Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 020029
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
429 PM AKDT MON JUN 1 2015

.ANALYSIS AND UPPER LEVELS...
IN THE UPPER LEVELS THERE IS A LOW OVER THE TANANA VALLEY THAT IS
EXPANDING SOUTHWEST ALONG THE YUKON RIVER VALLEY WITH A WEAK
RIDGE OF HIGH PRESSURE OVER THE GULF OF ALASKA AND ANOTHER UPPER
TROUGH EXTENDING FROM THE UPPER LOW OVER THE NORTHERN KAMCHATKA
PENINSULA ACROSS THE BERING SEA TO AN UPPER LOW SOUTH OF THE
EASTERN ALEUTIAN ISLAND. ANOTHER UPPER LEVEL LOW IS SOUTH OF THE
EXTREME WESTERN ALEUTIAN ISLANDS. AT THE SURFACE THE THERMAL
TROUGH EXTENDS FROM THE SOUTHERN YUKON TERRITORY ACROSS THE COPPER
RIVER BASIN TO A WEAK SURFACE LOW OVER THE SUSITNA VALLEY INTO
SOUTHWEST ALASKA. THE 850 MB TEMPERATURES OVER THE SOUTHERN
MAINLAND ARE AROUND 8 TO 10 CELSIUS CONTRIBUTING TO SUFFICIENT
VERTICAL TOTALS THAT RESULTING IN HIGHER INSTABILITY AND INCREASED
LIKELIHOOD OF THUNDERSTORM ACTIVITY AGAIN THIS AFTERNOON AND
EVENING.

&&

.MODEL DISCUSSION...

THE MODELS ARE IN GOOD AGREEMENT WITH THE OVERALL UPPER LEVEL
PATTERN BRINGING THE MAIN UPPER LOW TO SOUTH OF THE ALASKA
PENINSULA AND SOUTHERLY FLOW INTO THE SOUTHERN MAINLAND BY MID
WEEK. SIMILARLY THE MODELS ARE IN GOOD AGREEMENT WITH THE
MOVEMENT OF THE THERMAL TROUGH NORTH AND EXTENDING FROM THE YUKON
KUSKOKWIM DELTA EAST NORTH OF THE ALASKA RANGE AS A RIDGE BUILDS
IN ALONG THE EASTERN GULF OF ALASKA UP INTO PRINCE WILLIAM SOUND
IN ADVANCE OF THE INCOMING LOW FROM SOUTH OF THE ALEUTIANS. THE
MODELS ARE IN GOOD AGREEMENT WITH RESPECT TO THE UNSTABLE
CONDITIONS THIS EVENING ACROSS THE COPPER RIVER BASIN AND SOUTH
CENTRAL ALASKA TO SOUTHWEST ALASKA. THE NAM IS MORE UNSTABLE THAN
THE GFS OVER SOUTHWEST ALASKA AND IS THE MODEL OF CHOICE.

THE ATMOSPHERE IS BECOMING MORE STABLE TUESDAY AS THE CLOUD COVER
INCREASES AND COOLER LOW LEVEL AIR MOVES IN THE WITH SOUTHERLY
FLOW. THUNDERSTORM ACTIVITY WILL STILL BE A CONCERN OVER SOUTHWEST
ALASKA TUESDAY WITH THE COMBINATION OF WEAK DIURNAL INSTABILITY
COUPLED WITH STRONG UPPER LEVEL DYNAMICS.

