Heavy Freezing Spray Warning 8, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
400 PM AKST MON JAN 17 2011

.ANALYSIS AND UPPER LEVELS...VERY COLD ARCTIC AIRMASS REMAINS
ANCHORED OVER SOUTHWEST AND SOUTHCENTRAL ALASKA WHILE AN IMPRESSIVE
935 MB LOW SPINS SOUTH OF THE WESTERN ALEUTIANS. THE OCCLUDED FRONT
ASSOCIATED WITH THE MASSIVE LOW IS BRINGING HURRICANE FORCE GUSTS TO
MANY LOCATIONS ACROSS THE SOUTHWESTERN BERING SEA AND ALEUTIAN CHAIN.

SOUTHWESTERLY FLOW AROUND THE UPPER LEVEL LOW IS BRINGING SOME
MOISTURE TO THE NORTH GULF COAST. WITH TEMPERATURES SO COLD...IT IS
NOT TAKING MUCH LIFT TO SQUEEZE OUT SNOW SHOWERS ACROSS THE KENAI
PENINSULA. THIS AREA OF MOISTURE AND VERTICAL MOTION WILL SLOWLY
TRANSITION EAST TOWARD PRINCE WILLIAM SOUND OVERNIGHT.

.MODEL DISCUSSION...ALL MODELS DISPLAYING SIMILAR SYNOPTIC PATTERN
EVOLVING OVER THE NEXT 84 HOURS. THE CHALLENGE WILL BE FINE TUNING
THE TIMING AND STRENGTH OF THE WAVES EMBEDDED IN THE FLOW AROUND THE
LOW IN THE NORTHERN PACIFIC. THE GLOBAL MODELS SEEM TO BE IN BETTER
AGREEMENT OF THE STRENGTH OF THE JET WHILE THE NAM IS WEAKER AND THUS
SLOWER ON THE ARRIVAL OF MOISTURE WEDNESDAY MORNING. THIS FORECAST
PACKAGE WAS WEIGHTED HEAVILY TOWARD THE 12Z GFS.

.SHORT TERM FORECAST...
SOUTHCENTRAL...LIGHT SNOW SHOWERS WILL TAPER OFF OVER THE KENAI
PENINSULA AND THEN LINGER AROUND PRINCE WILLIAM SOUND OVERNIGHT. DRY
AIR WILL QUICKLY FILTER BACK OVER THE REGION TONIGHT. THE AIRMASS IS
MODIFYING SLOWLY BUT THE CLEARING SKIES AND CALM WINDS WILL AGAIN
HELP TEMPERATURES REMAIN WELL BELOW CLIMATOLOGICAL NORMAL. A
TRANSIENT UPPER LEVEL RIDGE BUILDS OVER THE REGION AHEAD OF THE
APPROACHING FRONTAL BOUNDARY. UPPER LEVEL CLOUDS ASSOCIATED WITH THE
FRONT WILL ARRIVE OVER SOUTHCENTRAL TUESDAY NIGHT. THE SOUTHWESTERLY
FLOW AND WARM AIR OVERRUNNING THE ARCTIC AIRMASS LENDS ITSELF TO
LIGHT SNOW SPREADING ACROSS THE KENAI PENINSULA UP TO THE SUSITNA
VALLEY WEDNESDAY MORNING.

SNOW WILL CONTINUE ACROSS SOUTHCENTRAL THROUGH WEDNESDAY NIGHT AS AN
OCCLUDED LOW DEVELOPS NEAR KODIAK ISLAND WEDNESDAY AND RAPIDLY MOVES
INLAND WEDNESDAY NIGHT EAST OF CORDOVA. THE SPEED OF THE SYSTEM WILL
HELP LIMIT SNOWFALL TOTALS INITIALLY ALTHOUGH SOUTHWESTERLY FLOW
REMAINS IN PLACE THE REST OF THE WEEK...SO MORE SNOW IS LIKELY AS
ADDITIONAL WAVES DEVELOP AND FOLLOW A SIMILAR PATH.

KODIAK ISLAND...SOMETHING WE WILL HAVE TO CONSIDER IS THE IMPACT OF
THIS STORM ON KODIAK ISLAND. A SIGNIFICANT AMOUNT OF SNOW FELL
RECENTLY WITH 17 INCHES CURRENTLY REPORTED ON THE GROUND. AS THE
FRONT APPROACHES...PRECIPITATION WILL INITIALLY FALL AS SNOW BUT
QUICKLY TRANSITION TO RAIN. THE MODELS ARE SUGGESTING THAT A
SIGNIFICANT AMOUNT OF RAIN SHOULD FALL WITH THIS FRONT...AS MUCH ONE
INCH. THIS COULD LEAD TO LOCAL FLOODING PROBLEMS BETWEEN THE NEW RAIN
AND MELTING SNOW.

SOUTHWEST ALASKA AND BERING SEA...CLEAR AND COLD WEATHER PERSISTS
OVER SOUTHWEST ALASKA AGAIN WITH TEMPERATURES 10 TO 20 BELOW NORMAL.
HIGH AND MID LEVEL CLOUDS ARRIVE TUESDAY WITH PRECIPITATION NOT TOO
FAR BEHIND...ARRIVING IN BRISTOL BAY TUESDAY EVENING AND SPREADING
INLAND OVERNIGHT. MOST AREAS WILL SEE SNOW BUT WE WILL START
ADVERTISING THE POTENTIAL FOR FREEZING RAIN AS WARM AIR OVERRUNS THE
COLD ARCTIC AIRMASS IN PLACE. THE CHANCE OF FREEZING RAIN DOES NOT
LAST LONG AS THE OCCLUSION DEVELOPS NEAR KODIAK AND COLD AIR FILTERS
BACK ACROSS THE AREA AT ALL LEVELS. WIDESPREAD SNOW SHOULD LAST
THROUGH THURSDAY MORNING WITH ONLY A BRIEF BREAK BEFORE THE NEXT
SYSTEM APPROACHES BY THE WEEKEND.

THE CAUSE OF THIS ACTIVE WEATHER PATTERN IS WAY OUT WEST...THE 935 MB
LOW SOUTH OF SHEMYA. WARNING LEVEL WINDS SHOULD DIMINISH THIS
AFTERNOON ACROSS THE CENTRAL AND WESTERN ALEUTIANS WHILE THE FRONT
APPROACHES THE EASTERN ALEUTIANS. BOUNDARY LAYER WINDS DO NOT SEEM
OVERLY IMPRESSIVE LATER TONIGHT WITH THE FRONTAL BOUNDARY ALTHOUGH
UPPER LEVEL SUPPORT DOES...WITH 70 KT WINDS PROJECTED AT JUST 2000
FEET OFF THE SURFACE.

WINDS SLOWLY DIMINISH AS THE FRONT MOVES NORTH AND EAST AND THE
PARENT LOW FILLS. CONDITIONS BECOME MORE BENIGN THROUGH THE REMAINDER
OF THE WEEK AS THE ACTION SHIFTS EAST.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WARNING 185
         BLIZZARD WATCH 195
MARINE...STORM WARNING: 170 172
         GALE WARNINGS: 130 132 138 140 150 155 160 165 171 175 176
                        179 181
         HEAVY FREEZING SPRAY WARNINGS: 121 127 128 129 140
FIRE WEATHER...NONE

AB JAN 11