Small Craft Advisory 1050, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
513 AM AKST MON DEC 29 2014

.ANALYSIS AND UPPER LEVELS...
THE SPRAWLING BROAD TROUGH CENTERED IN THE WESTERN BERING SEA
CONTINUES TO ACCEPT ENERGY FROM THE EXTENSION OF THE EAST ASIAN
JET AND SEND IT ACROSS THE PACIFIC WHERE IT IS THEN TURNED
NORTHWARD BY A NARROW HIGH AMPLITUDE EASTERN PACIFIC RIDGE. THE
SETUP HAS ENABLED WARM/MOIST AIR FROM THE SUBTROPICS/MID-LATITUDES
TO STREAM NORTHWARD AND PROVIDE FUEL FOR THE JET TO FEED STORM
SYSTEMS ON THE EASTERN PERIPHERY OF THE TROUGH. THUS FAR THE
FIREHOSE HAS BEEN POINTED AT THE SOUTHWEST MAINLAND BUT IS
SHIFTING SLIGHTLY EASTWARD TOWARD THE SOUTHCENTRAL.

THE SURFACE PRESSURE PATTERN TELLS MORE OF THE STORY. OBSERVATIONS
IN THE CANADIAN YUKON SHOW A 1050 MB HIGH PRESSURE WHILE THE MOST
OF THE BERING SEA TROUGH SITS JUST BELOW 1000 MB. THE GRADIENT
BETWEEN THESE TWO FEATURES IS PRODUCING WIDESPREAD GALE FORCE
WINDS IN THE GULF THAT ARE ACCELERATED THROUGH THE ALEUTIAN RANGE
GAPS BRINGING GUSTS IN THE 50 MPH RANGE FOR INTERIOR BRISTOL BAY.
THERMALLY...A WARM/OCCLUDED FRONT STRETCHES FROM KODIAK ISLAND
SOUTHEASTWARD INTO THE PACIFIC WHILE THE OVERRUNNING PRECIPITATION
ASSOCIATED WITH IT IS SPREADING OVER THE KENAI RANGE.

&&

.MODEL DISCUSSION...
GUIDANCE SEEMS TO BE PRETTY LOCKED IN TO THE CURRENT PATTERN
DESPITE ITS HIGH AMPLITUDE NATURE. THE MAIN DIFFERENCES IN THE
MODELS SEEMS TO ONLY BE RESOLUTION RELATED WITH THE COARSER
GUIDANCE NOT CATCHING ON TO THE EXTREME DOWNSLOPE SCENARIO. THE
BIGGEST DIFFERENCES IN GUIDANCE WERE IN THE DEVELOPMENT OF THE
SURFACE LOW PRESSURE FROM THE ALASKA PENINSULA THROUGH THE
EASTERN BERING SEA...WHERE TRACK WILL HAVE AN EFFECT ON WINDS FROM
THE SOUTHWEST MAINLAND THROUGH THE ANCHORAGE AREA. THE LATEST
INCARNATIONS (00Z AND 06Z GUIDANCE) SEEM TO HAVE SETTLED IN ON A
TRACK JUST WEST OF NUNIVAK ISLAND TUESDAY MORNING.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (MON DECEMBER 29 - TUE
DECEMBER 30)...

