Small Craft Advisory 1020, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
225 PM AKST FRI DEC 19 2014

.ANALYSIS AND UPPER LEVELS...
AN IMPRESSIVELY STRONG 190 KT EAST-ASIAN JET CONTINUES TO RIP
ACROSS THE PACIFIC SOUTH OF THE ALEUTIANS. THIS IS CARVING OUT A
VERY WIDE/BROAD LONGWAVE TROUGH ACROSS MUCH OF THE NORTH PACIFIC
INCLUDING MAINLAND ALASKA AND THE BERING SEA REGION. SATELLITE
IMAGERY SHOWS A PAIR OF VERTICALLY STACKED LOWS AFFECTING THE
STATE....ONE IN THE GULF AND ONE NEAR THE CENTRAL ALEUTIANS. BOTH
ARE WEAKENING...BUT THE CENTRAL PRESSURE OF THE BERING LOW IS
RISING SLOWER DUE TO FALLING HEIGHTS ALOFT RESULTING FROM THE
BUCKLING/AMPLIFYING OF THE JET OVERHEAD. AN AREA OF GALE-FORCE
WINDS ON THE NORTHWEST SIDE OF THE GULF LOW HAS MOVED ACROSS
KODIAK ISLAND ALONG WITH STEADY RAINFALL. ELSEWHERE IN THE
GULF...LITTLE MORE THAN ISOLATED TO SCATTERED RAIN SHOWERS ARE
AFFECTING THE NORTH GULF COAST. SUFFICIENT CROSS-BARRIER WINDS
CONTINUE TO KEEP INLAND AREAS ALMOST UNIFORMLY DRY.
OUT WEST...THE SLOW-MOVING LOW HAS BROUGHT ENOUGH WARM AIR
INTO THE AREA THAT PRECIP IS FALLING AS MOSTLY RAIN EAST OF DUTCH
HARBOR...MOSTLY SNOW WEST OF ADAK...AND A MIX IN BETWEEN. GUSTY
NORTH WINDS ARE BEGINNING TO INCREASE ACROSS THE WESTERN ALEUTIANS
AS A STRONGER SURGE OF COLD AIR BEGINS TO FILTER DOWN OFF THE
RUSSIAN LANDMASS...A TREND ALSO SUPPORTED BY AFTERNOON SATELLITE
IMAGERY.

&&

.MODEL DISCUSSION...
THE MAIN FORECAST CHALLENGE IN THE GULF REGION OVER THE COMING
DAYS WILL BE HOW FAR NORTH AND WEST A DEVELOPING LOW CENTER MOVING
TOWARD PRINCE WILLIAM SOUND MOVES SATURDAY NIGHT INTO SUNDAY. ALL
MAJOR MODELS HAVE NOW BEGUN TO SHOW A TREND FURTHER NORTHWEST
WITH THE LOW POSITION...THOUGH THE NAM REMAINS THE MOST EXTREME
AND BRINGS THE LOW ONSHORE THE KENAI PENINSULA BY EARLY SUNDAY
MORNING. WHILE WE WILL BE TRENDING THE FORECAST TOWARD A SOLUTION
THAT BRINGS MORE SHOWER ACTIVITY INTO PRINCE WILLIAM SOUND
AREA...WILL NOT BITE OFF ON THE OVERLY-AGGRESSIVE NAM SOLUTION.
MODEL CONFIDENCE IS NEAR OR SLIGHTLY BELOW AVERAGE.

