Small Craft Advisory 716, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
510 AM AKDT SAT SEP 12 2015

.ANALYSIS AND UPPER LEVELS...

AN AMPLIFYING UPPER-LEVEL TROUGH OVER MUCH OF THE STATE IS THE
DOMINANT WEATHER FEATURE. ONSHORE UNSTABLE SOUTHWESTERLY FLOW
WRAPPING AROUND THE BASE OF THE TROUGH OVER SOUTHCENTRAL IS
BRINGING SHOWERS TO MUCH OF THE NORTHERN GULF COAST. SOME
STRONGER BANDS OF RAIN ARE MOVING ONSHORE ALONG COOK INLET AND
PRINCE WILLIAM SOUND. A COLD FRONT IS VISIBLE ON SATELLITE IMAGERY
PUSHING EASTWARD ACROSS THE CENTRAL MAINLAND THROUGH THE ALASKA
PENINSULA. ALONG AND AHEAD OF THE FRONT...NORTHWESTERLY SURFACE
WINDS ARE GUSTING THROUGH FAVORABLE GAPS IN THE ALEUTIAN RANGE AND
THROUGH SHELIKOF STRAIT. BEHIND THE FRONT...MORE STABLE CONDITIONS
EXIST OVER THE KUSKOKWIM DELTA WITH A FEW SHOWERS VISIBLE ON THE
RADAR AS SOME WEAK UPPER DISTURBANCES ROTATE AROUND THE BASE OF
THE TROUGH. OVER THE BERING...NORTHWESTERLY FLOW IS KEEPING THE
AREA COOL AND STABLE. A WEATHER FRONT ASSOCIATED WITH THE TROPICAL
REMNANTS OF FORMER TYPHOON KILO IS APPROACHING THE WESTERN
ALEUTIANS.

.MODEL DISCUSSION...MODELS REMAIN IN GOOD SYNOPTIC AGREEMENT...
LENDING TO MODERATE TO HIGH FORECAST CONFIDENCE. THE TWO MOST
SIGNIFICANT DIFFERENCES ARE HOW THEY HANDLE THE QPF AMOUNTS OVER
SOUTHCENTRAL TODAY AND SOME OF THE TIMING ASPECTS OF THE REMNANTS
OF FORMER TYPHOON KILO APPROACHING THE WEST COAST ON SUNDAY. FIRST
THINGS FIRST...THE COLD FRONT APPROACHING THE ALASKA RANGE IS
PROGGED TO BRING A MODERATE AMOUNT OF RAIN TO AREAS FROM THE
WESTERN KENAI PENINSULA UP THROUGH THE SUSITNA VALLEY THIS
MORNING. THE GFS IS CLEARLY THE MOST BULLISH WITH THIS
FEATURE...WITH THE EC AND GEM- REG ON THE LOWER END. FROM WATCHING
THIS FEATURE SWEEP THROUGH SOUTHWEST AK YESTERDAY...WE DO EXPECT A
CONVECTIVE ELEMENT WITH IT. IN FACT...WE HAVE HAD SOME ENHANCEMENT
ON RADAR OVERNIGHT ALONG THIS FRONT. IT APPEARS THAT THE HI-RES
ARW HAS THE BEST HANDLE ON THIS...SO WE HAVE RELIED ON THE HIGHER
RES MODELS IN FORECASTING THE PRECIPITATION AMOUNTS. REGARDING
PRECIPITATION REACHING THE WEST COAST LATER IN THE WEEKEND...THE
NAM IS SLIGHTLY SLOWER. ALL THE GLOBAL MODELS ARE PRETTY
UNIFORM...AND SINCE THEY TYPICALLY PERFORM BETTER IN HANDLING
FORMER TROPICAL SYSTEMS...WE HAVE UTILIZED A GFS/EC COMBO WITH
THAT FEATURE.

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...

A COLD FRONT SWEEPING ACROSS WESTERN ALASKA IMPACTS SOUTHCENTRAL AS
IT MOVES INTO WESTERN COOK INLET/SUSITNA VALLEY TODAY AND ACROSS
THE COPPER RIVER BASIN AND EASTERN GULF TONIGHT. THE MAIN IMPACTS
WILL BE RAINFALL POTENTIAL FROM THE SUSITNA VALLEY TO THE ANCHORAGE
BOWL TODAY AND THE BRISK GAP FLOWS FLOWS DEVELOPING IN ITS WAKE.
DEEP AND MOIST SOUTHWESTERLY FLOW WILL ENHANCE UPSLOPE RAINS FROM THE
EASTERN AND NORTHERN SUSITNA VALLEY TO THE ANCHORAGE BOWL...AND
COMBINED WITH UPPER JET DYNAMICS WILL GIVE RISE TO PERIODS OF
MODERATE TO LOCALLY HEAVY RAIN (ESPECIALLY ALONG UPSLOPE TERRAIN)
TODAY. THE COLD FRONT PUSHES EAST THIS EVENING SO RAIN SHOULD END
WEST OF THE COPPER RIVER BASIN AS COOLER AND DRIER AIR PUSHES IN
FROM THE WEST. BRISK TO STRONG WESTERLY GAP FLOWS WILL DEVELOP
ALONG THE ALASKA/ALEUTIAN RANGE WITH GALES DEVELOPING ACROSS THE
BARREN ISLANDS TODAY AND CONTINUING THROUGH TONIGHT. FREEZING
LEVELS ACROSS THE DENALI HIGHWAY SHOULD DROP TO AROUND 1500 FT
THIS EVENING THEN TO BELOW 500 FT AFTER FRONTAL PASSAGE...SO SOME
OF THE HILLS WILL BE A LITTLE WHITER.

