Small Craft Advisory 1016, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
440 AM AKST MON DEC 21 2015

.ANALYSIS AND UPPER LEVELS...

A DECAYING UPPER LOW PERSISTS OVER THE NORTHEAST GULF THIS
MORNING...WITH A MUCH MORE WIDESPREAD UPPER TROUGH OVER KAMCHATKA
AND MOST OF THE BERING AND ALEUTIANS. A SMALL RIDGE REMAINS OVER
THE AKPEN AND SE AK. A NEARLY ZONAL MID LATITUDE TRANSPACIFIC JET
PERSISTS FROM SOUTH OF THE ALEUTIANS TO THE PACIFIC NORTHWEST. AT
THE SURFACE...A LOW IS OFF THE SOUTHEAST AK COAST...PART OF A
LARGER TROUGH ALONG THE NORTH GULF COAST. AN ELONGATED LOW
STRETCHES FROM THE NORTHWEST BERING TO UNIMAK PASS. A FRONT
EXTENDS FROM THE CENTRAL BERING SOUTHEAST INTO THE PACIFIC. A WEAK
SURFACE RIDGE PERSISTS OVER THE AKPEN. STORM AND GALE FORCE WINDS
ARE ASSOCIATED WITH THE BERING FRONT. RESIDUAL MOISTURE FROM A
PREVIOUS LOW CONTINUE TO SPREAD LOW CLOUDS...FOG..AND SNOW SHOWERS
OVER SW AK.

&&

.MODEL DISCUSSION...

MODELS ARE IN AGREEMENT THAT THE TRANSPACIFIC JET WILL BEGIN TO
BUCKLE OUT WEST OVER THE NEXT COUPLE OF DAYS. THIS WILL BE
REFLECTED BY A BETTER HANDLING OF THE ELONGATED BERING LOW...WHICH
BY THIS AFTERNOON WILL CONSOLIDATE INTO SEPARATE CENTERS...ONE
OVER THE WESTERN BERING AND THE OTHER JUST SOUTH OF KODIAK ISLAND.
THE LATTER WILL RACE TO HAIDA GWAI AND BEYOND TUE NIGHT INTO WED.
THE JET BUCKLE WILL CAUSE THE WESTERN CENTER TO SPIN UNTIL IT
MERGES WITH A NEW NORTH PACIFIC LOW AIMED AT AMCHITKA TUE NIGHT
INTO WED. ALTHOUGH THE GFS AND EC SOLUTIONS HAVE BECOME VERY
SIMILAR...THE FORECAST UTILIZED THE GFS FOR BETTER DETAIL.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE WEAK UPPER TROUGH THAT IS JUST NORTH OF KODIAK WILL SLOWLY
DRIFT NORTHEAST FOR THE NEXT COUPLE OF DAYS. THIS TROUGH WILL EXIT
INTO THE YUKON TERRITORY ON TUESDAY AFTERNOON...THOUGH SOME
RESIDUAL "TROUGHINESS" WILL REMAIN OVER SOUTH CENTRAL ALASKA. THIS
TROUGH WILL BRING SOME SHOWERS TO SOUTH CENTRAL ALASKA...BUT IN
GENERAL THE WEATHER WILL BE FAIRLY QUIET. ON TUESDAY NIGHT THE
OFFSHORE SURFACE GRADIENT WILL BEGIN TO INCREASE...AND THIS WILL
LEAD TO INCREASING WINDS THROUGH THE FAVORED TERRAIN GAPS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE DOMINANT FEATURE OVER THE MAINLAND FOR THE NEXT COUPLE OF DAYS
WILL BE FOG AND LOW CLOUDS LINGERING BEHIND THE DECAYING LOW
PRESSURE ALOFT. LINGERING LOW LEVEL MOISTURE AND SLACKENING WINDS
HAVE PROMOTED THE DEVELOPMENT OF STRATUS AND FOG. GIVEN TODAY IS
WINTER SOLSTICE AND A STEEP SURFACE BASED INVERSION IS IN
PLACE (12.21.00Z/12Z PABE SOUNDING) IT DOES NOT APPEAR TO BE ABLE
TO MIX OUT VERY FAST OR AT ALL. THE MOST LIKELY SCENARIO IS THAT
VISIBILITY IMPROVES DURING THE DAY BUT LOW STRATUS HANGS AROUND
AND THICKENS AGAIN OVERNIGHT. CAVEATS TO SAID FORECAST...HIGH
CLOUDS STREAMING OFF THE STALLING BERING SEA FRONT...WHILE
LIMITING DAYTIME MIXING....COULD PREVENT RADIATIONAL COOLING
TONIGHT AND INHIBIT STRATUS BUILD-DOWN. ALSO...THE WEAK OFFSHORE
GRADIENT WILL BRING IN SLIGHTLY DRIER SURFACE AIR FROM THE
INTERIOR. THE CLOUD FORECAST WILL ALSO AFFECT THE SURFACE
TEMPERATURE FORECAST...A MUCH COLDER AIRMASS OFF THE SURFACE WILL
SETTLE IN...HOWEVER LINGERING LOW CLOUDS WILL PREVENT TEMPERATURES
FROM FALLING OFF TOO MUCH. ALL THESE THINGS TAKEN INTO
CONSIDERATION...CLOUDY WITH OVERNIGHT/MORNING FOG AND VERY LIGHT
NORTHERLY WINDS WILL BE THE FORECAST FOR THE NEXT TWO DAYS WITH
SLOWLY DECREASING TEMPERATURES DAILY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
AN ELONGATED FRONTAL BOUNDARY/SURFACE TROUGH STRETCHES ACROSS THE
BERING SEA THROUGH THE ALASKA PENINSULA. RAIN AND SNOW WILL BE IN
THE IMMEDIATE VICINITY OF THE FRONT...WHILE A CONVECTIVE SHOWERY
REGIME SETS UP ACROSS MUCH OF THE SOUTHERN BERING IN WESTERLY COLD
ADVECTION. THAT AIRMASS BEHIND THE FRONT IS UNSTABLE ENOUGH FOR
SOME ISOLATED LIGHTNING STRIKES. THIS REGIME WILL STICK AROUND FOR
THE NEXT TWO DAYS BEFORE YET ANOTHER CYCLONE COMES IN FROM THE
NORTH PACIFIC.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
WHILE THERE IS GOOD MODEL AGREEMENT IN THE IDEA OF A STRONG LOW
LIFTING NORTH ACROSS THE ALEUTIANS OUT NEAR KISKA ISLAND AROUND
WEDNESDAY...THERE IS HOWEVER SIGNIFICANT DISAGREEMENT IN THE BOTH
THE TIMING AND THE DISTANCE NORTH THE LOW MAKES IT UP INTO THE
BERING. THE COMPLEXITIES APPEAR TO BE ARISING FROM AN INTERESTING
BUCKLING IN THE JET STREAM AROUND A FAST MOVING UPPER LEVEL RIDGE
EMBEDDED IN THE BROADER AND RATHER STRONG WESTERLY JET STREAM TO
THE SOUTH. A STRONG JET STREAK ON THE UPSTREAM SIDE OF THE RIDGE
BECOMES ORIENTED SOUTH TO NORTH BETWEEN 40 AND 50N ALONG 180 EARLY
WEDNESDAY MORNING. IT IS THIS JET STREAK THAT PROPELS THE RAPIDLY
DEEPENING SURFACE LOW UP NORTH INTO THE BERING. THE QUESTION IS
HOW FAR NORTH THE LOW WILL MAKE IT BEFORE THE RIDGE BUCKLES AND
AMPLIFIES ENOUGH TO BE UNDERCUT THE LARGER JET COMING IN FROM THE
WEST BETWEEN 35 AND 40N AND THE ENTIRE FEATURE IS SWEPT OFF TO
THE EAST. BASED ON THE POSITION OF THE JET STREAK...WHICH IS
SIGNIFICANTLY MORE CONSISTENT BETWEEN THE VARIOUS MODELS THAN THE
SURFACE FEATURES...IT LOOKS LIKE THE SURFACE LOW SHOULD MAKE IT
NORTH TO AROUND 54N WEDNESDAY NIGHT BEFORE PUSHES OFF TO THE EAST
SOUTHEAST AS IT FILLS THURSDAY AND FRIDAY.

