Small Craft Advisory 174, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
444 AM AKST TUE FEB 24 2015

.ANALYSIS AND UPPER LEVELS...

AN UPPER LEVEL CLOSED LOW IS LOCATED OVER THE EASTERN RUSSIA WITH
AN ASSOCIATED TROUGH EXTENDING THROUGH SAINT MATTHEW ISLAND INTO
THE EASTERN BERING SEA. AT THE SURFACE THIS IS REFLECTED AS A WEAK
LOW NEAR 65N 178E WITH A WEATHER FRONT THROUGH THE WESTERN BERING
SEA/ALEUTIANS AND A TROUGH OVER THE NUNIVAK ISLAND AREA. THE
SATELLITE IMAGERY IS SHOWING A SWATH OF LOWER CLOUDS ASSOCIATED
WITH THE AFOREMENTIONED TROUGH WHICH IS PRODUCING SNOW SHOWERS.
THE MAJORITY OF THE BERING SEA AND ALEUTIANS WILL BE UNDER
SOUTHWESTERLY FLOW WITH THE WEATHER FRONT AT THE SURFACE PUSHING
INTO THE WESTERN BERING SEA AND ALEUTIANS TODAY. THE SURFACE
OBSERVATIONS OVER THE WESTERN ALEUTIANS ARE REPORTING SNOW
SHOWERS.

THE SOUTHWEST ALASKA REGION IS BEING INFLUENCED BY ONSHORE FLOW.
THIS IS RESULTING IN LOW STRATUS/FOG IN THE BRISTOL BAY REGION AND
IS BEING SHOWN ON THE GOES IFR PROBABILITY SATELLITE PRODUCT. THE
SURFACE OBSERVATIONS FROM KING SALMON NORTHWARD INTO THE BRISTOL
BAY INTERIOR ARE REPORTING LOW STRATUS AND FOG THIS MORNING.

THE GULF AND THE SOUTHCENTRAL ALASKA REGION ARE SITTING UNDER THE
HIGH PRESSURE RIDGE WITH LIGHT WINDS FOR MAJORITY OF SOUTHCENTRAL
THIS MORNING. THIS IS RESULTING IN LOW STRATUS AND FOG COVERING
THE NORTHERN GULF...AND SPREADING INTO THE CORDOVA AND VALDEZ
AREAS. UPSTREAM THERE IS A CLOSED UPPER LEVEL LOW SOUTH OF THE
SHUMAGIN ISLANDS...AND REFLECTED WITH A GALE FORCE SURFACE LOW
NEAR 50N 156W. THE ASSOCIATED WEATHER FRONT WITH THIS SYSTEM IS
APPROACHING THE SOUTHWESTERN GULF THIS MORNING.

&&

.MODEL DISCUSSION...

THE MODELS ARE IN GOOD AGREEMENT HEADING INTO THE MIDWEEK TIME
FRAME. THE PREFERRED MODELS OF CHOICE WERE THE GEM-REG/ECMWF. THE
NAM CONTINUES TO BE THE OUTLIER WITH THE NORTH PACIFIC LOW
TRACKING JUST SOUTH OF THE WESTERN GULF THIS MORNING. THE NAM
KEEPS THE LOW PRESSURE SYSTEM FARTHER WEST THAN THE OTHER MODELS.
THE FORECAST CONFIDENCE CONTINUES TO REMAIN ABOVE AVERAGE THROUGH
THE MIDWEEK TIME FRAME.

&&

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

A FEW SHOWERS LINGER THIS MORNING AS AN UPPER LEVEL LOW EXITS THE
AREA. OTHERWISE...DRY WEATHER IS ON TAP FOR THE NEXT COUPLE OF
DAYS OVER MAINLAND SOUTH CENTRAL ALASKA AS A RIDGE BUILDS OVER THE
AREA. A LOW PRESSURE SYSTEM WILL MOVE INTO THE GULF OF ALASKA FROM
THE SOUTHWEST TODAY AND THEN TRAVERSE EASTWARD ACROSS THE GULF
WEDNESDAY THEN WELL SOUTHEAST OF THE AREA WEDNESDAY NIGHT. BEHIND
THIS THE RIDGE WILL STRENGTHEN OVER SOUTHERN ALASKA AND INCREASE
THE OFFSHORE GRADIENTS...THUS INCREASING THE WINDS THROUGH THE
FAVORED GAPS.

&&

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

A FRONTAL ZONE IS TRACKING INTO THE KUSKOKWIM DELTA THIS
MORNING...BRINGING SNOW SHOWERS TO THE AREA. ELSEWHERE...CLEARING
SKIES BEHIND THE LAST LOW PRESSURE SYSTEM HAS ALLOWED FOR AREAS
OF FOG TO DEVELOP...ESPECIALLY IN SHALLOW BASINS AND VALLEYS. THIS
FOG SHOULD DIMINISH BY THIS AFTERNOON AS NORTHERLY OFFSHORE WINDS
INCREASE...AND SOLAR RADIATION BURNS THE REMAINDER OFF. HIGH
PRESSURE WILL THEN SETTLE IN THROUGH THURSDAY...WITH COOLING
OVERNIGHT TEMPERATURES AND CLEARING SKIES. PATCHY FOG CAN NOT BE
RULED OUT ACROSS THE KUSKOKWIM DELTA...ESPECIALLY DURING THE
OVERNIGHT AND MORNING PERIODS.

