Small Craft Advisory 418, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
439 PM AKDT FRI MAY 15 2015

.ANALYSIS AND UPPER LEVELS...
THE DOMINANT FEATURE FOR THE ENTIRE FORECAST PERIOD IS THE UPPER
LEVEL RIDGE OVER NORTHWEST CANADA AND EASTERN/CENTRAL ALASKA. THIS
RIDGE IS BLOCKING ALL SYSTEMS MOVING IN FROM THE WEST...WITH THE
ENERGY SPLITTING EITHER NORTHWARD THROUGH WESTERN ALASKA OR TO THE
SOUTH TOWARD CALIFORNIA. THERE IS AN UPPER LEVEL LOW OVER THE
ALASKA PENINSULA AND BRISTOL BAY THAT IS MOVING NORTH...WITH A
MOISTURE PLUME ORIENTED NORTHWEST TO SOUTHEAST FROM SOUTHWEST
ALASKA THROUGH THE KENAI PENINSULA AND THEN ACROSS THE GULF OF
ALASKA. THERE IS ANOTHER LOW OVER THE CENTRAL AND EASTERN
ALEUTIANS THAT IS MOVING TOWARD THE NORTHEAST.

&&

.MODEL DISCUSSION...
THE NUMERICAL MODELS ARE IN GOOD AGREEMENT FOR THE SHORT TERM
PORTION OF THE FORECAST. THERE ARE SOME MINOR DISAGREEMENTS ON
WHERE THE LINE OF MOISTURE/PRECIPITATION IS BETWEEN THE UPPER
RIDGE AND UPPER LOW...BUT THESE DIFFERENCES WILL NOT CREATE TOO
MANY PROBLEMS WITH THE FORECAST. FORECAST CONFIDENCE IS THUS
HIGHER THAN NORMAL.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
A WEAKENING FRONT CONTINUES TO PUSH ONTO THE MAINLAND THIS
EVENING. RAIN WITH THE FRONT WILL STAY CONFINED TO THE WESTERN
PRINCE WILLIAM SOUND AREA AND MAINLY WEST OF COOK INLET. THERE
WILL BE A CHANCE FOR SCATTERED SHOWERS FROM THE KENAI PENINSULA
NORTHWARD THROUGH THE MAT-SU OVERNIGHT AS THE TROUGH PASSES BUT
ACTIVITY SHOULD BE RATHER MEAGER. GAP WINDS THROUGH TURNAGAIN ARM
AND HIGHER ELEVATIONS AS WELL AS KNIK ARM WILL CONTINUE THROUGH
THE EVENING AND OVERNIGHT AS THE SURFACE GRADIENT REMAINS TIGHT
BUT WILL RELAX OVERNIGHT AFTER THE TROUGH PASSAGE.

OVER THE WEEKEND...THE MAINLAND WILL STAY SQUEEZED BETWEEN AN
UPPER LEVEL RIDGE OVER WESTERN CANADA AND BROAD TROUGHING OVER THE
BERING SEA/SOUTHWEST MAINLAND. THE MOISTURE AND ACTIVE SOUTHERLY
FLOW WILL STAY OUT OF THE SOUTHCENTRAL EXCEPT FOR KODIAK ISLAND
WILL SEE SOME RAIN ON SUNDAY. THE REMAINDER OF THE MAINLAND SHOULD
SEE A NICE SUNNY WEEKEND WITH ABOVE AVERAGE TEMPERATURES.

.FIRE WEATHER...WITH THE UPPER RIDGE REMAINING CENTERED OVER
WESTERN CANADA THE COPPER RIVER BASIN WILL SEE SOME OF THE
WARMEST AND DRIEST CONDITIONS ACROSS SOUTHCENTRAL OVER THE NEXT
WEEK. AS THE FRONT NEAR THE KENAI PENINSULA DISSIPATES OVERNIGHT
A WEAKER AND MORE BROAD SURFACE RIDGE WILL SETTLE IN FROM THE
GULF UP TO SOUTHCENTRAL. THUS...EXPECT WEAKER WINDS THAN THE PAST
COUPLE DAYS. HOWEVER...CONTINUED VERY WARM AND DRY CONDITIONS WILL
LEAD TO CONTINUED FIRE DANGER IN THE COPPER RIVER BASIN. VEGETATION
HAS YET TO FULLY GREEN UP SO THERE IS LITTLE EVAPOTRANSPIRATION TO
CONTRIBUTE TO MOISTURE AT THE SURFACE. FOR NOW HAVE EXTENDED THE
RED FLAG WARNING FOR THE COPPER BASIN THROUGH SATURDAY...THOUGH
THESE CONDITIONS MAY EXTEND INTO NEXT WEEK.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
A WEAK LOW AND ITS ASSOCIATED FRONT WILL MOVE THROUGH THE REGION
OVER THE NEXT 24 HOURS BRINGING WITH IT WIDESPREAD SHOWERS AND
GUSTY WINDS TO THE SOUTHWEST MAINLAND. WINDS TODAY WILL BE THE
STRONGEST ALONG THE ALASKA/ALEUTIAN RANGE AS THE FRONT PUSHES
NORTHWARD. THERE SHOULD BE ENOUGH MIXING DOWN TO THE SURFACE
AS WELL AS LOCAL TERRAIN EFFECTS TO PRODUCE GUSTS TO 45 MPH.

