Small Craft Advisory 943, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 PM AKST TUE NOV 26 2013

.ANALYSIS AND UPPER LEVELS...

MOST OF SOUTHWEST ALASKA...THE EASTERN BERING...AND THE AKPEN TO
KODIAK REGION LIES UNDERNEATH A COMPLEX UPPER LEVEL LONGWAVE TROUGH.
WITHIN THIS REGION ARE SEVERAL SHORTWAVE DISTURBANCES THAT BECAUSE OF
THE WEAK FLOW ALOFT AND THEIR PROXIMITY TO ONE ANOTHER ARE DRIVING
THE KEY MODEL DIFFERENCES CURRENTLY.

OTHERWISE...UPPER RIDGING PERSISTS OVER THE EASTERN GULF...WITH A
MUCH STRONGER AND BUILDING UPPER RIDGE OVER THE FAR WESTERN BERING
SEA JUST EAST OF KAMCHATKA. THE LATTER RIDGE WILL BUILD AND CUT-OFF
OVER THE CENTRAL BERING SEA BY FRIDAY.

.MODEL DISCUSSION...

THERE REMAIN MINOR MODEL DIFFERENCES THAT REVEAL LINGERING
UNCERTAINTIES ESPECIALLY CONCERNING SNOW AMOUNTS IN AND NEAR THE
ANCHORAGE AREA THROUGH WEDNESDAY AFTERNOON.

THE GFS AND NAM CONTINUE TO SHOW LIGHT SNOW FALLING ACROSS MOST OF
SOUTHCENTRAL FROM ANCHORAGE NORTH THROUGH TONIGHT AND INTO WEDNESDAY
AFTERNOON. THE GFS AND NAM BRING THE LAST OF THE SHORTWAVE
DISTURBANCES CRAWLING ACROSS THE UPPER COOK INLET REGION TOWARD
ANCHORAGE WEDNESDAY MORNING. BECAUSE OF THIS SLOW MOVEMENT...AMPLE
MOISTURE IS PUSHED NORTHWARD ACROSS THE AREA AND THIS WILL ALLOW FOR
THE SNOW GROWTH LAYER TO BECOME SUPER SATURATED WITH ICE CRYSTALS.
THUS...EXPECTING LARGE DENDRITIC SNOWFLAKES...WITH INTENSITY DICTATED
BY THE STRENGTH OF THE LIFT ASSOCIATED WITH THE SLOW-MOVING
DISTURBANCE. GIVEN THE LACK OF DRY AIR AS WELL THROUGH THE
COLUMN...THERE IS THE POTENTIAL FOR THE SNOW FROM LATE TONIGHT
THROUGH EARLY WEDNESDAY TO OUTPERFORM EXPECTATIONS. IF THE EUROPEAN
MODEL VERIFIES WITH A MORE PHASED SOLUTION DURING THIS TIME...EVEN
HIGHER SNOW ACCUMULATIONS WOULD BE EXPECTED.

WEDNESDAY NIGHT INTO THURSDAY...ATTENTION TURNS TO A POWERFUL
DISTURBANCE MOVING SOUTH AND EAST FROM THE NORTHERN BERING TO
SOUTHCENTRAL ALASKA. THIS WILL RESULT PRIMARILY IN THE GENERATION OF
STRONG OUTFLOW WINDS ACROSS COASTAL SOUTHCENTRAL AND SOUTHWEST ALASKA
LOCATIONS.

.SHORT TERM FORECAST...

SOUTHCENTRAL...

LIGHT SNOW WILL CONTINUE OFF AND ON THROUGH WEDNESDAY
AFTERNOON...ESPECIALLY TOWARD ANCHORAGE AND POINTS NORTH. THE BEST
CHANCE AT A MORE STEADY SNOW COMES OVERNIGHT...WHEN THE BEST DYNAMICS
AND THE POTENTIAL FOR PHASING WITH A SECOND SYSTEM OVER THE BARREN
ISLANDS REGION EXISTS. WILL CARRY A GENERAL 1 TO 3 INCHES MOST
LOCATIONS...INCLUDING FOR ANCHORAGE AND THE MATANUSKA VALLEY. SEE THE
MODEL DISCUSSION ABOVE FOR HOW THIS SYSTEM COULD OUTPERFORM
EXPECTATIONS.

