Small Craft Advisory 474, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
400 PM AKDT WED JUN 12 2013

.ANALYSIS AND UPPER LEVELS...THE UPPER LEVEL RIDGE OVER THE MAINLAND
PART OF THE STATE IS WEAKENING SOME AS IT IS PUSHED WESTWARD BY A
COLD UPPER LEVEL LOW ELONGATING ALONG THE ALCAN BORDER THAT WILL
DESCEND INTO THE COPPER RIVER BASIN OVERNIGHT. THIS UPPER LEVEL LOW
WILL BECOME THE FOCUS FOR MOST OF THE WEATHER IN THE EASTERN PART OF
THE STATE FOR THURSDAY AND FRIDAY.
AT THE SURFACE THE RIDGE IS CENTERED OVER THE MAINLAND PART OF THE
STATE AND EXTENDS OVER THE GULF OF ALASKA AS WELL. A LARGE COMPLEX
LOW IS IN THE WESTERN AND CENTRAL BERING SEA WHERE IT WILL CONTINUE
TO BRING A SERIES OF LOWS AROUND ITS PERIPHERY FOR THE NEXT FEW DAYS.

.MODEL DISCUSSION...THE MODELS ARE IN GOOD AGREEMENT ON THE OVERALL
PATTERN. THEY WERE HOLDING CONSISTENT ON THE UPPER LEVEL LOW ON THE
ALCAN BORDER THROUGH THE 12Z RUN THIS MORNING. THE 18Z RUN OF THE NAM
IS SHIFTING THE LOW A LITTLE FARTHER EASTWARD WHICH WOULD SHIFT THE
PRECIPITATION FARTHER EAST...ESPECIALLY ANY LINGERING AROUND BY
FRIDAY. MODELS ARE IN GOOD AGREEMENT AS TO THE COLD AIR ALOFT AND THE
ASSOCIATED INSTABILITY OF THE ATMOSPHERE IN SOUTH CENTRAL ALASKA THE
NEXT TWO DAYS.

.SHORT TERM FORECAST...
SOUTH CENTRAL...THE ATMOSPHERE IS BECOMING MORE UNSTABLE OVER SOUTH
CENTRAL ALASKA TODAY WITH THE COPPER RIVER BASIN BEING THE MOST
UNSTABLE AREA. THERE HAS ALREADY BEEN A NUMBER OF LIGHTNING STRIKES
DETECTED IN THE COPPER RIVER BASIN AS OF EARLY THIS AFTERNOON. THIS
WILL PERSIST THROUGH THE EVENING AND SHOWERS WILL PERSIST THROUGH THE
NIGHT AS THE UPPER LEVEL LOW KEEPS THE CONVECTION GOING. THERE WILL
BE A SHORT WAVE EXTENDING OUT OF THE LOW IN THE COPPER RIVER BASIN
THAT MOVES FROM NORTH TO SOUTH TOMORROW. THIS WAVE WILL BE OVER THE
SUSITNA VALLEY IN THE MORNING...MOVING OVER ANCHORAGE BY MID
AFTERNOON AND THEN OVER THE KENAI PENINSULA FOR THE EVENING. THIS
WILL AMPLIFY SHOWERS AND LIKELY BRING SOME THUNDERSTORMS TO THE
INTERIOR OF THE KENAI PENINSULA TOMORROW AFTERNOON AND EVENING. THERE
IS ALSO A CHANCE OF THUNDERSTORMS OVER THE TALKEETNA AND CHUGACH
MOUNTAINS TOMORROW AS THIS WAVE MOVES THROUGH THE AREA.
THE NEXT ITEM OF NOTE IS THE EXTENSIVE AREA OF STRATUS IN THE GULF OF
ALASKA. THE SOUTHWEST FLOW WITH PRESSURE RISES IS PROMOTING ITS
MOVEMENT INTO THE NORTH GULF COAST AN INTO COOK INLET AS WELL. COOK
INLET IS ALWAYS A CHALLENGE TO DETERMINE HOW FAR NORTH IT WILL
PROTRUDE. THERE IS A CHANCE IT COULD MAKE A SECOND AND FARTHER NORTH
PUSH UP COOK INLET ON FRIDAY WHICH COULD MAKE IT TO THE ANCHORAGE
AREA.

SOUTHWEST...THE ATMOSPHERE IS MUCH MORE STABLE OVER SOUTHWEST ALASKA
WITH MOST OF THE CUMULUS CLOUDS DEVELOPING OVER ELEVATED TERRAIN WITH
MOSTLY CLEAR SKIES OVER LOWER ELEVATIONS. THIS SHOULD PERSIST INTO
TOMORROW UNDER THE UPPER LEVEL RIDGE. OFFSHORE FLOW SHOULD CONTINUE
TO KEEP THE STRATUS OVER MARINE AREAS THROUGH TOMORROW.

BERING SEA/ALEUTIANS...THE LARGE COMPLEX LOW HAS A FRONT MOVING
SLOWLY THROUGH THE CENTRAL BERING SEA WHICH WILL BRING RAIN TO THE
AREA OVERNIGHT. A SERIES OF THESE LOW WILL MOVE THROUGH OVER THE NEXT
FEW DAYS KEEPING THE RAIN AROUND.

.LONG TERM FORECAST...THE UPPER LEVEL RIDGE WILL BUILD AGAIN OVER
SOUTHWEST ALASKA FRIDAY AND MOVE OVER SOUTH CENTRAL ALASKA SATURDAY.
THIS WILL BECOME A BLOCKING RIDGE WITH THE POTENTIAL FOR VERY WARM
TEMPERATURES NEXT WEEK OVER SOUTH CENTRAL ALASKA...ESPECIALLY OVER
INLAND AREAS. SOUTHWEST ALASKA WILL REMAIN SOMEWHAT COOLER WITH AN
UPPER LEVEL LOW IN THE BERING SEA BRINGING MOIST AND COOLER AIR INTO
THAT AREA.

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

JUN 13