Small Craft Advisory 31, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
527 AM AKST MON JAN 12 2015

.ANALYSIS AND UPPER LEVELS...

THE UPPER LEVEL PATTERN REMAINS DOMINATED BY AN UPPER RIDGE OVER
CENTRAL AND SOUTHERN ALASKA...WITH SEPARATE WESTERLY FLOW REGIMES
ACROSS THE ARCTIC CIRCLE AND THE NORTH PACIFIC. THE WESTERN NORTH
AMERICAN RIDGE IS ONCE AGAIN AMPLIFYING...WITH THE FIRST STRONG
GALE FORCE LOW FORMING WHERE THE NORTH PACIFIC JET STREAM AND
NORTH AMERICAN RIDGE INTERSECT. WATER VAPOR SATELLITE IMAGERY
DEPICTS THE IMPRESSIVE WARM CONVEYOR BELT BRANCHING OFF THE LEFT
EXIT REGION OF THE POWERFUL PACIFIC JET...WHICH IS TRACKING A
STRONG GALE TO NEAR STORM FORCE FRONT TOWARD KODIAK ISLAND AND
THE ALASKA PENINSULA. THE PRESSURE GRADIENT WILL RAPIDLY INCREASE
THIS MORNING THROUGH TONIGHT AS THE FRONT MOVES INLAND. STRATUS
AND FOG...MAINLY OVER SOUTHCENTRAL ALASKA THIS MORNING...WILL
DIMINISH AS A RESULT. EVENTUALLY THE FRONT WILL SUPPORT SHOWERS
AND CLOUDS OVER SOUTHERN ALASKA AS IT MOVES NORTH...WITH RAIN
ACROSS COASTAL LOCATIONS.

THE NORTH PACIFIC JET STREAM...IN EXCESS OF 190-200 KT ACROSS
MOST OF THE NORTH PACIFIC...WILL BECOME THE DOMINANT WEATHER MAKER
ACROSS ALASKA THROUGH LATE WEEK AS A SERIES OF STRONG PACIFIC LOWS
MOVE INTO THE GULF OF ALASKA. THIS WILL KEEP PERSISTENT WARM
ANOMALIES ACROSS MOST OF SOUTHERN ALASKA AS WARM FRONTS PARADE
TOWARD THE NORTHERN GULF COAST.

&&

.MODEL DISCUSSION...

THE NUMERICAL MODELS ARE IN EXCELLENT AGREEMENT WITH THE UPPER
AIR PATTERN...AND IN GOOD AGREEMENT WITH THE GENERAL SURFACE
PRESSURE PATTERN AS A SERIES OF NORTH PACIFIC LOWS MOVES INTO THE
GULF OF ALASKA THROUGH THE FORECAST PERIOD. THE LARGEST
DISCREPANCIES ARE WITH RESPECT TO MOISTURE AND PRECIPITATION
FIELDS AS THE FIRST FRONT TRACKS INTO SOUTHERN ALASKA TODAY
THROUGH TUESDAY. THE PATTERN...WITH AN ELONGATED WARM FRONT WELL
DISPLACED FROM THE LOW CENTER...TENDS TO FAVOR DOWNSLOPE DRYING
ACROSS INLAND LOCATIONS. AS A RESULT...THE DRIER NAM AND REGIONAL
GEM WERE FAVORED...WITH A BLEND TO THE ECMWF ACROSS MARINE AREAS
TO CAPTURE THE LOW POSITIONS.

&&

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

A STRONG FRONT IS MOVING RAPIDLY NORTHWARD THROUGH THE GULF OF
ALASKA AND WILL MOVE OVER SOUTH CENTRAL ALASKA TONIGHT. THIS FRONT
IS BRINGING WARM AIR WITH IT AND MOST OF THE PRECIPITATION THAT
FALLS WILL BE RAIN. TEMPERATURES ALOFT WERE ALREADY ABOVE
FREEZING IN ANCHORAGE FROM THE MORNING BALLOON LAUNCH AND THIS
SERVES AS AN INDICATION OF THE WARM AIR ALOFT OVER MUCH OF THE
AREA. THERE WILL BE SOME AREAS OF FREEZING RAIN AS THE
PRECIPITATION MOVES IN BUT IT IS NOT EXPECTED TO BE WIDESPREAD AND
AREAS TO THE LEE OF THE MOUNTAINS SUCH AS ANCHORAGE WILL MISS MOST
OF THE PRECIPITATION DUE TO DOWNSLOPING.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2...MON AND
TUE)...THE PATTERN THAT IS TAKING SHAPE THIS MORNING IS NOT TOO
DISSIMILAR TO WHAT WE SAW JUST ABOUT A WEEK AGO. A FAIRLY ROBUST
JET IS MOVING FROM SOUTH TO NORTH FROM THE NORTH PACIFIC INTO THE
GULF OF ALASKA. SEVERAL WEAK WAVES ARE TRYING TO CONSOLIDATE INTO
A CLOSED SURFACE LOW THIS MORNING. MODELS THEN SHOW THIS LOW
PUSHING THROUGH THE AKPEN AND INTO BRISTOL BAY BY TUE MORNING. SO
MUCH LIKE LAST WEEKEND AND EARLY LAST WEEK...THIS WILL SWING
ANOTHER WARM FRONT FROM THE ALEUTIAN RANGE ALL THE WAY THROUGH THE
YK DELTA. PROBABLY THE BIGGEST DIFFERENCE WITH THIS SYSTEM IS THAT
SURFACE TEMPERATURES THIS MORNING ARE MUCH WARMER THAN THEY WERE
LAST WEEK. THUS...MOST PLACES WILL START AS RAIN AND REMAIN THAT
WAY. THERE ARE A FEW DEEPER VALLEYS NORTH OF DILLINGHAM THAT ARE
BELOW FREEZING THIS MORNING. WHILE THEY COULD START WITH SOME
FREEZING RAIN...THE WARM AIR SHOULD BE ABLE TO SCOURER OUT THE
SUB-FREEZING TEMPERATURES AND CHANGE THINGS TO ALL RAIN BY LATER
ON TODAY. WINDS WILL ALSO BE ON THE INCREASE THROUGH THE DAY
TODAY. THE STRONGEST WILL CERTAINLY BE THROUGH THE GAPS ALONG AND
OVER THE HIGHER TERRAIN OF THE ALEUTIAN RANGE. BY THE TIME THE LOW
MAKES IT TO BRISTOL BAY TUE IT WILL BE WEAKENING SIGNIFICANTLY.
THIS COUPLED WITH PLENTY OF WARM AIR ADVECTION IN THE BOUNDARY
LAYER SHOULD HOLD THE STRONGEST WINDS ALOFT.