MEANWHILE FURTHER TO THE EAST COLD AIR BUILDS OVER MAINLAND
ALASKA THROUGH MIDWEEK AS A COLD UPPER LEVEL LOW CROSSES THE
NORTHERN PORTIONS OF THE STATE. AN ASSOCIATED SHORTWAVE TROUGH
ROTATES ACROSS SOUTHWEST ALASKA WEDNESDAY AFTERNOON AND EVENING
AND OVER SOUTH CENTRAL ALASKA WEDNESDAY NIGHT AND THURSDAY
MORNING. ASIDE FROM SOME ISOLATED TO POSSIBLY SCATTERED MOUNTAIN
SHOWERS THE MAIN IMPACT OF THE TROUGH WILL BE TO PUSH MORE COLD
INTERIOR AIR INTO THE AREA AND FURTHER STRENGTHEN OFFSHORE GAP
WINDS.

THE UPPER LEVEL LOW COMING IN FROM THE WEST WILL REACH THE WESTERN
TIP OF THE ALASKA PENINSULA AROUND FRIDAY AFTERNOON WITH THE
ASSOCIATED FRONTAL SYSTEM STRETCHING FROM BRISTOL BAY ACROSS THE
NORTHERN ALASKA PENINSULA...KODIAK ISLAND AND THE SOUTHERN TIP OF
THE KENAI PENINSULA AND INTO THE GULF. AS WITH THE MIDWEEK SYSTEM
THERE IS ALSO SIGNIFICANT UNCERTAINTY OF REGARDING HOW FAR NORTH
THIS SYSTEM WILL MAKE IT. CURRENTLY THINKING THAT IT WILL BRUSH
THE NORTHERN GULF COAST BUT THE COMBINATION OF THE OFFSHORE FLOW
AND THE FRONT SHEARING APART AS IT GETS MORE DISTANT FROM THE LOW
WILL KEEP THE MOISTURE FROM MAKING IT VERY FAR INLAND.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...HEAVY FREEZING SPRAY 181 185
         STORM 155
         GALES 132 150 165 170 172 173 178 179 191 180 181 185 352
         412 413 414

&&

SYNOPSIS AND MODEL DISCUSSION...DS
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ML
LONG TERM...JR