Small Craft Advisory 880, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
438 PM AKST WED NOV 5 2014

.ANALYSIS AND UPPER LEVELS...
THERE IS A BROAD UPPER LEVEL TROUGH STRETCHING FROM THE SOUTHERN
GULF OF ALASKA EASTWARD TO JUST SOUTH OF DUTCH HARBOR THEN
EAST/NORTHEAST ACROSS THE SOUTHWEST BERING SEA. THERE ARE SEVERAL
EMBEDDED LOWS IN THIS TROUGH. ONE OF THESE IS CENTERED JUST SOUTH
OF KODIAK ISLAND...ONE IS CENTERED NEAR COLD BAY...AND ONE IS
SOUTH OF DUTCH HARBOR. THERE IS A WEAKENING/DISSIPATING FRONT
STRETCHING NORTHWESTWARD FROM DUTCH HARBOR ACROSS THE BERING SEA.
AN UPPER LEVEL HIGH IS CENTERED OVER JUST OFF THE NORTHWEST COAST
OF ALASKA AND EXTENDS SOUTHWARD INTO SOUTHWEST ALASKA.

&&

.MODEL DISCUSSION...
THE NUMERICAL MODELS ARE IN DECENT AGREEMENT THROUGH 48 HOURS INTO
THE FORECAST (EARLY FRIDAY MORNING). THERE ARE SOME DIFFERENCES ON
WHERE EXACTLY THEY PLACE THE LOW IN THE SOUTHWEST GULF ON THURSDAY
AND ESPECIALLY FRIDAY...BUT MOST WEATHER ELEMENTS ARE SIMILAR
EXCEPT MARINE WINDS NEAR THE LOW. THE MODEL CONSENSUS OF THE
SPINNING UP LOW SOUTHWEST OF THE WESTERN ALEUTAINS HAS ALSO
IMPROVED WITH THE 12Z RUNS OF THE MODELS...BUT IS STILL SHOWING
MORE DIFFERENCES BY 48 HOURS THAN WOULD BE DESIRED FOR A STORM OF
THIS MAGNITUDE. BUT WITH THE GFS AND ECMWF IN GOOD AGREEMENT THE
CONFIDENCE FOR THIS TIME FRAME IS FAIRLY HIGH. FROM 48 TO 84
HOURS (SATURDAY AFTERNOON) THE GUIDANCE SPLITS INTO TWO
CAMPS...WITH THE CANADIAN GEM AND GFS TAKING A FURTHER EAST
(FASTER) AND FURTHER NORTH TRACK WITH THE MAJOR LOW MOVING EAST
ACROSS THE BERING SEA AND THE ECMWF SLOWER AND FURTHER SOUTH. WITH
VERY IMPACTFUL WEATHER (HIGH WINDS AND SEAS) IT WOULD BE PREFERRED
IF THE MODELS WERE IN BETTER AGREEMENT. AS IT STANDS...THE ECMWF
IS THE MODEL OF CHOICE DUE TO ITS BETTER HISTORY OF HANDLING SUCH
EVENTS.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE UPPER LEVEL TROUGH OVER THE NORTHERN GULF IS MOVING AT A FAST
CLIP AND WILL EXIT QUICKLY TO THE WEST THIS AFTERNOON. AS HAS
BEEN THE CASE RECENTLY THE BULK OF PRECIP WITH THIS WILL FALL
ALONG THE GULF COAST. HOWEVER...WITH A STEADY BAND OF PRECIP
NOTED IN RADAR IMAGERY THIS MORNING AND FAIRLY WEAK CROSS BARRIER
FLOW...EXPECT A FEW SHOWERS MAY MAKE IT OVER THE MOUNTAINS TO
ANCHORAGE AND THE WESTERN KENAI THIS MORNING. MEANWHILE...A
COMPACT SURFACE LOW EAST OF THE BARREN ISLANDS WILL BE FORCED
SOUTHWARD TO KODIAK ISLAND...BRINGING SHOWERS AND GUSTY WINDS
WITH IT.

