Small Craft Advisory 701, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
451 AM AKDT THU SEP 12 2013

.ANALYSIS AND UPPER LEVELS...

THE UPPER LEVEL DISTURBANCE THAT PASSED ACROSS SOUTHCENTRAL ALASKA
WEDNESDAY MORNING HAS PUSHED INTO THE INTERIOR. A RIDGE OF HIGH
PRESSURE IS BUILDING ACROSS SOUTHCENTRAL BEHIND THE WAVE WHICH
HAS BROUGHT PARTIAL CLEARING AND AN END TO PRECIPITATION ACROSS OUR
REGION. OVER THE BERING...THE EX-TROPICAL LOW WHICH HAS BEEN BRINGING
WINDS GUSTING TO 50 KT ACROSS THE CENTRAL ALEUTIANS HAS OCCLUDED AND
WILL BEGIN TO WEAKEN THROUGHOUT THE DAY. THE AIR MASS ASSOCIATED WITH
THE LOW HAS MODIFIED SIGNIFICANTLY OVER THE PAST 24 HOURS...LEADING
TO WARMER CLOUD TOPS AND SIGNIFICANTLY LESS MOISTURE WITH THE SYSTEM.
THE OCCLUDED FRONT REMAINS ACROSS THE EASTERN BERING SEA AND WILL
PUSH ACROSS SOUTHWEST ALASKA TODAY...BRINGING RAINFALL ONCE AGAIN. A
RIDGE OF HIGH PRESSURE EAST OF RUSSIA HAS BEGUN TO BUILD INTO THE
WESTERN BERING SEA.

.MODEL DISCUSSION...

MODELS REMAIN IN FAIRLY GOOD AGREEMENT THROUGH THE FIRST 48 HOURS.
THE LOW OVER THE ALEUTIANS WILL PUSH TO THE EAST/SOUTHEAST AS IT
MOVES INTO THE NORTHERN GULF AND WEAKENS AS ANOTHER AREA OF LOW
PRESSURE OVER THE FAR NORTHERN BERING SEA WILL ACT TO KEEP THE LOW
FROM TRACKING FURTHER NORTH INTO THE SOUTHWEST MAINLAND. PAST 48
HOURS...THE NAM DISSIPATES THIS LOW PRESSURE FASTER THAN THE GFS AND
ECMWF AND ALSO PUSHES FURTHER EAST MORE RAPIDLY. SINCE THE GFS HAS
BEEN VERY CONSISTENT AND VERIFIED WELL OVER THE PAST WEEK...HAVE
CONTINUES TO UTILIZE THE GFS IN THE FORECAST PROCESS.

.SHORT TERM FORECAST...

SOUTHCENTRAL...

MODELS ALONG WITH THE ANCHORAGE MORNING SOUNDING INDICATE A MUCH MORE
STABLE AIR MASS ALOFT HAS MOVED UP COOK INLET AND INTO SOUTHCENTRAL
OVERNIGHT...THUS CONVECTIVE SHOWER ACTIVITY HAS GREATLY DIMINISHED
FROM THE SOUTHWEST AND WILL CONTINUE TO DO SO FARTHER INLAND THIS
MORNING INTO THE AFTERNOON. A WEAK SHORTWAVE DISTURBANCE MOVING NORTH
TOWARD THE AREA THIS MORNING WILL TEMPORARILY ALLOW FOR MARGINAL TO
LOW-END VFR CEILINGS TO RISE OR BREAK LATE THIS MORNING. HOWEVER...AS
THIS SHORTWAVE PASSES...LOW-LEVEL MARINE STRATUS SHOULD RETURN
ESPECIALLY TO COASTAL LOCATIONS WITH POTENTIALLY LOW-END VFR CEILINGS
EXTENDING THROUGH ANCHORAGE INTO LATE AFTERNOON BEFORE RISING
SIGNIFICANTLY THIS EVENING AS DOWNSLOPE DRYING DEVELOPS IN THE LOWEST
5-6 THOUSAND FEET. THE NEXT WEATHER MAKER MOVES ACROSS KODIAK ISLAND
THIS MORNING INTO AFTERNOON...THEN MOVES NORTH AND EAST ACROSS THE
KENAI PENINSULA AND INTO SOUTHCENTRAL TONIGHT. AS IT APPEARS NOW...IT
DOES NOT LOOK PROMISING FOR ANCHORAGE TO SEE MEASURABLE PRECIPITATION
ABOVE A TRACE UNTIL AFTER MIDNIGHT STANDARD TIME...WHICH WOULD END
THE IMPRESSIVE STREAK OF DAYS OF MEASURABLE PRECIPITATION.
HOWEVER...THERE IS STILL A GOOD AMOUNT OF UNCERTAINTY SO STAY TUNED.

