Area Forecast Discussion
Issued by NWS Anchorage, AK

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
000
FXAK68 PAFC 251400
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 AM AKST THU DEC 25 2014

.ANALYSIS AND UPPER LEVELS...OVERALL THE PATTERN HAS NOT CHANGED
MUCH OVER THE PAST FEW DAYS. THE BIGGEST DIFFERENCE IS THAT THE
PARENT LOW OUT WEST HAS PUSHED ENOUGH FRONTS THROUGH THE PATTERN
THAT THE ATMOSPHERE ACROSS THE MAINLAND IS SLIGHTLY MORE RECEPTIVE
TO PRECIPITATION. ONE FRONT IS SLOWLY LIFTING AWAY FROM THE
ANCHORAGE BOWL BUT IS GETTING SOMEWHAT HUNG UP ON THE ALASKA
RANGE. THIS HAS KEPT SNOW FALLING MOST OF THE NIGHT OVER THE
SUSITNA VALLEY. THERE MAY BE LITTLE PERCEIVABLE BREAK FROM THIS
FRONT TO THE NEXT ONE THAT IS CURRENTLY MAKING LANDFALL OVER THE
BRISTOL BAY AREA. THERE IS NOT NEARLY AS MUCH COLD AIR AT THE
SURFACE AHEAD OF THIS FRONT AS THERE WAS WITH THE FIRST ONE. SO
THERE SHOULD BE A LOWER THREAT FOR ANY FREEZING PRECIPITATION WITH
A MOIST ADIABATIC ATMOSPHERE. PRECIPITATION WILL JUST CHANGE OVER
FROM SNOW TO RAIN AS THE WARM AIR MOVES IN. THERE IS SOME MARKEDLY
COLD AIR ALOFT SHOWING UP AS ENHANCED CUMULUS FROM THE ALASKA
PENINSULA THROUGH THE CENTRAL ALEUTIANS. THIS MEANS THAT THINGS
WILL CHANGE FROM A STRATIFORM TO A CONVECTIVE NATURE BEHIND
TODAY`S FRONT. AND THIS TRANSITION SHOULD ALSO BE ACCOMPANIED BY A
MODEST SHOT OF GUSTY SOUTH TO WEST WIND FROM THE COOK INLET TO
BRISTOL BAY WITH PRESSURE RISES.
IN THE UPPER LEVELS...ONE DIFFERENCE BETWEEN TODAYS FRONT AND SOME
OF THE LIGHTER SNOW EVENTS OVER THE PAST WEEK IS THAT TODAY`S
SHOULD PICK UP SOME JET SUPPORT. A 120-130KT JET MOVES UP FROM
THE WESTERN GULF AND CLIPS THE SOUTH CENTRAL LATER TODAY. THIS
WILL SERVE TO PROVIDE SOME EXTRA LIFT IN THE COLUMN AS THE FRONT
MOVES THROUGH. INTO THE WEEKEND WE SEE THE CONTINUAL BUILDING OF
THE NORTH AMERICAN RIDGE OVER THE EASTERN HALF OF THE STATE. THIS
STILL LOOKS TO BRING A HEALTHY AMOUNT OF WARM AIR AND MOISTURE UP
FROM THE NORTH PACIFIC.

