Small Craft Advisory 665, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
430 AM AKDT MON AUG 24 2015

.ANALYSIS AND UPPER LEVELS...

A VERTICALLY STACKED SURFACE LOW IS CURRENTLY OVER THE NORTHERN
GULF. IT WAS RESPONSIBLE FOR SHOWERS ACROSS THE COPPER RIVER
BASIN YESTERDAY. A STRONG SUBTROPICAL HIGH IS CENTERED SOUTH OF
DUTCH HARBOR. BETWEEN THESE TWO FEATURES...NORTHWEST WINDS HAVE
BEEN GUSTING STRONGLY OUT OF BAYS AND PASSES THROUGH THE ALASKA
PENINSULA...BRISTOL BAY...AND COOK INLET REGIONS. THE PRESSURE
GRADIENT CAUSING THE STRONG WINDS WILL CONTINUE WEAKENING AS A
NORTH TO SOUTH FLOWING JET STREAK DIGS THE DOWNSTREAM TROUGH OVER
THE EASTERN GULF. IN RESPONSE...THE SURFACE LOW WILL QUICKLY SHIFT
SOUTHWARD AND SURFACE RIDGING WILL BUILD INTO SOUTHCENTRAL. OUT
WEST...WARM AIR IS BEING QUICKLY DRAWN NORTHWARD AHEAD OF A
SURFACE LOW TRACKING ALONG THE COAST OF RUSSIA. THE WARM AIR MOVING
OVER RELATIVELY COOLER WATER IS CAUSING OCCASIONALLY DENSE WARM
ADVECTION FOG OVER THE WESTERN ALEUTIANS.

THE JET IS FLOWING AROUND A VERY STRONG UPPER LEVEL HIGH
COLLOCATED WITH THE SUBTROPICAL SURFACE HIGH SOUTH OF DUTCH
HARBOR. THE STRENGTH OF THE UPPER LEVEL HIGH IS INDICATIVE OF VERY
UNUSUALLY WARM AIR IN THE MIDLEVELS. MODEL SOUNDINGS GIVING US OUR
BEST ESTIMATE OF THE CHARACTERISTICS OF THE UPPER LEVELS
ASSOCIATED WITH THE HIGH SHOW FREEZING LEVELS ABOVE 13000 FEET.
WHILE THE UPPER LEVEL HIGH WILL REMAIN STATIONARY...RIDGING
ASSOCIATED WITH THE HIGH IS BUILDING EAST INTO
SOUTHCENTRAL...ACTING TO CAP THE CHANCES FOR ACTIVE WEATHER.

&&

.MODEL DISCUSSION...

