Snow Advisory 10, NWS Fairbanks, AK

NORTHERN ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FAIRBANKS AK
335 PM AST SUN DEC 11 2005

.DISCUSSION...
THE SOMETIMES ELUSIVE COURSE OF RECENT CIRCULATION IN ALASKAS
OCTANT OF THE WORLD IS AGAIN A FACTOR IN THE DIVERGENCE OF THE
COMPUTER FORECASTS TODAY, BOTH IN THE SHORT AND MEDIUM TERM.
RARELY IS THE DISAGREEMENT AS MUCH AS NOW.

FIRST, THE SHORT TERM. THE ETA MODEL FORECAST IS SLOWER BRINGING
THE UPCOMING PACIFIC LOW PRESSURE SYSTEM TO BRISTOL BAY THAN IT
WAS YESTERDAY. INSTEAD OF A TUESDAY ARRIVAL, TODAYS CHARTS SHOW
AN ARRIVAL LATE TUESDAY NIGHT/WEDNESDAY MORNING. THE GFS MODEL,
RUN 6 HOURS LATER, DOES NOT BRING THE LOW IN UNTIL WEDNESDAY
AFTERNOON, WITH A FOLLOWING SYSTEM MUCH LIKE ITS PREDECESSOR,
ARRIVING MID DAY FRIDAY. OF THE TWO MODELS, THE ETA APPEARS MORE
REALISTIC. SATELLITE IMAGERY SHOWS A STRONG MASS OF CLOUDS
CENTERED NEAR 40 DEGREES NORTH BETWEEN 170 DEGREES EAST AND THE
DATELINE, HEADING EAST NORTHEASTWARD, AND VERY LIKELY TO TURN THE
CORNER UP TOWARD BRISTOL BAY IN 24 HOURS. THE OVERALL RESULT FROM
THESE FORECASTS IS CONSISTENT WITH A REWARMING OF MAINLAND ALASKA
STARTING 2 DAYS AND CONTINUING FOR THE REST OF THIS WEEK.

BOTH THE GFS AND THE ETA FORECAST A STRONG TROUGH ALOFT TO MOVE
NORTHEASTWARD OVER THE INTERIOR TONIGHT. BOTH MODELS FORECAST STRONG
COLD ADVECTION AROUND 850 HPA TONIGHT, SO THE FORECAST PACKAGES
ALL HAVE AN OUTBREAK OF SNOW IN THE WORKS FOR THE INTERIOR
STARTING LATER TONIGHT. THE CHANGE FROM YESTERDAY IS THAT THE GFS
IS NOT AS WEAK ON THE COLD ADVECTION FORECAST, AND MORE IN LINE
WITH THE ETA, WHICH APPEARS TO HAVE PROJECTED IT RIGHT IN EARLIER
MODEL RUNS.

THE CYCLONIC CIRCULATION OF SATURDAY DEPARTED THE NORTH SLOPE LAST
NIGHT, AND LOTS OF CLEAR OR VFR WEATHER PREVAILS EAST OF
WAINWRIGHT. A LOW ALOFT AND WEAK SURFACE LOW OVER KOTZEBUE SOUND
CONTINUE A NORTHWARD TRACK AROUND 20 KNOTS, BRINGING OVERCAST
SKIES AND SNOW TO NORTHWEST ALASKA. THE IMPACT OF THIS SYSTEM ON
THE ARCTIC COAST LOOKS LIKE IT WILL BE LIMITED TO THE SECTION FROM
POINT HOPE TO WAINWRIGHT TONIGHT AND MONDAY MORNING.

IN THE WEST, OVERCAST SKIES AND SOME FLURRIES WILL PREVAIL THROUGH
MONDAY/MONDAY NIGHT, WITH BREAKS IN THE CLOUDS MOVING IN FROM THE
SOUTH MONDAY NIGHT/TUESDAY.

IN THE INTERIOR, THE SNOW WILL BEGIN TAPERING OFF FROM THE WEST
MONDAY AFTERNOON, AND WILL LINGER OVER ONLY THE BROOKS RANGE BY
MID DAY TUESDAY.

THE MEDIUM RANGE FORECASTS HAVE VERY LARGE AND PUZZLING
DIFFERENCES TODAY. THE OUTCOME THROUGH WEDNESDAY MORNING IS
SIMILAR FOR BOTH, SHOWING A RIDGE ALOFT BEGINNING TO BUILD OVER
THE ALASKA MAINLAND AT THAT TIME. BY SATURDAY MORNING, THE TWO
HAVE GONE VERY DIFFERENT WAYS. THE GFS (GLOBAL FORECAST SYSTEM,
U.S.)  PREDICTS A VIGOROUS SHORT WAVE ALOFT TO MOVE SOUTHESTWARD
DOWN OVER THE EASTERN BROOKS RANGE, WITH A LARGE HIGH ALOFT
AGGRESSIVE BUILDING OVER THE WEST CHUKCHI SEA. THE MAGNITUDE OF
THE RIDGE ALOFT SEEMS UNREALISTIC. THE ECMWF (EUROPEAN) MODEL
FORECASTS A PERSISTENT LOW PRESSURE AREA ALOFT OVER THE CHUKCHI
SEA SATURDAY AND SUNDAY, WITH THE RIDGE ALOFT OVER WESTERN NORTH
AMERICA CONTINUING TO BUILD UP TOWARD THE YUKON TERRITORY. THE
ECMWF MODEL LOOKS MORE REALISTIC THAN THE GFS. BY WEDNESDAY, THE
ECMWF MODEL HAS A MAJOR AND PRESUMABLY LONG LIVED CHINOOK IN
PROGRESS FROM THE SUBTROPICS NORTH OF HAWAII UP OVER ALL OF THE
ALASKA MAINLAND. THIS LOOKS LIKE A STANDARD PINEAPPLE EXPRESS,
AS WE OFTIMES CALL IT, AND RESONABLE CAUSE TO EXPECT A PERIOD OF
WELL ABOVE NORMAL TEMPERATURES FOR MUCH OF THE REALM.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

TF DEC 05