Small Craft Advisory 1000, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
358 PM AKST MON DEC 14 2015

.ANALYSIS AND UPPER LEVELS...
THE STRONG LOW PRESSURE SYSTEM THAT HAS MOVED THROUGH THE BERING
SEA OVER THE WEEKEND HAS SHIFTED TO THE NORTH WITH A 961 MB LOW
PRESSURE CENTER LOCATED OVER THE NORTHERN BERING SEA. THIS SYSTEM
HAS BECOME VERTICALLY STACKED AND SHOULD CONTINUE TO
WEAKEN...ALTHOUGH THERE IS PLENTY OF COLD AIR ADVECTION ON THE
BACKSIDE OF THIS LOW WHICH WILL PREVENT IT FROM WEAKENING TOO
RAPIDLY. BROAD WEST TO SOUTHWEST FLOW COVERS THE BERING AND IS
BRINGING WINDS TO THE WEST COAST OVER A LONG FETCH OF
WATER...CAUSING SOME ISSUES WITH HIGH WATER LEVELS ALONG THE
SOUTHWEST COAST. A SURFACE TROUGH EXTENDS FROM THIS BERING SEA LOW
ACROSS THE SOUTHCENTRAL REGION AND A WEAK LOW PRESSURE CENTER IS
OVER PRINCE WILLIAM SOUND. COMBINED WITH SOUTHWEST FLOW AT THE
UPPER LEVELS...WEAKLY UNSTABLE AIR EXISTS OVER SOUTHCENTRAL WHICH
IS REFLECTED IN THE SHOWERS VISIBLE ON RADAR AND SATELLITE.

SOUTH OF THE CENTRAL ALEUTIANS...SATELLITE INDICATES A LOW
PRESSURE SYSTEM IS FORMING ALONG THE BOUNDARY OF THE UPPER LEVEL
JET THAT IS CURRENTLY TRANSITING THE UPPER PACIFIC. THIS SYSTEM IS
SUPPORTED BY A 110KT SOUTHWESTERLY JET STREAK WHICH SHOULD HELP
PUSH IT RAPIDLY ALONG THE ALEUTIANS AND INTO THE MAINLAND OF
ALASKA.

&&

.MODEL DISCUSSION...
THE UPCOMING SYNOPTIC SITUATION HAS BEEN VERY DIFFICULT FOR THE
MODELS TO HANDLE AND AS SUCH THERE ARE A NUMBER OF DIFFERENCES.
THE NEXT SYSTEM OF INTEREST IS CURRENTLY JUST SOUTH OF ADAK AND IS
FORECAST TO MOVE NORTHEASTWARD UP OVER THE BRISTOL BAY WHERE IT
WILL DEVELOP INTO A CLOSED LOW. MODELS DIFFER GREATLY ON THE
TIMING AND LOCATION OF THIS SYSTEM ONCE IT HITS THE MAINLAND. THE
12Z NAM SEEMS TO BE THE OUTLIER BY SLOWING DOWN THE SYSTEM
SIGNIFICANTLY AND DEVELOPING A CLOSED LOW OVER THE BRISTOL BAY
REGION. THE GFS/GEM/EC SOLUTIONS VARY SLIGHTLY BUT ALL SEEM TO
TAKE A FASTER TRACK. THE NAM HAS ALSO NOT INITIALIZED WELL WITH
THE SATELLITE IMAGE...LOCATING THE CURRENT LOW FURTHER TO THE
SOUTHWEST THAN IS SHOWN ON SATELLITE. GIVEN THESE FACTS THE NAM
SOLUTION WAS NOT CHOSEN...WITH THE INITIAL PORTION OF THE SHORT
TERM LEANING TOWARDS THE GFS.

