Small Craft Advisory 542, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
113 PM AKDT WED JUL 16 2014

.ANALYSIS AND UPPER LEVELS...
THERE IS AN UPPER LEVEL RIDGE OF HIGH PRESSURE OVER THE BERING
SEA WITH AN ARM STRETCHING ACROSS SOUTHERN ALASKA AND THEN JOINING
UP WITH A RIDGE ALONG THE CANADIAN/U.S. WEST COAST. THERE IS A
WEAK ELONGATED UPPER LEVEL LOW THAT STRETCHES FROM SOUTH OF THE
WESTERN ALEUTIANS TO SOUTH OF KODIAK ISLAND. THIS LOW IS
ASSOCIATED WITH THE SUBTROPICAL JET. ANOTHER UPPER LOW IS CENTERED
OFF THE NORTHWEST ALASKA COAST...ASSOCIATED WITH THE POLAR JET.

&&

.MODEL DISCUSSION...
THE NUMERICAL MODELS ARE STRUGGLING A BIT WITH THE CURRENT
PATTERN. THE MAIN AREA OF STRUGGLE IS ASSOCIATED WITH THE LOW
SOUTH OF ALASKA AND THE SUBTROPICAL JET. BY 48 HOURS THERE IS
ALMOST 1000 MILES OF SPREAD ON WHERE A SURFACE LOW WILL BE LOCATED
IN THE GULF. FORTUNATELY THIS ONLY AFFECTS THE VERY SOUTHERN EDGE
OF THE FORECAST AREA...BUT GIVES CAUSE FOR CONCERN WHEN IT COMES
TO FORECAST CONFIDENCE IN THE MODELS. THERE IS BETTER AGREEMENT
WITH THE LOW TO THE NORTH AND THE POLAR JET...WITH THE NORMAL
TIMING/STRENGTH ISSUES WITH SMALL SCALE FEATURES. FORECAST
CONFIDENCE IS NEAR TO BELOW NORMAL FOR THIS FORECAST PACKAGE.

&&

.SHORT TERM FORECAST...

FOR SOUTH CENTRAL ALASKA...THE AREA WILL REMAIN UNDER THE
PROTECTION OF THE RIDGE FOR THE NEXT COUPLE OF DAYS. THERE IS
ENOUGH MOISTURE AROUND AND THE RIDGE IS WEAK ENOUGH THAT SOME
DIURNAL SHOWERS ARE POSSIBLE...MAINLY OVER THE MOUNTAINS. DURING
THIS TIME THE SUBTROPICAL JET WILL BE PUSHING SYSTEMS
EAST/NORTHEAST THAT WILL JUST SCRAPE THE SOUTHERN MARINE/OFFSHORE
ZONES.

A PATTERN TRANSITION IS IN STORE FOR LATER IN THE WEEK. THE UPPER
LOW TO THE NORTHWEST OF ALASKA WILL SLIDE EASTWARD THROUGH
THURSDAY AND SETTLE IN TO THE NORTH OF BARROW THURSDAY NIGHT. THIS
WILL PUSH THE POLAR JET SOUTHWARD TOWARD SOUTH CENTRAL. 500 MB
HEIGHTS WILL BEGIN TO DROP THURSDAY NIGHT. BY FRIDAY AFTERNOON
FLOW ALOFT WILL BE FROM THE SOUTHWEST. THIS WILL PUSH A FRONTAL
SYSTEM INTO SOUTH CENTRAL ALASKA FRIDAY NIGHT AND SATURDAY THAT
WILL BRING RAIN TO MUCH OF THE AREA.

FOR SOUTHWEST ALASKA...THE PATTERN TRANSITION WILL TAKE PLACE A
LITTLE SOONER THAN IN SOUTH CENTRAL. FOR TONIGHT INTO
THURSDAY...HIGH PRESSURE WILL HOLD OFF A FRONTAL SYSTEM THAT IS
JUST PUSHING INTO THE KUSKOKWIM DELTA AREA. A REINFORCING SURGE
FROM THE LOW NORTH OF ALASKA WILL PUSH THE FRONT SOUTHEAST ACROSS
THE AREA THURSDAY NIGHT AND FRIDAY. NORTHWEST FLOW ALOFT WILL KEEP
CONSIDERABLE CLOUDS AND SOME SHOWERS OVER SOUTHWEST ALASKA ON
SATURDAY.

FOR THE BERING SEA/ALEUTIANS...THE UPPER LEVEL RIDGE OVER THE
SOUTHWEST BERING SEA WILL WEAKEN AND RETREAT WESTWARD TONIGHT
THROUGH FRIDAY. THIS WILL ALLOW A FRONT TO SLIDE SOUTH. THIS FRONT
WILL REACH THE PRIBILOFS THURSDAY MORNING...AND WILL APPROACH THE
ALEUTIAN CHAIN ON FRIDAY. THE FRONT WILL THEN ESSENTIALLY
DISSIPATE FRIDAY NIGHT AS IT ATTEMPTS TO CROSS THE ALEUTIANS. THE
HIGH WILL THEN RE-ASSERT ITSELF EASTWARD ACROSS THE BERING FRIDAY
NIGHT AND SATURDAY.

&&

.LONG TERM FORECAST...
MODELS CONTINUE TO STRUGGLE WITH RUN-TO-RUN CONSISTENCY TODAY...SO
WE STUCK WITH THE ECMWF ENSEMBLE MEAN THAT WAS USED BY WPC AS IT
HAS BEEN MUCH MORE CONSISTENT. IT IS LOOKING MORE AND MORE LIKELY
THAT A BLOCKING RIDGE WILL BUILD OVER THE REGION AGAIN...KEEPING
MUCH OF THE FORECAST AREA BETWEEN THE MAIN WEATHER SYSTEMS THAT
WILL PASS BY TO THE NORTH AND SOUTH. TEMPERATURES LOOK TO BE
FAIRLY SIMILAR TO HOW THEY HAVE BEEN LATELY...AND ANY
PRECIPITATION WILL LIKELY BE IN THE FORM OF SHOWERS RATHER THAN
STRATIFORM RAINFALL.

&&

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

LUDWIG/SCHRECK JUL 14