Small Craft Advisory 42, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
423 PM AKST WED JAN 14 2015

.ANALYSIS AND UPPER LEVELS...
A VERY LARGE CYCLONIC MERRY-GO-ROUND CONTINUES OVER THE NORTH
PACIFIC/BERING SEA THANKS TO THE DOWNSTREAM BLOCKING RIDGE ALONG
THE WEST COAST OF NORTH AMERICA. SATELLITE IMAGERY SHOWS THREE
DEEP LOWS OVER THE NORTH PACIFIC. THE PRIMARY ONE OF CONCERN IS
A STORM FORCE LOW TRACKING TOWARD THE ALASKA PENINSULA WITH A
FRONTAL SYSTEM TRACKING NORTH AND WEST ACROSS THE GULF OF ALASKA.
THERE IS ALSO A VERY SHARP SHORT-WAVE ALOFT TRACKING RIGHT BEHIND
THE SURFACE FRONT. RADAR IMAGERY REFLECTS THE STRONG VERTICAL
MOTION OUT AHEAD OF THIS...WITH MODERATE TO HEAVY PRECIPITATION
OVER THE NORTHERN TO WESTERN GULF.

THE ORIENTATION OF THE FRONT CROSSING THE GULF IS SOUTHWEST TO
NORTHEAST SO LOW LEVEL FLOW OUT AHEAD OF IT IS NORTHERLY.
THUS...AS PRECIPITATION CONTINUES TO PROGRESS ONSHORE OF
SOUTHCENTRAL AND BRISTOL BAY THIS AFTERNOON AND EVENING THERE IS
LITTLE OR NO CROSS BARRIER FLOW...SO MOST AREAS SHOULD SEE A BRIEF
PERIOD OF LIGHT PRECIPITATION. HOWEVER AS FRONT MOVES THROUGH THE
LOW LEVEL FLOW WILL QUICKLY BECOME STRONG EASTERLY PRODUCING
DOWNSLOPE DRYING FOR MANY AREAS. WITH THE EXCEPTION OF THE COPPER
RIVER BASIN SURFACE TEMPERATURES ARE PRIMARILY ABOVE FREEZING
ACROSS SOUTHCENTRAL ALASKA AND OVER INTO BRISTOL BAY. THUS...THE
ONLY POSSIBILITY OF FREEZING RAIN WILL BE IN THE COPPER RIVER
BASIN.

THERE ARE A COUPLE OTHER MUCH WEAKER FEATURES IN THE FORECAST
AREA. AN UPPER LEVEL SHORT-WAVE IS EXITING THE KUSKOKWIM DELTA
AND HEADED ACROSS THE NORTHERN BERING...BRINGING AN END TO THE
MOST RECENT FREEZING RAIN EVENT. A WEAK LOW NORTH OF THE WESTERN
ALEUTIANS IS ABOUT TO EXIT THE AREA. LASTLY...A DEEP LOW SOUTH OF
THE EASTERN ALEUTIANS IS THROWING SOME PRECIP AND WINDS TOWARD THE
CENTRAL TO EASTERN ALEUTIANS...BUT THE GREATEST IMPACTS ARE OVER
THE NORTH PACIFIC.

&&

.MODEL DISCUSSION...
MODELS REMAIN IN GOOD SYNOPTIC AGREEMENT THE NEXT COUPLE DAYS WITH
JUST SOME MINOR DIFFERENCES IN SURFACE LOW POSITIONS. THUS FORECAST
CONFIDENCE WITH THE CURRENT STORM SYSTEM IS ABOVE AVERAGE. MODELS
DO QUICKLY DIVERGE WITH DEVELOPMENT AND TRACK OF A LOW OVER THE
NORTHEAST PACIFIC AND UP TO THE GULF OF ALASKA FRIDAY AND FRIDAY
NIGHT. WITH NO REASON TO FAVOR ANY PARTICULAR SOLUTION AT THIS
POINT IN TIME WILL STICK CLOSE TO INHERITED GRIDS.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
MORE OF THE SAME IS IN STORE THROUGH FRIDAY AS THE GULF LOW
SLOWLY WEAKENS NEAR THE ALASKA PENINSULA AND DEEP SOUTHERLY FLOW
FOCUSES ABUNDANT PRECIPITATION ALONG THE GULF COAST...WITH STRONG
DOWNSLOPE FLOW HELPING TO KEEP INLAND AREAS LIMITED TO JUST A FEW
SHOWERS. PRECIPITATION TYPE WILL CONTINUE TO BE MAINLY
RAIN...ALTHOUGH A FEW PATCHES OF LIGHT FREEZING RAIN CANNOT BE
RULED OUT TONIGHT FROM ANCHORAGE INTO THE MAT-SU AS SURFACE
TEMPERATURES DIP BELOW FREEZING AND A WARM LAYER PERSISTS ABOVE
THE SURFACE. FREEZING RAIN POTENTIAL WILL DIMINISH ON THURSDAY AS
TEMPERATURES GRADUALLY COOL ALOFT...ALLOWING SOME SNOW TO BEGIN TO
MIX IN BY THURSDAY NIGHT.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (TONIGHT THROUGH FRIDAY)...