THE SECOND PORTION OF THE SHORT-TERM CONTINUES TO BE A CHALLENGE
FOR THE MODELS. AFTER THE INITIAL WAVE A SECOND LOW MOVES UP
TOWARD THE GULF OF ALASKA SOUTH OF COLD BAY AND THE MODELS DIFFER
SIGNIFICANTLY ON THE LOCATION OF THIS ONE AS WELL. ON THE 12Z RUNS
THE GFS WAS THE OUTLIER AS MUCH FURTHER NORTHWEST THAN THE NAM/EC
SOLUTION...HOWEVER THE NEW 18Z RUN OF THE NAM SHOWS A SIGNIFICANT
SHIFT TO ALIGN WITH THE GFS. THIS RUN TO RUN INCONSISTENCY DOES
NOT LEND ITSELF TO HIGH FORECAST CONFIDENCE...AT THE TIME OF THIS
DISCUSSION THE EC/12Z NAM SOLUTION WAS CHOSEN FOR THIS STORM WHICH
KEEPS NORTHERLY WINDS AND SNOW IN KODIAK BEFORE THE LOW SHIFTS OFF
TO THE EAST.

BOTTOM LINE...SIGNIFICANT DIFFERENCES IN THE MODELS LEAD TO A
LOWER THAN NORMAL CONFIDENCE IN THE SHORT TERM FORECAST.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
AN UPPER LEVEL WEAK SHORTWAVE WILL PUSH THROUGH THE ANCHORAGE BOWL
PRODUCING SCATTERED SNOW SHOWERS THROUGH THE OVERNIGHT HOURS GOING
INTO TUESDAY MORNING. THERE WILL BE BRIEF DRIER PERIOD WITH A WEAK
RIDGE MOVING THROUGH LATER TUESDAY MORNING. BY TUESDAY MIDDAY AN
UPSTREAM TROUGH WILL BE MOVING THROUGH THE SOUTHCENTRAL REGION
BRINGING SNOW TO THE AREA. THIS TROUGH WILL BE FAST MOVING BUT
SHOULD RESULT IN MORE FAVORABLE SNOW ACCUMULATION WITH
SOUTHWESTERLY FLOW AT THE SURFACE AND ALOFT IN THE ATMOSPHERE. BY
WEDNESDAY A RIDGE BUILDS THROUGH THE BRISTOL BAY AREA EXTENDING
ALONG NORTHERN GULF COASTLINE. THIS WILL RESULT IN WARMER
TEMPERATURES AND GUSTY TURNAGAIN ARM WINDS. KODIAK ISLAND WILL
SEE INCREASED CLOUD COVER WITH MOISTURE SPREADING FROM THE SOUTH
TO NORTH WITH A STRONG NORTH PACIFIC LOW APPROACHING FROM THE
SOUTH. THIS WILL BRING GALE FORCE EASTERLY/NORTHEASTERLY WINDS TO
THE WESTERN GULF. THE PRECIPITATION WILL BE ALL RAIN TO KODIAK
ISLAND ON WEDNESDAY WITH TEMPERATURES IN THE UPPER 30S TO LOWER
40S.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...

ONSHORE FLOW WITH WIDESPREAD SNOW SHOWER ACTIVITY WILL CONTINUE
THROUGH THE NIGHT ACROSS THE AREA. AS A FAST-MOVING DISTURBANCE
MOVES IN FROM THE BERING SEA TONIGHT STEADIER PRECIPITATION WILL
MOVE INTO THE BRISTOL BAY AREA AND REACH THE LOWER KUSKOKWIM
VALLEY TOMORROW. THE RAIN/SNOW LINE SHOULD BE APPROXIMATELY NEAR
KING SALMON FOR MOST OF THIS EVENT...WITH SEVERAL INCHES OF SNOW
LIKELY NORTH OF DILLINGHAM AND ACROSS THE KUSKOKWIM VALLEY BY THE
TIME THINGS WIND DOWN TUESDAY EVENING. SNOWFALL RATES COULD BE
FAIRLY IMPRESSIVE...WITH THE LIMITING FACTOR FOR TOTAL SNOWFALL
AMOUNTS BEING THE VERY FAST FORWARD SPEED OF THE SYSTEM. ON A
RELATED NOTE...WINDS WILL BE GUSTY WHILE IT IS SNOWING IN MOST OF
THESE AREAS...BUT OVERALL NOT TERRIBLY IMPRESSIVE...SO WE DO NOT
ANTICIPATE ANY BLOWING SNOW CONCERNS AT THIS TIME. MEANWHILE...THE
KUSKOKWIM DELTA WILL REMAIN JUST OUT OF REACH OF THIS SMALLER
STORM SYSTEM...AND INSTEAD REMAIN IN THE UNSTABLE SOUTHWESTERLY
FLOW AROUND THE LARGER SYSTEM FROM THE WEEKEND THAT IS MOVING
TOWARD THE BERING STRAIT.