THE PATTERN WILL UNDERGO A SHIFT TONIGHT AS A DIGGING TROUGH
SOUTH OF THE ALEUTIANS INITIATES CYCLOGENESIS SOUTH OF THE ALASKA
PENINSULA HELPING TO PULL THE UPPER LOW SOUTH OF KODIAK WESTWARD
INTO THE EASTERN BERING. SOUTHCENTRAL WILL DRY OUT WITH THE EXIT
OF THIS LOW.

MODELS HAVE TRENDED TOWARD A MORE INTENSE AND RAPID DEEPENING OF
THE LOW SOUTH OF THE ALASKA PENINSULA. FORECASTS NOW REFLECT THIS
WITH A GALE FORCE FRONTAL SYSTEM MOVING NORTHWARD ACROSS THE GULF
THURSDAY AND THURSDAY NIGHT. AS THE FRONT REACHES SOUTHCENTRAL
STRONG EASTERLY FLOW WILL PRODUCE DOWNSLOPE DRYING IN THE LEE OF
THE CHUGACH AND KENAI MOUNTAINS...WITH THE GULF COAST ONCE AGAIN
RECEIVING THE LIONS SHARE OF PRECIP.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
DRY CONDITIONS WILL REMAIN FOR THE MAINLAND TODAY. CLEAR SKIES AND
LIGHT WINDS HAVE ALLOWED TEMPERATURES TO DROP BELOW ZERO FOR LOWER
ELEVATIONS OF THE LOWER KUSKOKWIM VALLEY. TEMPERATURES WILL
REBOUND THIS AFTERNOON WITH TEMPERATURES IN THE TEENS FOR THE
KUSKOKWIM DELTA AND VALLEY WITH TEMPERATURES IN THE LOW 20S FOR
PARTS OF INTERIOR BRISTOL BAY. SOME LOW STRATUS AND FOG HAS
MOVED ACROSS THE ALEUTIAN RANGE AND ARE AFFECTING PARTS OF THE
ALASKA PENINSULA. EXPECT THEM TO HANG AROUND UNTIL THE AFTERNOON
HOURS BEFORE LIFTING/DISSIPATING. ON THURSDAY A DEVELOPING LOW
PRESSURE SYSTEM SOUTH OF THE ALASKA PENINSULA WILL SPREAD CLOUDS
BACK OVER THE MAINLAND AND INTRODUCE A CHANCE FOR SNOW...MAINLY
FOR INTERIOR BRISTOL BAY. UNTIL THEN EXPECT DRY AND SEASONABLY
COLD CONDITIONS WITH LIGHT NORTHERLY WINDS IN MOST AREAS.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE FRONTAL BOUNDARY OVER THE CENTRAL BERING SEA IS RAPIDLY
WEAKENING THIS MORNING. AREAS OF RAIN ARE CONCENTRATED RIGHT ALONG
THE FRONT FROM DUTCH HARBOR TO JUST WEST OF THE PRIBILOF ISLANDS.
SOME SCATTERED RAIN AND SNOW SHOWERS ARE WITHIN THE SOUTHEASTERLY
FLOW CLOSE TO THE FRONT AND WILL DIMINISHING TONIGHT INTO
THURSDAY. ON THE WESTERN SIDE OF THE FRONT SCATTERED SHOWERS ARE
AFFECTING THE WESTERN ALEUTIANS AND WILL SLOWLY TAPER OVER THE
NEXT COUPLE DAYS. A FRONTAL BOUNDARY WILL WORK TOWARD KODIAK
ISLAND ON THURSDAY BRINGING GALE FORCE WINDS AND A RAIN/SNOW MIX.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...

