Blizzard Watch 14, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
500 AM ADT MON APR 16 2007

.MODEL DISCUSSION...
OZ MODEL RUNS WERE IN GOOD AGREEMENT THROUGH TUESDAY MORNING...THEN
DIVERGED SIGNIFICANTLY IN THE CENTRAL TO EASTERN BERING/ALEUTIAN
REGION. AS AN UPPER LEVEL TROUGH MOVES EAST THROUGH THE REGION...THE
0Z GFS/UKMET/ECMWF HAVE TWO DISTINCT SURFACE LOWS BY TUESDAY
AFTERNOON...ONE BEING AROUND THE PRIBILOFS AND A NEW ONE
INTENSIFYING SOUTH OF SAND POINT. THE 0Z WRF...ON THE OTHER
HAND...HAS A SINGLE SURFACE LOW AROUND COLD BAY. STRONGLY PREFER THE
TWO LOW SOLUTION FOR SEVERAL REASONS. FIRST...GFS ENSEMBLE SPREAD IS
RELATIVELY SMALL. SECOND...THE UPPER LEVEL JET STRUCTURE SEEMS TO
SUPPORT TWO DISTINCT LOWS. IN USUAL WRF FORM...THE 6Z RUN HAS COME
IN COPYCATTING THE 0Z GFS...FURTHERING THE BELIEF THAT THE WRF WAS
THE ODDBALL MODEL IN THE FIRST PLACE. GFS HAS BEEN LESS THAN STELLAR
IN ITS PERFORMANCE...HOWEVER...AS THE GFS RUNS FROM TODAY HAD
TRENDED TOWARD THE ONE LOW SOLUTION...WHILE THE 0Z RUN WENT BACK TO
ITS TWO LOW SOLUTION OF LAST NIGHT.

AFTER THIS HICCUP IN THE MODELS...THEY ARE ACTUALLY QUITE CONSISTENT
LATE WEDNESDAY ONWARD.

.ANALYSIS AND UPPER LEVELS...
A WEAK SURFACE LOW IS PRESENT OVER THE NORTH CENTRAL GULF OF ALASKA
THIS MORNING...BRINGING SOME FAIRLY LIGHT VALLEY RAIN AND MOUNTAIN
SNOW TO WESTERN PRINCE WILLIAM SOUND/EASTERN KENAI...AND TO PORTIONS
OF KODIAK ISLAND. THIS LOW WILL DISSIPATE AS IT DRIFTS SOUTHEAST
TODAY...BRINGING A DECREASE IN THE PRECIPITATION. LIGHT FLOW AT
UPPER LEVELS IS PRESENT OVER THE MAINLAND THIS MORNING.

A MORE SIGNIFICANT SURFACE LOW IS PRESENT THIS MORNING APPROACHING
THE CENTRAL ALEUTIANS FROM THE SOUTHWEST...BRINGING WITH IT SNOW
CHANGING TO RAIN. THIS LOW HAS STRONG UPPER LEVEL JET SUPPORT. A
WEAK RIDGE OF HIGH PRESSURE IS PRESENT THIS MORNING OVER THE CENTRAL
TO EASTERN BERING AND ALEUTIANS.

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA AND THE GULF...
A WEAK SURFACE LOW IN THE NORTH CENTRAL GULF WILL DISSIPATE THIS
EVENING AS IT DRIFTS SOUTHEAST. AS THIS HAPPENS...PRECIPITATION WILL
ALSO TAPER OFF FROM KODIAK TO PRINCE WILLIAM SOUND.
OTHERWISE...TODAY LOOKS LIKE A QUIET DAY OVER SOUTHCENTRAL WITH
PERHAPS A FEW AFTERNOON CONVECTIVE SHOWERS OVER INTERIOR
SOUTHCENTRAL. WEAK HIGH PRESSURE BUILDS IN TONIGHT AND TUESDAY OVER
SOUTHCENTRAL. A STRONGER LOW PRESSURE WITH MORE JET SUPPORT WILL
BEGIN TO BRING RAIN TO KODIAK ON TUESDAY. THIS LOW SHOULD REMAIN IN
THE CENTRAL TO SOUTHERN GULF OF ALASKA INTO WEDNESDAY...THUS
PRECIPITATION WILL PROBABLY STAY SOUTHWEST OF AN ANCHORAGE TO
MIDDLETON ISLAND LINE. TEMPERATURES WILL REMAIN FAIRLY CLOSE TO
NORMAL THROUGH WEDNESDAY.

SOUTHWEST ALASKA...
FAIRLY QUIET WEATHER IS IN STORE TODAY OVER SOUTHWEST ALASKA...WITH
HIGH PRESSURE BUILDING IN FROM THE WEST. THE MAIN WEATHER CONCERNS
FOR TODAY WILL BE LOW CLOUDS ALONG THE COAST AS WELL AS SOME
ISOLATED TO SCATTERED SHOWERS. MORE SIGNIFICANT PRECIPITATION IS DUE
TUESDAY INTO WEDNESDAY AS AN ELONGATED TROUGH OF LOW PRESSURE MOVES
IN FROM THE WEST. PRECIPITATION WILL PROBABLY MAINLY FALL AS RAIN
TUESDAY AND TUESDAY NIGHT WITH A CHANGEOVER TO MOSTLY SNOW WEDNESDAY
AS COLDER AIR MOVES IN FROM THE WEST.

BERING SEA AND ALEUTIANS...
A STRENGTHENING LOW AND ASSOCIATED FRONT IS BRINGING MOSTLY
RAIN...POSSIBLY BEGINNING AS SNOW...TO MUCH OF THE ALEUTIANS TODAY.
THIS LOW WILL MOVE TO AROUND THE PRIBILOFS TUESDAY MORNING...THOUGH
PRECIPITATION WILL BEGIN WELL BEFORE THE LOW ARRIVES. CONCERNED FOR
THE PRIBILOFS FOR A PERIOD OF SNOW AND STRONG WINDS THIS
EVENING...THUS HAVE ISSUED A BLIZZARD WATCH. PRECIPITATION WILL FALL
AS RAIN FOR THE MAJORITY OF THE REGION ON THE FRONT END OF THE
SYSTEM...WITH A COOLER AIRMASS AND SNOW SHOWERS ON THE BACK END OF
THE SYSTEM. ANOTHER STRONG LOW WILL BEGIN TO APPROACH THE CENTRAL
ALEUTIANS FROM THE WEST ON WEDNESDAY...WITH SIGNIFICANT
PRECIPITATION ON WEDNESDAY NIGHT FOR THE CENTRAL ALEUTIANS.

.LONG TERM FORECAST...
A STRONG UPPER LEVEL JET IS LIKELY TO BRING STRONG LOW PRESSURES
TRACKING FROM WEST TO EAST ALONG OR JUST SOUTH OF THE ALEUTIANS FROM
THURSDAY INTO EARLY NEXT WEEK. LONG RANGE MODELS ARE IN FAIRLY GOOD
AGREEMENT ON THIS SOLUTION.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WATCH 195.
MARINE...GALE WARNINGS 155 160 165 170 171 172 175 176 179 180 185
         410.
         HEAVY FREEZING SPRAY WARNINGS 185 AND 410.
FIRE WEATHER...NONE.

FOISY APR 07