BY WEDNESDAY...A STRONGER STORM WILL MOVE NORTHWARD FROM THE NORTH
PACIFIC AND PARK SOUTH OF KODIAK ISLAND. WHETHER SNOWFALL IS ABLE
TO SPREAD ACROSS THE ALEUTIAN RANGE INTO BRISTOL BAY WILL BE
DEPENDENT ON HOW FAR NORTHWEST THE LOW CENTER MOVES...WHICH IS
STILL UNCERTAIN AT THIS POINT.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...

THE REGION WILL GENERALLY REMAIN UNDER THE BROAD CYCLONIC
INFLUENCE OF THE REMNANTS OF THE STRONG BERING SEA STORM FROM LAST
WEEKEND. COUPLED WITH ONGOING COLD AIR ADVECTION OFF THE RUSSIAN
LANDMASS...INSTABILITY SNOW SHOWERS AND GUSTY WINDS WILL BE THE
NORM. THE ONE EXCEPTION WILL BE THE WEAK STORM CURRENTLY
APPROACHING DUTCH HARBOR THAT WILL RACE INTO THE SOUTHWEST
MAINLAND TONIGHT. THE EASTERN ALEUTIANS AND ALASKA PENINSULA
SHOULD SEE ANOTHER QUICK INCREASE IN WINDS AND A FAIRLY SHORT-
LIVED BURST OF SNOWFALL OVERNIGHT TONIGHT AS A MOSTLY ZONAL JET
CARRIES THE SYSTEM RAPIDLY FORWARD.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THERE IS DECENT AGREEMENT WITH THE MODELS MOVING A STORM-FORCE LOW
INTO THE WESTERN BERING THURSDAY. THE EC IS A LITTLE BIT FASTER
THAN THE OTHERS BUT FROM AN IMPACTS STANDPOINT THEY ALL HAVE THE
FRONT FROM THIS SYSTEM MAKING IT TO THE WEST COAST FRIDAY BEFORE
FALLING APART AT THE SURFACE...WITH A WEAKENING FRONT ALOFT
MOVING INLAND. THE PRIMARY IMPACT FROM THIS STORM WILL BE
WIDESPREAD GALE-FORCE OR STRONGER WESTERLY WINDS ON THE SOUTH SIDE
OF THIS LOW ACROSS MUCH OF THE SOUTHERN HALF OF THE BERING SEA.

THE LOW APPROACHING KODIAK ISLAND FROM THE SOUTH IN THE SHORT TERM
WILL REACH PEAK STRENGTH WEDNESDAY NIGHT...THEN RETREAT SOUTH AND
EAST ACROSS THE NORTHEAST PACIFIC WHILE SLOWLY WEAKENING THURSDAY
INTO FRIDAY. REGARDLESS OF WHICH TRACK OCCURS...STRONG GALE FORCE
WINDS WILL IMPACT MOST OF THE MARINE WATERS...ESPECIALLY FOR INNER
COASTAL WATERS FROM COOK INLET THROUGH THE BARREN ISLANDS TO
SHELIKOF STRAIT...AND EAST ALONG THE NORTH GULF COAST THROUGH
WEDNESDAY NIGHT. THE EC SOLUTION WAS PREFERRED FOR THE WINDS FOR
WEDNESDAY NIGHT INTO THURSDAY...WITH AN ENSEMBLE MODEL APPROACH
FOR POPS AND QPF.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...COASTAL FLOOD ADVISORY 155 161.
MARINE...GALE WARNING 119 120 130 131 132 138 150 155 160 172 179
180 181 185
 HEAVY FREEZING SPRAY 185.

&&

SYNOPSIS AND MODEL DISCUSSION...LF
SOUTHCENTRAL ALASKA...PD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AD
LONG TERM...CC