Small Craft Advisory 489, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
151 PM AKDT WED JUN 18 2014

.ANALYSIS AND UPPER LEVELS...
THERE IS A BROAD RIDGE OVER THE NORTHWEST PACIFIC AND FAR WESTERN
BERING SEA. MEANWHILE...A DEEP AND PERSISTENT LONGWAVE TROUGH
REMAINS IN PLACE OVER THE NORTHEAST PACIFIC AND GULF OF ALASKA
REGIONS...KEEPING MAINLAND ALASKA UNDER A GENERALLY CLOUDY AND
COOL PATTERN. THERE ARE 3 SEPARATE SYSTEMS APPARENT ON SATELLITE
AND RADAR IMAGERY AROUND THE MAINLAND. THE FIRST IS THE REMNANT OF
THE STRONG STORM FROM MONDAY THAT IS NOW SPINNING ITSELF OUT IN
THE CENTRAL GULF...BRINGING SCATTERED SHOWERS AND GUSTY GAP WINDS
TO PARTS OF THE GULF COASTLINE. THE SECOND IS AN UPPER LEVEL LOW
THAT HAS DEVELOPED OVER INTERIOR ALASKA...AND IS BRINGING
SIGNIFICANT RAINFALL TO THE NORTHWEST CORNER OF THE COPPER RIVER
BASIN AND INTERIOR ALASKA. IN FACT...TEMPERATURES HAVE BEEN COLD
ENOUGH TO SUPPORT SNOW AT HIGHER ELEVATIONS...WITH SEVERAL INCHES
OF SNOW HAVING LIKELY ACCUMULATED ALONG PARTS OF THE DENALI AND
RICHARDSON HIGHWAYS. A THIRD LOW PRESSURE CENTER IS TRACKING
QUICKLY ALONG THE COAST OF SOUTHWEST ALASKA...ENROUTE TO THE GULF
OF ALASKA. THIS LOW IS ACCOMPANIED BY A SMALL BUT INTENSE BAND OF
RAIN CURRENTLY STRETCHING FROM THE KUSKOKWIM DELTA DOWN INTO
BRISTOL BAY...AND ALSO FEATURES WIDESPREAD FOG/STRATUS AS MOIST
ONSHORE FLOW IS ONGOING WELL AHEAD OF THE LOW ITSELF. IN THE
FAR WESTERN BERING...A WEAK LOW AND ASSOCIATED FRONT IS MOVING
TOWARD THE ALEUTIAN CHAIN BUT IS BEING WEAKENED BY UPPER LEVEL
RIDGING OVER THE AREA.

&&

.MODEL DISCUSSION...
THE MODELS ARE IN OVERALL GOOD SYNOPTIC AGREEMENT ON THE EVOLUTION
OF MAJOR FEATURES THROUGHOUT THE SHORT TERM (3 1/2 DAY) FORECAST
PERIOD. THE HIGHER AVAILABLE RESOLUTIONS OF THE CANADIAN RDPS AND
AMERICAN NAM WILL BE UTILIZED AS APPLICABLE IN FORECAST
PREPARATION TODAY. WHILE THERE REMAINS SOME TIMING DISCREPANCY
WITH THE SUPPORTING UPPER-LEVEL SHORTWAVE...ALL MODELS ARE NOW
BEGINNING TO SUGGEST A SIGNIFICANT RAIN EVENT ACROSS MUCH OF
INLAND AND COASTAL SOUTHCENTRAL MOVING FROM EAST TO WEST DURING
THE DAY SATURDAY AND CONTINUING THROUGH SUNDAY MORNING.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...
THE POPULATIONS CENTERS AROUND UPPER COOK INLET WILL CONTINUE TO
BE "TRAPPED" IN A BUBBLE OF GOOD WEATHER AS MULTIPLE LOW PRESSURE
SYSTEMS PINWHEEL IN PLACE TO THE NORTH...SOUTHEAST...AND
WEST/SOUTHWEST. A RIDGE BUILDING ALONG THE NORTH GULF COAST WILL
CONTINUE TO ENHANCE WINDS THROUGH TURNAGAIN ARM AND INTO ANCHORAGE
THROUGH LATE THIS EVENING...BUT THIS WILL BE THE LAST DAY OF THESE
DIURNAL WINDS FOR A WHILE AS WEAK LOW PRESSURE WILL SLIDE INTO THE
GULF TONIGHT FROM SOUTHWEST ALASKA. RAIN ASSOCIATED WITH THIS
SYSTEM WILL MOVE SOLIDLY INTO KODIAK ISLAND THIS EVENING...BUT NOW
APPEARS THAT THE RAIN SHIELD WILL STAY JUST SOUTH OF KACHEMAK BAY
BEFORE RETREATING BACK INTO THE GULF TOMORROW MORNING. IN THE
MEANTIME...MUCH OF THE REST OF SOUTHCENTRAL WILL SEE SOME BREAKS
OF SUN AND LIKELY ENOUGH INSTABILITY BUILDING TO PRODUCE SOME
AFTERNOON/EVENING SHOWERS OVER THE WESTERN KENAI AND INLAND AREAS
NORTH OF ANCHORAGE. HOWEVER...WITH WARMING TEMPERATURES ALOFT
THESE SHOWERS ARE NOT EXPECTED TO BECOME AS STRONG AS THOSE SEEN
YESTERDAY (TUESDAY) THAT DROPPED SMALL HAIL ACROSS PARTS OF THE
SUSITNA VALLEY AND KENAI PENINSULA.