THE UPPER LEVEL TROUGH OVER THE GULF ON FRI WILL BE ABSORBED INTO
A MASSIVE UPPER LEVEL RIDGE ON SAT. THIS RIDGE WILL RESIDE OFF THE
WEST COAST OF NORTH AMERICA AND INTO THE ALCAN AT LEAST THROUGH
THE MIDDLE OF NEXT WEEK. THIS PATTERN CHANGE WILL ALLOW AN UPPER
LEVEL TROUGH AND EMBEDDED CUT-OFF LOW THAT CONTAINS THE REMNANTS
OF SUPER TYPHOON NURI TO MOVE FROM JAPAN AND KAMCHATKA TO THE
BERING FRI THROUGH SAT. BECAUSE OF THE STRENGTH OF THE NORTH
AMERICAN RIDGE...THIS CUTOFF WILL THEN SPIN AROUND IN THE BERING
AS IT SLOWLY WEAKENS THROUGH THE MIDDLE OF NEXT WEEK.

AT THE SURFACE...A LOW OVER THE EASTERN DOMAIN NEAR KODIAK ON FRI
WILL DISSIPATE ON SAT. A FRONT ASSOCIATED WITH THE REMNANTS OF
NURI IN THE BERING WILL THEN MOVE AS FAR EAST AS THE ALEUTIAN
RANGE. IT WILL BE STOPPED BY HIGH PRESSURE OVER THE EASTERN HALF
OF AK AND THE GULF OF AK ON SAT. THIS FRONT WILL PUSH AGAINST THE
COASTAL RIDGE...TAKING UNTIL EARLY NEXT WEEK TO CROSS THE GULF
AND DISSIPATE. RAIN AND SHOWERS ARE EXPECTED ALONG THE COAST WITH
THIS SYSTEM INTO NEXT WEEK...WITH OCCASIONAL SNOW SHOWER ACTIVITY
CROSSING THE COASTAL MOUNTAINS INTO INTERIOR ZONES OF SOUTHCENTRAL.

OF MUCH MORE CONCERN IS THE REMNANTS OF NURI AS THEY APPROACH AND
MOVE INTO THE WESTERN DOMAIN. BY FRI THE REMNANT LOW OF NURI WILL
BE MOVING PAST KAMCHATKA. INTERACTION OF NURI'S WARM AIR ALOFT
WITH EXTREMELY COLD AIR OFF KAMCHATKA WILL SPIN UP A STRONG JET.
IN TURN THIS JET MOVING NEAR NURI WILL CREATE UPPER LEVEL
DIVERGENCE THAT WILL AID IN EXPLOSIVE DEEPENING OF THE LOW. THIS
DEEPENING OF THE LOW WILL PEAK FRI EVENING JUST WEST OF ATTU.
MODELS HAVE BEENS STRUGGLING WITH THE EXACT PLACEMENT OF THE LOW
AT THAT TIME...BUT THE EC SEEMS TO BE LOCKING ONTO A SOMEWHAT
CONSISTENT SOLUTION. THIS WILL BRING THE LOW INTO THE WESTERN
BERING EARLY SAT AND THEN ACROSS THE REST OF THE BERING THROUGH
THE MIDDLE OF NEXT WEEK...WEAKENING STEADILY AS IT DOES SO. THE
CURRENT FORECAST THINKING IS THAT WINDS WILL DEVELOP FRI MORNING
OVER THE WESTERN ALEUTIANS AND REACH HURRICANE FORCE BY
AFTERNOON. THE STRONGEST WINDS WILL REMAIN OVER THE WESTERN
ALEUTIANS THROUGH SAT MORNING BEFORE WEAKENING. STORM FORCE WINDS
WILL AFFECT THE WESTERN HALF OF THE BERING INTO LATE SAT WITH
GALES INTO EARLY NEXT WEEK. SIGNIFICANT SEAS WILL ACCOMPANY THE
STRONGEST WINDS...ESPECIALLY OVER THE WESTERN ALEUTIANS AND BERING
SEA WITH COMBINED SEAS OVER 40 FT INTO SAT. POTENTIALLY DANGEROUS
SWELL WILL MAKE ITS WAY ACROSS THE BERING BEGINNING THIS WEEKEND
AND ABUNDANT RAINFALL WILL ALSO BE WIDESPREAD. DETAILED GUIDANCE
AND INFORMATION WILL BE RELEASED AS FORECAST CONFIDENCE INCREASES.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...JA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MO
LONG TERM...KH