Freezing Rain Advisory 4, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
523 AM AKST THU JAN 28 2016

.ANALYSIS AND UPPER LEVELS...
THE PRIMARY FEATURE DOMINATING THE UPPER LEVELS ACROSS SOUTHERN
ALASKA IS A BROAD UPPER LEVEL LOW CENTERED BETWEEN THE PRIBILOFS
AND UNALASKA. THE LOW IS ACTING AS THE FOCAL POINT AROUND WHICH
ALL OF THE OTHER DISTURBANCES AFFECTING THE AREA ARE ROTATING. THE
MOST SIGNIFICANT OF THESE ARE TWO TROUGHS WHICH ARE DRIVING THE
ONGOING ACTIVE WEATHER ACROSS PARTS OF THE AREA.

THE AREALLY LARGER TROUGH EXTENDS WELL EAST FROM THE LOW CENTER
INTO THE GULF. THIS IS PROVIDING THE SOUTH TO NORTH STEERING OF
AT LEAST TWO WEAK LOW LEVEL CIRCULATION CENTERS APPROACHING THE
NORTHERN GULF COAST. NORTH OF THE LOW LEVEL CIRCULATION
CENTERS...BROAD STRONG SOUTHEAST FLOW IN THE MIDLEVELS IS BRINGING
COPIOUS MOISTURE INTO THE NORTHERN GULF COAST AND PRINCE WILLIAM
SOUND. THOSE SAME STRONG SOUTHEAST WINDS ARE PROMOTING DOWNSLOPING
TO THE LEE OF THE CHUGACH AND KENAI MOUNTAINS...KEEPING THE
EASTERN COOK INLET REGION LARGELY DRY. THE RAINFALL THEN REDEVELOPS
OVER THE WESTERN SUSITNA VALLEY AND COOK INLET AS UPSLOPE AS THE
ALASKA RANGE LIFTS THE REMAINING MOISTURE ONCE AGAIN.

THE OTHER TROUGH EXTENDING WESTWARD FROM THE LOW PRESSURE CENTER
IS KEEPING THE PRECIPITATION IN BROAD NORTHWEST FLOW IN A BAND
COVERING THE WESTERN BERING AND CENTRAL ALEUTIANS...WITH THE
WESTERN ALEUTIANS CURRENTLY IN A MORE SHOWERY REGIME BETWEEN UPPER
LOWS.

IN SOUTHCENTRAL...STRONG WINDS DOWNSLOPING OFF THE TALKEETNA
MOUNTAINS TODAY ALLOWED TEMPERATURES TO SPIKE INTO THE 40S FOR THE
FIRST TIME SINCE JANUARY 5TH IN ANCHORAGE. WITH DIMINISHING WINDS
OVERNIGHT...TEMPERATURES HAVE FALLEN BACK TO AROUND THE FREEZING
MARK.

&&

.MODEL DISCUSSION...
ACROSS THE EASTERN DOMAIN...THE MODELS ARE IN VERY GOOD AGREEMENT
THROUGHOUT THE TWO DAY PERIOD. THE NAM WAS THE MODEL OF CHOICE FOR
ITS HIGHER RESOLUTION ON THE KEY FEATURES MOVING ACROSS THE
AREA...NAMELY THE LOW MOVING NORTHWARD ACROSS THE GULF AND ITS
ASSOCIATED PRECIPITATION. SMALL MODEL DIFFERENCES EXIST CONCERNING
THE APPROACH OF A WEAK FRONT ACROSS THE AREA THURSDAY NIGHT INTO
THE DAY ON FRIDAY. SOME LIGHT PRECIPITATION WILL BE ASSOCIATED
WITH IT. HOWEVER WITH TODAY'S WARM-UP THE QUESTION BECOMES WHETHER
OR NOT THE COLD AIR ARRIVES IN TIME TO GENERATE SNOWFALL. THE
CANADIAN WAS THE EARLIEST MODEL TO BRING IN THE COLD AIR EARLY
FRIDAY MORNING...WHEREAS THE OTHER MODELS HOLD OFF ON THE ARRIVAL
OF THE COLD AIR UNTIL LATER ON IN THE MORNING. THE NAM AGREED WITH
THE GLOBAL MODELS ON SOME COLD AIR MAKING IT IN WHILE PRECIPITATION
IS ONGOING...BUT NOT THE ENTIRE TIME. FORECAST CONFIDENCE IS HIGH
OWING TO THE GOOD MODEL AGREEMENT.

