Heavy Freezing Spray Warning 45, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
429 PM AKDT SUN MAR 13 2016

.ANALYSIS AND UPPER LEVELS...
GENERALLY CLEAR SKIES DOMINATE THE ALASKA MAINLAND TODAY... WITH
A WEAK RIDGE IN PLACE THAT STRETCHES WESTWARD FROM CANADA INTO
SOUTHERN ALASKA. AT THE SURFACE...A LOW CONTINUES TO MEANDER IN
THE SOUTHEAST GULF OF ALASKA. THE PRESSURE GRADIENT BETWEEN THESE
TWO FEATURES IS SUPPORTING LIGHT OFFSHORE FLOW...WHICH HAS KEPT
THE SOUTHCENTRAL MAINLAND MAINLY FOG FREE. MEANWHILE A LOW
SPINNING NEAR THE PRIBILOFS HAS BEEN SUPPORTING STEADY SNOW
SHOWERS THIS MORNING ACROSS THE PRIBILOFS AND ALASKA PENINSULA.

&&

.MODEL DISCUSSION...
MODELS REMAIN IN RELATIVELY GOOD AGREEMENT AS AN UPPER LEVEL LOW
IN NORTH CENTRAL ALASKA...INITIATES A PATTERN CHANGE AS IT DIVES
TOWARDS SOUTHCENTRAL BY EARLY THIS WEEK. HOWEVER...MODELS SHOW A
LITTLE MORE UNCERTAINTY ON THE INTENSITY AND LOCATION OF A SURFACE
LOW THAT SUBSEQUENTLY DEVELOPS IN THE NORTHERN GULF. AS A
RESULT...THERE IS SOME UNCERTAINTY IN THE LOCATION OF
PRECIPITATION IN SOUTH CENTRAL TOWARDS THE END OF THE SHORT TERM.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
ANOTHER GORGEOUS EVENING IN STORE WITH AN EXTRA HOUR ON THE END
TO BOOT! A WEAK DISTURBANCE ALOFT IS SKIRTING THE SOUTHERN KENAI
PENINSULA AND COULD BRING AN ISOLATED SHOWER TO THE SEWARD
AREA...BUT FOR THE MOST PART THE SOUTHCENTRAL WILL REMAIN DRY.
THIS DISTURBANCE WILL SPREAD CLOUD COVER OVER THE AREA TONIGHT
INTO THE MORNING HOURS. THERE WILL BE A FEW MORE CLOUDS IN THE
COOK INLET REGION ON MONDAY AS SOUTHWESTERLY FLOW ALOFT BECOMES
MORE ESTABLISHED. GUIDANCE IS HINTING AT A NARROW CORRIDOR OF
ISENTROPIC LIFT LATE MONDAY NIGHT AND TUESDAY...COMBINED WITH WEAK
STABILITY COULD MAKE FOR SOME LIGHT SNOW AROUND THE CHUGACH INTO
THE SUSITNA VALLEY BUT THE PROBABILITY IS LOWER AT THIS POINT...IT
WILL NEED TO BE MONITORED. THE BEST CHANCE FOR SNOW OF THIS SETUP
IS NORTH OF TALKEETNA WHERE THE LIFT WILL ALSO COINCIDE WITH
OROGRAPHIC LIFT ON THE ALASKA RANGE.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...

THE DRY OFFSHORE FLOW WILL CONTINUE TO DRIVE THE WEATHER FOR THE
SOUTHWEST MAINLAND FOR THE NEXT COUPLE OF DAYS. THE SOUNDINGS THIS
MORNING DID SHOW INVERSIONS OVER THE SOUTHWEST MAINLAND AND THE
THINKING FOR TONIGHT IS ALTHOUGH IT IS VERY DRY IN THE LOWER
ATMOSPHERE THERE IS STILL A SLIM CHANCE FOR SOME FOG.

AS WE MOVE INTO LATE TUESDAY INTO WEDNESDAY AN UPPER LEVEL TROUGH
DIGS SOUTHWEST INTO THE KUSKOKWIM DELTA REGION. THE MAIN CONCERN
WITH THIS WILL BE THE SOUTHWEST FLOW ALONG THE ALEUTIAN MOUNTAINS TO
THE ALASKA RANGE INCREASING THE CHANCE FOR SNOW. IT APPEARS THE
TEMPERATURES WILL REMAIN COLD ENOUGH OVER SOUTHWEST ALASKA TO KEEP
ANY PRECIPITATION AS SNOW.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...