THE ONE BIG QUESTION MARK FOR THE SOUTHWEST IS PRECIPITATION NEAR
BETHEL. THIS PATTERN TYPICALLY SETS UP WELL FOR THEM TO BE MOSTLY
DRY UNDER DOWNSLOPING CONDITIONS. HOWEVER...SOME OF THE MODELS
CONTINUE TO PAINT SOME QPF OVER THEM EARLY TUE COURTESY OF A WEAK
UPPER LEVEL WAVE MOVING IN FROM THE SOUTH. AND IF PRECIPITATION
WERE TO FALL...IT WOULD MOST LIKELY FALL AS FREEZING RAIN. THAT
SAID...ANY AMOUNTS WOULD BE EXTREMELY LIGHT. AND AT THIS
POINT...ONLY GOING FOR A CHANCE OF PRECIPITATION AT ALL UNTIL
MODELS RESOLVE SOME OF THOSE FINER FEATURES A BIT BETTER.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2...MON AND
TUE)...NO MAJOR SYSTEMS IN THE PICTURE. A GALE FORCE LOW NEAR THE
WESTERN ALEUTIANS IS WEAKENING AND DRIFTING SOUTH THIS MORNING.
OTHER THAN THAT...HIGH PRESSURE OVER THE MAINLAND NORTH OF THE
ALASKA RANGE IS WORKING IN TANDEM WITH THE LOW MOVING TOWARDS THE
AKPEN TO INCREASE THE OFFSHORE WINDS FOR THE EASTERN BERING. THIS
WILL PRODUCE A FEW AREAS OF GALES ALONG THE COAST. THE HIGH
PRESSURE REFUSES TO BUDGE AND WILL DEFLECT THE VARIOUS WEAK LOWS
FROM BRISTOL BAY BACK TOWARDS THE CENTRAL ALEUTIANS.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...

MODELS ARE IN GENERAL AGREEMENT THAT AN UPPER LOW WILL DIVE FROM
THE POLE AND END UP OVER THE EASTERN BERING AND WESTERN AK BY THE
WEEKEND. A BROAD AREA OF SURFACE LOW PRESSURE WILL TAKE UP
RESIDENCE OVER THE EASTERN ALEUTIANS AND AKPEN DURING THE SAME
PERIOD. THE UNCERTAINTY OF MODEL SOLUTION MEANS THE FORECAST IS
BASED ON A COMPROMISE WPC SOLUTION.

THE INITIAL FRONT GENERATED BY THE TRIPLE POINT LOW TRACKING
THROUGH THE GULF WEDNESDAY WILL BRING PRECIPITATION AND GUSTY
WINDS TO THE GULF COAST...WITH POSSIBLE FREEZING RAIN INLAND. A
SECONDARY FRONT ASSOCIATED WITH THE ANCHOR NORTH PACIFIC LOW WILL
QUICKLY PUSH INTO THE NORTHERN GULF COAST BY THURSDAY MORNING.
THIS FEATURE ALONG WITH A SERIES OF WAVES THAT FORM OFF THE LOW
BECOMING STATIONARY OVER THE AKPEN WILL ACT TO KEEP PRECIPITATION
AND GUSTY COASTAL WINDS IN THE FORECAST THROUGH MUCH OF THE LONG
TERM. AS THE LOW BECOMES ENTRENCHED OVER THE EASTERN
ALEUTIANS/BERING ON FRIDAY...SIBERIAN AIR WILL BEGIN TO ADVECT
SOUTHWARD OVER THE BERING REACHING THE ALEUTIANS AND WESTERN AK
ON SATURDAY. THE COLD AIR MASS THEN STRENGTHENS WEST OF THE ALASKA
AND ALEUTIAN RANGES ON SUNDAY. THIS WILL BRING MORE SNOW SHOWER
ACTIVITY TO SOUTHWEST AK...WITH PRECIPITATION OVER THE CHAIN
CHANGING OVER TO SNOW SHOWERS OVER THE WEEKEND.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM 130 131 138
         GALE 119 120 132 136 137 139 150 155 160 165 178 180 185
FIRE WEATHER...NONE.

&&

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