OUT WEST...THE GFS WAS THE CHOSEN MODEL CONCERNING ITS HANDLING
OF THE NEXT LOW TO MOVE INTO THE ALEUTIANS STARTING LATE THURSDAY
AFTERNOON THROUGH THE OVERNIGHT. THE GFS WAS THE SLOWER AND
FURTHER WEST THAN MOST OF THE REST OF MODELS...YET ALSO KEEPS THE
RESULTING LOW STRONGER AND MORE CONCENTRIC. THE EC SHOWS A MORE
DIFFUSE LOW EVENTUALLY DEVELOPING MULTIPLE CENTERS. THIS WAS
EXCLUDED BECAUSE THE EXPECTED PATTERN OF A DIGGING TROUGH IN THE
UPPER LEVELS DEVELOPING A STRONG SOUTHERLY JET STREAK OUT AHEAD OF
IT TENDS TO RESULT IN THE CYCLOGENESIS OF JUST ONE STRONGER
LOW...MOVING SLOWER AND REMAINING FURTHER WEST...AS THE GFS
INDICATES. FORECAST CONFIDENCE IS NORMAL.

&&
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
A WEAKENING LOW PRESSURE CENTER OVER THE NORTHERN GULF MOVES
ON SHORE OVER THE EASTERN KENAI PEN THIS AFTERNOON BRINGING A
BRIEF PERIOD OF GALES TO THE NORTHERN GULF THIS MORNING. THIS LOW
THEN DRIFTS SLOWLY EAST MERGING WITH A BROAD WEST TO EAST TROUGH
FORMING OVER THE NORTH GULF FRI. GENERALLY WARM TEMPS ACROSS
SOUTHCENTRAL(EXCEPT COPPER RIVER BASIN/NORTHERN SUSITNA VALLEY)
WILL CONTINUE THROUGH EARLY THIS EVENING. SO PRECIPITATION IN MOST
LOWER ELEVATIONS BELOW A COUPLE OF THOUSAND FEET SHOULD BE
GENERALLY RAIN OR MIX. COLDER AIR MOVES IN FROM THE SOUTHWEST
ACROSS COOK INLET THIS EVENING AND SPREADS NORTH AND EAST
OVERNIGHT. AREAS WITH RAIN ACROSS SOUTHCENTRAL WILL SHIFT OVER TO
SNOW/SNOW SHOWERS WITH THE COLD PUSH TONIGHT AND BRING MINOR SNOW
ACCUMULATIONS SOUTH OF THE SUSITNA VALLEY. HIGHER SNOW AMOUNTS(SUB
ADVISORY) ARE EXPECTED OVER THE SUSITNA VALLEY AND ALONG THE
TALKEETNA MOUNTAINS TONIGHT. SNOW/SNOW SHOWERS SHOULD DIMINISH
THROUGH FRI AS THE UPPER SUPPORT EXITS TO THE NORTH. AN UPPER
TROUGH MOVING IN FROM THE WEST FRI NIGHT WILL BRING ANOTHER SHOT
OF SNOW SHOWERS...BUT ACCUMULATIONS AGAIN WILL BE RELATIVELY
MINOR.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
A SURFACE LOW IN THE EASTERN BERING MOVES A TROUGH ACROSS THE
SOUTHWEST THROUGH THE AFTERNOON. SNOW WILL DEVELOP ALONG THE
TROUGH TODAY WITH RAIN IN THE MORNING ACROSS EASTERN AREAS OF
BRISTOL BAY. PERIODS OF SNOW CAN BE EXPECTED THROUGH THE SHORT
TERM FORECAST THROUGH FRIDAY NIGHT AS THE NEXT NORTH PACIFIC FRONT
PUSHES ANOTHER LOW INTO THE EASTERN BERING WITH COLD AIR ADVECTION
KEEPING COOLER TEMPERATURES ACROSS THE SOUTHWEST.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
AN ACTIVE WEATHER PATTERN CONTINUES THROUGH THE END OF THE WEEK
WITH A LOW OVER THE EASTERN BERING TODAY BEING REPLACED BY A
STRONGER STORM SYSTEM MOVING INTO THE WESTERN ALEUTIANS TONIGHT.
ISOLATED THUNDERSTORMS ARE POSSIBLE TONIGHT AS THE UPPER LOW IN
THE EASTERN BERING SWINGS A STRONG WAVE ACROSS THE EASTERN
ALEUTIANS TO THE ALASKA PENINSULA.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
AN ANCHOR LOW IN THE VICINITY OF THE WESTERN ALEUTIANS WITH JET
ENERGY ROUNDING THE BASE OF THE TROUGH WILL ALLOW FOR TRIPLE POINT
LOWS TO FORM SOUTH OF THE ALEUTIANS BEFORE MOVING NORTH AND WEST
THROUGH THE BERING. MODELS ARE IN GOOD AGREEMENT ON A POWERFUL YET
COMPACT TRIPLE POINT LOW TO FORM SOUTH OF THE CENTRAL/EASTERN
ALEUTIANS BEFORE CROSSING THE ISLAND CHAIN BETWEEN ATKA AND DUTCH
HARBOR SATURDAY. GIVEN THE SIZE OF THIS FEATURE...NO POPULATED
AREAS MAY SEE MORE THAN STORM FORCE GUSTS...BUT FOR MARINE AREAS
A SMALL CORE OF HURRICANE FORCE WINDS WILL BE POSSIBLE SATURDAY.
WHILE THE CENTRAL ALEUTIANS WILL HAVE THE POSSIBILITY OF REACHING
HIGH WIND WARNING THRESHOLDS FROM ADAK WESTWARD BY SATURDAY NIGHT
AS THIS LOW PRESSURE SYSTEM MOVES FARTHER INTO THE BERING SEA.
THIS WILL COINCIDE AS COLDER AIR ON THE BACKSIDE OF THIS SYSTEM
ADVECTS INTO THE REGION PRODUCING STRONG GUSTY WESTERLY WINDS FOR
THE CENTRAL ALEUTIANS HEADING INTO SUNDAY. THIS FEATURE WILL
WEAKEN ALMOST AS QUICK AS IT INTENSIFIES BUT MOVES SWIFTLY NORTH
AND WEST THROUGH THE CENTRAL/WESTERN BERING AS IT BROADENS AND
BECOMES THE PRIMARY CENTER OF ACTION BY EARLY TO MID NEXT WEEK.

