Small Craft Advisory 233, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
310 PM AKDT MON MAR 17 2014

.ANALYSIS AND UPPER LEVELS...
THE MAIN SYSTEM TODAY IS A LOW IN THE NORTHEAST BERING SEA HEADING
NORTH THROUGH THE BERING STRAIT WITH A SECONDARY LOW JUST NORTH OF
THE ALASKA PENINSULA THAT IS SCOOTING ALONG TO THE EAST INTO THE
NORTHER GULF OF ALASKA. A COLD FRONT EXTENDS FROM THE LOW MAIN LOW
SOUTH TO THE SECONDARY LOW ON THE NORTH SIDE OF THE ALASKA PENINSULA.
THIS FRONT WILL SWEEP INTO THE BERING SEA COAST RESULTING IN
WIDESPREAD SNOW SHOWERS. IN THE GULF OF ALASKA A WEAKER LOW IS NOW
NEAR THE BARREN ISLANDS AND WILL DRIFT EAST DISSIPATING TO A TROUGH
TONIGHT. THIS SUPPORTS THE ONSHORE PUSH OF MOISTURE ALONG THE NORTH
GULF COAST AND OVER SOUTH CENTRAL ALASKA THAT IS PRODUCING A MIX OF
RAIN AND SNOW SHOWERS.

ANOTHER LARGE STORM SYSTEM IS BEARING DOWN ON THE WESTERN ALEUTIANS.
THE PARENT LOW IS NOW WELL SOUTH OF SHEMYA AND IS EXPECTED TO MOVE TO
JUST WEST OF SHEMYA OVER THE NEXT COUPLE OF DAYS. THE FRONTAL LOW
ASSOCIATED WITH THIS STORM WILL BE THE MAIN PLAYER AND HAVE THE
GREATEST IMPACT TO THE CENTRAL TO EASTERN ALEUTIANS TUE NIGHT AND
WED. ENOUGH WARM AIR WILL BE PUSHED INTO THE CHAIN TO KEEP THE
PRECIPITATION ON THE LIQUID SIDE ALTHOUGH SOME MAY INITIALLY FALL AS
SNOW. THE WARMER AIR IS ALSO EXPECTED TO MITIGATE THE HIGHER WIND
GUST POTENTIAL AND AT THIS TIME WE ARE HOLDING OFF ON ANY HIGH WIND
WARNINGS.

.MODEL DISCUSSION...
MODELS REMAIN IN RELATIVELY GOOD AGREEMENT WITH THE OVERALL SYNOPTIC
PATTERN INTO THE END OF THE WEEK. THUS CONFIDENCE IN THE FORECAST
OVERALL IS MODERATE TO HIGH. THE TYPICAL ISSUES WITH THE ONSET AND
ENDING OF SNOW IN THE SNOW SHOWERS REMAINS MORE CHALLENGING. THE ONLY
SIGNIFICANT DIFFERENCE IS WITH RESPECT TO THE NEXT MAJOR STORM TO
IMPACT THE WESTERN BERING SEA FRI NIGHT AND SAT. THE GFS IS A TAD
FASTER THAN THE ECMWF THOUGH BOTH MODELS ARE IN GOOD AGREEMENT ON A
CENTRAL PRESSURE IN THE LOW 960 MB RANGE.

THE OVERALL WEATHER PATTERN IS SHIFTING TO AN UPPER LEVEL HIGH
ANCHORED OVER THE BERING STRAIT BY THIS WEEKEND WITH A TROUGH
EXTENDING FROM THE NORTHWEST TERRITORIES INTO THE GULF OF ALASKA.
EXPECT A WEAK AREA OF HIGH PRESSURE OVER THE MAINLAND WITH A STRONG
LOW IN THE WESTERN BERING SEA AND SOUTH OF THE GULF OF ALASKA BY THIS
WEEKEND.

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...
WE ARE ANTICIPATING SOME STRONGER WIND THROUGH THE CHUGACH MOUNTAIN
PASSES IN PARTICULAR THOMPSON PASS. THIS COUPLED WITH ABOUT ONE FOOT
OF TRANSPORTABLE SNOW WILL RESULT IN REDUCED VISIBILITIES IN BLOWING
SNOW TONIGHT AND TUE.

