Small Craft Advisory 485, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
225 PM AKDT TUE JUN 17 2014

.ANALYSIS AND UPPER LEVELS...
WEATHER TODAY ACROSS MAINLAND ALASKA IS DOMINATED BY AN
UNSEASONABLY STRONG LOW CURRENTLY LOCATED OFF THE NORTHEAST COAST
OF KODIAK ISLAND. THE CENTRAL PRESSURE LIKELY DROPPED INTO THE LOW
980S MB RANGE...SUPPORTED BY AN EQUALLY STRONG 5280 METER CENTER
AT 500 MB. A STORM-FORCE BARRIER JET DEVELOPED ALONG THE NORTH
GULF COAST OVERNIGHT AND EVEN NOSED INTO PRINCE WILLIAM SOUND
BRIEFLY. MEANWHILE...3-6 INCHES OF RAIN FELL ALONG THE EASTERN
COAST OF THE KENAI PENINSULA IN A PERIOD OF A LITTLE OVER 24
HOURS. SATELLITE DATA AND LIMITED SURFACE OBSERVATIONS INDICATE
THIS LOW HAS BEGUN TO WEAKEN AND HAS ALSO BEGUN AN EXPECTED
MOVEMENT TO THE EAST. WITH THE DEEP ATMOSPHERIC MOISTURE HAVING
NOW MOVED AWAY TO THE EAST...SIGNIFICANT CLEARING OF SKIES
DEVELOPED IN THE LEE OF THE COASTAL MOUNTAIN RANGES. THIS CLEARING
HAS ALLOWED SURFACE TEMPERATURES TO JUMP AT MANY AREAS...AND WHEN
COMBINED WITH STEEP LAPSE RATES FROM THE COLD POOL ALOFT...HAS LED
TO A RAPID INITIATION OF SHOWERS AND SOME THUNDERSTORM ACTIVITY
EARLY THIS AFTERNOON FROM THE WESTERN KENAI PENINSULA TO THE MAT-
SU VALLEY AND TALKEETNA MOUNTAINS. SHOWERS AND THUNDERSTORMS HAVE
ALSO FORMED OVER INTERIOR AREAS OF THE SOUTHWEST MAINLAND...AND
WILL LIKELY CONTINUE TO INCREASE IN COVERAGE AND INTENSITY FOR THE
REMAINDER OF THE AFTERNOON. OUT WEST...A RIDGE OF HIGH PRESSURE
OVER THE WESTERN BERING IS LEADING TO THE CONTINUATION OF
WIDESPREAD MARINE FOG/STRATUS CONCERNS...WITH RELATIVELY BENIGN
WEATHER OTHERWISE. A WEAK VORT MAX ROTATING AROUND THE PERIPHERY
OF THE LARGE CIRCULATION IN THE GULF IS PASSING OVER THE CENTRAL
AND EASTERN ALEUTIANS...BUT HAS PRODUCED LITTLE MORE THAN GUSTY
WINDS AND SCATTERED SHOWERS.

&&

.MODEL DISCUSSION...
THE MODELS ARE IN GOOD OVERALL AGREEMENT...BUT AS IS OFTEN THE
CASE THERE ARE SOME SMALLER DIFFERENCES THAT COULD POTENTIALLY
HAVE BIG IMPACTS ON SENSIBLE WEATHER ACROSS THE AREA. CONCERNING
THE CURRENT LOW IN THE GULF...THE MODELS ARE SLOWLY TRENDING
TOWARD THE SOLUTION ADVERTISED BY THE ECMWF THAT KEEPS THE
REMNANTS OF THE CIRCULATION SOUTH OF PRINCE WILLIAM SOUND.
SIMILARLY...AS A SECONDARY UPPER LOW DEVELOPS OVER INTERIOR ALASKA
DURING THE DAY WEDNESDAY THERE HAD BEEN SOME QUESTION OF HOW
QUICKLY AND HOW FAR SOUTH THIS FEATURE WOULD DROP. THE CONSENSUS
OF AVAILABLE MODELS HAVE AGAIN MOVED TOWARD THE ECMWF SOLUTION
THAT KEEPS THIS LOW LARGELY STATIONARY...AND WHICH KEEPS
ASSOCIATED STEADY RAINFALL OVER AND NORTH OF THE SUSITNA
VALLEY...RATHER THAN BRINGING SIGNIFICANT RAINFALL DOWN TOWARD
UPPER COOK INLET. OUT WEST...A VORT MAX MOVING THROUGH THE
SOUTHWEST MAINLAND ON WEDNESDAY HAS MINOR TIMING
DIFFERENCES...WITH THE 12Z NAM FASTER AND FURTHER NORTH.
OVERALL...THE ECMWF IS PREFERRED OVER THE EASTERN DOMAIN...AND THE
GFS PREFERRED OVER THE WESTERN DOMAIN.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...
CONVECTION WILL BE THE NAME OF THE GAME FOR THE REST OF THE
DAY...AS THE POOL OF COLD AIR ALOFT HAS LED TO SOME IMPRESSIVE
LAPSE RATES AND INSTABILITY ACROSS MUCH OF THE REGION. SOUTHEAST
WINDS FROM TURNAGAIN ARM HAVE BEGUN TO SPREAD INTO SOUTH AND WEST
ANCHORAGE...AND SHOULD CONTINUE THROUGH THE EVENING AS THE COOK
INLET GRADIENT CONTINUES TO REVERSE. WEDNESDAY WILL BE ANOTHER
CONVECTIVE DAY...BUT WITH WARMING TEMPERATURES ALOFT THERE SHOULD
NOT BE ENOUGH WIDESPREAD INSTABILITY TO RESULT IN
THUNDERSTORMS...BUT SIGNIFICANT SHOWER ACTIVITY WILL STILL BE
PRESENT. BY THURSDAY...WITH A FURTHER NORTH UPPER LOW POSITION
OVER THE INTERIOR THERE MAY BE SOME MORE STRATIFORM RAIN THAT
WORKS ITS WAY DOWN FROM THE NORTH. AS MENTIONED ABOVE...MODELS ARE
TRENDING FURTHER NORTH WITH THIS FEATURE. STAYED TUNED FOR
DETAILS.

