Small Craft Advisory 382, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 AM AKDT MON MAY 12 2014

.ANALYSIS AND UPPER LEVELS...
VESTIGES OF THE BLOCKED UPPER-LVL PATTERN CONTINUING OVER THE
AOR...WITH A STATIONARY UPPER HIGH CENTER NEAR MERILL PASS. BROAD UPPER
RIDGING OVER THE EASTERN BERING SEA IS FLANKED TO THE SOUTHEAST BY
AN OLD NE PACIFIC LOW WELL SOUTH OF THE GULF OF AK AND A NW
PACIFIC LOW SW OF SHEMYA. A SHARP UPPER TROUGH IS NOTED IN
SATELLITE IMAGERY IN E SIBERIA MOVING EAST TOWARDS THE MAINLAND.
A 993 MB SURFACE LOW IS CENTERED 500 MI SW OF SHEMYA AND NEARLY
STATIONARY. RAIN AND GALES ASSOCIATED WITH IT SMACK THE FAR
WESTERN CHAIN AND BERING SEA. OTHERWISE THE REMAINDER OF THE AOR
IS LARGELY PRECIPITATION FREE. FOG/STRATUS ENVELOPS MUCH OF THE
SOUTHCENTRAL/GULF AND AKPEN AREAS UNDER A VERY STABLE AIRMASS.

&&

.MODEL DISCUSSION...
MODELS HAVE AN ADEQUATE HANDLE ON THE MAIN WEATHER FEATURES. THE
NAM HAD A DECENT HANDLE ON THE TROUGH THAT WILL SWING THROUGH THE
SOUTHERN MAINLAND ON TUE...THOUGH ALL MODELS ARE CLOSE IN SPIRIT.
MODELS SHOW WITH GOOD AGREEMENT THE BROAD RIDGING OVER THE
EASTERN BERING SEA CONSOLIDATING IN EARNEST AND BUILDING BACK
TOWARDS SW AND SOUTHCENTRAL AK IN THE WAKE OF THE TROUGH MID WEEK.
THE LOW SW OF SHEMYA IS DEPICTED FILLING AS IT MOVES TO AROUND 250
MILES NW OF SHEMYA BY EARLY WED. IN SHORT...THE RETURN OF A BLOCKED
PATTERN IS SHOWN SIMILARLY.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL TO SOUTHWEST ALASKA...
FORECAST CHALLENGES FOR THE SOUTHERN MAINLAND TODAY ARE THE
MARINE LAYER IN COOK INLET. MUCH OF THE REAL ESTATE ALONG THE
INLET HAS BEEN SOCKED IN SINCE LATE LAST NIGHT AND PENDING IT'S
DEPTH...IT COULD TAKE TILL LATE AFTERNOON FOR IT TO RETREAT OR
BURN OFF. IN SOME LOCALES...IT MAY NOT BE TILL EVENING. THE SOONER
IT DOES RETREAT...THE WARMER THE HIGH TEMPERATUERS...AND VICE
VERSA. THE UPPER HIGH OVER SW AK SHOULD BE DAMPENING WITH TIME AND
IT'S ASSOCIATED SUBSIDENCE WHICH MAY BE AIDING IN THE MARINE
LAYER'S SCOPE SHOULD WEAKEN. FORECAST CHALLENGES THEREAFTER ARE
NEARLY EXCLUSIVELY FIRE WEATHER CONCERNS. THE PASSAGE OF THE UPPER
TROUGH TUE NIGHT WILL USHER IN A REINFORCING SHOT OF DRY AIR. THE
DEGREE OF DRYNESS IS VERY SIGNIFICANT...WITH WIDESPREAD DEWPOINT
DEPRESSIONS AT GROUND LEVEL POSSIBLY REACHING 40 TO 50 DEGREES
FAHRENHEIT AT TIMES...PARTICULARLY IN THE SUSITNA VALLEY AND
INTERIOR WESTERN KENAI PENINSULA. WITH TEMPERATURES DURING MAX
HEATING WELL INTO 60S EXPECTED...THIS WOULD PUT RELATIVE
HUMIDITIES IN THE 15 TO 30 PERCENT RANGE OVER A LARGE SWATH OF
SOUTHCENTRAL AK. TROUGH PASSAGE WILL OCCUR DURING THE OVERNIGHT
HOURS TUE FOR MANY LOCATIONS...AND BECAUSE THE STRONGEST WINDS
WILL BE OCCURRING DURING A PERIOD WHEN IT IS TYPICALLY COOLEST
THIS WILL PROBABLY TEMPER THE FIRE DANGER FROM BECOMING WORSE. BUT
THE LOW HUMIDITY ALONE STILL HAS POTENTIAL TO CONTINUE THE FIRE
DANGER INTO THURSDAY. MULTIPLE FIRE WEATHER HAZARDS ARE BEING
PREPPED TO CAPTURE THIS THREAT IN SOUTHCENTRAL AND SOUTHWEST AK.

BERING SEA/ALEUTIANS/AKPEN...
THE STRONG BLOCKING HIGH OVER THE EASTERN BERING/SW AK STILL LOOKS
TO RETARD EASTWARD PROGRESSION OF THE WESTERN ALEUTIAN FRONT. RAIN
SHOULD BE FOCUSED ON THE WESTERN TO CENTRAL CHAIN...WITH GALE
FORCE WINDS DIMINISHING AS THE LOW FILLS. OTHERWISE RUN OF THE
MILL FOG/STRATUS REGIME TO PERSIST IN EARNEST OVER THE REMAINDER
OF THE BERING SEA IN A STABLE AIRMASS.

&&

.LONG TERM FORECAST...
THE LONG TERM FORECAST IS CHARACTERIZED BY THE STRENGTHENING BLOCKED
PATTERN MID TO LATE THIS WEEK. HOWEVER BY LATE WEEKEND...MODELS SEEM
TO BE TRENDING TO A SIGNIFICANT PATTERN SHIFT FOR THE AOR. IN GENERAL
TERMS...THE UPPER HIGH AND RIDGING THAT HAS BEEN DOMINANT OVER THE
SOUTHERN AK FOR QUITE SOME TIME WILL BE REPLACED BY A STRONG UPPER
TROUGH OR LOW DIGGING DOWN FROM THE HIGH ARCTIC TOWARDS SW AK OR THE
GULF OF AK. THE NET EFFECT WOULD BE CONSIDERABLY INCREASED CLOUD
COVER...WETTER CONDITIONS AND DRAMATICALLY LOWER TEMPERATURES. THE
OPERATIONAL ECMWF IS PARTICULARLY ANOMALOUS WITH THE TEMPERATURE
COOL DOWN. OUT WEST...THE LONGWAVE TROUGH WHICH HAS BEEN FAIRLY
PREDOMINANT LOOKS TO TRANSITION TO SHARP UPPER-RIDGING. IN ESSENCE
THIS WOULD DIMINISH THE CHANCES FOR STRONG LOW PRESSURE SYSTEMS OR
FRONTS FROM TRACKING THROUGH THE BERING SEA.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE...177 178 411
FIRE WEATHER...RED FLAG WARNING...(TUE) 152 161
               FIRE WEATHER WATCH...(WED) 111 121 141 145 152
                                          155 161

&&

JAM