Small Craft Advisory 557, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
146 PM AKDT MON JUL 21 2014

.ANALYSIS AND UPPER LEVELS...
A VERY PROMINENT RIDGE IS THE BIGGEST FEATURE THAT IS NOTED ON
SATELLITE IMAGERY TODAY. THE RIDGE AXIS IS LINED UP WITH THE
ALEUTIAN RANGE THIS AFTERNOON...AND WILL SLOWLY BE SLIDING EAST.
LOW LEVEL FOG AND STRATUS IS MOVING WITH THE RIDGE AT THE
SURFACE ACROSS BRISTOL BAY. IN THE UPPER LEVELS IS A
THIN...BUT WIDESPREAD AREA OF CIRRUS THAT COVERS A LARGE PORTION
OF THE STATE...FROM THE TALKEETNA MOUNTAINS AND WEST. A FAIRLY
WOUND UP AND STACKED LOW IS MOVING SOUTHEAST ALONG THE PANHANDLE
TODAY...AND IS THE REMNANTS OF THE SYSTEM THAT MOVED THROUGH
YESTERDAY...BRINGING RAIN SHOWERS TO THE ANCHORAGE AREA. SOUTH OF
ADAK IS THE NEXT WEATHER MAKER FOR OUR AREA. THIS LOW IS BRINGING
RAIN AND CLOUDS TO MUCH OF THE ALEUTIAN CHAIN AS WELL AS THE
PRIBILOF ISLANDS.

&&

.MODEL DISCUSSION...
THE MODELS ARE IN GOOD AGREEMENT TODAY WITH THE EVOLUTION OF THE
RIDGE MOVING EAST AND THE INTERACTION OF THE ALEUTIAN LOW AND A
NORTHERN STREAM SHORTWAVE TROUGH THAT IS SLIDING ACROSS THE BERING
STRAIGHT THIS AFTERNOON. THE BIGGEST DIFFERENCES ARE IN LOCATION
OF THE UPPER LEVEL LOW BY THE WEDNESDAY TIMEFRAME. IT IS AROUND
THAT TIME THAT THE NAM/GFS/GEM KEEP THE UPPER LOW ABOUT 200 NM
SOUTH OF SEWARD...WHILE THE EURO PULLS IT FARTHER NORTH AND INTO
COPPER RIVER DELTA (THE PREVIOUS RUN OF THE EURO WAS CLOSE TO THE
NAM/GFS)...OUTSIDE OF THAT MINOR DIFFERENCE...TIMING OF THE
FEATURES STILL SEEMS CONSISTENT. OVERALL THE GEM AND GFS WERE
FAVORED FOR THE FORECAST PACKAGE TODAY.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...
EXTENSIVE THIN CIRRUS  CLOUDS COVER THE AREA TODAY...BEST DENOTED
BY THE MILKY WHITE COLOR IN THE SKY. GIVEN THE RIGHT ANGLE...YOU
COULD ALMOST SEE A SLIGHT REDDISH HUE THAT MEANS THAT THERE IS
SMOKE PARTICULATE THAT IS COMBINED IN THE ATMOSPHERE.
REGARDLESS...PLEASANT SUMMER WEATHER WILL CONTINUE FOR SOUTH
CENTRAL THROUGH LATE TOMORROW AS THE RIDGE SLOWLY PASSES THROUGH.
BY THAT TIME THE ALEUTIAN LOW WILL BE CROSSING KODIAK AND HEADING
FOR SOUTHERN PWS. ALONG WITH THIS LOW WILL BE THE INCREASE TO MID
AND HIGH LEVEL CLOUDS AHEAD OF IT...AND STRATUS MOVING IN ALONG
THE COAST. GIVEN THE LACK OF A SIGNIFICANT SURFACE
REFLECTION...AND RELATIVELY LIGHT LOWER LEVEL FLOW...EXPECT TO SEE
SPRINKLES AND EVENTUALLY WEAK SHOWER ACTIVITY TO IMPACT THE
ANCHORAGE AREA LATE TOMORROW NIGHT AND INTO WEDNESDAY MORNING WITH
NO SIGNIFICANT DOWNSLOPE HOLE EXPECTED. AS THE LOW SLIDES SOUTH
OF PWS...RAIN ALONG THE TYPICAL UPSLOPE AREAS OF THE COAST WILL BE
EXPECTED.

