Blizzard Watch 27, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 AM AKST TUE DEC 17 2013

.ANALYSIS AND UPPER LEVELS...
FROM WEST TO EAST...WEAK RIDGING REMAINS OVER THE BERING WITH WEAK
UPPER LEVEL FLOW. SOUTH OF THE WESTERN ALEUTIANS...A COMPLEX AREA OF
LOW PRESSURE CONTINUES TO DEVELOP WITH THE HELP OF A 130+KT JET
STREAM. OVER THE CENTRAL ALEUTIANS AND EXTENDING THROUGH THE ALASKA
PENINSULA IS A PORTION OF THE BERING RIDGE. A WEAK CLIPPER TYPE
SYSTEM IS MOVING THROUGH THE NORTHWEST PORTION OF AK UNDER MODERATE
NORTHWEST FLOW. A SHORTWAVE RIDGE IS STARTING TO MOVE INTO
SOUTHCENTRAL AND REPLACE THE THE REMNANT TROUGH THAT IS PULLING OUT
OF THE NE GOA AND INTO CANADA.

.MODEL DISCUSSION...
MODELS CONTINUE TO COME INTO AGREEMENT WITH THE COMPLEX LOW SOUTH OF
THE ALEUTIANS. THEY NOW ALL ADVERTISE A WARM FRONT SPREADING UP
THROUGH THE EASTERN ALEUTIANS EARLY WEDNESDAY WITH A TRIPLE POINT LOW
DEVELOPING JUST SOUTH OF ADAK. THIS INITIAL SYSTEM IS THEN PROGGED TO
OCCLUDE LATE WEDNESDAY. A NEW TRIPLE POINT LOW WILL THEN DEVELOP NEAR
KODIAK ISLAND AND MOVE EAST NORTHEAST THROUGH THE GULF ON THURSDAY.
WITH A FAIRLY TIGHT MODEL CLUSTER...THERE IS SLIGHTLY ABOVE AVERAGE
CONFIDENCE IN THIS PORTION OF THE FORECAST. LATE THURSDAY INTO THE
WEEKEND...THERE IS A VERY BROAD SPECTRUM AMONGST THE MODELS. THE
GENERAL IDEA OF A LOW IN THE EASTERN GULF WEAKENING AND A NEW LOW
DEVELOPING NEAR THE CENTRAL ALEUTIANS IS CONSISTENT. BUT THE STRENGTH
OF THE NEW LOW AND TIMING OF SMALLER SCALE FEATURES IS NOT. IT
APPEARS THAT THE HANDLING OF A COLD TROUGH DROPPING THROUGH THE
BERING STRAIT IS CAUSING MANY OF THE DIFFERENCES. THUS...CONFIDENCE
IN THIS PORTION OF THE FORECAST IS LOW.

.SHORT TERM FORECAST...

SOUTHCENTRAL....FOG AND LOW STRATUS WILL BE AN ISSUE ONCE AGAIN THIS
MORNING. NASA SATELLITE IMAGERY SHOWS SOME LOW CLOUDS COVERING THE
KNIK ARM ALL THE WAY UP TO THE KNIK GLACIER. FOR THE MOST PART...DRY
NORTHWEST FLOW SHOULD KEEP IT CONFINED TO THESE AREAS. BUT CERTAINLY
CANNOT RULE OUT IT CREEPING INTO THE ANCHORAGE BOWL IF THE WINDS
SHIFT JUST A BIT. OTHERWISE...GAP WINDS DRIVEN BY THE COLD AIR OVER
THE MAINLAND SHOULD PEAK THIS MORNING AND THEN START TO SUBSIDE LATER
TODAY. THESE WINDS WILL CONTINUE TO KEEP BLIZZARD CONDITIONS GOING
THROUGH THOMPSON PASS UNTIL LATE THIS AFTERNOON.

THEN ATTENTION SHIFTS TO THE WARM FRONT COMING UP WEDNESDAY
AFTERNOON. WINDS WILL SWITCH TO SOUTH THROUGH SOUTHEAST AND INCREASE
THROUGH THE AFTERNOON INTO THE OVERNIGHT HOURS. KODIAK PRECIPITATION
WILL START AS ALL SNOW AND SHOULD BE ABLE TO ACCUMULATE A FEW INCHES
BEFORE THE WARM AIR PUSHES IN AND TURNS IT TO RAIN. AS THE LOW WORKS
ITS WAY FURTHER NORTH AND EAST...WINDS WILL INCREASE THROUGH THE
PORTAGE VALLEY AND TURNAGAIN ARM. COUPLED WITH THE FALLING
SNOW...WHICH WILL LIKELY BE HEAVY AT TIMES...BLIZZARD CONDITIONS WILL
BE POSSIBLE THERE WEDNESDAY NIGHT. A BLIZZARD WATCH HAS BEEN ISSUED
TO ADDRESS THIS.

