Small Craft Advisory 69, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1200 PM AKST MON JAN 21 2013

.ANALYSIS AND UPPER LEVELS...THE LARGE SCALE PATTERN IS GENERALLY
THE SAME AS YESTERDAY ALTHOUGH THE ORIENTATION OF THE HIGH AMPLITUDE
TROUGH AND RIDGE HAS CHANGED. A LARGE UPPER LOW IS RETROGRADING
WESTWARD OVER THE FAR SOUTHWEST BERING WITH A TROUGH AXIS EXTENDING
EAST-SOUTHEAST TO A NEARLY STATIONARY LOW A FEW HUNDRED MILES SOUTH
OF THE ALASKA PENINSULA. SHORT-WAVES MOVING ACROSS THE NORTH PACIFIC
ALONG THE UPPER JET ARE TRACKING SOUTH OF THIS LOW CAUSING THE
LARGER SCALE TROUGH TO DIG SOUTHEASTWARD INTO THE NORTHEAST PACIFIC
AND FORCE THE RIDGE WHICH HAS BEEN SITTING ALONG THE WEST COAST OF
NORTH AMERICA TO PROGRESS EASTWARD. THE SUBTROPICAL JET MOVING UP
THE WEST SIDE OF THE RIDGE HAS TILTED AND IS NOW MOVING FROM
SOUTHEAST TO NORTHWEST TRANSPORTING WARM AIR AND MOISTURE TO THE
GULF OF ALASKA AND SOUTHERN MAINLAND OF ALASKA. A WARM FRONT IS
CURRENTLY CROSSING THE GULF THIS MORNING FROM SOUTHEAST TO NORTHWEST.
CONDITIONS OUT AHEAD OF THIS ACROSS THE SOUTHERN MAINLAND OF ALASKA
ARE GENERALLY QUIET. THE MAIN AREA OF PRECIP THIS MORNING IS FOCUSED
ALONG WHAT HAS BEEN A STATIONARY FRONT EXTENDING FROM THE LOW SOUTH
OF THE ALASKA PENINSULA NORTHWESTWARD ACROSS THE EASTERN ALEUTIANS
AND ALASKA PENINSULA INTO THE CENTRAL TO EASTERN BERING. THIS FRONT
IS NOW PROGRESSING EASTWARD AS A COLD FRONT.

.MODEL DISCUSSION...MODELS CONTINUE TO BE IN GOOD AGREEMENT WITH
THE GENERAL SYNOPTIC SCALE PATTERN. THERE ARE MINOR DIFFERENCES
IN LOW TRACKS/POSITIONS WHICH HAVE LITTLE IMPACT ON THE SENSIBLE
WEATHER IMPACTS OVER THE NEXT FEW DAYS. ONLY MINOR ADJUSTMENTS
WILL BE MADE TO THE CURRENT FORECASTS.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE LOW SOUTH OF THE ALASKA PENINSULA WILL
WEAKEN AS ANOTHER LOW DEVELOPS OVER THE NORTHEAST PACIFIC TODAY
AND TRACKS NORTHWARD TO THE GULF OF ALASKA ON TUESDAY. THE APPROACH
OF THIS NEW LOW WILL CAUSE THE MEAN FLOW OVER THE GULF AND
SOUTHCENTRAL TO BACK TOWARD THE EAST. THIS WILL HELP KEEP THE
BULK OF PRECIP CONFINED TO THE COAST AND KODIAK ISLAND. THERE MAY
BE A FEW BRIEF PERIODS WHERE PRECIP MAKES IT OVER THE COASTAL RANGE
AND AFFECTS AREAS FURTHER INLAND. MOST NOTABLY THE SOUTHERN COPPER
BASIN WILL LIKELY SEE A LITTLE BIT OF LIGHT SNOW ON WEDNESDAY AS
A WEAK UPPER SHORT-WAVE ROTATING AROUND THE GULF LOW APPROACHES.
WARMER AIR WILL ACCOMPANY THE FIRST BATCH PF PRECIP MOVING INTO
TODAY RESULTING IN PREDOMINANTLY RAIN ALONG THE GULF COAST. AS THE
NEXT LOW MOVES INTO THE GULF TUESDAY AND FLOW BACKS A LITTLE MORE
TOWARD THE NORTHEAST TEMPERATURES WILL BEGIN TO SLOWLY COOL AND
MAY SEE SOME SNOW START TO MIX BACK IN. THE GULF LOW WILL DISSIPATE
THURSDAY AS A STRONGER LOW CROSSING THE NORTH PACIFIC FOCUSES THE
ENERGY FURTHER SOUTH...SO PRECIP WILL BEGIN TO TAPER OFF ACROSS THE
GULF.