SOUTHWEST ALASKA...
AS MENTIONED ABOVE...THUNDERSTORMS HAVE INITIATED AND WILL
CONTINUE THROUGH THIS EVENING AT MANY INLAND LOCATIONS. THIS IS
LARGELY DUE TO THE SIGNIFICANT POOL OF COLD AIR AT THE UPPER
LEVELS ASSOCIATED WITH AN UNSEASONABLY STRONG UPPER-LEVEL TROUGH.
THESE TEMPERATURES ALOFT WILL WARM SIGNIFICANTLY BY
TOMORROW...PRECLUDING WIDESPREAD THUNDERSTORM ACTIVITY.
HOWEVER...A SHORTWAVE TROUGH MOVING SOUTHEASTWARD THROUGH THE AREA
MAY COMBINE WITH LINGERING INSTABILITY OVER PORTIONS OF THE
KUSKOKWIM VALLEY TO KICK OFF AN ISOLATED THUNDERSTORM...AND WILL
THUS ADD THIS MENTION TO THE AFTERNOON FORECAST. THIS SAME FEATURE
WILL BRING ANOTHER ROUND OF STEADY RAIN TO THE KUSKOKWIM DELTA AND
WESTERN PORTIONS OF THE BRISTOL BAY ZONE BEFORE CONDITIONS IMPROVE
WEDNESDAY NIGHT.

BERING SEA/ALEUTIANS...
MOST OF THE AREA WILL REMAIN UNDER THE INFLUENCE OF HIGH PRESSURE
AND RELATIVELY WARM TEMPERATURES AND BENIGN WEATHER FOR THE NEXT
SEVERAL DAYS. A WEAKENING FRONT WILL BRING A ROUND OF RAIN ON
THURSDAY MORNING TO THE WESTERN HALF OF THE ALEUTIANS...BUT WILL
DISSIPATE BEFORE REACHING DUTCH HARBOR.

&&

.LONG TERM FORECAST...
THE EXTENDED FORECAST WILL REVOLVE AROUND THE UPPER LEVEL LOW
CURRENTLY SETTING UP SHOP IN THE GULF OF ALASKA. NUMEROUS
DISTURBANCES WILL PROPAGATE AROUND THE SYSTEM WITH ONE MOVING EAST
OF THE PANHANDLE OVER THE ALASKA RANGE. GUIDANCE HAS BEEN
INCONSISTENT RECENTLY WITH THIS FEATURE BUT LOOKS TO BRING
NUMEROUS SHOWERS TO THE COPPER RIVER BASIN ON SATURDAY...SLOWLY
SPREADING WESTWARD OVER THE WEEKEND. TEMPERATURES SHOULD BE NEAR
NORMAL TO SLIGHTLY ABOVE NORMAL WITH RAIN SHOWERS...ESPECIALLY
ALONG MOUNTAINOUS TERRAIN. THE SOUTHWEST MAINLAND WILL HAVE ABOVE
NORMAL TEMPERATURES WITH RAIN SHOWERS MAINLY ALONG THE ALASKA
RANGE.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 132
FIRE WEATHER...NONE.

&&

AMD/MTL JUN 14