ON SUNDAY...WESTERLY GAP FLOWS WILL GIVE RISE TO A GENERALLY
BROADER SOUTHERLY FLOW ACROSS THE WESTERN GULF AND COOK INLET AS A
FRONTAL SYSTEM ASSOCIATED WITH OLD TROPICAL KILO PUSHES EASTWARD.
RAIN ASSOCIATED WITH THIS FRONTAL SYSTEM WILL LIKELY SPREAD ACROSS
MUCH OF SOUTHCENTRAL SUN NIGHT.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
A DISTURBANCE WITH RAIN AND ONSHORE WINDS IN WEST TO NORTHWEST
FLOW ALOFT WILL MOVE INTO THE KUSKOKWIM DELTA THIS MORNING AND
SLOWLY SWEEP EAST THROUGH TONIGHT. BEFORE IT CAN EXIT SOUTHWEST
ALASKA THE NEXT SYSTEM LOADED WITH DEEP TROPICAL MOISTURE AHEAD
OF A STRONG WARM FRONT WILL RAPIDLY ARRIVE AT THE COAST SUNDAY
MORNING AND BEGIN WIDESPREAD RAIN FOR SOUTHWEST ALASKA. AFTER THE
WARM FRONT MOVES INLAND LATE SUNDAY...THE COLD FRONT MOVES ACROSS
SOUTHWEST ALASKA SUNDAY NIGHT AND SETS UP A STATIONARY BOUNDARY
ALONG THE SOUTHWEST COAST...WHICH WILL BECOME THE FOCUSING
MECHANISM FOR ADDITIONAL DISTURBANCES TO MOVE ALONG LATER IN THE
WEEK.

A POTENTIAL IMPACT WITH THIS UPCOMING SYSTEM WILL BE WITH STRONG
ONSHORE FLOW AND THE POTENTIAL FOR MINOR STORM SURGES...PARTICULARLY
TOWARD THE BRISTOL BAY COASTLINE WHERE FUNNELING CAN OCCUR. AS OF
RIGHT NOW...IT APPEARS THAT THE GREATEST POTENTIAL SURGE WILL
OCCUR AT LOW TIDE AND DURING A PERIOD OF LOWER ASTRONOMICAL
TIDE...SO NO SIGNIFICANT IMPACTS ARE EXPECTED.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
MAIN STORY OVER THE NEXT COUPLE OF DAYS WILL BE THE WEATHER SYSTEM
MOVING WEST TO EAST SWIFTLY OVER THE CENTRAL BERING...WITH THE
PRIMARY IMPACTS BEING GALE FORCE WINDS AND INCREASED WAVE HEIGHTS
IN THE WARM SECTOR OF THE STORM. THE WORST OF THESE
CONDITIONS...INCLUDING THE STEADY RAIN...WILL MISS THE ALEUTIAN
CHAIN TO THE NORTH...BUT WILL IMPACT THE PRIBILOFS AND ALASKA
PENINSULA PARTICULARLY SUNDAY INTO MONDAY.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE REMNANTS OF TYPHOON KILO WILL MOVE INTO THE NORTHERN BERING
SEA ON SUNDAY...BRINGING WIDESPREAD RAIN TO THE SOUTHERN MAINLAND
THROUGH MONDAY. WHILE THIS SYSTEM WILL BRING RAIN TO MOST
AREAS...IT SHOULD BE NOTABLY LIGHTER THAN PREVIOUS
SYSTEMS...ESPECIALLY FOR COMMUNITIES ALONG THE GULF COAST...AS
THE FLOW ALOFT WILL GENERALLY BE NORTHWESTERLY AND WILL NOT TAP
INTO THE DEEP MOISTURE OVER THE NORTH PACIFIC. GALE FORCE WINDS
ARE STILL EXPECTED WITH THIS SYSTEM FROM THE CENTRAL BERING TO THE
SOUTHWEST COAST. AFTER THIS SYSTEM CROSSES THE AKPEN INTO THE
GULF ON TUESDAY...AN ARCTIC TROUGH OVER THE BROOKS RANGE WILL
SLOWLY DESCEND INTO THE MAINLAND THROUGH THE MIDDLE OF NEXT
WEEK...KEEPING CYCLONIC FLOW AND ACTIVE WEATHER FOR MUCH OF THE
AREA THROUGH THE MIDDLE OF NEXT WEEK.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES 130 131 160 165 170 178-181.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RD/MSO
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CC
LONG TERM...DEK/DS