SOUTHWEST ALASKA...
OTHER THAN AN AREA OF LIGHT SNOW MOVING ACROSS THE
KUSKOKWIM DELTA THIS MORNING...SKIES ARE CLEAR OVER THE SOUTHWEST
MAINLAND. THIS PRECIPITATION WILL NOT BE ABLE TO MAKE IT MUCH FURTHER
SOUTH AS HIGH PRESSURE HOLDS OVER THE SOUTHERN MAINLAND. THE NEXT
SYSTEM TO AFFECT THE AREA WILL BE ON WEDNESDAY AND WEDNESDAY NIGHT AS
A FRONT SWINGS NORTHWARD. MOST OF THE SOUTHWEST MAINLAND WILL REMAIN
BELOW FREEZING AND SEE SNOW AS PRECIPITATION TYPE...HOWEVER WARM
ENOUGH AIR WILL MOVE INTO THE ALASKA PENINSULA TO CHANGE
PRECIPITATION TYPE TO RAIN. WE WILL BE KEEPING OUR EYE ON THE BRISTOL
BAY AREA FOR A WINTER WEATHER ADVISORY FOR SNOW ON WEDNESDAY
AFTERNOON AND EVENING.

ALEUTIANS/BERING SEA...
THE NORTH PACIFIC LOW HAS BEGUN TO AFFECT THE
ALEUTIANS THIS MORNING WITH ATKA REPORTING WIND GUSTS OVER 40 MPH.
WINDS WILL INCREASE OVER THE EASTERN ALEUTIANS AND WESTERN ALASKA
PENINSULA LATER TODAY AND TONIGHT AS THE FRONT SWINGS NORTHWARD.
WHILE PRECIPITATION WILL LIKELY START AS SNOW...WARM AIR WILL CHANGE
PRECIPITATION TYPE TO RAIN BEFORE LONG.

AS THE PRECIPITATION REACHES THE PRIBILOF ISLANDS...PRECIPITATION
TYPE IS STILL SOMEWHAT IN QUESTION...WITH TEMPERATURES WITHIN A FEW
DEGREES OF FREEZING. WINDS WILL PICK UP ALONG WITH THE
PRECIPITATION...AND IT LOOKS LIKE PRECIPITATION WILL CHANGE OVER TO
RAIN WITH TEMPERATURES CLIMBING ABOVE FREEZING. HOWEVER...EVEN IF
PRECIPITATION TYPE IS SNOW WE DO NOT EXPECT BLIZZARD CONDITIONS AT
THIS TIME DUE TO THE RELATIVELY WARM TEMPERATURES.

.LONG TERM FORECAST (SATURDAY THROUGH MONDAY)...
A MODERATE NORTH PACIFIC RIDGE WILL HOLD OVER THE EASTERN HALF OF AK
INTO THE WEEKEND. A BROAD TROUGH OVER THE BERING WILL KEEP MUCH OF
THE WESTERN HALF OF THE STATE UNDER RELATIVELY WARM AND WET SOUTHWEST
FLOW. IT DOES APPEAR THAT THIS PATTERN WILL EVENTUALLY PULL UP ENOUGH
WARM AIR TO CAUSE SNOW TO CHANGE OVER TO RAIN OR AT LEAST MIXED
PRECIPITATION FOR MOST OF THE SOUTHERN HALF OF THE STATE WITH A WARM
FRONT SATURDAY. HIGH TEMPERATURES TODAY WILL STRUGGLE TO GET OUT OF
THE SINGLE DIGITS IN MOST PLACES. THIS WILL BE QUITE THE CONTRAST TO
THE WEEKEND WHEN HIGHS SHOULD GET NEAR FREEZING FOR THE ANCHORAGE
BOWL. HOWEVER...THIS WARM UP COULD ALSO MAKE FOR VERY SLOPPY
CONDITIONS WITH ALL OF THIS FRESH NEW SNOW.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 131
         BLIZZARD WATCH 125
MARINE...STORM WARNING 170 172 173 174 175 176 177 413 414
         GALE WARNING 121 127 129 130 131 132 136 137 138 352 150 155
                      160 165 171 178 179 180 185 411 412
         HEAVY FREEZING SPRAY 121 126 127 128 129 130 131 139 150 160
                              185
FIRE WEATHER...NONE

MSO/MBS DEC 13