Small Craft Advisory 551, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
345 PM AKDT THU JUL 18 2013

.ANALYSIS AND UPPER LEVELS...
STRONG CLOSED LOW NEAR THE POLE WITH A TROUGH EXTENDING THROUGH A
CLOSED LOW IN SIBERIA INTO THE NORTH PACIFIC TO ANOTHER CLOSED LOW. A
RIDGE EXTENDS FROM THE CLOSED HIGH JUST SOUTH OF THE GULF TO THE
CANADIAN ARCHIPELAGO WITH ANOTHER LOW OVER HUDSON BAY. SHORT WAVE
ENERGY MOVING OUT OF THE BERING KNOCKING DOWN RIDGE OVER THE
MAINLAND. THE MOST CURRENT WAVE IS MOVING THROUGH SOUTHWEST ALASKA
PRODUCING WIDESPREAD RAINFALL. WAVES ARE NOT STRONG AS JET SUPPORT IS
ONLY MODERATE AND BAROCLINICITY IS MEAGER. AT THE SURFACE...LOW
PRESSURE IS DOMINATING THE BERING SEA WITH HIGH PRESSURE OVER THE
GULF AND NORTH PACIFIC. LOADS OF STRATUS AND FOG OVER THE BERING AND
WESTERN ALASKA CURRENTLY. SOUTH CENTRAL ALASKA IS UNDER A SOMEWHAT
MOIST AND CONDITIONALLY UNSTABLE AIR MASS. WITH THE CLOUD COVER OF
THE WEST...CONVECTION IN THE FORM OF THUNDERSTORMS WILL BE LIMITED
PRIMARILY TALKEETNA MOUNTAINS EAST THIS AFTERNOON AND EVENING. DUE TO
THE WEAK LOW PRESSURE ALONG THE NORTHERN GULF COAST AND A FAVORABLE
WESTERLY FLOW ALOFT...WINDS AT WHITTIER HAVE BEEN RATHER GUSTY THE
PAST COUPLE DAYS. THIS WILL GIVE WAY THIS EVENING FINALLY.

.MODEL DISCUSSION...
THE 4 WAVE PATTERN OVER THE HEMISPHERE TO CHANGE A BIT. THE RIDGE
OVER THE MAINLAND FLATTENS AND REBUILDS OVER THE BERING LATER THIS
WEEKEND INTO EARLY NEXT WEEK. TROUGH OVER THE BERING TO SLIDE INTO
THE YUKON AND BC. FEATURES BECOME MORE ZONAL BY THE END OF THE WEEK.
IN MORE DETAIL...THE CLOSED LOW OVER EASTERN RUSSIA TO BECOME AN OPEN
WAVE AND MOVE THROUGH THE MAINLAND FRIDAY AND SATURDAY AND THEN STICK
OVER THE BC AND PANHANDLE THROUGH MID WEEK. HIGH PRESSURE NEAR THE
GULF TO RETROGRADE TO EASTERN BERING IN THIS TIME FRAME. THE LOW OVER
THE WESTERN NORTH PACIFIC TO DRIFT TOWARD THE KAMCHATKA PENINSULA
WHILE THE POLAR LOW DROPS INTO THE CHUKCHI AND MOVES TO THE BEAUFORT
MID WEEK. AT THE SURFACE...WEAK AREA OF LOW PRESSURE OVER THE
NORTHERN GULF TO BE RE-INFORCED BY SATURDAY WITH THE UPPER LEVEL WAVE
MOVING THROUGH SOUTH CENTRAL AND THE GULF. HIGH PRESSURE TO CENTER
OVER THE EASTERN ALEUTIANS WITH LOW PRESSURE OVER THE NORTHWEST
BERING SEA. THE LOW OVER THE ARCTIC TO MOVE TO FOLLOW THE UPPER LOW
ACROSS THE CHUKCHI AND BEAUFORT THIS WEEKEND INTO MID WEEK.

OVERALL...MODELS ARE AMAZINGLY IN AGREEMENT AT THE SURFACE AND UPPER
LEVELS. OF COURSE THERE ARE SLIGHT DETAILS THAT MAKE A DIFFERENCE IN
THE COMPLEX TERRAIN. FOR INSTANCE...THE DETAILS OF THE LOW MOVING
OVER SOUTH CENTRAL FRIDAY NIGHT AND SATURDAY COULD BRING WIDESPREAD
RAIN OR NOT. BASED UPON THE BETTER REPRESENTATION OF TERRAIN AND
TERRAIN FEATURES...THE FORECAST IS LEANING TO THE NAM FOR MORE
RAINFALL THAN NOT.

