Small Craft Advisory 589, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
149 PM AKDT TUE AUG 5 2014

.ANALYSIS AND UPPER LEVELS...COLD UPPER LOW OVER THE NORTHWEST
GULF IS SLOWLY TRACKING SOUTHWARD JUST EAST OF KODIAK ISLAND.
NUMEROUS WEAK WAVES ROTATING AROUND THE LOW CENTER CONTINUE TO
PRODUCE SHOWERS...MAINLY OVER THE GULF AND KODIAK ISLAND. AN AREA
OF SUBSIDENCE (IN BETWEEN UPPER WAVES) FROM COOK INLET NORTHEAST
ACROSS ANCHORAGE TO THE COPPER BASIN IS PRODUCING MOSTLY SUNNY
SKIES THIS MORNING...BUT EXPECT SURFACE HEATING TO ELIMINATE CAP
THIS AFTERNOON...ESPECIALLY ALONG THE TERRAIN. OVER SOUTHWEST
ALASKA THERE IS AN AREA OF SHOWERS FOCUSED ALONG THE THERMAL
TROUGH OVER THE KUSKOKWIM VALLEY AIDED BY A SHORT-WAVE ROTATING
DOWN FROM THE INTERIOR. MEANWHILE A MARINE LAYER HAS SETTLED IN
ALONG COASTAL SOUTHWEST ALASKA. WITH SUCH EXTENSIVE CLOUD COVER
OVER THE REGION THREAT OF THUNDERSTORMS IS SIGNIFICANTLY REDUCED
COMPARED WITH THE LAST COUPLE DAYS.

LOOKING UPSTREAM A 100KT+ SUBTROPICAL JET IS DRIVING A TROUGH
EASTWARD INTO THE WESTERN BERING AND ALEUTIANS AND TAPPING IN TO
ABUNDANT WARM AND MOIST TROPICAL AIR OVER THE NORTHWEST PACIFIC. A
WEAK SURFACE LOW HAS DEVELOPED OVER THE WESTERN BERING WITH WARM
FRONT PUSHING INTO CENTRAL BERING ALONG WITH STEADY RAIN.

&&

.MODEL DISCUSSION...MODELS CONTINUE TO STRUGGLE WITH HANDLING OF
WEAK FEATURES IN THE WAKE OF EXITING COLD CORE LOW OVER THE GULF.
IT DOES LOOK LIKE SOME OF THE ENERGY OVER INTERIOR SOUTHWEST
ALASKA WILL HEAD BACK EAST AS BERING SYSTEM APPROACHES WEDNESDAY.
NAM SOLUTION SEEMS OVERDONE WITH QPF IN COOK INLET/ANCHORAGE/MAT-
SU AREA WEDNESDAY NIGHT. HOWEVER...DO THINK THERE WILL BE
EXTENSIVE CLOUD COVER AND SOME SCATTERED RAIN SHOWERS WITH WEAK
FORCING ALOFT. MEANWHILE...ALL MODELS HAVE SHIFTED HANDLING OF
BERING SYSTEM WITH A MORE AGGRESSIVE SHORT-WAVE DRIVING EASTWARD
ACROSS THE SOUTHERN BERING (AS IS EVIDENT IN CURRENT SATELLITE
IMAGERY) WITH FRONTAL SYSTEM ARRIVING IN SOUTHWEST ALASKA SOONER
AND PENETRATING FARTHER INLAND. MEANWHILE THE LOW QUICKLY WRAPS UP
AND STALLS OVER THE NORTHERN BERING. ALTHOUGH EXACT LOW POSITIONS
VARY...CONFIDENCE IS HIGH ENOUGH IN HANDLING OF FRONT TO BUY INTO
THIS FASTER SOLUTION.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...AFTER DIURNAL CONVECTION DIES DOWN TONIGHT
EXPECT MORE STABLE AIR MASS TO GRADUALLY MOVE IN FROM THE WEST.
THERE IS CURRENTLY A LOT OF MID LEVEL MOISTURE OVER THE KUSKOKWIM
VALLEY...SO THIS MAY PROVIDE FOR A MUCH GRIMMER DAY FROM THE
WESTERN KENAI TO ANCHORAGE AND THE MAT-SU ON WEDNESDAY. FORCING IS
WEAK...BUT THERE WILL LIKELY BE SOME SHOWERS AROUND. ELSEWHERE
ACROSS SOUTHCENTRAL EXPECT A MIX OF SUN AND CLOUDS WITH DIURNALLY
DRIVEN SHOWERS...ESPECIALLY ALONG THE MOUNTAINS. FASTER TIMING OF
THE FRONT BARRELING ACROSS THE BERING SEA MEANS RAIN WILL REACH
KODIAK ISLAND THURSDAY AND SPREAD TO THE REST OF THE GULF COAST
THURSDAY NIGHT AND FRIDAY. THIS LIKE A CLASSIC DOWNSLOPE EVENT FOR
THE WESTERN KENAI/ANCHORAGE/MAT VALLEY AS THE FRONT SWINGS
NORTHWARD INTO THE GULF (BECOMING ORIENTED EAST-WEST) WITH RIDGE
BUILDING OUT AHEAD OF IT. IN FACT...THIS LOOKS LIKE MAINLY A
COASTAL EVENT WITH THE MAIN IMPACT INLAND BEING SOME CLOUDS AND
LOCALIZED GAP WINDS.