OUT WEST...THE MODELS IN THE FIRST FEW DAYS ARE IN BETTER
AGREEMENT WITH MOST OF THE FEATURES. THE CHAIN OF MULTIPLE (WEAK)
LOWS ALONG THE POLEWARD SIDE OF THE STRONG JET CONTINUE TO BE
PROBLEMATIC AS ALL MODELS HAVE A SLIGHTLY DIFFERENT SOLUTION.
FORTUNATELY THE IMPACTS OF THESE DIFFERENCES WILL BE FAIRLY
MINIMAL DURING THE SHORT TERM FORECAST PERIOD AS THE SHOWERY AND
ACTIVE WEATHER REMAINS ALONG AND MOSTLY SOUTH OF THE EASTERN
ALEUTIANS/ALASKA PENINSULA. THE REGIONAL CANADIAN GEM WAS USED TO
TAKE ADVANTAGE OF SUPERIOR RESOLUTION AND ALSO COORDINATE WITH
SURROUNDING OFFICES.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE UPPER LOW WILL REMAIN NEARLY IN PLACE OVER THE SOUTHWEST GULF
THROUGH SUNDAY...AND WILL SLOWLY BE ABSORBED INTO THE LOW FURTHER
WEST. A NUMBER OF SYSTEMS ASSOCIATED WITH THIS LOW WILL ROTATE
THROUGH THE NORTHERN GULF. THE FIRST OF THESE IS OVER SOUTH
CENTRAL THIS EVENING AND WILL DISSIPATE TONIGHT. ANOTHER WILL
SCRAPE THE GULF COAST LATER TONIGHT. A STRONGER SYSTEM WITH A
DEFINED SURFACE LOW WILL REACH THE COAST. BY THEN THE PATTERN WILL
BE CHANGING...WHICH WILL OPEN UP SOUTHERLY FLOW AND ALLOW THAT
SYSTEM TO WORK ITS WAY INTO INLAND SOUTH CENTRAL ALASKA. CHANCES
OF PRECIPITATION WILL BEGIN IN ANCHORAGE SUNDAY AFTERNOON AS THE
LOW MOVES ONSHORE.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
A WEAKENING LOW EXITING THE SOUTHWESTERN GULF TODAY WILL CONTINUE
TO TRACK WESTWARD...KEEPING SOME SCATTERED SHOWERS ALONG THE
ALEUTIAN RANGE AND PARTS OF THE ALASKA PENINSULA THROUGH TOMORROW
NIGHT. OTHERWISE...DRY CONDITIONS WILL PERSIST ACROSS THE REGION
THROUGH THE WEEKEND. A SHORT-WAVE RIDGE BUILDING AHEAD OF A TROUGH
MOVING OUT OF ASIA WILL HELP AMPLIFY THE UPPER LEVEL FLOW THIS
WEEKEND ALLOWING COLDER AIR TO GRADUALLY MAKE ITS WAY DOWN FROM
THE NORTH. EXPECT TEMPERATURES TO DROP A LITTLE MORE EACH DAY. BY
SUNDAY HIGH TEMPS ACROSS MUCH OF THE REGION WILL BE BELOW
NORMAL...WITH WIDESPREAD SINGLE DIGITS FROM THE KUSKOKWIM DELTA TO
THE KUSKOKWIM VALLEY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE VERTICALLY STACKED LOW JUST SOUTH OF THE CENTRAL ALEUTIANS
WILL SLOWLY WEAKEN AS IT TRACKS FURTHER EASTWARD THROUGH THE
WEEKEND...KEEPING SHOWERY AND GUSTY CONDITIONS OVER PARTS OF THE
ALEUTIAN CHAIN AND BERING. COLDER AIR WILL BEGIN TO FILTER DOWN
BEHIND THIS SYSTEM TOMORROW...BRINGING GALE FORCE WINDS AND
INCREASING INSTABILITY (ENHANCING STABILITY SHOWERS) ALONG THE
WESTERN ALEUTIANS THROUGH SUNDAY MORNING. THIS COLDER AIR WILL
ALSO LEAD TO A TRANSITION TO A PREDOMINANT PRECIP-TYPE OF SNOW FOR
THE WESTERN ALEUTIANS AND MUCH OF THE BERING SEA.

&&

.LONG TERM FORECAST (MONDAY THROUGH FRIDAY)...
AN ACTIVE WEATHER PATTERN CONTINUES THROUGH THE NEXT WEEK WITH A
LONG WAVE PATTERN DOMINANT OVER THE EASTERN BERING. A STORM SYSTEM
ON MONDAY ORGANIZES FROM THE NORTH PACIFIC PUSHING A WARM FRONT
INTO THE SOUTHERN BERING BY TUESDAY MORNING. GUSTY GALE WINDS AND
RAIN WILL ACCOMPANY THE FRONT AS IT PUSHES QUICKLY TOWARD THE
CENTRAL BERING. THERE ARE STILL LARGE DIFFERENCES IN THE MODEL
SOLUTIONS ON THE TRACK AND STRENGTH OF THIS SYSTEM. MODELS ARE IN
DECENT AGREEMENT THAT THE SURFACE LOW DEEPENS TO AROUND 960 MB
TUESDAY NIGHT AS IT MOVES INTO THE SOUTHWESTERN BERING. FUTURE
UPDATES SHOULD BE MONITORED AS STORM FORCE WINDS AROUND THE CORE
OF THE LOW ARE LIKELY TO IMPACT THE BERING AND ALEUTIAN CHAIN
MONDAY NIGHT AND TUESDAY.

AT THE START OF THE WEEK FOR THE SOUTHERN MAINLAND...A DRIER AND
COOLER PATTERN ENSUES AS A LOW DIMINISHES IN THE NORTHERN GULF.
THE COOLER PATTERN AT THE START OF THE WEEK WILL CREATE PRECIPITATION
CHALLENGES FOR WEDNESDAY INTO FRIDAY AS A MODIFIED WARMER AIR
MASS PUSHES INTO SOUTHERN ALASKA AS THE BERING FRONT MOVES ACROSS
THE SOUTHERN MAINLAND.

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 119 120 130 131 138 176 177 178.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AD
SOUTHCENTRAL ALASKA...LUDWIG
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PEPE
LONG TERM...KH