Flooding in Alaska, May 24 to 31, 2013

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
130 PM AKDT FRI MAY 24 2013

.ANALYSIS AND UPPER LEVELS...
A LONGWAVE TROUGH REMAINS OVER THE BERING SEA...WITH WEAK SOUTHERLY
FLOW ACROSS MOST OF THE MAINLAND. HIGH PRESSURE OVER NORTHWEST CANADA
IS GAINING STRENGTH AND BEGINNING TO EXPAND INTO THE INTERIOR OF THE
STATE...WITH THE WARMEST TEMPERATURES OF THE SEASON ALREADY OCCURRING
AT MANY LOCATIONS. A FAIRLY WEAK 997 MB LOW SOUTH OF THE ALEUTIANS
CONTINUES TO MOVE SLOWLY NORTHWARD...WITH THE ASSOCIATED FRONT
BEGINNING TO IMPACT THE EASTERN ALEUTIANS AND ALASKA PENINSULA WITH
WIND AND RAIN. CLOUD-COVER IS DECLINING ACROSS MOST PARTS OF THE
MAINLAND...AND IS COMBINING WITH WARMER TEMPERATURES TO PRODUCE SOME
DIURNAL CONVECTIVE CLOUDS ALONG AREA MOUNTAIN RANGES. A WEAK TROUGH
ALONG THE NORTH GULF COAST IS PRODUCING SOME LOCALLY GUSTY OFFSHORE
WINDS IN WHITTIER AND THROUGH THOMPSON PASS...BUT IS ALSO HELPING TO
PULL THE WIDESPREAD MARINE STRATUS AWAY FROM THE GULF COAST
COMMUNITIES AND OUT TO SEA.

.MODEL DISCUSSION...
MODELS REMAIN IN EXCELLENT AGREEMENT THAT THE OVERALL WEATHER PATTERN
WILL BE DOMINATED BY THE STRONG RIDGE AND HIGH PRESSURE BUILDING INTO
THE INTERIOR THROUGH NEXT WEEK. THIS MEANS UNSETTLED WEATHER WILL BE
CONFINED TO THE BERING SEA REGION AND WELL SOUTH OF THE GULF OF
ALASKA. THE BIG STORY WILL BE TEMPERATURES RISING TO ABOVE NORMAL
ACROSS MOST OF THE MAINLAND...AND WARMING TO NEAR-NORMAL OVER THE
ALEUTIAN DOMAIN. THE LARGEST AREA OF MODEL DISCREPANCY INVOLVES THE
EVOLUTION OF THE UPPER LOW CURRENTLY MOVING AWAY FROM KODIAK ISLAND
INTO THE GULF. ALL MODELS SHOW THIS LOW RE-CURVING NORTHWESTWARD BY
SUNDAY AND MOVING INTO SOUTHCENTRAL...THOUGH TIMING AND POSITION
DIFFERENCES EXIST. THE ECMWF IS THE FASTEST AND FURTHEST WEST...WHILE
THE NAM IS A BIT OF AN OUTLIER TO THE EAST. THE GFS IS A GOOD
MIDDLE-GROUND SOLUTION TODAY...AND WAS CLOSE TO THE MODEL CONSENSUS
OF THE OVERNIGHT MODEL RUNS. THUS THE GFS SOLUTION WAS PREFERRED
DURING THE FORECAST PROCESS TODAY.

.SHORT TERM FORECAST...
SOUTHCENTRAL...SUN AND WARM TEMPERATURES WILL BE THE RULE FOR MOST OF
THE MAINLAND THROUGH THE MIDDLE OF NEXT WEEK. GRADUALLY INCREASING
INSTABILITY WILL LEAD TO INCREASING AMOUNTS OF DIURNAL CLOUDS FORMING
EACH AFTERNOON AND EVENING...ESPECIALLY OVER MOUNTAINOUS AREAS. THE
BEST CHANCES FOR SHOWERS OR AN ISOLATED THUNDERSTORM WILL BE OVER THE
COPPER RIVER BASIN ON SUNDAY AND MONDAY. AS MENTIONED IN THE MODEL
DISCUSSION...THE MODELS ARE STRUGGLING A BIT WITH BRINGING AN
EASTERLY WAVE THROUGH SOUTHCENTRAL ALASKA SUNDAY AFTERNOON. THE EXACT
TRACK AND TIMING WILL MAKE A BIG DIFFERENCE ON CHANCES FOR RAIN AT
ANY GIVEN LOCATION. WITH MUCH UNCERTAINTY REMAINING...WILL OPT TO
LEAVE MOST OF THE AREA AT FAIRLY LOW POPS...BUT IT IS IMPORTANT TO
NOTE THAT THE TREND IS TOWARD A CLOUDIER AND WETTER SCENARIO ON
SUNDAY EVENING FROM COOK INLET OVER TO THE COPPER BASIN.

SOUTHWEST MAINLAND... WEAK SOUTHERLY FLOW AND PROXIMITY TO THE
LONGWAVE TROUGH ARE KEEPING CONSIDERABLE CLOUDINESS ACROSS MUCH OF
THE AREA SO FAR TODAY...THOUGH WITH TIME THE TREND WILL BE DEFINITELY
BE TOWARD CLEARING SKIES AND WARMER CONDITIONS OVER THE NEXT SEVERAL
DAYS. SATELLITE IMAGERY OVER INLAND AREAS SHOW CONVECTIVE CLOUDS
FORMING ALMOST IMMEDIATELY AFTER STRATIFORM CLOUDS MOVE OUT. THIS
WILL BECOME THE NORM OVER THE COMING DAYS AS WARMER TEMPERATURES
ALLOW INCREASING INSTABILITY TO SLOWLY SPREAD TO THE WEST.

BERING SEA AND ALEUTIANS...A COMPLEX LOW WITH MULTIPLE CENTERS SOUTH
OF THE ALEUTIANS WILL DRIFT NORTH AND BECOME STATIONARY OVER THE
SOUTHERN BERING THROUGH MONDAY. THIS WILL KEEP UNSETTLED WEATHER OVER
MUCH OF THE REGION...THOUGH NOTHING PARTICULARLY UNUSUAL. WARMER
TEMPERATURES WILL BLEED INTO THE AREA FROM THE BUILDING RIDGE OVER
THE MAINLAND...ALLOWING MORE SEASONABLE TEMPERATURES TO TAKE HOLD.

.LONG TERM FORECAST...
THE MUCH-ANTICIPATED WARMING OVER THE MAINLAND APPEARS THAT IT WILL
STAY IN PLACE THROUGH AT LEAST THE MIDDLE OF NEXT WEEK. NO MAJOR
STORM SYSTEMS ARE EXPECTED TO MOVE THROUGH THE ALASKAN DOMAIN...AND
LOCAL INFLUENCES SUCH AS SEA BREEZES AND AFTERNOON CONVECTION WILL BE
THE PRIMARY WEATHER IMPACTS FOR THE NEXT WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE 150 155
FIRE WEATHER...NONE

DIXON MAY 13