Small Craft Advisory 574, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
325 PM AKDT THU AUG 1 2013

.ANALYSIS AND UPPER LEVELS...
THE PATTERN ALOFT FEATURES RIDGING OVER THE SOUTHCENTRAL MAINLAND.
HEIGHT FALLS ASSOCIATED WITH THE BERING SEA/NORTH PACIFIC TROUGH ARE
BEGINNING TO ERODE THE RIDGE AND SHIFT IT EASTWARD. THE UPPER LOW IS
CURRENTLY CENTERED OVER THE CENTRAL ALEUTIANS WITH SEVERAL SHORTWAVE
TROUGHS ROTATING AROUND ITS PERIPHERY. THE STRONGEST OF WHICH IS
CURRENTLY ROUNDING THE BASE OF THE TROUGH ALONG WITH A 115 KT JET
STREAK. THE FIRST SHORTWAVE/FRONT IS PUSHING INLAND OVER THE EASTERN
ALASKA PENINSULA IS BRINGING PERIODS OF RAIN TO THE BRISTOL BAY AND
KUSKOKWIM DELTA REGIONS. AT THE SURFACE...RIDGING OVER THE EASTERN
GULF EXTENDS THROUGH THE NORTH GULF COAST AND INLAND PROMOTING A
MARINE LAYER THAT HAS BEEN EXTENDING FROM THE COASTAL AREAS UP
THROUGH THE MAT-SU DURING THE OVERNIGHT HOURS. A FRONTAL BOUNDARY
CURRENTLY OVER KODIAK ISLAND/WESTERN GULF IS BRINGING STEADY RAIN TO
THE AREA.

.MODEL DISCUSSION...
WHILE GUIDANCE HAS HAD A PRETTY GOOD HANDLE ON THE GENERAL SYNOPTIC
PATTERN FOR A COUPLE DAYS THE DETAIL ARE STILL NOT WELL AGREED UPON.
THE COMPLEX INTERACTION OF THE STRONG SHORTWAVE/JET STREAK WITH THE
ALREADY EXISTING PARENT LOW PRESSURE COMBINED WITH RAPID CYCLOGENESIS
AND PHASING OF THE UPPER LEVEL/LOW LEVEL POTENTIAL VORTICITY
ANOMALIES IS CAUSING MODEL DISCREPANCY IN BOTH POSITION AND STRENGTH
OF THE LOW. THAT BEING SAID CONFIDENCE IS HIGH IN A MODERATELY STRONG
AND COMPACT SURFACE LOW MOVING TO THE WEST OF KODIAK ISLAND BY LATE
TOMORROW EVENING. THE GEM GLOBAL/ECMWF ARE STILL FASTER WITH THE
SYSTEM WHILE THE NAM/GFS CONTINUE TO BE SLOWER. THE GEM REGIONAL AND
UKMET ALSO FAVOR A SLOWER SOLUTION. SREF AND GFS ENSEMBLE MEAN
GUIDANCE HAVE BEEN TRENDING TOWARD A SLOWER SOLUTION AS WELL. THE GFS
CONTINUES TO BE THE DEEPEST OF ALL GUIDANCE AND FARTHEST WESTWARD.
CURRENT WATER VAPOR IMAGERY SUPPORTS THE GFS DEPICTION. BOTH DOMAINS
PREFERRED THE GFS SOLUTION.