TOWARD THE GULF AND SOUTHERN MAINLAND...MODELS ARE IN
ASTONISHINGLY GOOD AGREEMENT THAT A SHARP HIGH-AMPLITUDE RIDGE
WILL BUILD OVER THE EASTERN HALF OF ALASKA THIS WEEKEND. THIS WILL
ALLOW FOR WEAKENING WINDS OUTSIDE OF SOME WESTERLY GAP WINDS TO
IMPACT THE WHITTIER AREA AS A WEAK GRADIENT ESTABLISHES ITSELF
WITH A SURFACE TROUGH OVER THE NORTHEAST GULF. TOWARD KODIAK WEST
INTO THE EASTERN BERING...DEEP SOUTHERLY FLOW WILL ESTABLISH
ITSELF AND BECOME THE FOCUS FOR INDIVIDUAL DISTURBANCES TO MOVE
NORTH AND WEST ALONG A NEARLY STATIONARY FRONTAL BOUNDARY...AND
WILL BE ON THE WARM AND WET SIDE OF THINGS. PLACES UNDER THE HIGH
PRESSURE RIDGING ALOFT (SUCH AS GLENNALLEN AND PAXSON) WILL BE
CLEAR...COLD...AND DRY. AT THIS POINT IT LOOKS LIKE ANCHORAGE WILL
BE CAUGHT RIGHT IN THE MIDDLE OF THE TWO WITH JUST SOMEWHAT ABOVE
NORMAL TEMPS AND DRY CONDITIONS FROM THIS WEEKEND THROUGH EARLY
NEXT WEEK.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING...119 155 172 173 174 175 176 177 178 181
                        185.
         HEAVY FREEZING SPRAY WARNING...185.

&&

SYNOPSIS AND MODEL DISCUSSION...JW
SOUTHCENTRAL ALASKA...BC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KH
LONG TERM...CC/PD