Small Craft Advisory 42, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
400 AM AST THU JAN 11 2007

.DISCUSSION...

...SUMMARY...
SOUTHWEST FLOW IS NOW PRESENT OVER ALL OF THE FORECAST AREA...WITH A
RIDGE CENTERED OVER THE ALASKA/YUKON BORDER...AND AN UPPER LEVEL
TROUGH CENTERED BETWEEN THE WESTERN ALEUTIANS AND THE KAMCHATKA
PENINSULA NEAR THE COMMANDER ISLANDS. MUCH WARMER AIR IS PRESENT
THROUGH THE ENTIRE REGION IN BETWEEN...ALONG WITH NUMEROUS WEATHER
SYSTEMS IN FAST MOVING FLOW. THIS PATTERN WILL PERSIST FOR THE NEXT
WEEK.

...MODELS...
MODELS IN FAIR AGREEMENT ON MAJOR FEATURES. WHERE MINOR DIFFERENCES
EXIST...WE ARE SIDING WITH GFS...IN PARTICULAR WITH A SHORTWAVE
AROUND KODIAK ISLAND ON SATURDAY...WHICH THE GFS HAS WEAKER AND
FURTHER EAST THAN THE NAM/WRF. MODELS WILL MOST LIKELY BE SLOW IN
PICKING UP THE DEVELOPMENT OF LOWS IN THIS PATTERN...AS IS THE CASE
THIS MORNING WITH A SMALL LOW NEAR THE PRIBILOFS.

...SOUTHCENTRAL FORECAST SOUTH AND EAST OF THE ALASKA RANGE...
THE FIRST IN AN UPCOMING PARADE OF SYSTEMS HAS ARRIVED OVER
SOUTHCENTRAL...WITH AREAS OF RAIN AND SNOW...ALONG WITH MUCH WARMER
TEMPERATURES. THERE ARE SOME INTERESTING TOPOGRAPHICAL EFFECTS ON
THE PRECIPITATION THIS MORNING OVER SOUTHCENTRAL WITH LOWER LEVEL
SOUTHEASTERLY FLOW...STRONG IN AREAS...AND UPPER LEVEL SOUTH TO
SOUTHWEST FLOW. FOR ANCHORAGE...DESPITE THE FAVORABLE UP INLET
SOUTHWEST FLOW...DOWNSLOPE AND DRYING IS OCCURRING BECAUSE OF THE
STRONG LOW LEVEL SOUTHEASTERLY FLOW. THE HEAVIER PRECIPITATION IS
CONCENTRATED FROM THE FAR WEST EDGE OF THE KENAI TO THE WEST SIDE OF
COOK INLET...AND NORTH INTO THE SUSITNA VALLEY. THE UPPER LEVEL
SOUTHWEST FLOW IS HELPING TO DOWNSLOPE OUT THE EASTERN KENAI FROM
SEWARD UP TO WHITTIER AND PORTAGE WITH ONLY LIGHT SNOW IN THOSE
AREAS. SUBTLE CHANGES IN WIND DIRECTIONS AT VARIOUS LEVELS OF THE
ATMOSPHERE WILL MAKE ALL THE DIFFERENCE AS TO WHO EXACTLY GETS
PRECIPITATION OVER THE NEXT WEEK IN THIS SUPER MOIST SOUTH TO
SOUTHWEST FLOW. GENERALLY SPEAKING...IT WILL BE TOUGH FOR THE
ANCHORAGE BOWL AND MATANUSKA VALLEY TO GET SIGNIFICANT PRECIPITATION
OVER THE NEXT WEEK BECAUSE THE WINDS GENERALLY STAY EAST OF DUE
SOUTH AT LEAST AT SOME LEVEL OF THE ATMOSPHERE...WHICH MEANS
DOWNSLOPING MOST OF THE TIME. THERE MAY HOWEVER BE BRIEF PERIODS ON
THE TAIL END OF SHORTWAVES WHERE THE FLOW BECOMES JUST WESTERLY
ENOUGH FOR ANCHORAGE TO GET SNOW. ON THE OTHER HAND...THE WESTERN
SIDE OF COOK INLET UP INTO THE SUSITNA VALLEY WILL GET HAMMERED IN
THIS PATTERN. THE EASTERN KENAI OVER TO PRINCE WILLIAM SOUND WILL
ALSO BE VULNERABLE TO PRECIPITATION MOST OF THE TIME. TIMING OF THE
FREQUENT SYSTEMS IN THIS PATTERN WILL BE DIFFICULT. IN THE SHORT
TIME...EXPECT LITTLE BREAK IN THE PRECIPITATION OVER FAVORED AREAS
THROUGH SATURDAY...WITH A BIT OF A HEAVIER SHOT OF PRECIP FRIDAY
INTO FRIDAY NIGHT AS A STRONGER FRONT MOVES THROUGH. THE FLOW WILL
BECOME MORE SOUTHEAST TONIGHT AHEAD OF THIS SHORTWAVE.

NOW ONTO THE CHALLENGE OF TEMPERATURES. WITH THE MUCH WARMER
TEMPERATURES OVER SOUTHCENTRAL...RAIN VS SNOW WILL BE A CHALLENGE.
MODELS HAVE UNDERDONE THE DRAMATIC TRANSITION TO WARMER
TEMPERATURES...WITH RAIN EVEN MIXING IN THIS MORNING AS FAR NORTH AS
KACHEMAK BAY. BELIEVE THAT PRECIPITATION WILL REMAIN MOSTLY SNOW
THROUGH FRIDAY DAY NORTHEAST OF KACHEMAK BAY. HOWEVER...WITH
UPCOMING FRONTS...INCLUDING THE FRONT TO HIT THE NORTHERN GULF COAST
FRIDAY NIGHT...WARMER TEMPERATURES WILL MOVE IN...MEANING A CHANCE
OF RAIN MIXING IN FROM THE KENAI OVER TO CORDOVA FROM FRIDAY NIGHT
ONWARD.

...SOUTHWEST MAINLAND AND ALEUTIANS/BERING SEA FORECAST...
THROUGH SATURDAY...NUMEROUS SMALL LOWS...MANY LIKELY NOT TO BE
PICKED UP BY MODELS...WILL TRACK NORTHEAST THROUGH THE BERING AND
ALEUTIANS...BRINGING SHOTS OF RAIN AND SNOW. A STEADIER STREAM OF
MOISTURE FROM THE SOUTH WILL REMAIN AIMED AT THE SOUTHWEST MAINLAND
THROUGH SATURDAY...WITH PLENTY OF SNOW WITH RAIN SNOW MIXED AROUND
BRISTOL BAY. AFTER SATURDAY...ALTHOUGH UNSTABLE WEST TO SOUTHWEST
FLOW CONTINUES...THE CHANCE WILL EXIST FOR SOME STRONGER LOW
PRESSURE SYSTEMS ACROSS OR JUST SOUTH OF THE ALEUTIANS...AS A STRONG
JET STREAM INCHES NORTH CLOSER TO THE CHAIN AND SOME COLDER AIR
MOVES SOUTH INTO THE BERING. COLDER AIR MAY ALSO MOVE BACK INTO THE
SOUTHWEST MAINLAND BEGINNING SUNDAY...WITH SOMEWHAT LESS
PRECIPITATION FROM SUNDAY ONWARD.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HEAVY SNOW WARNING 145.
MARINE...GALE WARNINGS 120 130 132 150 176 185 350.
         HEAVY FREEZING SPRAY WARNING 140.

FOISY JAN 07