Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 221321
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
521 AM AKDT WED OCT 22 2014

.ANALYSIS AND UPPER LEVELS...

ALASKA CONTINUES TO REMAIN UNDER THE INFLUENCE OF A LARGE AND
SPRAWLING UPPER LEVEL TROUGH...WITH THE MAIN LOW CENTER OVER THE
SOUTHERN GULF OF ALASKA. SHORTWAVE TROUGHS EMBEDDED ALONG THE
PERIPHERY OF THE LOW CAN BE SEEN ON SATELLITE...WITH THE MAIN
CENTER OF ACTION ACROSS THE GULF AS A NEAR STORM FORCE 972 MB LOW
ROTATES NORTHWESTWARD. A CYCLONICALLY CURVED 145 KT NORTH PACIFIC
JET ANCHORS THE TROUGH IN THE VICINITY OF 40-45N. SHORTWAVE
RIDGING IS BUILDING INTO THE WESTERN BERING AHEAD OF A LARGE
EASTERN SIBERIA LOW CURRENTLY TRANSITING THE KAMCHATKA PENINUSULA.
WEAK SHORTWAVE RIDGING IS BUILDING INTO MOST OF SOUTHERN
ALASKA...WITH AN OFFSHORE PRESSURE GRADIENT HELPING TO DRY THE
REGION OUT. HOWEVER...WITH A LACK OF STRONG UPPER LEVEL DOWNWARD
DESCENT AND/OR COLD AIR ADVECTION...GAP WINDS ARE A BIT WEAKER
THAN THE PRESSURE GRADIENT ALONE WOULD SUGGEST. WITH TIME...THE
LARGE SCALE TROUGH OVER THE REGION WILL BEGIN TO SHIFT EAST AS THE
RIDGING ALOFT MOVES INTO THE EASTERN BERING. THIS WILL SET IN
MOTION A CHANGE IN THE PERSISTENT WEATHER PATTERN...SHIFTING MORE
TO A PROGRESSIVE AND FAST ZONAL PATTERN THIS WEEKEND INTO NEXT
WEEK.

&&

.MODEL DISCUSSION...

THE NUMERICAL MODELS ARE IN EXCELLENT AGREEMENT THROUGH THE
WEEKEND. HOWEVER...THEY BEGIN TO DIVERGE RAPIDLY WITH MORE
SPECIFIC DETAILS EARLY NEXT WEEK AS THE PATTERN SWITCHES TO A MORE
PROGRESSIVE AND FAST ZONAL FLOW. THIS IS QUITE TYPICAL...AND WHILE
THEY ARE IN DISAGREEMENT WITH SPECIFIC WAVE PATTERNS...THEY ARE
ALL CONSISTENT IN DEPICTING A CHANGE IN THE OVERALL LONGWAVE
EVOLUTION. FORECAST CONFIDENCE IS HIGH IN THE SHORT TERM AND
MODERATE IN THE EXTENDED.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...
QUIET WEATHER WILL PERVAIL ACROSS MOST OF SOUTHCENTRAL ALASKA AS
DRY OFFSHORE FLOW PERSISTS THROUGH TONIGHT. THE LACK OF A STRONG
PUSH OF DRY AIR INTO THE COPPER BASIN WILL LIKELY KEEP SOME DEGREE
OF LOW LEVEL CLOUDS AND PATCHY FOG IN THE BASIN...BUT MOST OTHER
LOCATIONS WILL STAY DRY AND LARGELY CLEAR. SOME RAIN SHOWERS
WILL IMPACT THE NORTH GULF COAST AND PRINCE WILLIAM SOUND THIS
EVENING AND TONIGHT. A FRONT MOVING IN FROM THE WEST WILL SPREAD
CLOUDS AND SCATTERED RAIN AND SNOW SHOWERS OVER SOUTHCENTRAL
FRIDAY AND SATURDAY.

SOUTHWEST ALASKA...
LARGELY QUIET WEATHER WILL PREVAIL AS THE PRESSURE GRADIENT
BECOMES OFFSHORE/OUTFLOW ACROSS THE REGION. NORTHERLY WINDS WILL
BECOME GUSTY TODAY...ESPECIALLY ACROSS THE BRISTOL BAY COAST AND
THROUGH GAPS IN THE ALASKA RANGE. A FRONT WILL PROGRESS WEST TO
EAST THURSDAY MORNING THROUGH FRIDAY MORNING...BRINGING RAIN AND
SNOW SHOWERS TO THE REGION.

BERING SEA/ALEUTIANS...
NORTHERLY WINDS AND SHOWERS WILL RAPIDLY DIMINISH TODAY AS WEAK
HIGH PRESSURE BUILDS IN OVER THE CENTRAL AND EASTERN BERING. A
FAST MOVING FRONT WILL TRACK INTO THE WESTERN ALEUTIANS AND WILL
SPREAD TO THE EASTERN BERING BY THURSDAY NIGHT.

&&

.LONG TERM FORECAST...

RUN TO RUN GUIDANCE OF THE EXTENDED MODELS HAS NOT BEEN
GOOD...AT LEAST PARTIALLY DUE TO HANDLING OF THE MOISTURE RESIDUE
FROM TROPICAL STORM ANA. EARLIER EC MODELS WERE BRINGING THE
RESIDUE ALONG WITH A DEEPENING LOW INTO THE GULF OF AK ON MON...BUT
MORE RECENT RUNS ARE SENDING THE MOISTURE FIELD EAST...WITH A MUCH
WEAKER LOW OVER THE EASTERN GULF MON THROUGH WED.

WHILE THIS IS HAPPENING...A FRONT ASSOCIATED WITH A LOW OVER
NORTHWEST AK WILL MOVE ACROSS MAINLAND AK THROUGH THE
WEEKEND...FOLLOWED BY HIGH PRESSURE EARLY NEXT WEEK. A KAMCHATKA
LOW WILL SEND A FRONTAL COMPLEX ACROSS THE BERING TO WESTERN AK
SUN THROUGH WED.

THE FORECAST UTILIZES THE WPC SOLUTION...WHICH RELIED HEAVILY ON
THE 06Z GFS ENSEMBLE FORECAST THAT PROVIDED SOME RUN TO RUN
CONSISTENCY.

-DS

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 150 155 170 172 174 178 185.
FIRE WEATHER...NONE.

&&

$$

AHSENMACHER OCT 14



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