Small Craft Advisory 955, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1227 PM AKST SAT NOV 30 2013

.ANALYSIS AND UPPER LEVELS...A VERY HIGH AMPLITUDE PATTERN REMAINS
IN PLACE WITH A STRONG RIDGE CENTERED OVER THE BERING EXTENDING
NORTHEASTWARD ACROSS NORTHWEST ALASKA AND A LARGE MULTI-CENTERED
LOW OVER THE EASTERN ALASKA MAINLAND AND INTO NORTHWEST CANADA.
ARCTIC AIR IS FIRMLY ENTRENCHED OVER THE MAINLAND AND GAP WINDS ARE
IN FULL FORCE ALONG THE GULF COAST. A VORT-MAX ON THE WEST SIDE OF
THE UPPER LEVEL LOW IS TRACKING SOUTHWARD ACROSS SOUTHCENTRAL THIS
MORNING ON ITS WAY TO THE GULF. STRONG SYNOPTIC SCALE SUBSIDENCE
WITH THIS FEATURE WILL ENHANCE WINDS ACROSS SOUTHCENTRAL AS IT MOVES
THROUGH. ALSO OF NOTE IS A 100 KT+ NORTHERLY JET BETWEEN THE RIDGE
AND LOW WHICH WILL ALSO AID IN ENHANCING WINDS IN THE WAKE OF THE
VORT-MAX. MEANWHILE...ON THE WEST SIDE OF THE BERING SEA RIDGE A
SHORT-WAVE TROUGH WHICH MOVED OUT OF ASIA HAS LED TO DEVELOPMENT
OF A SURFACE LOW SOUTH OF THE WESTERN ALEUTIANS. THIS LOW IS BEING
FORCED NORTHWARD UP THE WEST SIDE OF THE RIDGE ACCOMPANIED BY WARMER
AND MOISTER AIR.

.MODEL DISCUSSION...MODELS ARE IN GOOD AGREEMENT WITH LARGE SCALE
FEATURES OVER THE NEXT FEW DAYS. MINOR DIFFERENCES DEVELOP WITH
SYSTEM OVER THE NORTH CENTRAL PACIFIC MONDAY AND TIMING OF WARM
FRONT MOVING INTO THE BERING SEA. OF MORE SIGNIFICANCE IS A CHANGE
FROM YESTERDAY IN DEPICTION OF THE UPPER LEVEL RIDGE AS IT MOVES
EASTWARD OVER MAINLAND ALASKA. WHEREAS MODEL SOLUTIONS FROM THE
PAST FEW DAYS INDICATED THE RIDGE WOULD SLIDE QUICKLY EASTWARD
SUNDAY INTO MONDAY AND ALLOW WARM AIR TO RAPIDLY RIDE NORTHWARD
INTO WESTERN ALASKA...THE LATEST SOLUTIONS ALL REFLECT MORE
SIGNIFICANT RIDGING OUT AHEAD OF THE SYSTEM OVER THE NORTH-CENTRAL
PACIFIC WHICH CAUSES A DELAY IN ARRIVAL OF THE WARMEST AIR AND
PRECIPITATION UNTIL MID WEEK. THERE WILL STILL BE SOME WARMING AS
THE RIDGE MOVES OVER THE MAINLAND...JUST NOT QUITE AS MUCH AS
EARLIER THOUGHT.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE PASSAGE OF THE UPPER LEVEL VORT-MAX WILL
KICK WINDS UP ACROSS SOUTHCENTRAL ALASKA THIS AFTERNOON. WITH A
STEEP SURFACE-BASED INVERSION IN PLACE THIS WILL LEAD TO SIGNIFICANT
JUMPS IN TEMPERATURE. AND AS WINDS DIE BACK DOWN OVERNIGHT
TEMPERATURES WILL BE QUICK TO FALL. IN THE WAKE OF THE VORT-MAX
THE UPPER RIDGE WILL BEGIN TO BUILD IN FROM THE WEST WITH THE STRONG
NORTHERLY JET TRANSLATING EASTWARD WITH THE RIDGE. VERTICAL
CIRCULATIONS ASSOCIATED WITH THE JET WILL ENHANCE DOWNWARD MOTION
OVER SOUTHCENTRAL AND STRONGER WINDS FROM ALOFT WILL MIX DOWNWARD
TOWARD THE SURFACE. ALTHOUGH WINDS WILL WILL INTENSIFY ACROSS THE
REGION THE MOST FAVORABLE SET-UP WHEN LOOKING AT ALL THE CONTRIBUTING
FACTORS WILL BE IN THE VALDEZ AREA AS WELL AS THROUGH THE COPPER
RIVER DELTA - WHERE HIGH WIND WARNINGS ARE IN EFFECT THROUGH SUNDAY
AFTERNOON. THE UPPER JET WILL EXIT TO THE EAST DURING THE DAY
SUNDAY...BUT WITH A VERY STRONG SURFACE HIGH OVER INTERIOR ALASKA
PRESSURE GRADIENTS WILL BE SLOW TO SLACKEN AND GAP WINDS ALONG THE
NORTH GULF COAST WILL CONTINUE TO BLOW. WINDS WILL FINALLY WIND DOWN
SUNDAY NIGHT AS THE UPPER RIDGE BUILDS OVERHEAD AND A SURFACE HIGH
DEVELOPS OVER THE GULF. THERE WILL BE SOME MODERATION OF TEMPERATURES

