Small Craft Advisory 827, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
555 AM AKDT TUE OCT 22 2013

.ANALYSIS AND UPPER LEVELS...
THE OVERALL SYNOPTIC PATTERN REMAINS THE SAME THIS MORNING WITH A
BROAD LONGWAVE TROUGH OVER THE BERING SEA AND ONSHORE FLOW CONTINUING
TO PRODUCE SCATTERED SHOWERS OVER THE SOUTHERN MAINLAND. SHOWER
ACTIVITY IS BEING ENHANCED ACROSS SOUTHCENTRAL AS A SHORTWAVE TROUGH
EMBEDDED IN THE SOUTHWESTERLY FLOW MOVES QUICKLY OVERHEAD. AT THE
SURFACE...A LOW OVER THE NORTHERN BERING CONTINUES TO DRIFT WESTWARD
AND SLOWLY WEAKEN NEAR SAINT LAWRENCE ISLAND. MEANWHILE ANOTHER LOW
IS TRACKING EASTWARD OVER THE CENTRAL ALEUTIANS...BRINGING GALE FORCE
WINDS AND ADDITIONAL RAIN TO MUCH OF THE EASTERN BERING.

.MODEL DISCUSSION...
MODELS SHOW GOOD AGREEMENT IN THE IMMEDIATE SHORT TERM BUT CONTINUE
TO DIFFER SOMEWHAT WITH RESPECT TO THE STRONG NORTH PACIFIC LOW THAT
WILL BE APPROACHING THE EASTERN ALEUTIANS AND AKPEN LATE WEDNESDAY
INTO EARLY THURSDAY. UPPER LEVEL RIDGING WILL BUILD OVER THE SOUTHERN
MAINLAND TODAY AND PROVIDE A BREAK IN PRECIPITATION BEFORE A
RELATIVELY WEAK NORTH PACIFIC LOW TRACKS QUICKLY TO THE NORTHEASTERN
GULF COAST ON WEDNESDAY. THE LOW CURRENTLY AFFECTING THE EASTERN
BERING WILL BEGIN TO STALL AND DRIFT NORTHWARD TODAY...THEN
RETROGRADE BACK TOWARDS THE CENTRAL ALEUTIANS ON WEDNESDAY AND
EVENTUALLY DISSIPATE AS IT INTERACTS WITH THE APPROACHING NORTH
PACIFIC LOW. THE EC HAS BEEN THE MOST CONSISTENT WITH THIS SYSTEM
OVER THE PAST FEW DAYS...TAKING A ROUGHLY 950 MB LOW INTO THE EASTERN
BERING ON THURSDAY MORNING NEAR THE SOUTHERN TIP OF THE AKPEN WHEREAS
MOST OF THE OTHER GUIDANCE IS SLIGHTLY WEAKER AND HAS THE LOW
POSITION FURTHER EAST OVER THE AKPEN. THE NAM LOOKS TO BE THE OUTLIER
WITH THE FURTHEST POSITION TO THE EAST AND THE INTENSITY MUCH WEAKER
AROUND 970 MB. CONTINUED TO UTILIZE THE EC FOR NOW GIVEN SUPERIOR RUN
TO RUN CONSISTENCY.

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...
SHOWERS WILL BEGIN TO TAPER OFF LATER THIS MORNING AS THE SHORTWAVE
MOVES INTO THE INTERIOR. UPPER LEVEL RIDGING WILL THEN BUILD IN FROM
THE SOUTHWEST...YIELDING CLEARING SKIES AND ABUNDANT SUNSHINE OVER
MUCH OF THE AREA THROUGH WEDNESDAY. THE EXCEPTION WILL BE OVER FAR
EASTERN PORTIONS OF PRINCE WILLIAM SOUND AND THE EASTERN COPPER RIVER
BASIN WHERE THE PREVIOUSLY MENTIONED LOW MOVING TOWARDS THE
NORTHEASTERN GULF COAST WILL BRING A CHANCE OF PRECIPITATION
WEDNESDAY INTO WEDNESDAY NIGHT. MORE WIDESPREAD RAIN AND WINDS WILL
RETURN TO SOUTHCENTRAL ON THURSDAY AS THE STRONG NORTH PACIFIC LOW
MOVES INTO THE EASTERN BERING AND AN ASSOCIATED FRONT TRACKS
NORTHWARD THROUGH THE GULF.

SOUTHWEST ALASKA...
SHOWERS WILL CONTINUE TO TAPER OFF THROUGH THE MORNING AS THE UPPER
RIDGE BEGINS TO BUILD IN OVERHEAD...PROVIDING A BRIEF PERIOD OF DRIER
WEATHER AND OCCASIONAL SUNSHINE THROUGH WEDNESDAY BEFORE THE
APPROACHING NORTH PACIFIC LOW BEGINS TO IMPACT THE SOUTHWEST
MAINLAND. A FRONT LOOKS TO REACH THE COAST BY THURSDAY MORNING
ACCOMPANIED BY RAIN AND GUSTY SOUTHEASTERLY WINDS. THE AKPEN IS
LIKELY TO BE IMPACTED BY STRONG WINDS BEGINNING WEDNESDAY NIGHT AND
LASTING INTO THURSDAY AS THE LOW CROSSES INTO THE EASTERN BERING.
THIS SITUATION WILL HAVE TO BE MONITORED CLOSELY TO WORK OUT THE
EXACT DETAILS GIVEN THE CONTINUED MODEL UNCERTAINTY REGARDING THE
TRACK AND INTENSITY OF THE SYSTEM AS IT APPROACHES THE AREA.

ALEUTIANS/BERING SEA...
WIDESPREAD SHOWERY WEATHER WILL PERSIST OVER THE REGION TODAY AS THE
LONGWAVE TROUGH REMAINS OVERHEAD...WITH THE EMBEDDED LOW OVER THE
EASTERN ALEUTIANS SUPPORTING GALE FORCE WINDS OVER MUCH OF THE
EASTERN BERING. ATTENTION WILL THEN TURN TO THE POWERFUL NORTH
PACIFIC LOW POISED TO APPROACH THE EASTERN ALEUTIANS AND AKPEN LATE
WEDNESDAY...RESULTING IN HEAVY RAIN AND STRONG SOUTHEASTERLY WINDS
OVER MUCH OF THE EASTERN BERING THROUGH THURSDAY AS WELL AS STRONG
NORTHWESTERLY WINDS OVER THE WESTERN AND CENTRAL BERING ON THE
BACKSIDE OF THE SYSTEM.

.LONG TERM FORECAST...
UPPER RIDGING LOOKS TO BUILD OVER THE MAINLAND EARLY THIS WEEKEND
ONCE THE NEXT BERING SYSTEM WINDS DOWN...POTENTIALLY PROVIDING
ANOTHER BRIEF PERIOD OF QUIETER WEATHER LATE IN THE WEEK. MODELS THEN
SUGGEST THAT BROAD SOUTHERLY FLOW WILL ONCE AGAIN TAKE HOLD OVER THE
SOUTHERN MAINLAND...RESULTING IN A RETURN TO A MORE SHOWERY PATTERN
IN THE EXTENDED TERM.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE WARNING 155 172 173 174 175 176 177 180 181 185
FIRE WEATHER...NONE

CB OCT 13