Small Craft Advisory 573, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKDT WED JUL 31 2013

.MODEL DISCUSSION...
THE OVERALL SYNOPTIC PATTERN IS SIMILAR BETWEEN THE MODELS. THE
DIFFERENCES COME IN THE MOVEMENT OF A NORTH PACIFIC LOW WHICH HEADS
TOWARD THE AK PEN FRI. THE NAM AND GFS MODELS ARE IN RELATIVELY GOOD
AGREEMENT ON PRESSURE...BUT OFF SOME ON POSITION. THE ECMWF IS
SIGNIFICANTLY FASTER. ALTHOUGH THE GFS/NAM SOLUTIONS DIFFER
SOME...THE SENSIBLE WEATHER IN THE EAST SHOULD BE SIMILAR. OUT
WEST...THE MAIN ISSUES WOULD BE THE MOVEMENT OF THE FRONTAL BOUNDARY
OVER SW ALASKA FRI NIGHT AND SAT. FOR NOW LOOKING AT USING BLENDS OF
THE NAM WITH OFFICIAL TROUGH THE SHORT TERM.

.ANALYSIS AND UPPER LEVELS...
.500 MB...
A SHORT WAVE MOVING EAST ACROSS THE COPPER RIVER BASIN KICKED OFF
NUMEROUS SHOWERS AND THUNDERSTORMS ACROSS THE NORTHERN HALF OF THE
COPPER RIVER BASIN THIS MORNING. THE UPPER WAVE WILL CONTINUE TO MOVE
EAST THROUGH THIS AFTERNOON AND LIKELY BE A CONTRIBUTOR TO ENHANCED
CONVECTIVE ACTIVITY. RIDGING WAS EVIDENT OVER THE REMAINDER OF THE
GULF AND SOUTHCENTRAL ALASKA. A BROAD MULTI-CENTERED LOW COMPLEX
SOUTH OF THE ALEUTIANS WAS PUSHING MOISTURE OVER THE AK PEN AND THE
EASTERN BERING SEA AS IT HEADED NORTH.

.SURFACE...NUMEROUS THUNDERSTORMS WITH MULTIPLE LIGHTNING STRIKES
WERE EVIDENT ACROSS THE NORTHERN COPPER RIVER BASIN. THE STRONGER
ACTIVITY SHIFTED EAST LATE THIS MORNING WITH THE UPPER SHORT WAVE.
MARINE STRATUS AND FOG WAS EVIDENT ACROSS MUCH OF THE GULF AND IN LOW
LYING AND VALLEY SECTIONS OF THE COPPER RIVER BASIN AND MATSU. A
FRONTAL TROUGH ASSOCIATED WITH A LOW NEAR THE EASTERN ALEUTIANS
BROUGHT RAIN TO THE AK PEN AND EASTERN ALEUTIANS OVERNIGHT. THE
MOISTURE CONTINUES TO SPREAD NORTH AND WEST WITH THE FRONT THIS
AFTERNOON. GUSTY WINDS WERE ALSO EVIDENT ALONG THE AHEAD OF THE
FRONTAL BOUNDARY.

.SHORT TERM FORECAST...
.SOUTHCENTRAL ALASKA...
THE SURFACE RIDGE OVER THE GULF MOVES SLOWLY EAST. THE WIDESPREAD
STRATUS AND FOG WILL BEGIN TO BREAKUP ON FRI AS A WEATHER FRONT MOVES
INTO THE GULF OF ALASKA. THE FRONT MOVING TOWARD THE WESTERN GULF
WILL SIGNAL A CHANGE IN THE PATTERN WHICH WELL BRING
GENERALLY COOLER AND CLOUDIER CONDITIONS WITH INCREASED CHANGES IN
RAIN INTO THE WEEKEND. DIURNAL CONVECTION WILL WEAKEN ACROSS INTERIOR
SOUTHCENTRAL OVER THE NEXT COUPLE OF DAYS AS COOLER AIR SPREADING IN
FROM THE GULF FORCES THE THERMAL TROUGH NORTH. THAT SAID...ANOTHER
ROUND OF SHOWERS AND THUNDERSTORMS ARE EXPECTED IN THE
SUSITNA...TALKEETNA MOUNTAINS...AND COPPER RIVER BASIN THROUGH THIS
EVENING. THE COPPER RIVER WILL LIKELY MAINTAIN SOME POTENTIAL FOR
THUNDERSTORMS INTO FRI. SMALL CRAFT TO GALE FORCE WINDS WILL SPREAD
NORTH INTO THE WESTERN GULF FRI AS A FAIRLY VIGOROUS LOW MOVES TOWARD
THE ALASKA PENINSULA. PRESSURE GRADIENTS WILL ALSO INCREASE ACROSS
SOUTHCENTRAL FRI AND SAT AND CREATE LOCALLY BRISK GAP FLOWS.

.SOUTHWEST ALASKA...
A NORTHWARD ADVANCING FRONT WILL BRING RAIN TO THE COASTS THIS
AFTERNOON AND WILL CONTINUE INTO TONIGHT. ELSEWHERE...FAVORABLE
CONDITIONS FOR THUNDERSTORM DEVELOPMENT CONTINUE TO BE PRESENT ALONG
THE ALASKA RANGE THROUGH THIS EVENING. A SERIES OF NORTH MOVING WAVES
FOLLOWING THE FRONT WILL BRING COOLER CONDITIONS WITH SHOWERS AND/OR
PERIODS OF RAIN ACROSS THE AREA INTO FRI.

BERING SEA AND ALEUTIANS...
UNSETTLED WEATHER WILL CONTINUE OVER THE EAST ALEUTIANS AND EAST
BERING SEA AS A SERIES OF WAVES MOVE THROUGH THE REGION. FURTHER
WEST...FOG AND MARINE STRATUS WILL BUILD BACK INTO THE WESTERN BERING
LATE THIS EVENING AND WILL CONTINUE THROUGH THE WEEKEND.

.LONG TERM FORECAST...

SATURDAY AND BEYOND...A STRONG LOW WILL BE IMPACTING MUCH OF SOUTHERN
ALASKA...THE ALASKA PENINSULA...AND KODIAK ISLAND. INTERIOR PORTIONS
OF SOUTHCENTRAL WILL LIKELY SEE STRONG DOWNSLOPE DRYING AS THE FRONT
APPROACHES...WITH A MORE SHOWERY PATTERN SUNDAY AND MONDAY. STRONG
LOCAL GAP WINDS WILL ALSO BE POSSIBLE...ESPECIALLY ACROSS TURNAGAIN
ARM AND PORTAGE VALLEY AS THE FRONT MOVES IN. EXPECT MUCH COOLER AND
WETTER CONDITIONS TO PERSIST INTO THE EARLY TO MIDDLE OF NEXT WEEK AS
A LONG WAVE TROUGH SETS UP OVER THE BERING STRAIT DOWN THROUGH THE
EASTERN BERING. DETAILS OF THE LARGE SCALE PATTERN BECOME MUDDY BY
LATE NEXT WEEK...BUT THERE ARE NO STRONG SIGNALS OF ANOTHER MAJOR
WARM AND DRY SPELL ACROSS SOUTHERN ALASKA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

RMC JUL 13