE LOW A DAY EARLIER.

THE MODELS ALSO ARE IN AGREEMENT IN THE NEAR SHORT TERM WITH THE
WESTERN LOW SOUTH OF THE AKPEN...BUT BEGIN TO DISAGREE IN THE
POSITION OF THE LOW BY TUESDAY MORNING. THE TRAILING TROUGH OF LOW
PRESSURE IS ALSO DEPICTED WELL...WITH THE NAM DEVELOPING A BRIEF
CLOSED LOW AT THE CREST OF THIS TROUGH ON MONDAY. THOUGH THE EXACT
TIMING IS IN QUESTION...THIS SYSTEM WILL BE QUICKLY ABSORBED BY A LOW
ADVANCING INTO THE GULF FROM THE SOUTHEAST AROUND MIDWEEK. WITH THE
MODELS REMAINING CONSISTENT AND IN GOOD AGREEMENT...FEW CHANGES WERE
MADE TO THE OVERALL FORECAST PACKAGE.

.SHORT TERM FORECAST...
.SOUTHCENTRAL...THE MAIN FORECAST CHALLENGE IS HOW MUCH SNOW THE LOW
IN THE NORTHERN GULF WILL PRODUCE AS IT MOVES INLAND TONIGHT. THE OFF
HOUR RUNS OF THE GFS AND NAM INCREASE THE CHANCE OF PRECIP ACROSS THE
ANCHORAGE BOWL AND LOWER SUSITNA VALLEY LATE THIS EVENING...WHICH IS
CONSISTENT WITH A CHANGE OF UPPER LEVEL WIND DIRECTION FROM
SOUTHEAST TO SOUTH. THIS SLIGHT SHIFT IN THE MOISTURE SOURCE COUPLED
WITH THE INCREASED INSTABILITY SHOULD LEAD TO LIGHT SNOW DEVELOPING
FROM THE NORTHERN KENAI PENINSULA UP TO THE SUSITNA VALLEY. MEANWHILE
THE ASSOCIATED OCCLUSION WILL MOVE OVER PRINCE WILLIAM SOUND AND GIVE
VALDEZ A FAVORABLE SETUP FOR MORE SIGNIFICANT SNOWFALL OVERNIGHT AND
MONDAY MORNING.

CONDITIONS IMPROVE ACROSS SOUTHCENTRAL MONDAY AFTERNOON AS SHORTWAVE
RIDGING BUILDS FROM THE YUKON TERRITORY AND EXTENDS INTO OUR AREA OF
RESPONSIBILITY. SCATTERED RAIN AND SNOW SHOWERS WILL CONTINUE THROUGH
MID WEEK ALONG THE COAST WHILE THE INTERIOR STAYS PARTLY TO MOSTLY
CLOUDY WITH SLIGHTLY ABOVE AVERAGE TEMPERATURES.

.SOUTHWEST...MID AND HIGH LEVEL CLOUDS ARE HELPING TO MODERATE
TEMPERATURES THIS MORNING AND EARLY AFTERNOON. WINDS HAVE ALSO
SLIGHTLY DIMINISHED FROM THE PREVIOUS 48 HOURS ACROSS THE KUSKOKWIM
DELTA...ALTHOUGH THE WIND CHILL ADVISORY REMAINS IN EFFECT THROUGH
TUESDAY WITH LOCAL WIND CHILLS STILL REACHING 40 BELOW. SOME MOISTURE
HAS CROSSED THE ALEUTIAN AND ALASKA RANGE ALONG THE ALASKA
PENINSULA...RESULTING IN LIGHT SNOW ALONG IN THIS REGION. THE WARM
ADVECTION ALOFT WILL CONTINUE TO MOVE ACROSS SOUTHWEST ALASKA THROUGH
TUESDAY AS AN UPPER LEVEL TROUGH DIGS OVER THE EASTERN BERING SEA.
THIS RETURN FLOW WILL HELP KEEP CLOUDS AND A CHANCE OF LIGHT SNOW
ACROSS THE REGION. TEMPERATURES WILL CONTINUE TO REBOUND TO MORE
CLIMATOLOGICALLY NORMAL VALUES.

.BERING SEA/ALEUTIANS...FORECAST IS AS STRAIGHT FORWARD AS IT GETS
FOR JANUARY IN THE BERING SEA. COLD AIR ADVECTING SOUTH RESULTING IN
WIDESPREAD SHOWER ACTIVITY THROUGH MID WEEK. HIGH PRESSURE BUILDS
ACROSS THE CENTRAL BERING WEDNESDAY AHEAD OF A STRENGTHENING SYSTEM
MOVING OUT OF EASTERN SIBERIA TOWARD THE END OF THE WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...WIND CHILL ADVISORY 155
MARINE...GALE...155 160 165 170 171 172 180 195
    HEAVY FREEZING SPRAY...160 165 170 171 179 185
FIRE WEATHER...NONE

KS/AB JAN 10