Small Craft Advisory 553, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
152 PM AKDT SUN JUL 20 2014

.ANALYSIS AND UPPER LEVELS...
THE MOST PROMINENT FEATURE TO ANALYZE THIS AFTERNOON IS A LARGE
TROUGH THAT HAS BEEN CARVING ITS WAY ACROSS ALASKA THESE PAST FEW
DAYS. AN UPPER LEVEL LOW HAS BEEN FORMING AT THE BASE OF THIS
TROUGH AND CAN BE SEEN QUITE WELL ON AFTERNOON WATER VAPOR
IMAGERY. AT THE SURFACE...A WEAK LOW FORMED ACROSS PRINCE WILLIAM
SOUND AND APPEARS TO BE SLOWLY RETROGRADING TO THE WEST. THIS IS
MOST APPARENT ON PAIH 0.5 DEGREE VOLUME SCAN. ACROSS BRISTOL BAY
AND THE EASTERN ALEUTIANS IS A TRANSIENT RIDGE. SOUTHWEST OF THE
THE ALEUTIANS IS AN UPPER LEVEL LOW THAT IS SLOWLY MOVING TO THE
EAST. ALONG THE WESTERN SIDE OF THE BERING SEA RIDGE IS A WEAK
SHORTWAVE THAT IS CLIMBING UP THE WESTERN EXTENT OF
RIDGE...CROSSING THE WESTERN CHAIN THIS AFTERNOON.

&&

.MODEL DISCUSSION...
ALL IN ALL...THE MODELS ARE IN GOOD AGREEMENT IN THE SHORT TERM.
THERE ARE ONLY MINOR DIFFERENCES IN THE UPPER LEVELS WITH THE LOW
DIVING SOUTHEAST FROM PWS. ALL GUIDANCE IS IN GOOD AGREEMENT WITH
THE STRENGTH OF THE RIDGE MOVING ACROSS THE CHAIN AND AKPEN TODAY.
DIFFERENCES BEGIN TO SHOW IN THE OVERNIGHT PERIOD OF TUESDAY WITH
THE ALEUTIAN LOW AND HOW IT WILL EVOLVE AS IT MOVES CLOSER TO THE
MAINLAND. THE LATEST GEM-REG / ECMWF AND GFS SEEM TO BE CONSISTENT
WITH TIMING OF THIS FEATURE. THE PAST FEW RUNS OF THE NAM HAVE
BEEN STRUGGLING TO SHOW ANY CONSISTENCY AND THAT WAS LARGELY
TOSSED FOR THIS FORECAST PACKAGE. SHORT TERM FORECASTS WERE TIED
CLOSER TO THE GEM FOR BOTH DOMAINS AND MID RANGE WAS A MIX OF THE
GFS AND ECMWF.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...
THE MAJORITY OF THE SHOWER ACTIVITY HAS WAINED FOR THE EASTERN
HALF OF THE REGION. CLOUD TOP TEMPERATURES CONTINUE TO WARM AND
SHOWER ACTIVITY ACROSS PWS AS WELL AS THE COPPER RIVER BASIN IS
COMING TO A CLOSE THIS EVENING. THE SURFACE LOW THAT DEVELOPED IN
WESTERN PWS LOOKS LIKE IT IS MOVING A BIT SLOWER THAN
EXPECTED...AND MAY BE RETROGRADING SLIGHTLY TO THE WEST...AND WILL
KEEP A BIT MORE CLOUD COVER ACROSS THE ANCHORAGE AREA THIS
EVENING. AS THE LOW PULLS OUT OF PWS...CLOUDS WILL DO THE SAME AND
WE SHOULD SEE GRADUAL CLEARING OVERNIGHT. RIDGING WILL BEGIN TO
SETTLE IN FROM THE WEST AND A PLEASANT START TO THE WORK WEEK WILL
TAKE PLACE. H85 TEMPERATURES WILL JUMP FROM ABOUT 1.5 DEG C TO
7-8 ACROSS THE ANCHORAGE AREA. ASSUMING MOST OF THAT WARMTH IS
REALIZED TOMORROW...WE CAN VERY EASILY SEE TEMPERATURES JUMP INTO
MID 70S BY THE AFTERNOON HOURS. THE NEXT FRONT WILL THEN SWEEP
ACROSS THE STATE STARTING LATE TOMORROW...AND INTERACT WITH A LOW
THAT IS MOVING ACROSS THE ALEUTIAN CHAINS TODAY...BRINGING THE
NEXT CHANCE FOR POPS TO SOUTH CENTRAL INTO THE TUESDAY
EVENING/WEDNESDAY TIME FRAME.

