Flood and High Wind in Alaska, October 24 to 28, 2013

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
550 AM AKDT THU OCT 24 2013

.ANALYSIS AND UPPER LEVELS...
THE MAIN FEATURE OF INTEREST THIS MORNING IS THE POWERFUL NORTH
PACIFIC LOW NEARING ITS PEAK INTENSITY AROUND 957 MB AS IT PUSHES
INTO THE EASTERN BERING SEA NEAR CAPE SARICHEF...BRINGING STORM FORCE
WINDS TO MUCH OF THE EASTERN HALF OF THE BERING. AN ASSOCIATED FRONT
IS SPREADING STRONG WINDS AND HEAVY RAIN OVER THE AKPEN AND INTO
BRISTOL BAY AND THE SOUTHERN GULF OF ALASKA AS IT ADVANCES
NORTHWARD...WITH WARNING LEVEL LEVEL WINDS THROUGH CHANNELED TERRAIN
ALONG THE AKPEN. MEANWHILE...CLEAR SKIES PREVAIL ACROSS MOST OF
SOUTHCENTRAL BENEATH UPPER LEVEL RIDGING AS A DISTURBANCE THAT
BROUGHT SNOW TO EASTERN PORTIONS OF THE COPPER RIVER BASIN YESTERDAY
MOVES QUICKLY INTO WESTERN CANADA. HOWEVER...CLOUDS ARE BEGINNING TO
SPREAD TOWARDS THE AREA FROM THE SOUTH AS THE AFOREMENTIONED FRONT
ADVANCES THROUGH THE SOUTHERN GULF.

.MODEL DISCUSSION...
MODELS HAVE GENERALLY COME INTO GOOD AGREEMENT REGARDING THE STRONG
LOW AS IT TRACKS THROUGH THE EASTERN BERING OVER THE NEXT FEW DAYS.
THERE IS NOW A BETTER CONSENSUS ON THE FORMATION OF A TRIPLE POINT
LOW OVER THE WESTERN GULF THIS EVENING...WHICH WILL HAVE LARGE
IMPLICATIONS ON THE TURNAGAIN ARM WINDS AND THEIR POTENTIAL TO MOVE
OVER ANCHORAGE TODAY AND TONIGHT. THE NAM REMAINS AN OUTLIER FROM
ABOUT FRIDAY AFTERNOON ONWARD AS THE SYSTEM RAPIDLY WEAKENS OVER THE
NORTHERN BERING. MOSTLY UTILIZED THE EC SOLUTION WITH SOME GFS AS
WELL GIVEN THE OVERALL AGREEMENT. THERE IS GREATER DISAGREEMENT ON
THE NEXT MUCH WEAKER LOW SET TO APPROACH THE CENTRAL ALEUTIANS THIS
WEEKEND. PREFERRED THE EC WITH THAT SYSTEM FOR NOW.

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...
RAIN AND GUSTY SOUTHEASTERLY WINDS WILL SPREAD OVER THE AREA FROM THE
SOUTH TODAY AND TONIGHT AS THE FRONT PROGRESSES THROUGH THE GULF.
RAIN WILL REACH THE SOUTHERN KENAI PENINSULA BY THIS MORNING AND THEN
SPREAD TO THE NORTHERN GULF COAST THIS AFTERNOON. PRECIPITATION WILL
BE LIMITED TO SCATTERED SHOWERS OVER THE ANCHORAGE BOWL AND THE
MATANUSKA VALLEY AS STRONG CROSS BARRIER FLOW LEADS TO DOWNSLOPING.
SNOW WILL MIX IN WITH RAIN OVER THE SUSITNA VALLEY AND HIGHER
ELEVATIONS...WITH LIGHT ACCUMULATIONS POSSIBLE THROUGH PASSES AND
OVER THE WESTERN SUSITNA VALLEY. WINDS WILL INCREASE ALONG TURNAGAIN
ARM AND HIGHER ELEVATIONS OF THE ANCHORAGE BOWL BY EARLY THIS
AFTERNOON AS THE PRESSURE GRADIENT TIGHTENS IN RESPONSE TO THE STRONG
LOW MOVING INTO THE EASTERN BERING AND THE FRONT APPROACHES FROM THE
SOUTH. HOWEVER...THE PREVIOUSLY MENTIONED TRIPLE POINT LOW FORMING
OVER THE WESTERN GULF THIS AFTERNOON COUPLED WITH THE WEAKENING OF
THE FRONT AS IT APPROACHES THE COAST WILL WORK AGAINST STRONGER WINDS
MAKING INTO ANCHORAGE AS THE GRADIENT BECOMES LESS FAVORABLE FOR
WINDS TO BEND INTO TOWN. PRECIPITATION WILL TAPER OFF TO SHOWERS ON
FRIDAY AND GIVE WAY TO SUNSHINE AS UPPER LEVEL RIDGING ONCE AGAIN
MOVES OVERHEAD.

SOUTHWEST ALASKA...
RAIN AND STRONG WINDS WILL CONTINUE TO SPREAD OVER THE SOUTHWEST
MAINLAND FROM THE SOUTH TODAY AS THE FRONT MOVES INLAND AHEAD OF THE
LOW TRACKING INTO THE EASTERN BERING. WARNING LEVEL WINDS WILL
PERSIST THROUGH CHANNELED TERRAIN ALONG THE AKPEN THROUGH EARLY
AFTERNOON BEFORE SUBSIDING AS THE LOW MOVES NORTH OF THE AREA.
SHOWERY WEATHER AND GUSTY WINDS WILL PERSIST INTO THE DAY ON FRIDAY
WITH THE LOW GRADUALLY WEAKENING AND MOVING INTO THE NORTHERN
BERING...WITH THE STRONGEST WINDS GENERALLY ALONG THE COAST.
CONDITIONS WILL IMPROVE LATER FRIDAY INTO SATURDAY AS TRANSITORY
UPPER LEVEL RIDGING YIELDS CLEARING SKIES.

ALEUTIANS/BERING SEA...
STORM FORCE WINDS AND HEAVY RAIN WILL REMAIN OVER MUCH OF THE EASTERN
BERING INTO TONIGHT AS THE POWERFUL LOW PASSES JUST EAST OF THE
PRIBILOF ISLANDS. FURTHER WEST...NORTHERLY GALE FORCE WINDS AND
NUMEROUS SHOWERS WILL PREVAIL OVER THE WESTERN AND CENTRAL ALEUTIANS
ON THE BACKSIDE OF THE CURRENT SYSTEM AND THEN CONTINUE INTO FRIDAY
AS A WEAKER LOW APPROACHES THE CENTRAL PART OF THE CHAIN FROM THE
SOUTH.

.LONG TERM FORECAST...
UPPER LEVEL RIDGING WILL HELP TO KEEP MUCH OF THE SOUTHERN MAINLAND
DRY THIS WEEKEND. AFTER THAT...MODELS ARE GENERALLY SUGGESTING A
RETURN TO TROUGHING OVER THE BERING AND DEEP SOUTHERLY FLOW OVER THE
MAINLAND. THIS WOULD KEEP PRECIPITATION IN THE FORECAST FOR MUCH OF
THE REGION INTO NEXT WEEK AND ALSO RESULT IN CONTINUED ABOVE NORMAL
TEMPERATURES FOR THE SOUTHERN MAINLAND IN THE EXTENDED TERM.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WARNING 161 181
MARINE...STORM WARNING 130 155 160 165 172 179 180 181 185
         GALE WARNING 119 120 125 131 132 136 137 138 139 150 170
                      170 171 173 174 176 177 178
FIRE WEATHER...NONE

CB OCT 13