SOUTHWEST ALASKA...
A DOUBLE WHAMMY WILL BE IMPACTING SOUTHWEST THROUGH TOMORROW. THE
FIRST IS FROM THE ALEUTIAN LOW MOVING TO THE EAST AND NORTHEAST.
THIS WILL BRING IN CLOUDS AND ASSOCIATED RAINS. AREAS TO THE
WEST...SUCH AS BETHEL...WILL ALSO BE SEEING RAIN AND CLOUDS BUT
THIS WILL BE DUE TO A NORTHERN STREAM WAVE AND FRONT THAT IS
DROPPING OUT OF THE ARCTIC. INSTABILITY LOOKS TO BE INCREASING
ACROSS THE LOWER Y-K DELTA LATE INTO THE AFTERNOON TOMORROW...AND
FORECAST SOUNDINGS SHOW A SLIGHTLY UNSTABLE PROFILE. NOT EXPECTING
ANY WIDESPREAD TS ACTIVITY...BUT PERHAPS A FEW STRIKES HERE OR
THERE. THE NORTHERN STREAM WAVE AND ALEUTIAN LOW WILL JOIN AND
EVOLVE TOGETHER AS THEY CROSS THE ALEUTIAN MOUNTAINS AND IMPACT
AREAS TO THE EAST.

BERING SEA/ALEUTIANS...
THE ALEUTIAN LOW WILL DOMINATE THE WEATHER PATTERN THROUGH
TOMORROW KEEPING RAIN AND LOW CLOUDS IN THE AREA. AS THE ALEUTIAN
LOW MOVES OUT OF THE BERING...ANOTHER RIDGE WILL BUILD AND TAKE
OVER THE BERING WEATHER PATTERN AGAIN. GUIDANCE IS HINTING AT SOME
BREAKS IN THE CLOUDINESS COME MID WEEK AS THE RIDGE BUILDS
IN...WITH COOLER AND DRIER AIR AHEAD OF IT. EXPECT THAT TO BE
SHORT LIVED AS THE USUAL RIDGE STRATUS DECK WILL MOVE BACK IN.

&&

.LONG TERM FORECAST...

THE LONG RANGE PATTERN (THURSDAY NIGHT THROUGH MONDAY) WILL
GENERALLY CONSIST OF A RIDGE OVER THE CENTRAL BERING SEA/ALEUTIANS
AND A TROUGH OVER THE GULF OF ALASKA AND OVER NORTHERN ALASKA.
THIS WILL RESULT IN NORTHWESTERLY FLOW ALOFT FOR THE MAINLAND. A
FEW SYSTEMS WILL PUSH THROUGH SOUTHERN ALASKA...BRINGING
CONSIDERABLE CLOUDS AND SOME PRECIPITATION. DUE TO THE DIRECTION
OF THE UPPER FLOW AND THE FACT THAT THE MAIN LOWS WILL BE TO OUR
WEST AND SOUTH...PRECIPITATION WILL GENERALLY BE SHOWERY AND
ACCUMULATIONS ARE NOT EXPECTED TO BE VERY HIGH.

THE WPC (WEATHER PREDICTION CENTER) FORECASTS ARE GENERALLY A
BLEND OF THE 00Z GFS ENSEMBLE MEAN...THE 12Z GFS DETERMINISTIC
MODEL (LESS INFLUENCE AS TIME INCREASES UNTIL BY DAY 8 IT IS NOT
USED AT ALL)...AND THE 00Z ECMWF ENSEMBLE MEAN. THE GFS IS
WEIGHTED SLIGHTLY HIGHER THAN THE ECMWF. THE AFTERNOON FORECAST
STRONGLY LEANS TOWARD THE WPC GUIDANCE.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.
&&

SHEA / LUDWIG JUL 14