THE HIGHLY AMPLIFIED FLOW PATTERN CONTINUES THIS MORNING...WITH A
FAST MOVING DISTURBANCE TRACKING ACROSS SOUTHWEST ALASKA. A STRONG
EAST TO WEST ORIENTED PRESSURE GRADIENT HAS DEVELOPED ACROSS THE
CHUGACH MOUNTAINS AND THE ALASKA AND ALEUTIAN RANGES...WITH STRONG
EAST SOUTHEAST GAP WINDS IMPACTING THE FAVORED LOCATIONS AROUND
SOUTHCENTRAL INCLUDING TURNAGAIN ARM...THE MAT VALLEY...PORTAGE
VALLEY...AND PASSAGE CANAL. THE AFOREMENTIONED DISTURBANCE WILL
TRACK NORTH...WITH A BRIEF WEAKENING OF THE PRESSURE GRADIENT
TODAY BEFORE INCREASING AGAIN THIS EVENING AS ANOTHER LOW MOVES
INTO THE SOUTHEAST BERING SEA. THIS SHOULD HELP DRIVE NEAR
HURRICANE FORCE WINDS DOWN TURNAGAIN ARM BY THIS EVENING...WITH
GUSTY WINDS POSSIBLE ACROSS PORTIONS OF THE SOUTHERN UPPER
HILLSIDE AROUND ANCHORAGE AS WELL. OTHERWISE...MODERATE TO HEAVY
RAIN WILL CONTINUE OVER KODIAK AND THE COASTAL KENAI
PENINSULA...WITH SHOWERY PRECIP ACROSS THE WESTERN KENAI. THE
HEAVIEST PRECIP WILL MOVE EAST TOWARD PRINCE WILLIAM SOUND TONIGHT
AND TUESDAY...WITH A MIX OF RAIN AND SNOW TOWARD VALDEZ AND
THOMPSON PASS. THE PRESSURE GRADIENT WILL RELAX DRAMATICALLY
TUESDAY AFTERNOON AS THE BERING LOW SHIFTS NORTH...WHICH WILL HELP
DRIVE SOUTHWESTERLY WINDS UP COOK INLET...WITH SOUTHEAST TO SOUTH
WINDS MOVING THROUGH ANCHORAGE TUESDAY EVENING AND INTO WEDNESDAY
MORNING. TEMPERATURES SHOULD WARM ABOVE FREEZING ACROSS MOST IF
NOT ALL OF SOUTHCENTRAL BY WEDNESDAY. INLAND LOCATIONS WILL BE
MORE PRONE TO RAIN AND RAIN SHOWERS AS THE UPPER LOW TRACKS INLAND
TUESDAY EVENING.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
SOUTHEASTERLY FLOW CONTINUES ACROSS THE AREA AS THE BROAD AND MOIST
FRONTAL SYSTEM REMAINS STRETCHED ACROSS SOUTHWEST ALASKA. THE
FIRST OF THE FRONTAL WAVES HAS LIFTED WELL NORTH AND CLEAR OF THE
AREA ALLOWING THE EAST TO SOUTH EAST SURFACE PRESSURE GRADIENT TO
RELAX SOMEWHAT...HOWEVER EVEN IN BETWEEN WAVES WINDS IN ZONE 161
ARE STILL GUSTING 40 TO 50 KNOTS AT SOME OF THE LOWER ELEVATION
SITES. THE NEXT WAVE...A SURFACE LOW AROUND 985 MB WILL CROSS THE
ALASKA PENINSULA THIS AFTERNOON AND TRACK INTO BRISTOL BAY THIS
EVENING. WHILE THIS LOWS TRACK IS A BIT FURTHER WEST THAN THE
PREVIOUS ONE IT IS DEEPER AND HAS BETTER JET SUPPORT SO STILL
SHOULD TIGHTEN THE PRESSURE GRADIENT SUBSTANTIALLY MORE THAN THE
PREVIOUS WAVE. THEREFORE LOOKS LIKE THE GUSTS IN THE 70 TO 75 MPH
IN THE RANGE ARE STILL REASONABLE THIS AFTERNOON THROUGH TONIGHT.
IN THE NON DOWNSLOPING REGIONS RAIN HEAVY AT TIMES WILL CONTINUE
WITH SNOW IN INLAND LOCATION SUCH AS PORTIONS OF 152.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
IN THE WESTERN ALEUTIANS FLAT RIDGING WILL BUILD THIS AFTERNOON
AND EVENING BRINGING A SOMEWHAT QUIETER IF BRIEF BREAK IN THE
WEATHER. THE NEXT RATHER POTENT LOOKING SYSTEM APPROACHES TUESDAY
AS A 950 MB LOW AND A FRONTAL SYSTEM WITH THE POTENTIAL TO BRING A
BROAD SWATH OF STORM FORCE WINDS TO THE WESTERN ALEUTIANS AND
BERING SEA IN THE TUESDAY NIGHT TIME FRAME.

&&

.LONG TERM FORECAST (WEDNESDAY DEC 31 - SUNDAY JANUARY 4)...

ANOTHER PATTERN SHIFT WILL BE UNFOLDING ACROSS ALASKA BEGINNING
WEDNESDAY AS THE LONGWAVE TROUGH OVER THE BERING DEAMPLIFIES AND
TRACKS EAST INTO THE YUKON THURSDAY. A POCKET OF COLDER AIR
ORIGINATING FROM SIBERIA WILL ACCOMPANY THE TROUGH...WITH A PART
OF THE UPPER LEVEL ENERGETIC WAVE GETTING CAUGHT UP ALONG THE
ALASKA RANGE. THERE HAS BEEN QUITE THE SHIFT IN THIS PERIOD FROM
THE PREVIOUS FEW DAYS WITH RESPECT TO THE UPPER AIR/SURFACE
PATTERN...AND IT IS NOW LIKELY THAT A NORTH PACIFIC LOW WILL MERGE
WITH THE AFOREMENTIONED REMNANT LOW OVER SOUTHWEST ALASKA. THE
OFFSHORE PRESSURE GRADIENT WILL INCREASE IN EARNEST THURSDAY
MORNING AND WILL REMAIN MODERATELY STRONG THROUGH FRIDAY AS THE
NORTH PACIFIC LOW MOVES TOWARD THE ALCAN. THE BIGGEST CHANGE WILL
BE THE POTENTIAL FOR SNOW ACROSS PORTIONS OF THE EASTERN COPPER
BASIN AND INTO PRINCE WILLIAM SOUND LATE THURSDAY AND FRIDAY.
THEREAFTER...MUCH UNCERTAINTY MUDDIES THE OVERALL PATTERN HEADING
INTO THE WEEKEND. THERE IS STRONG CONSENSUS AMONG THE
DETERMINISTIC GLOBAL GUIDANCE ON THE DEVELOPMENT OF A BLOCKING
HIGH OVER THE BEAUFORT SEA...BUT LITTLE TO NO AGREEMENT WITH THE
PLACEMENT OF A RETROGRADING LOW MOVING INTO SOUTHERN ALASKA FROM
THE YUKON. OVERALL...THIS PATTERN TENDS TO REMAIN DRIER AND
COLDER...HOWEVER...AND THERE SEEMS TO BE STRONG AGREEMENT WITH
THAT GENERAL THINKING. THERE IS POTENTIAL FOR SNOW AND SNOW
SHOWERS TO LINGER ACROSS SOUTHCENTRAL THROUGH SUNDAY...BUT THAT IS
HIGHLY DEPENDENT UPON UPPER LOW PLACEMENT...AND THAT IS CURRENTLY
A LOW CONFIDENCE FORECAST GIVEN THE SUBTLE DETAILS THAT FAR OUT.

&&

AHSENMACHER
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH WIND WARNING 101 161.
MARINE...GALE 119 120 125 129 132 136-139 141 150 160 165 180.
         STORM 130 131 178.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MTL
SOUTHCENTRAL ALASKA...AHSENMACHER
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR
LONG TERM...AHSENMACHER