THE MOIST ADVECTION ACROSS THE KENAI PENINSULA AND PRINCE WILLIAM
SOUND WILL RESULT IN SHOWERY CONDITIONS THROUGH THIS EVENING. AS THE
LOW MOVES INTO THE NORTHERN GULF OF ALASKA OVERNIGHT IT WILL RE
INVIGORATE THE SHOWERS AS THE UPPER LEVEL TROUGH SWINGS CROSS THE
REGION. AS THE LOW AND UPPER TROUGH PASS TO THE EAST AND WEAKEN
CONDITIONS WILL IMPROVE ACROSS THE SOUTH CENTRAL REGION TUE INTO WED.

SOUTHWEST ALASKA...
WIDESPREAD SNOW SHOWERS WILL CONTINUE ACROSS SOUTHWEST ALASKA AS THE
LOW IN THE NORTHERN BERING SEA AND THE LOW NEAR THE ALASKA PENINSULA
AND THE ASSOCIATED UPPER TROUGH AFFECT THE REGION. THE UPPER TROUGH
AND LOW NEAR THE ALASKA PENINSULA WILL MOVE OFF TO THE EAST AND THE
SHOWERS WILL TAPER OFF AS THEY DO SO. EXPECT THE PEAK IN THE SHOWER
ACTIVITY TONIGHT AS THE TROUGH MOVES OVERHEAD. FOLLOWING THE PASSAGE
OF THE UPPER LEVEL TROUGH CONDITIONS WILL BECOME MUCH DRIER INTO THE
END OF THE WEEK.

ALEUTIANS/BERING SEA...
RAIN AND SNOW SHOWERS WILL CONTINUE ALONG THE LENGTH OF THE ALEUTIAN
ISLANDS IN THE WESTERLY FLOW. COLD AIR MOVING IN BEHIND THE LOWS WILL
RESULT IN AL HE PRECIPITATION CHANGING OVER TO SNOW SHOWERS THIS
EVENING. THE SHOWERS WILL TAPER OFF AS THE HIGH PRESSURE BEGINS TO
BUILD IN OVER THE EASTERN BERING.
ANOTHER LARGE STORM SYSTEM IS BEARING DOWN ON THE WESTERN ALEUTIANS.
THE PARENT LOW IS NOW WELL SOUTH OF SHEMYA AND IS EXPECTED TO MOVE TO
JUST WEST OF SHEMYA OVER THE NEXT COUPLE OF DAYS. THE FRONTAL LOW
ASSOCIATED WITH THIS STORM WILL BE THE MAIN PLAYER AND HAVE THE
GREATEST IMPACT TO THE CENTRAL TO EASTERN ALEUTIANS TUE NIGHT AND
WED. ENOUGH WARM AIR WILL BE PUSHED INTO THE CHAIN TO KEEP THE
PRECIPITATION ON THE LIQUID SIDE ALTHOUGH SOME MAY INITIALLY FALL AS
SNOW. THE WARMER AIR IS ALSO EXPECTED TO MITIGATE THE HIGHER WIND
GUST POTENTIAL AND AT THIS TIME WE ARE HOLDING OFF ON ANY HIGH WIND
WARNINGS.

LONG TERM FORECAST...
THE OVERALL WEATHER PATTERN IS SHIFTING TO AN UPPER LEVEL HIGH
ANCHORED OVER THE BERING STRAIT BY THIS WEEKEND WITH A TROUGH
EXTENDING FROM THE NORTHWEST TERRITORIES INTO THE GULF OF ALASKA.
EXPECT A WEAK AREA OF HIGH PRESSURE OVER THE MAINLAND WITH A STRONG
LOW IN THE WESTERN BERING SEA AND SOUTH OF THE GULF OF ALASKA BY THIS
WEEKEND.

.ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...STORM WARNING 172 173 174 175 176
         GALE WARNING 130 131 160 170 171 177 178 179 411 412 413 414

FIRE WEATHER...NONE

SAM MAR 14