AS WARMER AIR MOVES IN WITH THE RIDGE. HOWEVER...AS DISCUSSED ABOVE
IN THE MODEL DISCUSSION SECTION THIS WARMING IS LOOKING LESS
IMPRESSIVE IN THE MOST RECENT MODEL RUNS. IN ADDITION THE BULK OF
WARMING WILL OCCUR ALOFT AND SURFACE TEMPERATURES WILL BE SLOWER TO
MODERATE. AS THE TEMPERATURE INVERSIONS STEEPEN DUE TO SUBSIDENCE
FROM THE RIDGE AND ADVECTION OF WARMER AIR FOG WILL BECOME MORE
WIDESPREAD...ESPECIALLY IN THE COOK INLET REGION.

SOUTHWEST ALASKA...TEMPERATURES WILL MODERATE A BIT OVER THE NEXT
FEW DAYS AS THE UPPER RIDGE MOVES BY AND FLOW SHIFTS AROUND TO THE
SOUTH. A MORE SIGNIFICANT WARM-UP NOW LOOKS LIKE IT WILL HOLD OFF
UNTIL TUESDAY AND WEDNESDAY AS A WARM FRONT MOVES UP FROM THE NORTH
PACIFIC. THIS WILL LEAD TO SOME PRECIP-TYPE ISSUES WHEN PRECIP FIRST
ARRIVES BEFORE TEMPS WARM ENOUGH FOR RAIN. THERE IS QUITE A BIT OF
UNCERTAINTY IN THE PROGRESSION OF THE FRONT...SO ITS A BIT TOO EARLY
TO FIGURE OUT THE DETAILS.

BERING SEA/ALEUTIANS...THE LOW NEAR THE WESTERN ALEUTIANS WILL
TRACK NORTH TONIGHT THROUGH MONDAY WHILE THE UPPER RIDGE BEGINS TO
EXIT TO MAINLAND ALASKA. A WEAKER RIDGE WILL TRANSIT THE REGION
MONDAY...BUT THEN TROUGHS MOVING OUT OF THE NORTH PACIFIC AND ASIA
WILL BRING MORE ACTIVE WEATHER BACK TO THE REGION BY MID WEAK.

.LONG TERM FORECAST...MODELS ARE STRUGGLING WITH CONSISTENCY IN
POSITION/ORIENTATION OF THE MEAN UPPER RIDGE DURING THE DAY 4
THROUGH 7 TIME PERIOD. THERE IS HIGH CONFIDENCE THAT ACTIVE WEATHER
WILL PERSIST ACROSS THE BERING SEA/ALEUTIANS UNDER THE UPPER TROUGH.
THE BIG QUESTION IS HOW FAR INTO MAINLAND ALASKA WILL THE INFLUENCE
OF SYSTEMS OUT WEST EXTEND. THERE HAS BEEN A TREND TOWARD STRONGER
RIDGING WHICH MAY KEEP SOUTHCENTRAL MOSTLY DRY UNTIL THE END OF NEXT
WEEK OR INTO NEXT WEEKEND. THERE IS HIGHER CONFIDENCE THAT SOUTHWEST
ALASKA WILL BE AFFECTED BY THESE SYSTEMS ON THE WESTERN PERIPHERY OF
THE UPPER RIDGE.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WARNING 131 135.
         WIND CHILL ADVISORY 131.
MARINE...STORM WARNING...127 128.
         GALE WARNING...121 126 129 131 132 173 174 175 176 177 178.
         HEAVY FREEZING SPRAY WARNING...121 125 126 127 128 129 130
                                        139 140 150 160.
FIRE WEATHER...NONE.

SEB NOV 13