Small Craft Advisory 207, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
416 PM AKST SAT MAR 7 2015

.ANALYSIS AND UPPER LEVELS...
AN UPPER LEVEL LOW CURRENTLY OVER MAINLAND ALASKA WITH A VIGOROUS
CLOSED LOW/SHORT WAVE TROUGH SITUATED IN THE NORTHWEST BERING SEA.
THESE SYSTEMS ARE QUITE PROGRESSIVE AND WILL EVENTUALLY PASS
THROUGH THE MAINLAND MONDAY. THEY WILL ALSO USHER IN QUITE A BIT
OF COLD AIR TO THE STATE. A SHORT WAVE RIDGE IS OVER THE NORTHEAST
PACIFIC SOUTH OF THE GULF OF ALASKA. ANOTHER SHORT WAVE RIDGE
EXISTS JUST WEST OF THE KAMCHATKA PENINSULA. ANOTHER SHORT WAVE
TROUGH SOUTH OF THE WESTERN ALEUTIANS WILL BECOME A PLAYER IN THE
WEATHER OVER THE CENTRAL AND WESTERN ALEUTIAN CHAIN.
THE JET STREAM STRETCHES FROM THE WESTERN ALEUTIAN LOW NEAR 40N
170E WITH A CORE OF 140 KT INTO THE YUKON WITH A JET CORE OF 120
KT. WITH THE PROGRESSIVE PATTERN...THE JET MOVES THROUGH TO
WESTERN CANADA TUESDAY.

AT THE SURFACE...A LOW IS OVER THE MAINLAND WITH PRECIPITATION
FROM THE CHUGACH MOUNTAINS EXTENDING UP THE SUSITNA VALLEY AND TO
THE EAST. TEMPERATURES REMAINED QUITE WARM LAST NIGHT WITH THE
ANCHORAGE BOWL REMAINING ALMOST ALL RAIN. SNOW IS PRESENT OVER THE
KUSKOKWIM DELTA AHEAD OF THE VIGOROUS UPPER LOW IN THE NORTHERN
BERING SEA. SNOW AND RAIN WILL TAPER OFF THIS EVENING FOR
SOUTHCENTRAL WITH SOME LINGERING PRECIP IN WESTERN ALASKA. THE BIG
LOW SOUTH OF SHEMYA TO GET CLOSER TONIGHT AND BRING SOME WINDS AND
SNOW TO THE WESTERN ALEUTIANS.