.SHORT TERM FORECAST...
.SOUTHCENTRAL...MOIST SOUTHWEST FLOW PREVAILS OVER THE AREA TODAY AND
TOMORROW AHEAD OF A STRONGER WAVE MOVING SOUTHEAST FROM THE NORTHERN
BERING. A WEAK WAVE TO PASS THROUGH TONIGHT AND WILL INITIATE
RAINFALL MAINLY UP THE SUSITNA VALLEY. THE WEAK LOW THAT IS KEEPING
STRONG GUSTS OUT OF THE WHITTIER AREA TODAY TO WEAKEN AS THIS WAVE
MOVES INTO PLACE. WE WILL REMAIN IN A VERY MOIST AND MODERATELY
UNSTABLE FRIDAY FOR SCATTERED SHOWERS OVER A LARGE PORTION OF SOUTH
CENTRAL. THE STRONGER WAVE TO MOVE THROUGH FRIDAY NIGHT AND SATURDAY.
THE BAROCLINICITY AND VORTICITY ADVECTION TO INITIATE WIDESPREAD
RAINFALL. AS IT PASSES SATURDAY...THE LOW IN THE NORTHERN GULF WILL
BE ENHANCED AND GAP FLOWS WILL ENSURE ESPECIALLY THROUGH WHITTIER AND
SEWARD AND PRINCE WILLIAM SOUND. BARREN ISLAND WINDS WILL NOT BE AS
STRONG BUT PRESENT. A DRIER PATTERN TO ENTER BEHIND THIS WAVE FOR
SUNDAY...BUT THE WINDS WILL REMAIN SUNDAY.

.SOUTHWEST...LARGE SCALE TROUGH OVER THE BERING WITH A SHORT WAVE
MOVING THROUGH SOUTHWEST ALASKA THIS EVENING. WIDESPREAD RAIN IS
ASSOCIATED WITH THE SHORT WAVE. LONG WAVE TROUGH TO TRANSITION ACROSS
THE MAINLAND FRIDAY. GOOD BAROCLINICITY WITH THIS FEATURE...SO EXPECT
WIDESPREAD RAIN...SOMETIMES MODERATE. IN ADDITION...HIGH PRESSURE
OVER THE NORTH PACIFIC AIDING STRONGER WINDS ALONG THE AKPEN. AFTER
THE TROUGH MOVES THROUGH FRIDAY...THE FLOW BECOMES DRIER AND
PRECIPITATION CHANCES DIMINISH THROUGH THE WEEKEND.

.BERING AND ALEUTIANS...WEAK LOW PRESSURE WITH UPPER LEVEL
DISTURBANCES WILL MOVE THROUGH THE BERING THROUGH TOMORROW. SURFACE
WINDS ARE NOT IMPRESSIVE. COMBINED WITH CURRENT MARINE LAYER AROUND
THE BERING...STRATUS AND DRIZZLE WILL REMAIN ACROSS THE BERING. AS
THE LOW PRESSURE EXITS THE BERING FRIDAY...HIGH PRESSURE TO BUILD
OVER MUCH OF THE BERING AND ALEUTIANS THROUGH THE WEEKEND. UPPER
LEVEL LOW OVER THE WESTERN BERING AND NORTHWEST FLOW OVER THE EASTERN
BERING WILL KEEP LIGHT RAIN AND STRATUS AND FOG OVER THE BERING
THROUGH THE WEEKEND.

.LONG TERM FORECAST...
BY THE END OF THE WEEKEND...THE MOIST SOUTHWEST FLOW OVER THE
MAINLAND TO GIVE WAY AS NORTHWEST FLOW MOVES OVER THE STATE. WARM
TEMPS WILL REMAIN. WITH HIGH PRESSURE OVER THE BERING...FOG AND
STRATUS TO RULE. AS THE LOW IN THE ARCTIC SWINGS INTO THE BEAUFORT
MID WEEK...A FRONT IS EXPECTED TO WORK ACROSS THE BROOKS RANGE INTO
CENTRAL ALASKA. OTHERWISE...A MOSTLY DRY PATTERN FOR THE MAINLAND.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

NELSON