THE MUCH STRONGER SYSTEM MOVING IN FROM THE NORTHWEST AFFECTS THE
AREA WEDNESDAY NIGHT INTO THURSDAY. IT WILL HELP BLEED COLD AIR
THROUGH THE GAPS IN THE ALASKA AND ALEUTIAN RANGES AND ALSO RESULT IN
GUSTY OUTFLOW WINDS FOR THE LATER PART OF THE WEEK...PARTICULARLY
TOWARD THE BARREN ISLANDS AND KAMISHAK BAY REGIONS AND EXTENDING EAST
OUT INTO THE GULF...BUT ALSO FOR WHITTIER AND THEN EVENTUALLY VALDEZ
AND THOMPSON PASS. PRECIPITATION CHANCES APPEAR TO BE MINIMAL FOR
ANCHORAGE AT THIS TIME FROM WEDNESDAY NIGHT ONWARD...BUT WILL NEED TO
WATCH TOWARD THE COPPER RIVER BASIN AND EASTERN PRINCE WILLIAM SOUND
FOR THE POTENTIAL FOR A SIGNIFICANT SNOW EVENT. GUSTY OUTFLOW WINDS
WILL ALSO DEVELOP FOR VALDEZ AND THOMPSON PASS AND THIS COULD RESULT
IN A BLIZZARD FOR THOMPSON PASS FRIDAY.

SOUTHWEST ALASKA...

MAIN CONCERN THE NEXT THREE DAYS IS WITH A PATTERN CHANGE TO A COLDER
REGIME ESPECIALLY LATE WEDNESDAY NIGHT THROUGH THURSDAY BEHIND THE
STRONG UPPER LEVEL SYSTEM THAT WILL MOVE SOUTH AND EAST ACROSS THE
INTERIOR SOUTHWEST LATE WEDNESDAY. STRONG NORTH TO NORTHWESTERLY
GUSTY OUTFLOW WINDS WILL DEVELOP OVER BRISTOL BAY AND EXTEND TOWARD
THE GULF TOWARD LATE WEEK.

BERING SEA/ALEUTIANS/AKPEN...

HIGH PRESSURE BUILDING OVER THE REGION THE NEXT FEW DAYS WILL KEEP
CONDITIONS ON THE CALM SIDE. NORTHEAST WINDS NEARING GALE FORCE AND
AN ISOLATED RAIN/SNOW SHOWERS MIX WILL EXIST TO THE SOUTH OF THE HIGH
CENTER ACROSS THE ALEUTIANS THROUGH WEDNESDAY NIGHT.

.LONG TERM FORECAST...

HIGH PRESSURE RIDGING OVER THE BERING SEA THIS WEEKEND WILL MOVE EAST
TOWARD THE MAINLAND. THE WILL RESULT IN COOL AND DRY WEATHER...WITH
GUSTY OUTFLOW WINDS THROUGH CHANNELED TERRAIN AT TIMES ALONG THE
NORTHERN GULF COAST. HIGHER ELEVATIONS WILL GENERALLY BE ABOVE
AVERAGE DURING THIS TIME...WHILE VALLEYS WILL BE BELOW NORMAL
UNDERNEATH A STRONG INVERSION. A WEATHER FRONT WILL LIKELY CLIP THE
FAR WESTERN ALEUTIANS WITH SOME LIGHT RAIN AND A SMALL INCREASE IN
SOUTHEAST WINDS FOR THE WEEKEND.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALES...130 131 170 172 173 174 175 176 177
FIRE WEATHER...NONE.

CC NOV 13