FOR FRIDAY ANCHORAGE LIES BETWEEN A SPLIT STREAM WEATHER PATTERN WITH
A LOW TO THE NORTH AND ANOTHER TO THE SOUTH OVER THE SOUTHERN GULF.
THE ACCOMPANYING DEFORMATION ZONE APPEARS TO SET UP JUST TO THE SOUTH
AND EAST OF TOWN SO THAT THE EASTERN KENAI PENINSULA AND PRINCE
WILLIAM SOUND SHOULD BE MUCH WETTER...THOUGH THERE WILL ALMOST
CERTAINLY BE LIGHT RAIN FRIDAY MORNING AND POSSIBLY EXTENDING INTO
AFTERNOON. BY THE WEEKEND...UPPER LEVEL RIDGING BEGINS TO DEVELOP TO
THE NORTH AND ALLOW FOR OFFSHORE FLOW TO INCREASE AT THE
SURFACE...RESULTING IN A DRYING TREND OVER THE REGION.

SOUTHWEST ALASKA...

SURFACE HIGH PRESSURE WILL SHIFT EAST THIS MORNING AS AN OCCLUDED
FRONT WILL MOVE INLAND OVER THE BRISTOL BAY AREA AND LOWER KUSKOKWIM
VALLEY AHEAD OF A 986 MB LOW LOCATED SOUTH OF DUTCH HARBOR. SCATTERED
SHOWERS WILL ACCOMPANY THE FRONT THIS MORNING BEFORE BECOMING
STRATIFIED PRECIPITATION THIS AFTERNOON AND EVENING. AS THE LOW OVER
THE CENTRAL ALEUTIANS PUSHES EAST DURING THE DAY...THE PRESSURE
GRADIENT WILL TIGHTEN CAUSING STRONG AND GUSTY WINDS TO GALE FORCE.
AS THE LOW MOVES SOUTH OF THE AKPEN THIS EVENING...STRONG WIND GUSTS
WILL BE POSSIBLE THROUGH THE GAPS ALONG THE ALEUTIAN RANGE UNTIL THE
LOW MOVES INTO THE NORTHERN GULF ON FRIDAY AND RAPIDLY WEAKENS.
PRECIPITATION SHOULD BECOME MORE SCATTERED THIS EVENING BEFORE
FINALLY PUSHING EAST BY SATURDAY MORNING. HIGH PRESSURE CURRENTLY
OVER THE WESTERN GULF WILL PUSH OVER SOUTHWEST ALASKA SATURDAY
AFTERNOON.

BERING SEA AND ALEUTIANS...

A STRONG AREA OF LOW PRESSURE CURRENTLY SITUATED SOUTH OF DUTCH
HARBOR WILL CONTINUE TO PUSH EAST QUICKLY DURING THE DAY AS IT IS
ABSORBED BY THE SUBTROPICAL JET. AHEAD OF THE LOW...GUSTY WINDS ARE
EXPECTED THROUGH CHANNELED TERRAIN. AS COLDER AIR WRAPS AROUND THE
BACK SIDE OF THE LOW...GALE-FORCE WINDS ARE EXPECTED FROM ADAK EAST.
WINDS WILL TAPER OFF IN THE LATE MORNING AND EARLY AFTERNOON AS THE
GRADIENT BEGINS TO RELAX AND THE LOW PUSHES EAST. HIGH PRESSURE WILL
BUILD OVER THE WESTERN BERING SEA THIS AFTERNOON. AN AREA OF LOW
PRESSURE OVER EASTERN RUSSIA WILL MOVE OVER THE NORTHERN BERING SEA
ON SATURDAY AS THE RIDGE AXIS SHIFTS EAST.

.LONG TERM FORECAST...

DRIER WEATHER ASSOCIATED WITH A WEAK HIGH PRESSURE ALOFT IS EXPECTED
OVER MOST OF SOUTHCENTRAL THIS WEEKEND...WITH LOW PRESSURE OVER THE
NORTHERN BERING EXPECTED TO DIVE SOUTH AND EAST INTO THE GULF AND
PHASE WITH ANOTHER UPPER LEVEL FROM THE SOUTHEASTERN GULF THE EARLY
TO MIDDLE PART OF NEXT WEEK. THUS...THE DRY PATTERN SHOULD BE VERY
SHORT-LIVED AS COLDER AIR FILTERS INTO SOUTHCENTRAL FROM THE NORTH
AND WEST WITH INCREASING MOISTURE INFLUX FROM THE SOUTH AND EAST THE
EARLY TO MIDDLE PARTS OF NEXT WEEK. MEANWHILE...HIGH PRESSURE RIDGING
ALOFT WITH WEAKER SURFACE WINDS WILL DEVELOP ACROSS THE BERING SEA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALES...130 132 150 160 170 179
         STORMS...172
FIRE WEATHER...NONE.

CASSELL/CLAY SEP 13