Small Craft Advisory 378, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1225 PM AKDT SAT MAY 10 2014

.ANALYSIS AND UPPER LEVELS...REX BLOCK IS BUILDING NORTHWARD OVER
MAINLAND ALASKA THIS MORNING WITH THE UPPER HIGH NOW CENTERED IN
THE VICINITY OF BRISTOL BAY. A SHORT-WAVE WHICH MOVED OVER TOP OF
THE RIDGE IS EXITING THE COPPER BASIN. SIMILAR TO WHAT OCCURRED
BEHIND A SHORT-WAVE YESTERDAY STRONG SUBSIDENCE HAS CAUSED WINDS
TO MIX DOWN IN A FEW LOCALES OVERNIGHT THROUGH THIS MORNING.
BECAUSE THE LOW LEVELS REMAINED FAIRLY WELL MIXED LAST NIGHT
THERE WAS LITTLE RECOVER IN RELATIVE HUMIDITIES...ESPECIALLY IN
PARTS OF ANCHORAGE AND THE MAT-SU. THE FOCUS OF THE FORECAST
REMAINS ON FIRE WEATHER CONCERNS...WITH RELATIVE HUMIDITIES
ALREADY DOWN INTO THE 20S IN PARTS OF THE SUSITNA VALLEY.
OFFSHORE FLOW OVER SOUTHCENTRAL HAS ALSO MAINTAINED TIGHT SURFACE
PRESSURE GRADIENTS ALONG THE GULF COAST WHICH IS ONCE AGAIN
LEADING TO GUSTY GAP WINDS.

UPSTREAM OF THE RIDGE A TROUGH IS LIFTING NORTHWARD ACROSS THE
WESTERN BERING SEA TOWARD SIBERIA. WATER VAPOR IMAGERY SHOWS DEEP
MOISTURE STREAMING NORTHWARD ACROSS THE EASTERN HALF OF THE
BERING SEA UP TO THE ARCTIC. ONSHORE FLOW IS JUST CLIPPING THE
KUSKOKWIM DELTA RESULTING IN LOW CLOUDS THIS MORNING...BUT THIS IS
BEGINNING TO BREAK UP INLAND AS THE ABUNDANT SUNSHINE CREATES SOME
VERTICAL MIXING.

&&

.MODEL DISCUSSION...ALL OF THE GUIDANCE HAS TRENDED TOWARD THE GFS
SOLUTION FROM YESTERDAY MORNING WITH DEPICTION OF AN ARCTIC TROUGH
CROSSING MAINLAND ALASKA MONDAY NIGHT AND TUESDAY AS UPPER RIDGE
MOMENTARILY WEAKENS. THERE ARE DIFFERENCES IN TIMING OF THIS
TROUGH. LEANING TOWARD THE MORE AGGRESSIVE GFS SOLUTION FOR NOW
SINCE IT WAS THE FIRST TO PICK UP ON IT AND NAM/GEM GLB AREN'T
TOO FAR BEHIND.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL AND SOUTHWEST ALASKA...THE UPPER RIDGE WILL CONTINUE
TO STRENGTHEN OVER THE REGION THROUGH SUNDAY...SO EXPECT A
CORRESPONDING INCREASE IN HIGH TEMPERATURES. SURFACE PRESSURE
GRADIENTS WILL RELAX SIGNIFICANTLY THIS AFTERNOON AND EVENING AS
CURRENT SHORT-WAVE MOVES OUT OF THE REGION. FLOW IN GENERAL WILL
BECOME LIGHTER UNDER THE BUILDING RIDGE. THUS...WON'T SEE MIXING
DOWN OF DRIER AIR FROM ALOFT THAT HAS BEEN OBSERVED IN SOME AREAS
THE PAST COUPLE DAYS. THIS WILL ALLOW RELATIVE HUMIDITIES TO
FULLY RECOVER AT NIGHT...BUT WITH THE WARMER TEMPERATURES STILL
EXPECT LOW HUMIDITY AND FIRE WEATHER CONCERNS TO PERSIST.

THERE WILL BE A BRIEF BREAK IN THE BLOCK PATTERN MONDAY AND
TUESDAY AS AN ARCTIC TROUGH EXITS RUSSIA AND PUSHES OVER THE
MAINLAND RIDGE...PROVIDING JUST ENOUGH WEAKNESS FOR THE POTENT
SHORT-WAVE TO TRACK ACROSS THE MAINLAND. MEANWHILE ANOTHER RIDGE
WILL BUILD OVER THE NORTH CENTRAL PACIFIC INTO THE BERING SEA OUT
AHEAD OF A DEVELOPING LOW OVER THE NORTHWEST PACIFIC. THIS WILL
CAUSE HEIGHTS TO RISE RAPIDLY BEHIND THE SHORT-WAVE TROUGH SO
THAT BY WEDNESDAY AN EVEN STRONGER RIDGE WILL BE BACK IN PLACE
OVER MAINLAND ALASKA. MOISTURE OVER THE SOUTHERN MAINLAND WILL BE
ON THE INCREASE MONDAY...SO FIRE WEATHER CONDITIONS WILL MODERATE.
AS THE TROUGH PASSES THROUGH MONDAY NIGHT AND TUESDAY EXPECT A
QUICK SHOT OF CLOUDS AND A FEW SHOWERS...ESPECIALLY OVER
SOUTHCENTRAL. THE RIDGE WILL THEN MOVE BACK IN WITH A
VENGEANCE...LEADING TO RAPID CLEARING ALONG WITH GUSTY WINDS AND
DRIER AIR MIXING DOWN FROM ALOFT. THUS...RED FLAG WARNINGS MAY BE
NEEDED ONCE AGAIN.

ONE OTHER ITEM OF NOTE IS THE MARINE LAYER OVER THE EASTERN GULF.
LOW CLOUDS AND FOG ARE TRACKING WESTWARD ACROSS THE NORTHERN GULF
THIS MORNING. EXPECT THE PREVAILING OFFSHORE FLOW TO KEEP THIS OUT
OVER THE GULF. HOWEVER...WITH SEA BREEZES EXPECTED TO DEVELOP THE
NEXT COUPLE DAYS AS PRESSURE GRADIENT BECOMES VERY WEAK WILL HAVE
TO CLOSELY WATCH THE MARINE LAYER TO SEE IF THERE IS A STRONG
ENOUGH ONSHORE FLOW TO PULL IT ONSHORE.

BERING SEA/ALEUTIANS...A DEVELOPING SYSTEM OVER THE NORTHWEST
PACIFIC WILL AFFECT THE WESTERN ALEUTIANS AND BERING WHILE AN
AMPLIFYING DOWNSTREAM RIDGE WILL MAINTAIN QUIET CONDITIONS FROM
THE CENTRAL TO EASTERN BERING. AS IS TYPICAL FOR THIS TIME OF
YEAR...THE STABLE AIR MASS PROVIDED BY THE UPPER RIDGE WILL LEAD
TO WIDESPREAD STRATUS AND FOG OVER MOST OF THE MARINE AREAS.

&&

.LONG TERM FORECAST...

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...RED FLAG WARNING 145 152 161.
               FIRE WEATHER WATCH 152 161 141 145.

&&

SEB MAY 14