PRECIPITATION HAS BEGUN TO DEVELOP ACROSS THE BRISTOL BAY AREA
THIS AFTERNOON AHEAD OF A WARM FRONT PUSHING TOWARD THE
NORTHWESTERN GULF COAST. RAIN WILL CONTINUE TO OVERSPREAD THE
BRISTOL BAY AREA THROUGH THE REMAINDER OF THE NIGHT. HOWEVER...STRONG
CROSS BARRIER FLOW OVER THE ALASKA AND ALEUTIAN RANGES WILL CREATE
AREAS OF DOWNSLOPING OVER KING SALMON (AS WELL AS OTHER IMMEDIATE
AREAS ON THE LEEWARD SIDE OF THE MOUNTAINS) AND THE EASTERN HALF
OF THE LOWER KUSKOKWIM VALLEY AFTER MIDNIGHT. PRECIPITATION IN THE
KUSKOKWIM DELTA AND THE EASTERN HALF OF THE LOWER KUSKOKWIM VALLEY
WILL LIKELY FALL IN THE FORM OF SNOW AS SURFACE TO 850 MB THICKNESSES
DROP BELOW 129 DECAMETERS. THIS IS DUE IN LARGE PART TO NORTHEASTERLY
WINDS AT BOTH THE SURFACE AND JUST OFF THE SURFACE THAT HAVE USHER
IN COOLER AIR FROM THE INTERIOR (AS SEEN IN THE JAN 14 12Z AND JAN
15 00Z RAOBS) WHICH HAS CHISELED AWAY AT THE WARM NOSE THAT BROUGHT
FREEZING RAIN TO THE BETHEL AREA THIS MORNING. NEVERTHELESS...A
SMALL AREA OF LIGHT FREEZING RAIN MIGHT BE POSSIBLE IN THE FAR
SOUTHEASTERN SECTION OF THE KUSKOKWIM DELTA BUT PRECIPITATION WILL
BE LIGHT AND LIKELY HAVE MINIMAL IF ANY IMPACT AT ALL.

THIS WET PERIOD WILL LIKELY PERSIST THROUGH THE REMAINDER OF THE
WORK WEEK...WITH CROSS BARRIER FLOW EATING UP A BIT OF THE
PRECIPITATION FALLING OVER THE BRISTOL BAY AREA. THE ANOMALOUSLY
WARM TEMPERATURES ARE EXPECTED TO PERSIST THROUGH THE REMAINDER OF
THE WEEK AS A LOW PARKS ITSELF OVER THE ALASKA PENINSULA AND
CONTINUES TO ADVECT WARM AIR NORTHWARD.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (TONIGHT THROUGH FRIDAY)...

AS THE AREA OF LOW PRESSURE OVER THE WESTERN BERING SEA CONTINUES
TO MOVE WESTWARD AND DISSIPATE...YET ANOTHER LOW FROM THE NORTH
PACIFIC WILL PUSH TOWARD THE ALASKA PENINSULA AND THE EASTERN
ALEUTIANS EARLY THURSDAY MORNING. THIS LOW WILL STALL OVER THE
ALASKA PENINSULA ON THURSDAY AFTERNOON AND BRING RAIN AND POSSIBLY
SOME SNOW TO THE EASTERN HALF OF THE BERING SEA. THE SNOW WOULD
LIKELY BE CONFINED TO THE PRIBILOF ISLANDS WHILE THE EASTERN
ALEUTIANS AND ALASKA PENINSULA REMAIN DOMINATED BY RAIN. SCATTERED
RAIN AND SNOW SHOWERS WILL BE SEEN OVER THE REMAINDER OF THE
BERING SEA THROUGH THURSDAY NIGHT BEFORE SHOWERS TURN TO ALL SNOW
AS A MUCH COLDER AIR MASS DROPS SOUTH FROM SIBERIA.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
BY EARLY SATURDAY THE LAST OF A SERIES OF GULF LOWS WILL APPROACH
THE NORTH GULF COAST...BRINGING YET ANOTHER ROUND OF RAIN AND WARM
TEMPERATURES MAINLY TO THE COASTAL AREAS. THE IMPACT OF THIS
SYSTEM TO THE INTERIOR SOUTHERN MAINLAND IS STILL UNKNOWN DUE TO
UNCERTAINTY OF THE LOW TRACK THROUGH THE GULF. THE NAM AND MOST
RECENT GFS ARE MUCH FURTHER WEST WITH THIS LOW...BRINING IT
TOWARDS THE KENAI BY LATE SATURDAY...WHILE THE EC HAS CONSISTENTLY BEEN
THE FURTHEST EAST BY TRACKING TOWARDS THE NORTHERN PANHANDLE. THE
GEM GLOBAL IS CURRENTLY THE PREFERRED MODEL FOR THIS SYSTEM AS IT
IS A COMPRISE BETWEEN THE NAM/GFS AND THE EC...AND KEEPS
SOUTHCENTRAL MOSTLY DRY THROUGH THE WEEKEND. CONFIDENCE IN THAT
FORECAST IS HOWEVER LOW DUE TO THE LARGE UNCERTAINTY OF THE LOW
TRACK. OUT WEST...A COLD FRONT APPROACHING THE SOUTHWEST MAINLAND
ON FRIDAY EVENING WILL BRING RAIN/SNOW AND COOLING TEMPERATURES TO
THE AREA THAT LOOKS TO CONTINUE INTO SATURDAY OR POSSIBLY SUNDAY.

STARTING ON SUNDAY THERE IS GOOD AGREEMENT CONDITIONS SHOULD
IMPROVE THROUGHOUT THE MAINLAND...BRINGING ANOTHER SHORT LIVED
PERIOD OF QUIET WEATHER (WITH CONTINUED WARM TEMPERATURES) THAT
SHOULD CONTINUE INTO EARLY NEXT WEEK. YET ANOTHER NORTH PACIFIC
LOW WILL THEN APPROACH THE GULF STARTING ON TUESDAY...BRINING A
RETURN TO WARM AND ACTIVE WEATHER TO THE REGION THROUGH MID WEEK.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES 119 120 130 131 138 160 165 179 351 352 412 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SB
SOUTHCENTRAL ALASKA...CB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MC
LONG TERM...DEK