High Wind in Alaska, October 24 to 25, 2011

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
355 PM AKDT MON OCT 24 2011

.ANYALYSIS...
DYNAMIC AND CHALLENGING WEATHER PATTERN DEVELOPING EARLY THIS
AFTERNOON. CURRENTLY...THE MAIN LOW IS LOCATED JUST NORTHWEST OF
BRISTOL BAY BUT A JET FLOWING AROUND THE BASE OF THE TROUGH IS
HELPING TO DEVELOP A STRONG LOW THIS AFTERNOON. THE NEW SURFACE LOW
WILL RAPIDLY DEEPEN TO 966 MB AS IT TRACKS TO NEAR KODIAK ISLAND
OVERNIGHT. COLD AIR ADVECTION IS APPARENT ON THE BACKSIDE OF THE
TROUGH BASED ON THE SATELLITE IMAGERY. FURTHER WEST...A WEAK RIDGE IS
BUILDING OVER THE WESTERN ALEUTIANS/BERING SEA.

.MODEL DISCUSSION...
THE BIGGEST CHALLENGE TODAY IS PICKING THE CORRECT MODEL SOLUTION.
SATELLITE IMAGERY SOUTH OF THE ALASKA PENINSULA IS ALREADY SHOWING
CIRCULATION AS THE LOW BEGINS TO RAPIDLY DEVELOP. THE NAM CONTINUES
TO BE VERY SLOW AND TOO FAR SOUTH WITH ITS INITIALIZATION OF THIS
FEATURE. THE GFS AND ECMWF HAVE A BETTER HANDLING BUT STILL SEEM A
BIT TOO FAR NORTH. A CREATIVE BLEND OF PREVIOUS MODEL RUNS WAS USED
TO BEST INDICATE OUR PROJECTED PATH OF THE LOW AS IT DEEPENS AND
MOVES JUST SOUTHEAST OF KODIAK ISLAND AND THEN INTO THE NORTHERN GULF
BY TUESDAY EVENING. GIVEN THE WIDE SPREAD OF MODEL SOLUTIONS AND LACK
OF OBSERVATIONS WHERE THE STORM IS ORIGINATING FROM...CONFIDENCE IS
BELOW AVERAGE FOR THE FIRST 48 HOURS.

SHORT TERM...
SOUTHCENTRAL ALASKA...SOUTHWEST FLOW ALOFT AND A RELATIVELY WARM
AIRMASS IS PROVIDING MUCH OF SOUTHCENTRAL WITH CLOUDY SKIES AND
SCATTERED RAIN SHOWERS. TEMPERATURES REMAINED JUST COLD ENOUGH TO
PRODUCE SNOW OVER THE NORTHERN SUSITNA VALLEY AND THROUGH THOMPSON
PASS WHERE SEVERAL INCHES OF HEAVY WET SNOW CONTINUES TO FALL EARLY
THIS AFTERNOON.

CHANGES TO THE CURRENT FORECAST WILL INCLUDE MUCH STRONGER WIND
THROUGH CHANNELED TERRAIN OVERNIGHT AND TUESDAY MORNING. AN INVERTED
TROUGH EXTENDING NORTH FROM THE ORIGINAL PARENT LOW WILL HELP TIGHTEN
UP THE PRESSURE GRADIENT ACROSS THE CHUGACH RANGE. UPPER LEVEL
SUPPORT OVERNIGHT WILL BE MINIMAL BUT THE GRADIENT SHOULD BE
SUFFICIENT TO BRING WARNING LEVEL WINDS TO TURNAGAIN ARM AND HIGHER
ELEVATIONS.

THEN AS THE FRONT APPROACHES...THE GRADIENT WILL CHANGE ITS
ORIENTATION ENOUGH TO ALLOW THE WESTERN TURNAGAIN ARM AND HILLSIDE
WINDS TO SUBSIDE WHILE THE PORTAGE VALLEY WINDS INCREASE. WE ARE
CONSIDERING THE POTENTIAL FOR A SHORT LIVED WARNING EVENT IN BOTH
PORTAGE AND CORDOVA AS THE FRONT APPROACHES AND THEN RAPIDLY MOVES
ONSHORE TUESDAY AFTERNOON.

SUCH A STRONG LOW IN THE NORTHWESTERN GULF WILL BE DIFFICULT TO
DOWNSLOPE...MEANING MOST OF THE TYPICALLY DRY AREAS SUCH AS THE
WESTERN KENAI PENINSULA AND ANCHORAGE BOWL WILL LIKELY STILL SEE RAIN
DURING THIS EVENT DESPITE THE SOUTHEASTERLY WINDS.

ANOTHER CONSIDERATION IS THE FIRST MEASURABLE SNOWFALL ANCHORAGE LATE
TUESDAY NIGHT AND WEDNESDAY MORNING. AS THE LOW TRACKS ACROSS THE
NORTHERN GULF...COLD AIR BEGINS TO FUNNEL IN FROM THE WEST AS THE
UPPER TROF APPROACHES. ASSUMING THERE IS ENOUGH MOISTURE...THESE ARE
ALL INGREDIENTS FOR MEASURABLE SNOWFALL IN ANCHORAGE. SO WE WILL
INTRODUCE RAIN CHANGING OVER TO LIGHT SNOW AND ACCUMULATING LATE
TUESDAY NIGHT AND WEDNESDAY MORNING FOR THE ANCHORAGE BOWL.

.SOUTHWEST AK/AK PEN...
THE WEATHER PICTURE IS A LITTLE MORE CLEAR OUT WEST WHERE OVERRUNNING
MOISTURE IS SPREADING NORTH. RAIN AND SNOW IS FALLING OVER MUCH
SOUTHWEST ALASKA AS THE INVERTED TROUGH EXTENDS FAR INTO THE
INTERIOR. THE LOW DEVELOPS AND THE WINDS RESPOND WITH A 75 TO 80 KT
LOW LEVEL JET STRENGTHENING ACROSS THE ALASKA PENINSULA BY TUESDAY
AFTERNOON. A HIGH WIND WATCH WILL BE UPGRADED TO A WARNING AS 80 MPH
WINDS ARE LIKELY THROUGH CHANNELED TERRAIN IN THIS REGION. THE EVENT
WILL BE SHORTLIVED AS THE RIDGE OVER THE WESTERN ALEUTIANS FLATTENS
AND SHIFTS EAST THROUGH TUESDAY. THIS IS ALSO IN RESPONSE TO ANOTHER
DEVELOPING LOW OFF THE KAMCHATKA PENINSULA THAT WILL RACE ACROSS THE
BERING TUESDAY AND TUESDAY NIGHT...REACHING BRISTOL BAY BY WEDNESDAY
AFTERNOON.

A TRANSIENT RIDGE GIVES WAY TO ANOTHER LOW WEDNESDAY NIGHT OUT WEST.
THE ACTIVE PATTERN CONTINUES.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WARNING...181
MARINE...STORM...120 125 130 132 150 155 160 165 170.
         GALE...129 138 140 171 172 175 176 179 180 185.
FIRE...NONE.

AB OCT 11