Small Craft Advisory 100, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
402 PM AKST SAT JAN 31 2015

.ANALYSIS AND UPPER LEVELS...

A LOOK AT THE MORNING WEATHER MAP REVEALS A GENERAL PATTERN
RESEMBLING A REX-BLOCK...AND CONSISTS OF A CLOSED UPPER HIGH OVER
THE INTERIOR OF THE STATE WITH A VERY LARGE AND COMPLEX LOW OVER
THE NORTHEAST PACIFIC. A MODERATE OFFSHORE PRESSURE GRADIENT HAS
ACTIVATED THE TYPICAL GAP WINDS AROUND SOUTHCENTRAL ALASKA
(WHITTIER..SEWARD...AND THOMPSON PASS) WITH A MORE WIDESPREAD
GUSTY OFFSHORE FLOW OVER THE SOUTHWEST MAINLAND. DESPITE SOME
LOCALIZED FOG/STRATUS AROUND UPPER COOK INLET AND IN THE COPPER
RIVER BASIN...THE AIRMASS REMAINS VERY DRY WITH IMPRESSIVE
SUBSIDENCE OBLITERATING ALL BUT A FEW HIGH BANDS OF CIRRUS OVER
SOUTHERN ALASKA. THE STORY IS A BIT DIFFERENT OVER KODIAK ISLAND
AND THE ALASKA PENINSULA WHERE CLOSER PROXIMITY TO THE LARGE
PACIFIC LOW IS RESULTING IN INCREASED CLOUDS. BY THIS EVENING
SOME OUTER BANDS OF PRECIP WILL MOVE INTO THESE AREAS...THOUGH
THE FRONT WILL BE WEAKENING OVERALL AND THE HEAVIEST RAIN WILL
REMAIN WELL OFFSHORE.

&&

.MODEL DISCUSSION...

THE MODELS ARE IN OVERALL OUTSTANDING AGREEMENT THROUGHOUT THE
FIRST 60 HOURS OF THE FORECAST. THE HIGH PRESSURE OVER THE
MAINLAND WILL BREAK DOWN ON MONDAY AS AN UPPER WAVE PLOWS IN FROM
THE NORTHWEST...AND AT THIS POINT IT LOOKS LIKE THE TWO WILL
MUTUALLY DESTROY EACH OTHER AND RESULT IN SHEARED OUT UPPER LEVEL
ENERGY THAT JOINS INTO THE BROADER ROTATION AROUND THE PERSISTENT
NORTH PACIFIC LOW. THE NET EFFECT WILL LIKELY BE SOME MID/HIGH
LEVEL CLOUDINESS TRANSITING ACROSS THE SOUTHERN MAINLAND...BUT
PRECIPITATION CHANCES WILL REMAIN VERY LOW.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...

RIDGING MOVING IN FROM THE WEST WILL DOMINATE THE WEATHER PATTERN
OVER THE NEXT COUPLE OF DAYS...KEEPING THE MAINLAND DRY AND
SEASONABLY COOL. THE EXCEPTION WILL BE A FRONTAL BOUNDARY
ASSOCIATED WITH A DEEP STATIONARY LOW IN THE NORTH PACIFIC. THIS
BOUNDARY WILL PUSH NORTHWARD SATURDAY NIGHT AND BRING SHOWERS AND
STRONGER WINDS TO SOUTHERN KODIAK ISLAND FOR THE FIRST HALF OF THE
WEEKEND. PATCHY OVERNIGHT AND MORNING FOG...AS SEEN ON SATELLITE
IMAGERY THIS MORNING...WILL REDEVELOP OVER COASTAL AREAS AND THE
VALLEYS OVER THE NEXT COUPLE OF NIGHTS. GUSTY OFFSHORE WINDS WILL
CONTINUE IN THOMPSON PASS AND THE COPPER RIVER DELTA THROUGH THE
WEEKEND...THEN DIMINISH SUNDAY NIGHT AS THE PRESSURE GRADIENT
WEAKENS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...