SOUTHWEST ALASKA...A STEADY STREAM OF WEAK UPPER WAVES WILL
CONTINUE TO ROTATE SOUTHWESTWARD FROM INTERIOR ALASKA ACROSS THE
KUSKOKWIM VALLEY THROUGH EARLY WEDNESDAY BEFORE UPSTREAM SHORT-
WAVE RIDGE ARRIVES AND CAUSES A REVERSAL OF FLOW...PUSHING
EVERYTHING EASTWARD. THE FRONT CROSSING THE BERING WILL ARRIVE
WEDNESDAY NIGHT...SO DON'T EXPECT ANY SIGNIFICANT BREAK IN CLOUDS
BETWEEN SYSTEMS. WITH A MORE AGGRESSIVE FRONTAL PROGRESSION
EXPECT RAIN TO SPREAD INLAND THURSDAY...ALTHOUGH RAIN WILL
CERTAINLY BE MUCH LIGHTER ACROSS THE SOUTHERN KUSKOKWIM VALLEY.
STRONG EASTERLY FLOW ALONG THE ALASKA RANGE WILL ALSO ALSO PRODUCE
SOME DOWNSLOPE DRYING ON THE WEST SIDE OF THE RANGE.

BERING SEA/ALEUTIANS...WITH FASTER FRONTAL PROGRESSION EXPECT LESS
RAIN THAN ORIGINALLY THOUGHT ALONG THE ALEUTIANS. HOWEVER...STILL
EXPECT A PERIOD OF MODERATE TO HEAVY RAIN AS IT PASSES THROUGH.
THE ENTIRE STORM SYSTEM WILL EXIT TO THE GULF FRIDAY WITH HIGH
PRESSURE BUILDING BACK IN. THIS WILL BE SHORT-LIVED THOUGH AS VERY
PROGRESSIVE FLOW BRINGS IN ANOTHER TROUGH OVER THE WEEKEND.

&&

.LONG TERM FORECAST (SAT AUG 9TH - TUE AUG 12TH)...

AN ACTIVE WAVE PATTERN ALOFT WILL CONTINUE THROUGH THE EXTENDED
PERIOD BEGINNING SATURDAY...WITH A LARGE AND DYNAMIC UPPER LOW
CENTERED OVER THE ALASKA PENINSULA. AN ASSOCIATED FRONT IN THE
GULF OF ALASKA WILL SPREAD RAIN OVER THE COASTAL LOCATIONS AND
COASTAL MOUNTAIN RANGES...WITH EXTENSIVE CLOUD COVER ACROSS
INTERIOR LOCATIONS. EVENTUALLY THE LOW AND ASSOCIATED FRONT WILL
WEAKEN AND TRACK EAST...LEAVING SHOWERY CONDITIONS ACROSS MOST OF
SOUTHERN ALASKA SUNDAY AND MONDAY....WITH TEMPERATURES CLIMBING
BACK TO NEAR OR SLIGHTLY ABOVE CLIMATOLOGY BY TUESDAY. ANOTHER
LARGE LOW WILL FORM ALONG THE NORTHEAST PACIFIC JET STREAM ACROSS
THE WESTERN BERING SUNDAY AND MONDAY...AND WILL TRACK INTO THE
EASTERN BERING AND ALEUTIANS TUESDAY.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 170 172 173 174 175 176 177 178.
FIRE WEATHER...NONE.

&&

SEB AUG 14