Brisk Wind Advisory 46, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
300 PM AKDT WED MAR 27 2013

.MODEL DISCUSSION...MODELS ARE IN GENERALLY GOOD AGREEMENT THROUGH
THE SHORT TERM. THOUGH THERE WERE SOME MINOR TIMING DIFFERENCES OF
THE FRONTAL TROUGH IMPACTING SOUTHWEST ALASKA AND THE
GULF/SOUTHCENTRAL. THE GFS/NAM BLEND WILL BE USED IN PART FOR
AFTERNOON FORECAST PACKAGES.

.UPPER LEVELS...
500 MB...THE TROUGH STRETCHING ACROSS THE CENTRAL MAINLAND LIFTS
NORTH AND EAST AS A LOW AMPLITUDE RIDGE MOVES ACROSS THE MAINLAND
THURSDAY. THE LOW NEAR THE WESTERN ALEUTIANS MOVES EAST TO NEAR THE
WESTERN AK PEN FRI. THE TROUGH ASSOCIATED WITH THIS SYSTEM BROADENS
NORTH AS A SECONDARY CENTER FORMS NEAR THE SEWARD PEN. A HIGH
AMPLITUDE RIDGE SETS UP OVER THE CENTRAL BERING SEA FRI NIGHT. THE
RIDGE IS PINCHED SOME ON SAT AS A TROUGH MOVES TOWARD THE WESTERN
ALEUTIANS.

SURFACE...
HIGH PRESSURE OVER SOUTHCENTRAL WHICH BROUGHT GENERALLY FAIR SKIES
AND ALLOWED RADIATIVE COOLING IS STARTING TO SLIP EAST WITH THE
APPROACH OF A FRONTAL SYSTEM TO WEST. SNOW AND BLOWING SNOW WERE
EVIDENT ALONG THE WESTERN CAPES OF SW ALASKA THIS MORNING AND SNOW
WAS SLOWLY SPREADING EAST AND NORTH. THE ASSOCIATED FRONT WILL
CONTINUE TO MOST EASTWARD AND IMPACT SOUTHCENTRAL ALASKA ON THU AND
FRI. THE 970S MB LOW ASSOCIATED WITH THE FRONTAL BAND IS LOCATED NEAR
THE WESTERN ALEUTIANS AND IS STACKED WITH THE UPPER CENTER. THIS LOW
WILL TRACK EAST UNDER THE UPPER CENTER TO NEAR THE WESTERN AK PEN
FRI. HIGH PRESSURE SETS UP OVER THE BERING SEA FRI. A WEATHER FRONT
MOVING TOWARD THE WESTERN ALEUTIANS BRINGS STRONG SOUTHERLY WINDS AND
RAIN FRI NIGHT.

.SHORT TERM FORECAST...

.SOUTHCENTRAL ALASKA...PRESSURE GRADIENTS WILL INCREASE ACROSS
SOUTHCENTRAL ALASKA WITH THE APPROACH OF THE OCCLUDED FRONT FRI. SO
EXPECTED STRONG GAP FLOWS TO DEVELOP IN FAVORED LOCATIONS. STRONG MID
LEVEL SE WINDS WILL CREATE GENERALLY DOWNSLOPE CONDITIONS TO LEE OF
MOUNTAINS WITH THE BRUNT OF PRECIPITATION FALLING ALONG THE COAST AND
SE EXPOSURES. PRECIPITATION WILL INITIALLY START AS SNOW...BUT AS MAY
BECOME MIXED WITH RAIN THU NIGHT AS TEMPS WARM. STRONG WINDS COMBINED
WITH MODERATE SNOWFALL MAY PRODUCE BLIZZARD CONDITIONS THROUGH
PORTAGE VALLEY THU AND THOMPSON PASS THU EVENING AND FRI.

.SW ALASKA...BLOWING SNOW IN ADVANCE OF FRONTAL SYSTEM WILL SPREAD TO
THE COASTAL DELTA THROUGH THIS EVENING AND MAY SPREAD FURTHER INLAND
OVER THE BRISTOL BAY ZONE TONIGHT AS WINDS INCREASE THROUGH GAPS IN
THE ALEUTIAN RANGE AND SNOW SPREADS INLAND. TEMPS WILL BE WARMING
OVERNIGHT IN THE BRISTOL BAY ZONE...SO SNOW MAY BECOME MIXED WITH
RAIN ALONG SOME COASTAL LOCATIONS AND END THE BLIZZARD THREAT. ALSO
WARMING TEMPS MAY PRODUCE SOME LIGHT FREEZING RAIN INLAND TONIGHT.
THE BLIZZARD THREAT ALONG THE COASTAL 155 ZONE SHOULD END ON THU
MORNING AS WINDS DIMINISH...TEMPS IN THIS ZONE SHOULD STAY SAFELY
COLD ENOUGH TO MINIMIZE FREEZING RAIN THREAT.

.ALEUTIANS...
BERING SEA AND ALEUTIANS...
BLIZZARD CONDITIONS OVER THE PRIBILOFS ENDED AS THE FRONTAL SYSTEM
MOVED NORTH THIS MORNING. THE SNOW NEAR THE WESTERN ALEUTIANS WILL
TRACK EAST ALONG THE CHAIN THU. THIS CENTER WILL BRING MORE SHOWERY
WEATHER AS IT TRACKS EAST. STRONG NORTHERLY ON THE BACKSIDE OF THIS
CENTER WILL SPREAD EAST ACROSS THE ALEUTIANS. RIDGING MOVES TO THE
WESTERN ALEUTIANS FRI MORNING.

.LONG TERM FORECAST...

SATURDAY AND BEYOND...THE UPPER TROUGH WILL BE IMPACTING MAINLAND
ALASKA WITH RAIN AND SNOW ALONG THE COAST...AND THE POSSIBILITY OF
RAIN AND SNOW ACROSS INLAND AREAS AS THE TROUGH AXIS SWINGS THROUGH.
HIGHLY AMPLIFIED WAVE PATTERN WILL RESULT IN THE TROUGH LINGERING
OVER THE MAINLAND THROUGH THE WEEKEND BEFORE IT CUTS OFF AND TRACKS
EAST. MONDAY AND BEYOND...ALL THE GLOBAL MODELS AND THE ENSEMBLE
GUIDANCE HINT AT A STRONG EASTERN PACIFIC RIDGE BUILDING INTO
MAINLAND ALASKA...BUT THE GUIDANCE CONTINUES TO STRUGGLE WITH THE
DETAILS OF THE WAVE PATTERN AND THE EXACT POSITIONING OF THE
RIDGE...WHICH WILL INFLUENCE BOTH TEMPERATURES AND PRECIPITATION
PATTERNS. THAT SAID...NO MAJOR STORMS SEEM LIKELY FOR SOUTHERN ALASKA
THROUGH THE MIDDLE OF NEXT WEEK...WITH THE PRIMARY STORM TRACK
REMAINING OVER THE BERING AND ALEUTIANS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 155 AND 161. UPCOMING BLIZZARD WATCHES 125
AND 131.
MARINE..GALE 120 125 129 130 140 160 172 175 176 179 180 185.
        HEAVY FREEZING 127 140
FIRE WEATHER...NONE.

RMC MAR 13