Storm Warning 215, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
530 PM AKST MON NOV 8 2010

.MODEL DISCUSSION...
THE POLAR VORTEX TO SHIFT FROM THE NORTHERN ATLANTIC TO THE POLE OVER
THE NEXT FEW DAYS. WITH A RIDGE BUILDING ALONG THE WEST COAST OF
NORTH AMERICA THIS WEEKEND AND HIGH PRESSURE REMAINING OVER SIBERIA
THROUGH THE WEEK...THE TROUGH OVER THE BERING WILL DEEPEN AND START
TO RETROGRADE LATER THIS WEEKEND. IN THE MEANTIME...HIGH PRESSURE TO
REMAIN OVER SIBERIA. THE MODELS ARE FAIRLY CONSISTENT AT 500MB WITH
THE POLAR LOW MOVING INTO THE ARCTIC OCEAN NEAR 180. THEREFORE...THE
MODELS ARE IN GOOD AGREEMENT THROUGH FRIDAY. HOWEVER...THEY ARE
HAVING SOME DIFFICULTY COMING INTO AGREEMENT WITH THE WAVE MOVING
INTO THE GULF THURSDAY. THE EC IS FARTHER EAST THAN THE GFS. THE GFS
WOULD BE THE PREFERRED SOLUTION DUE TO THE MEAN RIDGE ALONG THE WEST
COAST OF NORTH AMERICA. AFTER THIS TIME FRAME THE UNCERTAINTY COMES
INTO PLAY QUITE HEAVILY. MODELS SETTLE INTO BETTER AGREEMENT FRIDAY
BUT THE SPEED OF THE NEXT SURFACE FEATURE ON SATURDAY OUT OF THE
NORTHERN PACIFIC INTO THE GULF IS OF QUESTION. GFS IS FARTHER EAST
AND NOT AS STRONG AS THE EC. GFS ENSEMBLES HINT AT THE FARTHER WEST
SOLUTION AS WELL.

.ANALYSIS AND UPPER LEVELS...
ALOFT...A VERTICALLY STACKED LOW IN THE WESTERN BERING IS SLIDING
EASTWARD. TRANSIENT RIDGING AHEAD OF THIS LOW IS MOVING THROUGH
SOUTHWEST ALASKA...WHILE ANOTHER UPPER TROUGH IS HANGING TOUGH OVER
MOST OF THE MAINLAND. THE JET STREAM IS LOCATED ALONG OR JUST SOUTH
OF THE ALEUTIANS...AND THEN DROPS SOUTHWARD TO CARVE OUT THE
SIGNIFICANT UPPER LEVEL TROUGH OVER THE GULF OF ALASKA.

AT THE SURFACE...A WEAK LOW IS MOVING NORTH THROUGH THE GULF TOWARD
THE KENAI PENINSULA. THIS IS HELPING TO BREAK UP THE PERSISTENT
PATTERN OF THE LAST FEW DAYS THAT HAS FEATURED A BAND OF MODERATE TO
HEAVY SNOW OVER THE KENAI PENINSULA. THIS BAND OF SNOW IS ASSOCIATED
WITH THE COMBINATION OF A SURFACE TROUGH THAT HAS LINGERED OVER UPPER
COOK INLET FOR SEVERAL DAYS...AS WELL AS A MID-LEVEL DEFORMATION ZONE
THAT HAS ALSO REMAINED NEARLY STATIONARY. THIS IS ALSO THE SAME
FEATURE THAT BROUGHT SIGNIFICANT SNOW INTO THE ANCHORAGE AREA
OVERNIGHT. THIS BAND OF SNOW IS SLOWLY BREAKING UP INTO SNOW SHOWERS
THIS AFTERNOON. FURTHER WEST...SOUTHWEST ALASKA IS SEEING SOME SUNNY
BREAKS TODAY...WHILE A WEAK FRONT OVER THE CENTRAL BERING HAS USHERED
IN ENOUGH WARM AIR TO CHANGE PRECIPITATION TO RAIN AS FAR NORTH AS
THE PRIBILOF ISLANDS.

.SHORT TERM FORECAST...
.SOUTHCENTRAL...BAND OF MODERATE SNOW OVER THE KENAI PENINSULA WILL
CONTINUE TO DIMINISH TO SHOWERS BY EARLY EVENING. THIS IS HAPPENING
IN RESPONSE TO THE SURFACE LOW THAT IS MOVING NORTHWARD THROUGH THE
GULF...AS WELL AS AN UPPER LOW OVER THE LOWER SUSITNA VALLEY THAT IS
BEGINNING TO MOVE TO THE EAST. EXPECT MAIN FOCUS OF PRECIPITATION
ACROSS THE REGION TO SHIFT TO NORTHERN AND EASTERN PRINCE WILLIAM
SOUND OVERNIGHT AS MEAN FLOW BECOMES SOUTHERLY OR EVEN SOUTHWESTERLY.
TEMPERATURES SHOULD COOL STEADILY IN VALDEZ...CHANGING PRECIPITATION
TO ALL SNOW BY MID EVENING. AT THIS TIME...ANTICIPATE FAIRLY UNIFORM
8 TO 14 INCH ACCUMULATIONS IN TOWN AND THROUGH THOMPSON PASS BY
MIDDAY TUESDAY. AT THE SAME TIME...SHOWERS WILL REMAIN OVER THE COOK
INLET AND ANCHORAGE BOWL OVERNIGHT...WITH ADDITIONAL MINOR
ACCUMULATIONS POSSIBLE. SNOW MAY BECOME STEADIER IN ANCHORAGE
TOMORROW MORNING AS COLD AIR BEGINS TO MOVE NORTHWARD THROUGH COOK
INLET...BEFORE CONDITIONS IMPROVE IN THE AFTERNOON.

.WEST OF THE ALASKA RANGE...LARGE BUT RELATIVELY WEAK AREA OF LOW
PRESSURE IN THE BERING WILL BRING NUMEROUS RAIN AND SNOW SHOWERS TO
THE REGION FOR NEXT FEW DAYS. SOUTHWEST ALASKA WILL STAY RELATIVELY
DRY...AS WEAK FRONT IN THE CENTRAL BERING DISSIPATES BEFORE REACHING
THE COAST.

.LONG TERM FORECAST...
OVERALL NOT MUCH CONFIDENCE IN THE LONG TERM FORECAST AS THE TIMING
OF THE SYSTEMS IN VERY MUCH IN DOUBT. WE WILL LIKELY SEE SOME LOW
PRESSURE SYSTEMS MOVING SOUTH OF THE CENTRAL ALEUTIANS AND WRAPPING
INTO THE GULF AND BACK INTO THE EASTERN BERING. THIS IS A RESULT OF
THE LONG WAVE PATTERN SETTING UP AN ESTABLISHED TROUGH OVER THE
CENTRAL BERING WEDNESDAY AND RETROGRADING LATER IN THE WEEK.
THEREFORE...STORMS PASS THROUGH THE GULF TWICE IN THE LONG TERM AND
SOUTHWEST ALASKA HAVING SHOWERS JUST WRAP AROUND THESE LOWS.
INSTABILITY SHOWERS TO PREVAIL OVER THE BERING THROUGHOUT DUE TO THE
COLD AIR MASS AND RELATIVELY WARMER WATERS. WARMER THAN NORMAL
TEMPERATURES EXPECTED FOR SOUTHCENTRAL WITH COLDER THAN NORMAL
EXPECTED OVER THE BERING AND ALEUTIANS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE 172 175 176
FIRE WEATHER...NONE

JN/AMD NOV 10