SOUTHWEST ALASKA...
RAIN AND CLOUDS HAVE DIMINISHED AND CONDITIONS ACROSS THE AREA ARE
PROGGED TO BE DRY THROUGH TOMORROW AND EARLY INTO TUESDAY. WITH
FAIRLY ABUNDANT MOISTURE AND A RIDGE BUILDING OVERHEAD...FOG WILL
SPILL OVER FROM THE SEA AND ALSO DEVELOP ALONG SOME INLAND AREAS
TONIGHT. THE ALEUTIAN LOW THAT IS SOUTH OF SHEMYA WILL WORK
EAST/NORTHEAST AND WILL EVENTUALLY BRING SHOWERS SPREADING FROM
WEST TO EAST TO THE AREA.

BERING SEA/ALEUTIANS...
THE SUMMERTIME RIDGE WITH THE TYPICAL FOG AND STRATUS WILL
CONTINUE. A SHORTWAVE RIDGE AND THE ABUNDANT MOISTURE PLUME TO THE
SOUTH ARE HELPING TO PUSH AND ENHANCEMENT NOTED IN SATELLITE
IMAGERY NORTH BETWEEN ATKA AND DUTCH. GIVEN THE LACK OF
OBSERVATIONS/GROUND TRUTH...IT IS ASSUMED THAT THERE IS SOME RAIN
COMING OUT OF THIS FEATURE. ALL GUIDANCE TAKES THIS WAVE AND
WEAKENS IT AS IT WORKS NORTH THROUGH THE PRIBS...BRINGING THE NEXT
CHANCE OF RAIN INTO THE EVENING HOURS...WHICH IS JUST A LITTLE MORE
THAN THE -DZ THAT AS BEEN EVER PRESENT. THE LOW SOUTH OF SHEMYA
WILL THEN SLOWLY WORK EAST THROUGH THE BEGINNING OF THE
WEEK...BRINGING RAIN/CLOUD CHANCES EAST AND TOWARDS THE AKPEN BY
MIDWEEK.

&&

.LONG TERM FORECAST...
THE SECOND HALF OF THE WEEK WILL SEE A PERSISTENT UPPER LEVEL LOW
OVER THE GULF OF ALASKA WITH A TROUGH EXTENDING OVER SOUTH CENTRAL
THROUGH THE INTERIOR. THIS TROUGH AND LOW WILL SLOWLY MOVE
EASTWARD AS A LARGE UPPER LEVEL HIGH IN THE WESTERN BERING SEA
WEDNESDAY MOVES EASTWARD THROUGH THE REST OF THE WEEK. THERE WAS A
LITTLE BIT OF UNCERTAINTY YESTERDAY HOW STRONG THIS RIDGE WILL BE
AND HOW FAR EAST IT WILL MOVE BY NEXT WEEKEND. CONFIDENCE IS NOW
INCREASING THAT THIS RIDGE WILL BE SUFFICIENTLY STRONG TO DISLODGE
THE PERSISTENT LOW IN THE GULF AND BECOME THE MAIN WEATHER FEATURE
NEXT WEEKEND THROUGH EARLY NEXT WEEK. IN SOUTHCENTRAL THIS PATTERN
SHOULD TRANSLATE TO AFTERNOON AND EVENING SHOWERS...ESPECIALLY
OVER ELEVATED TERRAIN...IN THE MIDDLE OF THE WEEK WITH LESS SEEN
EACH DAY UNTIL THERE ARE NOT TOO MANY AROUND BY SATURDAY. THE ONE
SIGNIFICANT CONCERN TO WATCH TOWARD NEXT WEEKEND CONCERNING THIS
RIDGE IS THAT THERE IS STILL SOME COLD UPPER LEVEL LOWS LURKING
AROUND IN THE ARCTIC OCEAN. SHOULD ONE OR MORE OF THESE COLD LOWS
RIDE DOWN THE EASTERN SIDE OF THE RIDGE THEY COULD BRING A PERIOD
OF RAINFALL...AND THEN RAPIDLY CLEAR OUT AGAIN. IN SOUTHWEST
ALASKA THE SHOWERS OVER ELEVATED TERRAIN SHOULD BE MOSTLY OVER
AFTER THURSDAY. HOWEVER THE COASTAL AREAS WILL BE AT RISK FOR LOW
CLOUDS AND FOG AS THERE WILL LIKELY BE WIDESPREAD STRATUS OVER THE
BERING SEA UNDER THIS RIDGE.

&&

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

SHEA/EZ JUL 14