BY FRIDAY...THE AREA WILL COME UNDER THE INFLUENCE OF SHORTWAVE
TROUGHS MOVING IN FROM THE EAST. COMBINED WITH WARMING
TEMPERATURES AND INCREASING INSTABILITY...INCREASING WIDESPREAD
CONVECTION MAY DEVELOP FOR THE END OF THE WEEK. BY
SATURDAY...AS MENTIONED ABOVE...ALL MODELS ARE NOW BEGINNING TO
SUGGEST A MUCH MORE WIDESPREAD AND SUSTAINED RAIN EVENT IMPACTING
ALL INTERIOR AREAS OF SOUTHCENTRAL THROUGH SUNDAY.

SOUTHWEST ALASKA...
THE LOW AND FRONT BRINGING WIDESPREAD FOG AND RAIN TO THE COASTAL
ZONES THIS EVENING WILL RAPIDLY WEAKEN AND MOVE INTO THE GULF BY
THURSDAY MORNING. AN OVERALL DRIER AND WARMER PATTERN WILL THEN
COMMENCE FOR THE NEXT FEW DAYS AS THE THERMAL TROUGH BECOMES RE-
ESTABLISHED OVER THE SOUTHWEST INTERIOR. GRADUALLY INCREASING
LOW-LEVEL TEMPERATURES WILL RESULT IN A SIMILAR GRADUAL INCREASE
IN DIURNAL INSTABILITY OVER THE COMING DAYS...WITH THE POSSIBILITY
OF THUNDERSTORM ACTIVITY RETURNING TO THE AREA BY SATURDAY.

BERING SEA/ALEUTIANS...
A WEAK FRONT IS APPROACHING THE WESTERN ALEUTIANS TONIGHT...BUT
WILL BRING LITTLE MORE THAN GUSTY WINDS AND A BRIEF PERIOD OF RAIN
TO THE WESTERN AND CENTRAL ALEUTIANS BEFORE DISSIPATING BY
THURSDAY EVENING. OTHERWISE...WEAK TO MODERATE HIGH PRESSURE
ACROSS MUCH OF THE REST OF THE AREA WILL KEEP MARINE STRATUS/FOG
THE PRIMARY FORECAST CHALLENGE AS WARM AIR CONTINUES TO GRADUALLY
SEEP INTO THE REGION FROM THE WEST AND ENHANCE LOW-LEVEL
TEMPERATURE INVERSIONS.

&&

.LONG TERM FORECAST (SATURDAY NIGHT THROUGH WED)...
A BEEFY EASTERLY WAVE PROPAGATING IN FROM THE YUKON WILL BE THE
INITIAL FOCUS OF THE EXTENDED FORECAST. GUIDANCE HAS BEEN LATCHING
ON TO THIS FEATURE FOR THE PAST FEW DAYS BUT THE EVOLUTION HAS
BEEN ALL OVER THE PLACE FROM STALLING TO CLOSING OFF AND MOVING
NORTHWARD...OR PROGRESSING ALL THE WAY ACROSS THE MAINLAND INTO
THE SOUTHWEST. DESPITE THE VARIABILITY IN TIMING AND STRENGTH OF
INDIVIDUAL FEATURES THE LONGWAVE PATTERN HAS BEEN STABLE WHICH
GIVES INCREASED CONFIDENCE. LOOK FOR SHOWERS AND THUNDERSTORMS
MOVING OFF HIGHER TERRAIN SATURDAY EVENING TRANSITIONING TO A
STEADIER RAINFALL AS THE EASTERLY WAVE PASSES. SHOWERY
PRECIPITATION WITH SEASONABLE TEMPERATURES WILL ENCOMPASS MOST OF
THE LONG TERM FORECAST.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.
&&

AMD/MTL JUN 14