THE STORM SYSTEM SOUTH OF THE ALASKA PENINSULA WILL TIGHTEN THE
PRESSURE GRADIENT ACROSS THE PENINSULA AND BRISTOL BAY TONIGHT.
WINDS WILL INCREASE THROUGH THE EVENING PEAKING OVERNIGHT WITH
THE STRONGEST GUSTS EXPECTED ALONG THE PACIFIC SIDE OF THE ALASKA
PENINSULA. WINDS SHOULD TAPER OFF SUNDAY NIGHT AS THE LOW WEAKENS.
A DRIER AIR MASS AND OFFSHORE FLOW WILL PERSIST INTO THE BEGINNING
OF THE WEEK ACROSS THE SOUTHWESTERN MAINLAND.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...

GUSTY WINDS WILL INCREASE THIS EVENING ACROSS THE EASTERN
ALEUTIANS ACCOMPANIED WITH SCATTERED RAIN SHOWERS AS THE NORTH
PACIFIC STORM EDGES CLOSER TO THE ALASKA PENINSULA. THIS STORM
SYSTEM BEGINS TO WEAKEN BY LATE SUNDAY. THEREFORE...PRECIPITATION
WILL DIMINISH BY SUNDAY NIGHT...WITH GUSTY NORTHEASTERLY FLOW
CONTINUING ALONG THE BERING AND ALEUTIANS AS RIDGING BUILDS INTO
THE NORTHERN BERING INTO MONDAY.

&&

.LONG TERM FORECAST (TUESDAY THROUGH SATURDAY)...

AN ARCTIC TROUGH WILL DESCEND ACROSS ALASKA DURING THE DAY ON
TUESDAY ALLOWING FOR MUCH COLDER AIR FROM THE ARCTIC TO DIVE SOUTH
ACROSS MUCH OF ALASKA THROUGH MUCH OF THE UPCOMING WEEK. THERE IS
STILL A BIT OF QUESTION AS TO JUST HOW COLD IT WILL GET OVER
SOUTHWEST AND SOUTHCENTRAL ALASKA AS MODELS LACK CONTINUITY WITH
THE PATH THE ARCTIC TROUGH TAKES AS IT DIGS ACROSS ALASKA AND
TOWARD THE YUKON. IT CAN BE SAID IN HIGH CONFIDENCE THAT WELL
BELOW AVERAGE TEMPERATURES WILL BE COMMON ACROSS MOST LOCATIONS.
IN ADDITION...A SECOND ARCTIC TROUGH WILL DROP SOUTH QUICKLY
STARTING LATE THURSDAY NIGHT AND BRING A BLAST OF EVEN COLDER
TEMPERATURES. CONFIDENCE WITH THE TRACK OF THE UPPER TROUGH IS
MUCH LESS THAN ITS PREDECESSOR...BUT IT IS MORE THAN POSSIBLE THAT
THIS SECOND BLAST OF COLD AIR COULD BRING THE COLDEST TEMPERATURES
OF THE SEASON TO MUCH OF SOUTHWEST AND SOUTHCENTRAL ALASKA. IT IS
IMPORTANT TO NOTE THAT THE TRACK OF THE UPPER LEVEL LOW AND
POSITION OF THE UPPER LEVEL HIGH PRESSURE WILL PLAY A FACTOR INTO
WHERE EXACTLY THE COLDEST TEMPERATURES OCCUR. NONETHELESS...WELL
BELOW TEMPERATURES WILL ONCE AGAIN BE SEEN AND PERSIST INTO THE
UPCOMING WEEKEND.

A RELATIVELY DRY PERIOD WILL CONTINUE THROUGH THE LONG TERM AS
HIGH PRESSURE WILL DOMINATE THE WEATHER PATTERN THROUGH MUCH OF
THE WEEK. THE RIDGE BEGINS TO BREAK DOWN ON FRIDAY AS A STRONG LOW
MOVING NORTH FROM THE NORTH PACIFIC BEGINS TO FLATTEN OUT THE
RIDGE AND BRINGS PRECIP CHANCES BACK TO THE NORTHERN GULF COAST
AND THE EASTERN ALEUTIANS. OTHER THAN THAT...A SPELL OF MOSTLY
CLEAR TO CLEAR SKIES SHOULD BE OBSERVED FOR THE MAINLAND.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 127 132 138 150 155 165 172.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AD
SOUTHCENTRAL ALASKA...RD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KH
LONG TERM...MC