&&

.MODEL DISCUSSION...
THE MODELS TODAY ARE QUITE SIMILAR IN THE HANDLING OF SYSTEMS OVER
THE NEXT COUPLE DAYS. ALL MOVE THE TWO SHORT WAVES THROUGH THE
MAINLAND AT ROUGHLY THE SAME SPEED. HOWEVER...DETAILS IN THE
SURFACE WEATHER ARE A LITTLE BIT DIFFERENT. FOR THE WINDS WITH
THE NEXT COUPLE SYSTEMS WE ARE TRENDING HIGHER FOR THE GAP FLOWS.
THEREFORE...WINDS UPWARDS OF 60 MPH FROM THE WEST CAN BE EXPECTED
NEAR WHITTIER SUNDAY NIGHT INTO MONDAY. THE LOW SOUTH OF SHEMYA
WILL GET CLOSER TO THE CHAIN SUNDAY WITH STORM FORCE WINDS AND HOW
QUICKLY SNOW CHANGING OVER TO RAIN BEING THE TRICKY QUESTION FOR
THE FORECAST. THE LOW SHIFTS EAST MORE THAN NORTH THROUGH TUESDAY
AS COLD AIR DIGS ACROSS THE EASTERN BERING AND MAINLAND. THE ECMWF
AND CANADIAN MODEL ARE THE CHOICE FOR THE NEXT COUPLE DAYS WITH
LOW CENTERS BEING A BIT DEEPER IN THESE MODELS.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
COLD AIR WILL BE COMING BACK TO THE SOUTHCENTRAL THE NEXT COUPLE
OF DAYS FOLLOWING TWO DIFFERENT SHORT WAVES. THE FIRST IS MOVING
THROUGH THIS EVENING WHICH WILL KEEP THE POSSIBILITY OF SNOW
SHOWERS AROUND THE SOUTHCENTRAL...ESPECIALLY IN THE MOUNTAINS.
FOLLOWING THIS WAVE NORTHWEST FOLLOW WILL USHER IN COLD AIR AND
HELP ENHANCE GAP WINDS THROUGH MOST PASSES. THE SECOND WAVE WILL
COME TOMORROW EVENING WHICH WILL BRING SCATTERED SNOW SHOWERS TO
THE AREA AND EVEN MORE COLD AIR DROPPING TEMPERATURES DOWN INTO
THE SINGLE DIGITS TOMORROW NIGHT. THIS WILL ADDITIONALLY ENHANCE
GAP WINDS WITH WINDS GETTING UP TO AROUND 60 MPH IN SOME OF THE
MORE FAVORABLE LOCATIONS LIKE RESURRECTION BAY AND AROUND THE
BARREN ISLANDS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
SNOW SHOWERS AND WINDS OVER SOUTHWEST ALASKA WILL DIMINISH A BIT
OVERNIGHT AS ONE UPPER TROUGH EXITS TO THE EAST. HOWEVER...A COLD
UPPER LEVEL LOW DROPPING OUT OF SIBERIA WILL HEAD RIGHT FOR SOUTHWEST
ALASKA TOMORROW BRINGING ANOTHER BATCH OF SNOW SHOWERS...GUSTY
WINDS...AND EVEN COLDER AIR. SNOW SHOWERS WILL BE MOST WIDESPREAD
AND PERSISTENT ALONG THE KUSKOKWIM DELTA AND THE BRISTOL BAY COAST
AS THE ARCTIC AIR CONTINUES TO MOVE OVER THE RELATIVELY WARMER
WATERS OF THE BERING SEA. THERE IS SEA ICE OFF THE KUSKOKWIM DELTA
COAST...BUT THERE IS ENOUGH OPEN WATER WITHIN THE ICE PACK TO
GENERATE SHOWERS. AS THE UPPER LOW HEADS TO SOUTHCENTRAL SUNDAY
NIGHT COLD AIR WILL PUSH ACROSS THE ALASKA PENINSULA PRODUCING
STRONG GUSTY GAP WINDS AND BRINGING HEAVY FREEZING SPRAY SOUTH OF
THE PENINSULA FOR ONE OF THE FEW TIMES THIS WINTER. THE
COMBINATION OF GUSTY WINDS AND SNOW SHOWERS WILL PRODUCE AREAS OF
BLOWING SNOW...ESPECIALLY ALONG THE KUSKOKWIM DELTA...BUT PRECIP
AND REDUCED VISIBILITIES ARE NOT EXPECTED TO LAST LONG ENOUGH TO
WARRANT AN ADVISORY. TEMPERATURES WILL STEADILY FALL ACROSS THE
REGION...BUT FAIRLY EXTENSIVE CLOUD COVER WILL KEEP THEM FROM
DROPPING LIKE A ROCK. THUS...DO NOT EXPECT ANY ISSUES WITH LOW
WIND CHILL VALUES.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE STRONGEST COLD ADVECTION WILL BE ACROSS THE NORTHERN HALF OF
THE BERING SEA. THUS SNOW SHOWERS....STRONG GUSTY WINDS...AND
FREEZING SPRAY WILL BE WORST IN THIS AREA. MEANWHILE...A
DEVELOPING PACIFIC LOW WILL MOVE UP TO THE ALEUTIANS BRINGING
STRONG WINDS AND HEAVY PRECIPITATION. TEMPERATURES WILL INITIALLY
BE COLD ENOUGH TO SUPPORT ALL SNOW...BUT WILL BE NEAR FREEZING
WHICH WILL PREVENT ANY WIDESPREAD BLIZZARD CONDITIONS. AS THE LOW
NEARS SUNDAY AFTERNOON PRECIPITATION WILL TRANSITION TO MAINLY
RAIN ALONG THE CENTRAL ALEUTIANS.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
AS THE LOW OVER THE NORTH GULF COAST DRIFTS EAST AS IT WEAKENS ON
TUESDAY...OUTFLOW WINDS ALONG THE GULF COAST WILL ALSO SLOWLY
DIMINISH INTO THE MIDDLE OF NEXT WEEK. OFFSHORE FLOW AND RIDGING
WILL ALSO TAKE OVER MUCH OF THE SOUTHERN MAINLAND THROUGH THE
MIDDLE OF NEXT WEEK WHICH WILL KEEP CONDITIONS DRY UNDER CLEAR
SKIES THROUGHOUT THE AREA. OVER THE BERING...THE NORTH PACIFIC LOW
ENTERING THE WESTERN ALEUTIANS ON SUNDAY BRING CONTINUED GALE
FORCE WINDS ALONG WITH SNOW MIXING WITH RAIN TO THE CENTRAL
ALEUTIANS THROUGH TUESDAY. THIS LOW WILL THEN RETURN TO THE NORTH
PACIFIC ON WEDNESDAY AND BECOME ABSORBED IN A COMPLEX LOW WILL
BECOME THE FOCAL POINT FOR THE WEATHER OVER THE SOUTHERN MAINLAND
LATE NEXT WEEK.

THIS COMPLEX LOW REMAINS A CHALLENGE IN THE LONG TERM FORECAST AS
THERE HAS BEEN LITTLE IF ANY IMPROVEMENT IN THE MODEL AGREEMENT
SINCE YESTERDAY. THE GFS CONTINUES TO BE MORE AGGRESSIVE WITH AN
ARCTIC TROUGH THAT DEVELOPS OVER THE MAINLAND ON WEDNESDAY...AND
AS A RESULT IS MUCH DEEPER WITH THIS COMPLEX LOW AS IT MOVES INTO
THE GULF ON THU-FRI. ON THE OTHER SIDE OF THE COIN...THE EC CONTINUES
TO BE WEAKER WITH THE ARCTIC TROUGH...DEEPER WITH A LOW IN THE
BERING SEA...AND MUCH FURTHER EAST WITH THE GULF LOW WITH RIDGING
OVER THE MAINLAND. AFTER COORDINATION WITH WPC THIS MORNING IT WAS
DETERMINED THAT THE EC WILL BE THE PREFERRED SOLUTION IN THE LONG
TERM FOR THE TIME BEING AS THE GFS IS PROBABLY TOO DEEP WITH
ARCTIC TROUGH WITH A BUILDING NORTHEAST PACIFIC RIDGE. WITH LARGE
VARIABILITY IN THE MODELS...CONFIDENCE IN THE LONG TERM FORECAST
BEYOND THURSDAY IS QUITE LOW.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM WARNING 130 131 177 178.
 GALE WARNING 119 120 121 125 129 132 137 139 150 160 173 175 176
180 181 185.
 HEAVY FREEZING SPRAY 121 126 127 128 129 130 131 136 137 138 139
150 160 180 181 185.
FIRE WEATHER...NONE.

&&

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