THE AREA OF LOW PRESSURE EAST SOUTHEAST OF THE PRIBILOF ISLANDS
WILL CONTINUE TO DROP TO THE SOUTH OF THE NEXT COUPLE OF DAYS. THE
MODELS SHOW VORTICITY MAXIMUMS ROTATING THROUGH THE EASTERN BERING
SEA AROUND THIS LOW THAT MATCH WELL WITH THE SATELLITE IMAGERY
INDICATIVE OF CONTINUED SHOWERY CONDITIONS. THIS IS FUELING THE
STRONG GUSTY WIND NOW OCCURRING ACROSS THE EASTERN ALEUTIANS. AS
THIS LOW DRIFTS SOUTH IT WILL BE WEAKENING THUS EXPECT THE WIND TO
DROP OFF OVERNIGHT OVER THE EASTERN ALEUTIANS. THIS LOW WILL BRING
WITH IT SNOW SHOWERS TO THE ALASKA PENINSULA AS IT APPROACHES FROM
THE NORTH. A COUPLE OF WEAK LOWS TRANSITING THROUGH THE WESTERN
AND CENTRAL ALEUTIANS ARE HANDLED WELL BY THE MODELS AND WILL
RESULT IN SOME GUSTY WIND AND SNOW SHOWERS AS THEY PASS THROUGH
TONIGHT.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE PRIMARY FORECAST CONCERN IN THE MID TERM IS THE POTENTIAL FOR
ACCUMULATING SNOW ACROSS SOUTHCENTRAL AK TUESDAY NIGHT INTO
WEDNESDAY AS A SHARP UPPER TROUGH DIGS OVER THE SOUTHWEST MAINLAND
AND A SURFACE LOW MOVES OVER THE NORTHERN GULF. GUIDANCE CONTINUES
TO STRUGGLE IN HANDLING THE INTERACTION BETWEEN THESE TWO
FEATURES...WHICH WILL HAVE A LARGE IMPACT ON POTENTIAL SNOW
AMOUNTS FOR THE COOK INLET AND MAT-SU REGIONS INCLUDING THE
ANCHORAGE BOWL. STAYED WITH A FAIRLY GENERALIZED FORECAST OF A
CHANCE OF SNOW DURING THE MIDDLE OF THE WEEK TO REFLECT THE LOWER
MODEL CONFIDENCE. WILL CONTINUE TO MONITOR THE GUIDANCE OVER THE
COMING DAYS AS SMALL SCALE DETAILS COME INTO BETTER FOCUS.

MODEL SPREAD CONTINUES TO INCREASE DURING THE LATTER HALF OF THE
WEEK AS UPPER LEVEL RIDGING IS RE-ESTABLISHED OVER WESTERN CANADA.
THE GFS DEPICTS THE UPPER TROUGH DEPARTING TO THE VICINITY OF THE
NORTH SLOPE AND ALLOWS RIDGING TO BUILD OVER THE SOUTHERN MAINLAND
INTO THE BERING SEA. THIS WOULD SUGGEST WARMER AND DRIER
CONDITIONS LATE IN THE WEEK...WHEREAS EUROPEAN GUIDANCE KEEPS A
CONSOLIDATED UPPER LOW PARKED OVER THE CENTRAL INTERIOR AND FORCES
THE RIDGE FARTHER SOUTH INTO THE GULF...WHICH WOULD RESULT IN A
COOLER AND MORE SHOWERY REGIME. GIVE THESE DIFFERENCES...FORECAST
CONFIDENCE IN THE EXTENDED TERM IS BELOW AVERAGE.

MEANWHILE...THERE IS BETTER AGREEMENT ON A STRONG FRONT ENTERING
THE WESTERN ALEUTIANS TUESDAY NIGHT. THIS WILL SIGNAL THE START OF
A GRADUAL WARMING TREND OVER THE BERING FOR THE LATTER HALF OF
THE WORK WEEK AS NORTHERLY WINDS ARE REPLACED BY WARM AND MOIST
SOUTHERLY FLOW FROM THE PACIFIC.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 172.
 HEAVY FRZ SPRAY 180 185.

&&

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