Small Craft Advisory 455, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
502 AM AKDT THU MAY 28 2015

.ANALYSIS AND UPPER LEVELS...

AN UPPER LEVEL RIDGE OF HIGH PRESSURE IS CENTERED ACROSS THE
SOUTHERN ALCAN BORDER. THIS FEATURE IS KEEPING SOUTHCENTRAL DRY
WITH HIGH CLOUDS RIDING NORTHWARD ALONG A SHORTWAVE MOVING FROM
THE KENAI PENINSULA. A WEAK FRONT IS BRINGING RAIN ACROSS THE
SOUTHWEST MAINLAND WITH A RAIN BAND STRETCHING FROM JUST EAST OF
BETHEL TO NEAR ILIAMNA. THE MAIN WEATHER CHALLENGE IS MOVING INTO
THE SOUTHERN BERING THIS MORNING AS A STACKED LOW PRESSURE SYSTEM
MOVES FROM THE NORTH PACIFIC. THIS SYSTEM IS CURRENTLY BRINGING
GUSTY WINDS BETWEEN 20 TO 35 MPH WITH HIGHER GUSTS TO 45 MPH AND
RAIN WITH THE FRONTAL BOUNDARY ACROSS THE CENTRAL ALEUTIANS.

&&

.MODEL DISCUSSION...
MODEL AGREEMENT CONTINUES TO BE ABOVE AVERAGE WITH THE OVERNIGHT
PACKAGE. ONLY MINOR CHANGES WERE NEEDED THROUGH THE SHORT TERM
WITH THE USE OF THE NAM ACROSS THE EASTERN ZONES AND A COMBINATION
OF THE GFS AND ECMWF UTILIZED FOR THE WEST.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
HIGH PRESSURE WILL BUILD INTO SOUTH CENTRAL ALASKA TODAY AND
FRIDAY. THIS WILL USHER IN A WARMING AND DRYING TREND. ENOUGH
MOISTURE AND INSTABILITY REMAIN OVER THE COPPER RIVER BASIN
TODAY FOR A CONTINUED SLIGHT CHANCE OF AFTERNOON AND EVENING
SHOWERS AND THUNDERSTORMS NORTH AND EAST OF GLENNALLEN. OFFSHORE
WINDS...GUSTY IN PREFERRED LOCATIONS...WILL DEVELOP TONIGHT AND
AGAIN FRIDAY NIGHT AS THE SURFACE HIGH PUSHES INLAND DURING THE
NIGHTTIME HOURS. THESE WILL WEAKEN OR EVEN REVERSE IN THE
AFTERNOON AS DAYTIME HEATING CREATES A THERMAL LOW INLAND.

&&

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

AFTER A FEW SHOWERS ASSOCIATED THIS MORNING WITH THE DECAYING
FRONT...SKIES WILL BECOME PARTLY CLOUDY. ON FRIDAY WARMER AND
DRIER CONDITIONS WILL PERSIST NEAR THE AK RANGE...BUT THE NEXT
FRONT WILL BRING A CHANCE OF RAIN TO AREAS WEST OF BETHEL AND
ALONG THE WESTERN CAPES.

&&

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

THE LOW CROSSING THE WESTERN ALEUTIANS AND ITS ASSOCIATED FRONT
WILL SPREAD GALE FORCE WINDS AND SUBSTANTIAL RAIN ACROSS THE
REGION TODAY AND TONIGHT. WINDS WILL BEGIN TO DIMINISH TO SMALL
CRAFT LEVELS ON FRI WITH RAIN CONTINUING OVER THE EASTERN
ALEUTIANS. THE WESTERN ALEUTIANS WILL BECOME SHOWERY.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7 - SATURDAY THROUGH WEDNESDAY)...
A VERY HIGH AMPLITUDE PATTERN WILL BE IN PLACE ON SATURDAY WITH A
BLOCKING RIDGE EXTENDING FROM THE HIGH ARCTIC (BEAUFORT/CHUKCHI SEAS)
SOUTHWARD ACROSS MAINLAND ALASKA AND DOWN INTO THE NORTHEAST PACIFIC.
UPSTREAM A CORRESPONDING TROUGH WILL EXTEND FROM EASTERN RUSSIA
SOUTHEASTWARD ACROSS THE BERING SEA AND ALEUTIANS TO THE NORTH-
CENTRAL PACIFIC. THE STORM TRACK WILL REMAIN ON THE WESTERN EDGE
OF THIS TROUGH...MAINLY AFFECTING THE FAR WESTERN BERING SEA AND
WESTERN ALEUTIANS. THE REST OF THE REGION WILL BE DOMINATED BY
GENERALLY WEAK FLOW AND FORCING.

THE BIG HEADLINE FOR THIS WEEKEND INTO EARLY NEXT WEEK WILL BE
HOT AND DRY CONDITIONS ACROSS SOUTHCENTRAL AND INTERIOR SOUTHWEST
ALASKA. THE KEY TO THIS WARMTH IS ENERGY DROPPING OUT OF THE
CANADIAN ARCTIC SLIDING DOWN THE EAST SIDE OF THE UPPER RIDGE
ACROSS EASTERN MAINLAND ALASKA. THIS WILL ADVECT DRIER AIR FROM
THE INTERIOR AND HINDER OR PREVENT FORMATION OF SEA BREEZES ALONG
THE GULF COAST. IF THESE UPPER WAVES ACTUALLY TRACK SOUTHWARD INTO
THE GULF THERE IS POTENTIAL FOR GUSTY NORTHERLY WINDS WHICH WOULD
RESULT IN EVEN HOTTER AND DRIER CONDITIONS. THERE ARE MODEL
DIFFERENCES IN THE TIMING AND TRACK OF UPPER LEVEL WAVES. THUS IT
IS DIFFICULT TO NAIL DOWN THE DETAILS AT THIS POINT IN TIME.
HOWEVER...CHANCES ARE THAT CRITICAL FIRE WEATHER CONDITIONS WILL
DEVELOP SOMETIME OVER THE WEEKEND.

AS STEADY PARADE OF UPPER WAVES ALONG THE EASTERN PERIPHERY OF THE
RIDGE WILL CAUSE IT TO RETROGRADE WESTWARD EARLY NEXT WEEK. THIS
WILL RESULT IN A COOLING TREND BEGINNING TUESDAY ALONG WITH A
MORE FAVORABLE CONDITIONS FOR SHOWERS AS WE HEAD THROUGH THE
WEEK.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...170 172-179 181 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KH
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DS
LONG TERM...SB