&&

.MODEL DISCUSSION...MODELS REMAIN IN DECENT AGREEMENT WITH THE
SYNOPTIC PATTERN BUT CONTINUE TO STRUGGLE WITH SOME OF THE
SMALLER SCALE FEATURES. FOR THE BIG PICTURE...THIS FORECAST FAVORS
A BLEND OF THE GFS AND EC ACROSS THE AREA. ONE THING WAS FOR
CERTAIN WAS THAT WE DID NOT LIKE THE WAY THE 00Z NAM WAS SHOWING
SOME DOWNSLOPING (ESPECIALLY IN QPF FIELDS) OVER THE ANCHORAGE
AREA WITH THE FRONT TODAY. PHYSICALLY THIS DOES NOT MAKE MUCH
SENSE WITH THE VORTICITY MAXIMUM COMING STRAIGHT OVER THE KENAI
MOUNTAINS AND ESSENTIALLY NO CROSS BARRIER FLOW. SO WE DID NOT
UTILIZE THE NAM WITH THIS PACKAGE. OTHERWISE THE PATTERN WILL NOT
CHANGE MUCH WITH A COUPLE MORE FRONTS BEING SLUNG BY THE PARENT LOW
WAY OUT WEST TOWARDS THE MAINLAND THROUGH EARLY SATURDAY. THE
BLEND WAS THE BEST WAY TO HANDLE SOME OF THESE FEATURES FOR NOW
UNTIL THEY ARE BETTER RESOLVED BY ONE SPECIFIC MODEL AND/OR THE
HIGHER RESOLUTION MODELS. INTO SUNDAY...CONFIDENCE IS GROWING IN
THIS PART OF THE FORECAST AS BOTH THE EC AND GFS SHOW A RIDGE
BUILD OVER THE EASTERN HALF OF THE MAINLAND WITH AN ATMOSPHERIC
RIVER SETTING UP OVER THE SOUTHWEST.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
A FRONT MOVING INTO SOUTHCENTRAL ALASKA TODAY WILL BRING SNOW OVER
MUCH OF THE REGION. TEMPERATURES WILL BE WARM ENOUGH IN THE
SOUTHERN COOK INLET REGION AND ALONG THE GULF COAST TO MIX WITH OR
TURN TO RAIN WITH THE SOUTHERLY WINDS.
THE HEAVIEST SNOWFALL AMOUNTS WILL BE IN THE SUSITNA VALLEY FROM
TALKEETNA NORTH. THE HATCHER PASS AREA MAY ALSO SEE SIGNIFICANT SNOWFALL
AMOUNTS THROUGH TONIGHT IN THE SOUTHWEST FLOW.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
SOUTHWEST FLOW CONTINUES TO BRING PRECIPITATION TO THE SOUTHWEST
THAT WILL LAST INTO FRIDAY AS RIDGING WILL BUILD IN THIS EVENING
AND TONIGHT. THE SOUTHWEST FLOW HAS BEEN STRONG ENOUGH TO PULL UP
SOME WARMER AIR FROM THE NORTH PACIFIC AND CHANGE OVER SOME OF THE
SNOW AROUND BRISTOL BAY TO RAIN. HOWEVER...THE RAIN WILL BE SHORT
LIVED AS MORE COLD AIR WILL BROUGHT IN TODAY. THEN LATER ON FRIDAY
THE FLOW WILL BECOME MORE SOUTHERLY BRINGING BACK MORE WARM AIR TO
THE AREA.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE BROAD AREA OF LOW PRESSURE OVER THE BERING IS WEAKENING BUT
IS STILL BRINGING STRONGER WINDS TO THE ALEUTIANS. THIS AFTERNOON
A SYSTEM WILL MOVE IN TOWARDS THE WESTERN ALEUTIANS FROM THE NORTH
PACIFIC WITH A FRONT THAT WILL MAKE IT OVER THE CENTRAL ALEUTIANS
THIS EVENING. THIS SYSTEM WILL BRING STRONG GUSTY WINDS TO THE
WESTERN ALEUTIANS AND MORE PRECIPITATION TO THE ISLANDS. THE FRONT
ITSELF WILL HAVE ENOUGH OF A WARM PUSH TO BE ALL RAIN FOR THE
CENTRAL AND EVENTUALLY EASTERN ALEUTIANS.

&&

.LONG TERM FORECAST (SAT DEC 27 - THU JAN 1)...

A SIGNIFICANT SHIFT IN THE PATTERN WILL BE UNDERWAY BEGINNING THE
EXTENDED PERIOD SATURDAY AS A LARGE NORTHEAST PACIFIC RIDGE
AMPLIFIES INTO ALASKA...AND A LARGE AND SPRAWLING ALEUTIAN LOW
BEGINS TO INTERACT WITH A PLUME OF SUBTROPICAL MOISTURE
ORIGINATING FROM THE CENTRAL PACIFIC. BY LATE SATURDAY INTO
SUNDAY...AN ATMOSPHERIC MOISTURE RIVER AND PLUME OF WARM AIR WILL
PUSH INTO SOUTHWEST ALASKA...BRINGING SNOW AND RAIN TO THE
REGION...WITH THE POSSIBILITY OF FREEZING RAIN IN PRONE AREAS. A
SERIES OF POTENT UPPER LEVEL WAVE DISTURBANCES ALOFT WILL TRACK
ACROSS THE WESTERN PERIPHERY OF THE RIDGE AXIS...BRINGING MORE
MOISTURE AND WARM AIR WITH EACH SUCCESSIVE LOW...EVENTUALLY
RESULTING IN A TURNOVER TO ALL RAIN ACROSS MOST LOCATIONS. THE
MOISTURE RIVER WILL EVENTUALLY SET ITS SIGHTS ON SOUTHCENTRAL
ALASKA...WITH HEAVY RAIN IMPACTING COASTAL LOCATIONS.
PRECIPITATION TYPE WILL BE A CHALLENGE ACROSS INLAND LOCATIONS
SUNDAY AND EARLY MONDAY...WITH THE POTENTIAL FOR A MIX OF
RAIN...SNOW...AND FREEZING RAIN. HOWEVER...MOST INLAND LOCATIONS
ACROSS SOUTHCENTRAL WILL SEE A DRAMATIC DOWNSLOPE SHADOW...WITH
THE MAIN EXCEPTION BEING THE KENAI PENINSULA. EVENTUALLY THE
ALEUTIAN LOW DRIVING THE ATMOSPHERIC RIVER WILL SHIFT EAST
SOMETIME LATE MONDAY THROUGH EARLY WEDNESDAY...WITH COOLER AIR AND
DRIER CONDITIONS SETTING UP FOR THE REMAINDER OF THE EXTENDED
PERIOD.

WITH ALL THAT SAID...WINTER LOOKS TO REMAIN QUITE ELUSIVE ACROSS
SOUTHERN ALASKA. NO MAJOR COLD AIR OUTBREAKS OR SNOWY PATTERNS ARE
EXPECTED HEADING INTO EARLY JANUARY AS BLOCKING LOOKS TO REMAIN
STOUT ACROSS THE REGION.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER WEATHER ADVISORY 145.
MARINE...GALE 120 131 132 150 155 160 165 170 172-177 179 180.
         STORM 178 185.
         HEAVY FREEZING SPRAY 185.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...MSO
SOUTHCENTRAL ALASKA...--
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
LONG TERM...AHSENMACHER



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.