THE MODELS REMAIN IN GOOD AGREEMENT SYNOPTICALLY LOOKING THROUGH
MUCH OF THE NEXT WORKWEEK. SOME DIFFERENCES ARISE BY WEDNESDAY IN
THE MODEL DEPICTIONS OF HOW FAR SOUTH THE NEXT ZONALLY-ORIENTED JET
STREAK GETS. THE NAM AND GFS ARE STRONGER IN INTENSITY...BUT KEEP
THE AXIS OF THE JET MUCH FURTHER NORTH THAN THE EC. ULTIMATELY
THIS LEADS TO TIMING DIFFERENCES IN WHEN THE NEXT ROUND OF RAIN
MOVES INTO SOUTHERN ALASKA. FOR NOW...THE IMPACTS OF THESE
DIFFERENCES ON SURFACE WEATHER ARE NOT SIGNIFICANT.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE UPPER LEVEL RIDGE THAT IS CENTERED SOUTH OF THE EASTERN
ALEUTIANS WILL KEEP SOUTH CENTRAL ALASKA MOSTLY PROTECTED FROM
ANY CHANCE OF SHOWERS FOR THE NEXT COUPLE OF DAYS. PLENTY OF
CLOUDS WILL SPILL OVER THE TOP OF THE RIDGE INTO SOUTH CENTRAL
ALASKA...SLOWLY INCREASING TODAY INTO TONIGHT. THE GULF LOW WILL
DEPART TO THE SOUTHEAST TODAY. THIS WILL ALLOW THE SURFACE
GRADIENT TO SLACKEN AND OFFSHORE WINDS TO DIMINISH AND/OR END
BY LATE IN THE DAY. THE RIDGE WILL FLATTEN BY LATE TUESDAY NIGHT
AND THIS WILL ALLOW STRONG WESTERLIES ALOFT TO PUSH INTO THE AREA
BRINGING INCREASING MOISTURE.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
SCATTERED SHOWERS WILL PERSIST THROUGH TONIGHT AS ABUNDANT
SUBTROPICAL MOISTURE CONTINUES TO STREAM OVER THE TOP OF THE STOUT
NORTH PACIFIC RIDGE TOWARDS THE SOUTHWEST MAINLAND...WITH RAIN
GRADUALLY BECOMING STEADIER AND MORE WIDESPREAD TUESDAY INTO
WEDNESDAY AS THE RIDGE BEGINS TO FLATTEN OUT AND MORE ZONAL FLOW
IS ESTABLISHED OVER THE AREA. THIS WILL ALSO LEAD TO GRADUALLY
INCREASING SOUTHWEST WINDS ACROSS THE AREA THROUGH WEDNESDAY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
RAINFALL AND GUSTY SOUTH TO SOUTHWEST WINDS OVER THE WESTERN HALF
OF THE BERING WILL GRADUALLY SPREAD NORTH AND EASTWARD THROUGH
TUESDAY AS THE NORTH PACIFIC RIDGE BEGINS TO FLATTEN OUT AND THE
FRONT OVER THE WESTERN ALEUTIANS BEGINS TO TAKE ON MORE OF AN
EAST-WEST ORIENTATION. THIS WILL KEEP THE EASTERN ALEUTIANS AND
ALASKA PENINSULA MAINLY DRY THROUGH THE MIDDLE OF THE WEEK.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE MODELS REMAIN IN FAIR OVERALL AGREEMENT THROUGH MIDWEEK...BUT
CONTINUE TO DIVERGE LATER IN THE WEEK. THEY DIFFER WITH REGARDS TO
THE STRENGTH OF THE BERING SEA RIDGE AND ASSOCIATED ENERGY RIDING
OVER TOP OF IT. THE ECMWF...BEING THE FAVORED SOLUTION...CONTINUES
TO BRING AN UPPER LEVEL TROUGH DIGGING THROUGH THE BERING SEA AND
SOUTHWEST MAINLAND WEDNESDAY NIGHT THROUGH THURSDAY...AND INTO THE
GULF BY THURSDAY NIGHT. ONE TROUGH AFTER ANOTHER WILL DROP OUT OF
EASTERN SIBERIA AND FOLLOW A SIMILAR TRACK THROUGH THE BERING AND
INTO THE SOUTHERN MAINLAND THROUGH EARLY NEXT WEEK...KEEPING MUCH
OF THE SOUTHERN MAINLAND UNDER A WET AND COOLING REGIME FROM
MIDWEEK THROUGH EARLY NEXT WEEK. THE GFS ON THE OTHER HAND KEEPS
A MORE PERSISTENT RIDGE OVER THE NORTH PACIFIC AND BERING WHICH
KEEPS ANY ENERGY EXITING SIBERIA FURTHER NORTH BEFORE DIVING
SOUTHEASTWARD ACROSS MAINLAND ALASKA...AND EVENTUALLY INTO THE
GULF. THE GFS IS ALSO MORE AGGRESSIVE WITH SPINNING UP A STRONGER
SURFACE LOW OVER THE GULF BOTH OVERNIGHT THURSDAY AND SUNDAY
MORNING. THIS PATTERN WOULD BRING SLIGHTLY DRIER CONDITIONS LATER
IN THE WEEK INTO NEXT WEEKEND...ALONG WITH STRONGER NORTHWEST FLOW
AND OUTFLOW GAP WINDS OVER THE AREA IN THIS TIME FRAME.

IN EITHER CASE...RAIN WILL LIKELY AFFECT THE SOUTHERN MAINLAND
SOMETIME MID TO LATE IN THE WEEK...WITH A COOLING TREND SETTING UP
OVER THE BERING AND MAINLAND THURSDAY THROUGH EARLY NEXT WEEK.
HOWEVER...FORECAST CONFIDENCE REMAINS LOW DUE TO THE CONTINUED
LARGE SCALE DIFFERENCES BETWEEN THE MODELS.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES...175 176 177 179 185 411 412 413.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...JW
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB
LONG TERM...TP