&&

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

WEAK HIGH PRESSURE WILL DOMINATE THE CENTRAL AND EASTERN ALEUTIANS
HEADING INTO THURSDAY...WITH A SLOW MOVING FRONTAL ZONE OVER THE
WESTERN ALEUTIANS BRINGING STRONG GALE FORCE WINDS AND PERIODS OF
RAIN AND SNOW...EVENTUALLY BECOMING ALL RAIN. THIS FRONT WILL
SLOWLY TRACK EAST TOWARD THE CENTRAL ALEUTIANS ON THURSDAY.

&&

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

THE SURFACE LOW CROSSING THE GULF WILL BE EAST AND CLEAR OF THE
AREA THURSDAY MORNING AS IT TRACKS OVER HAIDA GWAII. UPPER LEVEL
RIDGING WILL BUILD RAPIDLY OVER THE GULF BEHIND IT PUSHING INTO
SOUTHWEST AND SOUTHCENTRAL ALASKA THURSDAY MAKING FOR A RATHER
NICE AND SUNNY DAY. OFFSHORE NORTHERLY SURFACE WINDS OVER SOUTH
CENTRAL ALASKA WILL PERSIST THROUGH MUCH OF THE DAY THURSDAY THEN
GRADUALLY TAPER OFF OVERNIGHT. THESE WINDS SHOULD STILL BE ENOUGH
HOWEVER TO PREVENT FOG AND LOW STRATUS IN MOST SOUTH CENTRAL AREAS
THURSDAY NIGHT BUT DO HAVE CONCERNS FOR FRIDAY AS THE WINDS WILL
BE MUCH LIGHTER WITH THE RIDGE AXIS DIRECTLY OVERHEAD.

THE NEXT PACIFIC FRONTAL SYSTEM WILL LIFT NORTH UP THE WEST SIDE
OF THE UPPER LEVEL RIDGE ON FRIDAY REACHING THE ALASKA PENINSULA
IN THE AFTERNOON. THE LOW WILL THEN CURVE NORTHEAST UP THE GULF
COAST AS IT GETS PICKED UP BY THE STRONG WESTERLY FLOW ALOFT TO
THE NORTH AND CARRIED UP AND OVER TOP THE RIDGE FRIDAY NIGHT AND
SATURDAY. CURRENTLY THERE IS SOME MODEL DIFFERENCES IN THE TRACK
OF THE LOW WITH THE GFS FURTHEST NORTH FOLLOWING THE COAST BUT
JUST INLAND...THE CANADIAN REMAINING OFFSHORE AND TRACKING
THROUGH THE NORTHERN GULF BUT DEEPEST WITH THE SURFACE LOW AND THE
EUROPEAN ALSO SOUTH AND OFFSHORE BUT WITH A SIGNIFICANTLY WEAKER
LOW. GIVEN THE INTERACTION OF THE LOW WITH THE STRONG UPPER LEVEL
SHORTWAVE AND BAROCLINIC ZONE TO THE NORTH AND THE LARGE RIDGE FOR
IT TO RIDE UP AND OVER I TEND TO FAVOR THE MORE NORTHERLY AND
STRONGER SOLUTIONS. HOWEVER GIVEN THE UNCERTAINTY OUT AT DAY 5 OF
THE FORECAST HAVE CHOSEN TO AVERAGE THE POSITIONS AND STRENGTH FOR
TODAYS FORECAST PACKAGE. RIDGING WILL RETURN SUNDAY CLEARING
THINGS OUT AGAIN RATHER RAPIDLY WITH DRY WEATHER FOR MOST OF THE
AREA THROUGH MONDAY.

OUT IN THE ALEUTIANS AND BERING SE...STORMIER WEATHER WILL
PERSIST FOR THE DURATION. BY THURSDAY THE CURRENT FRONTAL SYSTEM
WILL HAVE TRACKED TO THE CENTRAL ALEUTIANS AND BE WEAKENING
SOMEWHAT WHILE WESTERLY FLOW BRINGS COOL SHOWERY WEATHER TO THE
WESTERN ALEUTIANS. THE NEXT RATHER STRONG LOOKING FRONTAL SYSTEM
WILL REACH THE WESTERN END OF THE CHAIN FRIDAY NIGHT OR SATURDAY
MORNING BRINGING AT LEAST WIDESPREAD GALES AND THE POTENTIAL FOR
STORMS. THE FRONT WILL CONTINUE EAST TO THE CENTRAL ALEUTIANS
THROUGH SUNDAY WHILE THE LARGE PARENT LOW MOVES UP INTO THE
BERING.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 132 150 155 175 177 178 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...PD
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
LONG TERM...JER