AS THE SYSTEM MOVES THROUGH THIS AFTERNOON...THERE IS ENOUGH
UPPER LEVEL FORCING FOR THE POSSIBILITY OF ISOLATED WET
THUNDERSTORMS FROM WEST OF KING SALMON NORTHWARD THROUGH THE
KUSKOKWIM DELTA THIS AFTERNOON THROUGH EARLY THIS EVENING. THE
06Z NAM IS INDICATING CAPE VALUES OF NEAR 500 J/KG AND SOME LI
VALUES OF -2...SO SOME ISOLATED THUNDERSTORMS SHOULD FIRE OFF
THIS AFTERNOON INTO THIS EVENING WITH THE BEST LOCATIONS ALONG
BOTH SIDES OF THE AHKLUN/KILBUCK MOUNTAINS.

AS THE FIRST FRONT MOVES THROUGH THE REGION TONIGHT...A SECOND
FRONT ASSOCIATED WITH A LOW IN THE CENTRAL ALEUTIANS WILL BEGIN
IMPACT THE COASTAL AREAS...BRINGING WITH IT A SECOND ROUND OF
RAIN AND GUSTY WINDS WITH THE HIGHEST WINDS ALONG THE COAST.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
A LOW LOCATED SOUTH OF SHEMYA THIS MORNING AND ITS ASSOCIATED
FRONT WILL BEGIN TO IMPACT THE WESTERN ALEUTIANS THIS MORNING AS
THE LOW MOVES INTO THE CENTRAL BERING SEA THROUGH TOMORROW NIGHT.
IN THE SHORT TERM...AREAS OF FOG ARE EXPECTED OVER THE EASTERN
BERING SEA AND THE PRIBILOF ISLANDS THIS MORNING WITH VISIBILITIES
AS LOW AS ONE QUARTER MILE AT TIMES. AS THE LOW MOVES THROUGH THE
CENTRAL ALEUTIANS TONIGHT...EXPECT STEADY RAIN ALONG THE CENTRAL
ALEUTIANS TO THE ALASKA PENINSULA WITH THE HEAVIEST TOTALS AGAIN
FROM DUTCH HARBOR EASTWARD TO NEAR SAND POINT. THIS SYSTEM DOES
NOT HAVE THE DEEP MOISTURE TAP THAT THE PREVIOUS TWO SYSTEMS HAVE
HAD...SO RAINFALL TOTALS SHOULD BE MORE MODERATE. WINDS WILL
INCREASE LATER TONIGHT AND INTO TOMORROW ALONG THE EASTERN AND
WESTERN PERIPHERY OF THE LOW...BUT SHOULD REMAIN BELOW GALE FORCE.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7...MONDAY THROUGH FRIDAY)...
ON MONDAY...A VERY AMPLIFIED PATTERN WILL CONTINUE TO BE IMPACTING
THE REGION AS AN ELONGATED NEARLY STATIONARY FRONTAL ZONE CONTINUES
TO IMPACT SOUTHWEST ALASKA AND KODIAK ISLAND WITH PERSISTENT RAIN.
THE STRENGTH OF THE HIGH LATITUDE BLOCKING HIGH OVER WESTERN
CANADA WILL MODULATE HOW FAR EAST THE CLOUDS AND PRECIPITATION
MOVE...WITH MOST OF SOUTHCENTRAL (BESIDES KODIAK ISLAND AND THE
ALASKA RANGE) SEEING JUST MID AND HIGH LEVEL CLOUDINESS. THERE IS
SOME UNCERTAINTY WITH A SECONDARY FRONT MOVING IN FROM THE NORTH
PACIFIC MID TO LATE WEEK...AND HOW FAR EAST ASSOCIATED MOISTURE
AND PRECIPITATION MOVE ACROSS SOUTHCENTRAL...WHICH WILL PUT A CAP
ON SIGNIFICANTLY ABOVE AVERAGE TEMPERATURES FOR LOCATIONS WEST OF
THE CHUGACH MOUNTAINS. THAT SAID...TEMPERATURES WILL GENERALLY
REMAIN ABOVE AVERAGE ACROSS SOUTHCENTRAL. THE WARMEST AND DRIEST
REGION WILL BE THE COPPER BASIN WHERE STRONGER DOWNSLOPE FLOW WILL
KEEP CLOUDS AT BAY...ALLOWING THEIR TEMPERATURES TO RISE INTO THE
UPPER 60S TO LOW 70S. THIS GENERAL PATTERN WILL PERSIST THROUGH
FRIDAY...WITH THE MUCH MORE ACTIVE AND WET WEATHER REMAINING OVER
THE BERING SEA AND SOUTHWEST ALASKA AS A LARGE BERING TROUGH
REMAINS ENTRENCHED OVER THE REGION.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 155 160 165 172.
FIRE WEATHER...RED FLAG WARNING 141.

&&

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