Storm Warning 191, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
115 PM AKST MON DEC 30 2013

.ANALYSIS AND UPPER LEVELS...
SATELLITE IMAGERY THIS MORNING SHOWS A CONVOLUTED AND CHAOTIC PATTERN
ACROSS THE REGION AS A ZONAL JET STREAM HAS USHERED IN NUMEROUS WEAK
UPPER-LEVEL DISTURBANCES THAT ARE TAKING TURNS SPINNING UP AND THEN
DISSIPATING GENERALLY WEAK SURFACE LOWS. THE MOST ACTIVE WEATHER IS
ACROSS THE BERING SEA...WHERE NO LESS THAN 4 WEAK AND COMPACT LOW
CENTERS ARE BRINGING GUSTY WINDS AND RAIN TO MANY AREAS. FURTHER TO
THE EAST...SEVERAL WEAK LOWS IN THE GULF ARE BRINGING RAIN SHOWERS TO
THE NORTH GULF COAST AND KODIAK ISLAND...WHILE INTERIOR AREAS REMAIN
VARIABLY CLOUDY AND DRY. YET ANOTHER SHORTWAVE CURRENTLY SOUTH OF THE
CENTRAL ALEUTIANS IS DESTINED FOR A DIFFERENT FATE THAN THE
OTHERS...AS THE JET STREAM IS BEGINNING TO BUCKLE AND AMPLIFY WITH
THE BEGINNINGS OF A RIDGE MOVING TOWARD THE GULF OF ALASKA. AS A
RESULT...A BAROCLINIC LEAF IS APPARENT ON SATELLITE IMAGERY SOUTH OF
THE ALASKA PENINSULA.

.MODEL DISCUSSION...
UNFORTUNATELY THE MODELS CONTINUE TO STRUGGLE SIGNIFICANTLY WITH THE
RAPID DEVELOPMENT OF A LOW CENTER SOUTH OF THE ALASKA PENINSULA LATE
TONIGHT AND TOMORROW MORNING. ALL MODELS HAVE TRENDED A BIT EASTWARD
TODAY...WITH THE ECMWF REMAINING THE MOST CONSISTENT BRINGING THE LOW
ONSHORE EAST OF DILLINGHAM ALONG THE BRISTOL BAY COASTLINE EARLY
WEDNESDAY MORNING. THE ECMWF NOW HAS SOLID SUPPORT FROM BOTH THE
GEMGLB AND THE UKMET...WITH THE 12Z GFS A BIT TO THE EAST AND THE NAM
A SIGNIFICANT OUTLIER BEING MUCH FARTHER TO THE EAST THAN EVEN THE
GFS. THE CONSENSUS EC/GEMGLB/UKMET SOLUTION IS THE PREFERRED CHOICE
FOR TODAY...THOUGH CONFIDENCE REMAINS WELL BELOW NORMAL FOR A STORM
EXPECTED TO DEVELOP WITHIN THE FIRST 24-36 HOURS OF THE FORECAST
PERIOD. THE IMPORTANT TAKEAWAYS FROM ALL OF THE MODELS ARE THAT THIS
SYSTEM WILL DEVELOP AND INTENSIFY RAPIDLY AND REACH PEAK INTENSITY
TUESDAY EVENING SOUTH OF THE ALASKA PENINSULA BEFORE WEAKENING JUST
AS RAPIDLY AS IT MOVES NORTHWARD.

.SHORT TERM FORECAST...
SOUTHCENTRAL...SHOWERS WILL CONTINUE ALONG THE COAST THROUGH THE
EVENING HOURS BEFORE THE AMPLIFYING UPSTREAM RIDGE PUSHES PRECIP TO
THE EAST AND LARGELY OUT OF THE AREA. BY TUESDAY MORNING THE
AFORMENTIONED STRONG LOW AND ASSOCIATED FRONT WILL ROAR INTO KODIAK
ISLAND WITH WIND AND RAIN SPREADING NORTHWARD TOWARD THE MAINLAND
THROUGHOUT THE DAY. A STORM FORCE BARRIER JET WILL DEVELOP BY
AFTERNOON...WITH STRONG WINDS ALSO BLOWING DOWN COOK INLET. THE
EAST-WEST ORIENTATION OF THE FRONT WILL STRONGLY FAVOR THE UPSLOPE
PORTIONS OF THE COASTAL MOUNTAINS...WITH THE USUAL DOWNSLOPE AREAS
SUCH AS ANCHORAGE AND THE MAT-SU SEEING LITTLE OR NO SNOWFALL. MOST
COASTAL AREAS WILL SEE A RAIN/SNOW MIX OR EVEN ALL RAIN...WITH THE
EXCEPTION OF VALDEZ WHERE ENOUGH COLD AIR SHOULD REMAIN IN PLACE FOR
SIGNIFICANT SNOW AMOUNTS TO STEADILY ACCUMULATE BY THE MIDDLE OF THE
WEEK. AS THE DEPARTING LOW WEAKENS RAPIDLY AND MOVES INTO THE
INTERIOR OF THE STATE MUCH OF SOUTHCENTRAL WILL LIKELY SEE WINDS
SWITCH TO THE SOUTH ALLOWING TEMPERATURES TO WARM TO NEAR OR ABOVE
FREEZING EVEN AT PROTECTED LOCATIONS LIKE ANCHORAGE AND THE MATANUSKA
VALLEY.