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE UPPER LEVEL TROUGH AND LOW OVER THE TANANA VALLEY COMBINED
WITH INCREASED CLOUD COVER WILL COOL AND MOISTEN CONDITIONS OVER
THE SOUTH CENTRAL REGION AND COPPER RIVER BASIN OVER THE NEXT
COUPLE OF DAYS. INSTABILITY TODAY IS ALREADY PRODUCING ISOLATED
LOW TOPPED THUNDERSTORMS IN THE EASTERN COPPER RIVER BASIN. THE
THERMAL TROUGH COUPLED WITH WEAK RIDGING IN THE GULF IS PRODUCING
STRONGER TURNAGAIN ARM WINDS AND UP INLET WINDS IN COOK INLET. THE
AMPLIFICATION OF THE RIDGE THROUGH TUESDAY AND WEDNESDAY IN
ADVANCE OF THE INCOMING LOW WILL KEEP THESE WINDS UP THROUGH
WEDNESDAY. ISOLATED THUNDERSTORMS WILL CONTINUE TO BE A
POSSIBILITY TUESDAY AND WEDNESDAY AFTERNOON AND EVENING ALONG THE
ALASKA RANGE. THE UNSEASONABLY STRONG LOW AND ASSOCIATED FRONT
MOVING IN TO THE GULF TO ALONG THE NORTH GULF COAST WILL LIKELY
PRODUCE GALE FORCE WINDS ALONG THE NORTH GULF COAST WEDNESDAY.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE THERMAL TROUGH IS STILL IN PLACE OVER THE SOUTHWEST REGION.
THIS COMBINED WITH THE WARM AIR AND THE INSTABILITIES WILL KICK
OFF MORE THUNDERSTORMS THROUGH TUESDAY EVENING. THE SATELLITE
IMAGERY IS SHOWING CLEARING SKIES FROM SLEETMUTE EAST AND THIS
WILL ALLOW FOR GOOD DIURNAL HEATING AND COMBINED WITH THE UPPER
LEVEL TROUGH DROPPING DOWN FROM THE NORTH WILL PROVIDE THE EXTRA
KICKER FOR THUNDERSTORMS. THE THUNDERSTORMS WILL FORM AGAIN IN THE
GENERAL AREA LIKE YESTERDAY...WEST OF SLEETMUTE EXTENDING INTO THE
INTERIOR OF BRISTOL BAY. THE STORM MOTION IS TOWARDS THE WEST AND
THUNDERSTORMS WILL TRACK TRACK WEST ACROSS THE KUSKOKWIM DELTA
TONIGHT. BY TUESDAY AS THE TROUGH DROPS DOWN FROM THE NORTH IT
TRANSITIONS TO A WEAK DEFORMATION ZONE OVER THE SOUTHWEST REGION.
THE THUNDERSTORMS WILL LIKELY BE ISOLATED TO SCATTERED AS THE
THERMAL TROUGH CONTINUES TO WEAKEN AND MARINE LAYER STRATUS
COMBINED WITH ONSHORE FLOW WILL BRING IN COOLER TEMPERATURES
HEADING INTO THE MIDWEEK. THE OTHER ISSUE WILL BE FORECASTING THE
MARINE LAYER STRATUS AND FOG AS WE HEAD INTO THE MIDWEEK.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE KAMCHATKA GALE FORCE LOW CONTINUE TO TRACK SOUTH OF THE
WESTERN ALEUTIANS AND WILL BE LOCATED JUST SOUTH OF KISKA BY
TUESDAY. THE WEATHER FRONT ASSOCIATED WITH THIS SYSTEM IS MOVING
THROUGH THE WESTERN TO CENTRAL CHAIN. THIS WILL BRING GUSTY
SOUTHEASTERLY WINDS WITH STRATUS AND RAIN AS THE LOW CONTINUES TO
MOVE EASTWARD. THE CENTRAL BERING IS UNDER STRATUS WITH OCCASIONAL
LIGHT DRIZZLE AND PATCHY FOG WITH AREAS OF FOG EXTENDING TOWARDS
THE SOUTHWEST COASTLINE. BY LATE TUESDAY EVENING A NORTH PACIFIC
LOW IS TRACKING TOWARD KODIAK ISLAND AND WILL BRING MORE MARINE
LAYER STRATUS INTO THE EASTERN ALEUTIANS.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE IMPENDING SHIFT TO A COOLER AND WETTER PATTERN WILL BE WELL
UNDERWAY BY TUESDAY AS HIGH AMPLITUDE RIDGING OVER THE MAINLAND IS
REPLACED BY A SPRAWLING LONGWAVE TROUGH EXTENDING FROM THE
CANADIAN ARCTIC INTO THE NORTH PACIFIC SOUTH OF THE ALASKA
PENINSULA. THIS WILL YIELD A MORE SHOWERY REGIME AS TEMPERATURES
MODERATE TO AROUND SEASONAL NORMAL VALUES THROUGH THE END OF THE
WEEK. A FRONT APPROACHING THE GULF IN THE THURSDAY/FRIDAY
TIME FRAME ALONG WITH CONTINUED ONSHORE FLOW WILL KEEP ABUNDANT
RAINFALL FOCUSED ALONG THE COAST INTO THE WEEKEND. FARTHER TO THE
WEST...A PERSISTENT WEAK UPPER LEVEL FLOW PATTERN WILL KEEP
RELATIVELY BENIGN CONDITIONS OVER MUCH OF THE BERING THROUGH THE
NEXT WEEK AS THE MOST ACTIVE WEATHER REMAINS SOUTH OF THE ALEUTIAN
CHAIN.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 178.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...SA
SOUTHCENTRAL ALASKA...SA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD
LONG TERM...ML


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