SOUTHWEST ALASKA...SOUTHWEST ALASKA WILL SEE A FEW WAVES OF PRECIP
PASS THROUGH OVER THE NEXT FEW DAYS...FIRST WITH THE CURRENT LOW
SOUTH OF THE ALASKA PENINSULA AND THEN WITH A LOW IN THE GULF ON
TUESDAY AND WEDNESDAY. THIS IS AN UNFAVORABLE FLOW FOR ANY
SIGNIFICANT PRECIP PLUS THE WAVES WILL BE TRANSITORY...SO GENERALLY
EXPECT BRIEF PERIODS OF LIGHT PRECIP. ALSO...MOST OF THE PRECIP
WILL MOVE ACROSS BRISTOL BAY TO THE KUSKOKWIM DELTA COAST SO EXPECT
VERY LITTLE TO MAKE IT TO INTERIOR SOUTHWEST ALASKA. TEMPERATURES
ARE WARM ENOUGH TO PRODUCE PRIMARILY RAIN ALONG THE ALASKA
PENINSULA...WITH SNOW FOR AREAS TO THE NORTH AND WEST.

BERING SEA/ALEUTIANS...AS THE LOW SOUTH OF THE ALASKA PENINSULA
DRIFTS EASTWARD AND WEAKENS THIS AFTERNOON THROUGH TONIGHT THE
COLD FRONT WILL CONTINUE TO PROGRESS EASTWARD AND BEGIN TO FALL
APART AS IT REACHES THE SOUTHERN ALASKA PENINSULA. MEANWHILE A
RAPIDLY DEEPENING LOW DOWN AROUND 40N 175E WILL BOTTOM OUT TONIGHT
AND THEN WEAKEN AS IT TRACKS TO THE SOUTH OF CENTRAL TO EASTERN
ALEUTIANS TUESDAY AND WEDNESDAY. IT WILL BE JUST A GLANCING BLOW
ON THE NORTHERN PERIPHERY OF THIS STORM SYSTEM. ANOTHER DEEP LOW
WILL TRACK OUT OF THE NORTHWEST PACIFIC MID WEEK AND HEAD FOR THE
WESTERN ALEUTIANS LATER IN THE WEEK.

.LONG TERM FORECAST...THE UPPER LEVEL FLOW LOOKS TO BE LESS
AMPLIFIED AND MORE PROGRESSIVE AS WE HEAD INTO THE DAY 4 THROUGH 7
FORECAST PERIOD. THE ECMWF SEEMS TO SHOW A LITTLE MORE RUN-TO-RUN
CONSISTENCY WITH TRACK OF MAJOR SYSTEMS...BUT NOT GOOD ENOUGH TO
INSTALL MUCH FORECAST CONFIDENCE THIS FAR OUT. THE ONLY STORM WE
CAN SPEAK OF WITH SOME CONFIDENCE IS ONE THAT MOVES TO THE WESTERN
ALEUTIANS LATER THIS WEEK. IT LOOKS LIKE IT WILL STALL OVER THE
WESTERN ALEUTIANS AND WEAKEN AS WE HEAD INTO NEXT WEEKEND.
MEANWHILE...BY THE MIDDLE OF THIS WEEK A LARGE COMPLEX SERIES OF
LOWS WILL SET UP OVER THE NORTHEAST-PACIFIC AND GULF OF ALASKA.
IT IS ALWAYS DIFFICULT TO FORECAST WHICH LOW WILL DOMINATE AND
WHAT THE STORM TRACK WILL BE. HOWEVER...IT DOES APPEAR THERE WILL
BE ENOUGH PROGRESSION OF THE UPPER PATTERN THAT THIS COMPLEX WILL
TRACK EASTWARD...POSSIBLY WITHOUT ANY MAJOR IMPACTS ON SOUTHCENTRAL.
MODELS DUE INDICATE AN ARCTIC TROUGH DROPPING SOUTHWARD ACROSS
MAINLAND ALASKA LATE IN THE WEEK...SO COLDER AIR AND A GAP WIND
EVENT ARE LIKELY. FINALLY...THE BIGGEST QUESTION IN THE EXTENDED
IS THE TRACK OF A LOW UP FROM THE TROPICS TOWARD THE EASTERN
ALEUTIANS/ALASKA PENINSULA SOMETIME NEXT WEEKEND. YESTERDAY MORNINGS
MODELS DID NOT EVEN PICK UP ON THIS LOW. SUCH A TRACK WOULD BRING
A BETTER CHANCE OF PRECIP BACK TO THE SOUTHERN MAINLAND AFTER A
PERIOD OF RELATIVELY BENIGN WEATHER.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING 120 130 138 140 172.
FIRE WEATHER...NONE.

SEB JAN 13