Small Craft Advisory 177, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
351 PM AKST SAT MAR 3 2012

.SHORT TERM...
A 998 MB LOW QUASI-STATIONARY JUST EAST OF PAMD CONTINUES TO
SLOWLY FILL TODAY AND IS FORECAST WOBBLE OFF TO THE WEST TONIGHT.
A WEAK DISTURBANCE UNDER THE BASE OF THE UPPER TROUGH NEAR 57N
148W IS FORECAST TO ROTATE NW INTO THE NE GULF TONIGHT AND DEVELOP
INTO A 1003 MB LOW. THIS LOW THEN SLOWLY TRACKS OFF TO THE SE ON
SUNDAY.

 SATELLITE SHOW EXTENSIVE OPEN CELL CU ACROSS THE GULF WITH RADAR
INDICATING SCATTERED SHOWERS. THE CLOUDS STRATIFY A BIT ACROSS
SOUTHEAST ALASKA TERRAIN WITH MAINLY CLOUDY SKIES ALTHO SOME
BREAK HAVE OPENED UP THROUGH THE CENTRAL AND SOUTHERN INNER
CHANNELS. WITH TEMPS ALOFT ON THE COOL SIDE AND CAA IN SW FLOW
MOVING ACROSS THE GULF THESE SHOWERS ARE ALMOST ALL SNOW SHOWERS
WITH SOME RAIN MIXED IN ACROSS SOUTHERN AND COASTAL AREAS. THESE
SHOWERS WILL CONTINUE TO MOVE ONSHORE THROUGH SUNDAY. HEAVIEST
PRECIP WILL THE ALONG COAST WITH PAYA HAVING POTENTIAL FOR 1 TO
3 MORE INCHES SNOW TONIGHT BEFORE TAPERING OFF TONIGHT. ELSEWHERE
QPF AMOUNTS AROUND 1 TENTH OF AN INCH OF WATER OR AROUND 1 INCH
OF SNOW. WITH SOME BREAKS IN CLOUD COVER AND COLD AIR ALOFT
SHOULD SEE TEMPS DROP INTO THE UPPER 20S TO NEAR FREEZING
TONIGHT.

 STILL HAVE A MODERATE SLY GRADIENT THROUGH INNER CHANNELS WITH
LYNN CANAL AND STEPHENS STILL AT SMCR LEVELS. THIS WILL EASE
TONIGHT THROUGH SUNDAY. WINDS IN THE FAR NORTH INNER CHANNELS
GAIN A NORTHERLY COMPONENT AS HIGH PRESS RIDGE BUILDS OVER YUKON
BY LATE SUNDAY AFTERNOON AND SHOULD SOME CLEARING PAYA-PAHN BY
LATE AFTERNOON.

 OFFSHORE HAVE A SOLID SW SMCR ACROSS ALMOST ALL GULF. SEAS
REMAIN HIGH WITH 12 TO 16 FOOT RANGE WITH A SIGNIFICANT SW SWELL.
AKWAVE HINTING SEE INCREASE A TOUCH ACROSS THE SOUTHERN GULF AS
WEAK DISTURBANCE MOVES THROUGH BUT IT HAS BEEN RUNNING A FEW FEET
HIGH LATELY.

 GOOD AGREEMENT AMONG MODELS THROUGH THE SHORT TERM AND DID NOT
HAVE A STRONG MODEL PREFERENCE. USED THE 12Z NAM12 FOR PRES AND
WIND.

.LONG TERM...THE FORECAST MODELS ARE IN FAIR AGREEMENT THROUGH TUE
NIGHT WITH THE GFS BEING A SLOW OUTLIER WITH THE FRONT MOVING
INTO THE GULF MON NIGHT AND OVER THE PANHANDLE TUE. USED A BLEND
OF THE NAM/EC THROUGH TUE NIGHT BUT THAT DID CHANGE THE FORECAST
THAT MUCH. THE BIGGEST CHANGE WAS TO INCREASE THE WINDS OVER LAND
AND MARINE WATERS MON NIGHT INTO TUE. FROM WED THROUGH NEXT
WEEKEND REFRESHED THE FORECAST WITH THE LATEST HPC GUIDANCE.
THERE IS ABOUT AVERAGE FORECASTER CONFIDENCE THROUGH TUE WITH
BELOW AVERAGE FOR THE REST OF THE WEEK.

AT THE START OF THE LONG TERM PERIOD A UPPER LOW WILL BE SLIDING
SE OVER THE PANHANDLE. THIS UPPER LEVEL FEATURE WILL PRODUCE SOME
SNOW SHOWERS MAINLY OVER THE SOUTHERN HALF AS BEHIND THE UPPER LOW
OFFSHORE FLOW WILL INCREASE AND THE SKIES WILL BECOME PARTLY
CLOUDY. THIS WILL ALLOW TEMPS TO FALL INTO THE LOWER 20S OVER THE
SOUTHERN AREAS AND IN THE TEENS OVER THE NORTHERN AREAS. CLOUDS
WILL INCREASE FROM THE WEST THROUGH MON AS THE UPPER RIDGE TIPS
OVER AND WARM AIR ADVECTION INCREASES.

A WEATHER FRONT WILL MOVE ACROSS THE GULF MON NIGHT AND OVER THE
PANHANDLE THROUGH TUE. P-TYPE WITH THIS SYSTEM WILL BE TRICKY AS A
RIDGE WILL BUILD AND SHARPEN THROUGH MON NIGHT AND BEGIN TO
INCREASE THE SE FLOW. MOST PLACES WILL START OUT AS SNOW MON NIGHT
AS PRECIP SPREADS FROM THE NW TO SE. THE SNOW WILL MIX OR CHANGE
OVER TO ALL RAIN THROUGH TUE WITH SE WINDS CONTINUING TO INCREASE
AND MIX DOWN SOME WARMER AIR TEMPS. THE DEW POINTS MAY STAY AROUND
FREEZING SO SOME SNOW MAY STILL FALL BUT WITH LITTLE
ACCUMULATIONS. THE EXCEPTION TO THIS WILL BE THE FAR INNER
CHANNELS WHERE THEY COULD GET SOME SIGNIFICANT SNOW AMOUNTS. THE
WINDS OVER THE INNER CHANNELS WILL INCREASE TO MAX SMALL CRAFTS TO
GALES BY LATE MON NIGHT WITH WINDY CONDITIONS OVER THE FAR
NORTHERN INNER CHANNELS. THE RIDGE WILL PERSIST OVER THE AREA
THROUGH TUE NIGHT AS THE LOW MOVES INTO THE YUKON TO KEEP THE
SOUTHERN S WINDS GOING INTO TUE NIGHT. THE LOW WILL DRIFT EAST AND
THE PRESSURE GRADIENT WILL WEAKEN INTO WED.

FOR THE REST OF THE WEEK THE MODELS CONTINUE TO BE OUT OF PHASE
WITH THE TIMING OF LOWS MOVING INTO THE GULF. BUT MOST MODELS AND
ENSEMBLES AS POINT TO A SIGNIFICANT LOW MOVING INTO THE GULF FROM
THE NORTH PACIFIC LATE IN THE WEEK.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ012-022-031-041>043-051>053.

&&

MM/ABJ