SOUTHWEST...PERSISTENT UNSTABLE SOUTHEAST FLOW IS ALLOWING CONVECTIVE
SNOW SHOWERS TO LINGER THIS AFTERNOON...MAINLY OVER WESTERN PORTIONS
OF THE BRISTOL BAY ZONE WHERE A FEW INCHES OF SNOW HAS LIKELY
ACCUMULATED. THIS SHOWER ACTIVITY WILL DIMINISH BY EARLY THIS EVENING
IN ADVANCE OF THE RAPID STORM INTENSIFICATION THAT WILL OCCUR SOUTH
OF THE ALASKA PENINSULA OVERNIGHT. SNOW...BLOWING SNOW...AND STRONG
WINDS WILL MOVE INTO THE BRISTOL BAY AREA BY MIDDAY TUESDAY...WITH
RAIN LIKELY MIXING IN ALONG THE MOUNTAINS SOUTH OF KING SALMON. THERE
REMAINS SOME QUESTION HOW MUCH SNOW AND WIND WILL SPREAD NORTH AND
WEST INTO THE OTHER ZONES...SINCE THE STORM IS SO COMPACT AND WILL BE
WEAKENING SO RAPIDLY BY WEDNESDAY MORNING. SUFFICE IT TO SAY...WHILE
SOME SNOW AND WIND IS LIKELY IN THESE ZONES THE WORST WEATHER WILL
DEFINITELY BE CONFINED TO INTERIOR PORTIONS OF THE BRISTOL BAY ZONE.

BERING SEA AND ALEUTIANS...A COMPLEX LOW WITH RAIN SHOWERS AND
RELATIVELY LIGHT WINDS WILL REMAIN OVER THE CENTRAL BERING
TONIGHT...WITH ISOLATED TO SCATTERED SHOWERS OCCURRING ACROSS NEARLY
THE ENTIRE LENGTH OF THE ALEUTIAN CHAIN. TEMPERATURES WILL REMAIN
NEAR OR ABOVE NORMAL FOR THE NEXT FEW DAYS AS A PROGRESSIVE WEATHER
PATTERN CONTINUES WITH PERIODIC LOW PRESSURE CENTERS DEVELOPING ALONG
THE JET AND MOVING NORTHWARD INTO THE BERING AND WEAKENING. A
PARTICULARLY FAST-MOVING AND COMPACT STORM WILL MOVE INTO THE CENTRAL
ALEUTIANS ON WEDNESDAY...LIKELY WITH A BRIEF PERIOD OF STORM FORCE
WINDS...BEFORE WEAKENING QUICKLY AND SLIDING TOWARD THE MAINLAND ON
THURSDAY.

...LONG TERM FORECAST FROM PREVIOUS DISCUSSION...

THE ACTIVE PROGRESSIVE PATTERN CONTINUES THROUGH THE BEGINNING OF THE
EXTENDED FORECAST WITH A BERING SEA UPPER LOW SHIFTING OVER THE
MAINLAND. LATE THIS WEEK A PATTERN CHANGE WILL BE USHERED IN AS A
COMPLEX UPPER LOW SHIFTS OVER THE SEA OF OKHOTSK BRINGING A STRONG
SURFACE LOW EAST OF THE KAMCHATKA PENINSULA. THE EFFECT OF THIS
SYSTEM WILL BUILD RIDGING DOWNSTREAM OVER THE EASTERN BERING ONTO THE
SOUTHWESTERN MAINLAND. EXPECT ANOTHER ROUND OF LIGHT SNOW FOR MOST
AREAS OF THE MAINLAND EARLY THIS WEEKEND THEN A PROLONGED PERIOD OF
DRIER AND COOLER CONDITIONS. THE NEXT CHANCE FOR ACTIVE WEATHER
RESIDES WITH A MEANDERING NORTH PACIFIC LOW THAT IS POISED TO PHASE
WITH THE KAMCHATKA SYSTEM...SENDING A FRONT NORTHWARD OVER THE
MAINLAND EARLY NEXT WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...STORM 119 120 130 131
         GALE 132 136 137 138 139 141 150 155 160 165 177 178
FIRE WEATHER...NONE

AMD DEC 13