Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
428 PM AKDT MON APR 27 2015

.ANALYSIS AND UPPER LEVELS...
THERE IS AN UPPER LEVEL LOW OVER THE GULF OF ALASKA. THERE IS A
DISSIPATING LOW OVER THE CENTRAL BERING SEA WITH A WEAK FRONT
STRETCHING EASTWARD ACROSS THE PRIBILOFS AND THEN SOUTHEAST TO 
THE WESTERN ALASKA PENINSULA. THERE IS A STRENGTHENING LOW MOVING
INTO THE WESTERN ALEUTIANS FROM THE WEST. STRONG WESTERLY FLOW
ALOFT IS PUSHING ACROSS THE NORTH PACIFIC TO THE SOUTH OF THESE
LOWS. WEAK CYCLONIC FLOW EXISTS TO THE NORTH...COVERING MOST OF
SOUTHERN ALASKA AND THE BERING SEA. A WEAK RIDGE IS OVER THE
BERING STRAIT AND NORTHERN MAINLAND ALASKA. AT THE SURFACE THE
FLOW IS FAIRLY WEAK OVER LAND...WITH A BIT OF A THERMAL TROUGH
OVER CENTRAL ALASKA. HUMIDITIES IN SOUTH CENTRAL HAVE INCREASED
CONSIDERABLY TODAY AND AS A RESULT THERE ARE NO FIRE WEATHER
CONCERNS.

&&

.MODEL DISCUSSION...
THE NUMERICAL MODELS ARE IN GOOD AGREEMENT THROUGH THE SHORT TERM
PORTION OF THE FORECAST. THERE ARE OF COURSE SOME MINOR DIFFERENCES
IN THE TIMING OF IMPULSES AROUND THE UPPER LOWS. THESE IMPULSES
ARE FAIRLY WEAK AND MAINLY AFFECT THE TIMING OF INCREASING/DECREASING
SHOWER ACTIVITY...WHICH IS FAIRLY EASY TO HANDLE. FORECAST
CONFIDENCE IS A LITTLE HIGHER THAN NORMAL.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
A SUBTLE EASTERLY WAVE ALOFT IS SPREADING MOISTURE AND CLOUDS
OVER MOST OF MAINLAND SOUTHCENTRAL THIS EVENING. CONVECTIVE RAIN
SHOWERS ARE BREAKING OUT ACROSS THE SUSITNA VALLEY SOUTHWARD TO
THE KENAI PENINSULA. STEADIER AND MORE NUMEROUS RAIN AND SNOW
SHOWERS ARE IMPACTING THE COPPER BASIN AND THOMPSON PASS...WITH
LIGHT SNOW ACCUMULATION POSSIBLE THROUGH THE PASSES AND THE
WESTERN COPPER BASIN THROUGH TONIGHT. AN OFFSHORE PRESSURE
GRADIENT WILL DEVELOP ON TUESDAY...WITH DIMINISHING CLOUD COVER
AND SHOWERS. GUSTY GAP WINDS WILL ALSO DEVELOP ACROSS INLAND
COASTAL LOCATIONS. A WEAK LOW WILL TRACK OVER SOUTHCENTRAL
WEDNESDAY...WITH MORE CLOUDS AND SHOWERS REDEVELOPING OVER THE
MAINLAND. SOUTHEAST WINDS WILL BECOME GUSTY IN THE AFTERNOON...
ESPECIALLY ALONG TURNAGAIN ARM AND SOUTH AND WEST ANCHORAGE.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
SOUTHWEST ALASKA IS UNDER A LARGE AREA OF MOSTLY CLEAR SKIES THIS
AFTERNOON WITH A FEW CLOUDS SNEAKING IN FROM THE EAST AS WELL AS
CUMULUS DEVELOPMENT OVER HIGHER ELEVATIONS. THE BIG QUESTION FOR
THIS EVENING IS WHETHER THERE WILL BE ENOUGH INSTABILITY TO
REALLY KICK OFF SHOWERS...AND EVEN THUNDERSTORMS IN THE KUSKOKWIM
VALLEY. THIS IS ONE OF THOSE CASES WHERE THE LINE BETWEEN MOSTLY
CLEAR SKIES AND HAVING QUITE A FEW SHOWERS AND EVEN THUNDERSTORMS
MAY BE QUITE THIN. WHILE SATELLITE IMAGERY SHOWS NOT MUCH IN THE
WAY OF CONVECTIVE BUILD UP SO FAR THEY COULD DEVELOP QUICKLY IF
THE CAPPING INVERSION BREAKS. MEANWHILE...STRATUS LURKING JUST
OFF THE COAST OF BRISTOL BAY WILL LIKELY COME ON SHORE AS THE
TEMPERATURES COOL OFF LATER THIS EVENING.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE FIRST LOW IN THE BERING SEA LOCATED WEST OF THE PRIBILOF
ISLANDS IS ELONGATING AND WEAKENING AS IT PUSHES UP AGAINST THE
RIDGE OVER SOUTHWEST ALASKA. THE SECOND LOW TO THE WEST OF IT IS
TAPPING INTO JET SUPPORT AND IS STRENGTHENING IN THE WESTERN
ALEUTIANS. THIS WILL KEEP PRECIPITATION OVER THE BERING SEA AND
SOME GALES SOUTH OF THE ALEUTIANS THE NEXT FEW DAYS.

&&

.LONG TERM FORECAST (DAY 3 THROUGH 7)...
THE STRONG ZONAL JET STREAM OVER THE ALEUTIAN CHAIN CONTINUES TO
TRACK EASTWARD HEADING INTO THE WEEKEND. THERE WILL BE A BROAD
AREA OF LOW PRESSURE IN BERING SEA THAT WILL WEAKEN INTO A TROUGH
THROUGH FRIDAY. BY SATURDAY A NORTH PACIFIC LOW WILL TRACK INTO
THE WESTERN GULF WHILE ANOTHER LOW MOVES OUT OF ASIA AND INTO THE
BERING SEA.

THE GULF WILL HAVE SOUTH TO SOUTHWESTERLY FLOW WITH WEAK DISTURBANCES
MOVING INTO THE AREA THROUGH FRIDAY. THESE SYNOPTIC FEATURES WILL
BE ACCOMPANIED BY SHOWERS IN THE GULF AND ALONG THE COASTAL AREAS
FOR THE NEXT SEVERAL DAYS. BY THURSDAY AN UPPER LEVEL RIDGE BUILDS
INTO THE WESTERN GULF. THIS RIDGE WILL BECOME AMPLIFIED AND BE
POSITIONED OVER THE SOUTHCENTRAL REGION EXTENDING INTO MATSU VALLEY
FRIDAY THROUGH THE WEEKEND. THIS SYNOPTIC FEATURE WILL BRING WARMER
TEMPERATURES AND DRIER CONDITIONS TO THE SOUTHCENTRAL REGION. THERE
WILL BE A THERMAL TROUGH SETTING UP OVER THE WEEKEND...WHICH WILL
INCREASE THE CHANCES FOR AFTERNOON TO EVENING SHOWERY ACTIVITY FOR
THE INLAND AREAS. THE MODELS WERE IN BETTER AGREEMENT WITH THE
TIMING AND PLACEMENT OF THE DIFFERENT SYNOPTIC FEATURES...WITH WPC
USING A BLEND OF THE ENSEMBLE MEANS THROUGH THE WEEKEND.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 174 176 177. 
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...JA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...EZ
LONG TERM...PD

National Weather Service Glossary of Abbreviations