.SHORT TERM FORECAST...
.SOUTHCENTRAL ALASKA...
STRATUS TO BREAK UP TONIGHT AND TOMORROW AS FLOW INCREASES OVER THE
AREA. A WEAKENING FRONT EXTENDS FROM SOUTHWEST ALASKA INTO THE MIDDLE
OF THE GULF. THE JET AND BAROCLINIC STRUCTURE TO WEAKEN OVER THIS
TIMEFRAME RESULTING IN A GOOD CHANCE OF SHOWERS IN THE SOUTHERN KENAI
PENINSULA BUT LITTLE THREAT INLAND FRIDAY. WEAK SIGNAL AT MID LEVELS
FROM THE FRONTAL WAVE BUT ENOUGH MOISUTE AND SIGNAL FOR ISOLATED
SHOWERS INLAND. THE SURFACE RIDGE OVER THE NORTHERN GULF COAST IS TO
REMAIN AND STRENGTHEN TOMORROW AHEAD OF A DEEPEING LOW IN THE NORTH
PACIFIC. FLOW STRENGTHENS OUT OF THE SOUTHEAST TOMORROW NIGHT AND
CONTRIBUTES TO RAIN SHADOW OVER THE ANCHORAGE BOWL AND LOWER MAT-SU.
OVER AREAS OF THE LOWER WESTERN KENAI AND WINDWARD SIDE OF THE KENAI
AND KODIAK ISLAND...PRECIPITATION WILL BE WIDESPREAD AND MODERATE TO
HEAVY AT TIMES FRIDAY NIGHT AND SATURDAY. THE ASSOCIATED FRONT WILL
PASS THROUGH THE TURNAGAIN ARM AREA SATURDAY MORNING WITH SOME
STRONGER WINDS. DO NOT EXPECT HIGH WIND WARNING BUT DEFINITELY
GREATER THAN 45 MPH. PRECIPITATION WILL PUSH INLAND SATURDAY AS WELL
WITH THE FRONT SATURDAY AS GOOD SUPPORT AT MID AND UPPER LEVELS. THE
SUPPORT LEAVES SATURDAY NIGHT INTO SUNDAY...BUT THE LOW OPENS OVER
SOUTHWEST ALASKA SATURDAY NIGHT. THEREFORE...RAIN WILL BE PRESENT IN
MOST AREAS OF SOUTH CENTRAL SUNDAY AS WELL. CONTINUED SOUTHWEST FLOW
WILL RESULT IN SCATTERED SHOWERS INTO MONDAY.

.SOUTHWEST ALASKA...
A FRONT STRETCHES ACROSS SOUTHWEST ALASKA CURRENTLY BRINING
WIDESPREAD PRECIPITATION. NOT MUCH IN THE KUSKO VALLEY THOUGH AS THE
FRONT WILL WEAKEN AS IT WORKS INLAND WITH DISSIPATING SUPPORT ALOFT.
CONTINUED SOUTHERLY FLOW WILL KEEP SHOWERS IN THE AREA FRIDAY. A
DEEPENING LOW IN THE NORTH PACIFIC TO WORK TO THE AKPEN FRIDAY
INCREASING WINDS AND PRECIP FRIDAY NIGHT. THE LOW WILL WEAKEN FRIDAY
NIGHT INTO SATURDAY AS THE JET SUPPORT IS WITH THE FRONT THAT IMPACTS
SOUTH CENTRAL ALASKA. THE LOW TURNS INTO AN OPEN WAVE AND ROTATES
INTO THE LARGER STACKED LOW IN THE EASTERN BERING. THE STACKED LOW
WILL ROTATE INLAND SUNDAY AS AN ARCTIC LOW DEVELOPS A LARGER TROUGH
OVER THE BERING SEA.

BERING SEA AND ALEUTIANS...
THE LARGE STACKED LOW OVER THE CENTRAL BERING AND ALEUTIANS TO WEAKEN
OVER THE NEXT 24 HOURS AS A SHORT WAVE COUPLED WITH A JET MAX TO
DEVELOP A STRONG LOW IN THE NORTH PACIFIC THAT SWINGS TO THE AKPEN
FRIDAY NIGHT. UNSETTLED SHOWERS AND STRATUS TO REMAIN OVER THE BERING
IN THE MEANTIME. ANOTHER UPPER LEVEL LOW TO DROP INTO THE BERING
FRIDAY NIGHT NEAR EASTERN RUSSIA. THIS WILL CONTINUE THE UNSETTLED
SHOWERS AND STRATUS OVER THE AREA THROUGH THE WEEKEND.

.LONG TERM FORECAST...
LONG WAVE TROUGH TO REMAIN OVER THE BERING AND WESTERN ALASKA THROUGH
THE EXTENDED PERIOD. THIS WILL KEEP A COOL PATTERN WITH STRATUS AND
RAIN AT TIMES OVER THE BERING AND WEST COAST OF ALASKA. OVER THE
EASTERN MAINLAND...TEMPERATURES SHOULD REMAIN NEAR TO ABOVE NORMAL
BUT NOT EXCEEDINGLY ABOVE NORMAL AS THE RIDGE HAS MOVED OVER WESTERN
CANADA AND NORTHWEST CONUS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALES 130 132 138 150
FIRE WEATHER...NONE.

NELSON/LAWSON JUL 13