Small Craft Advisory 470, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
203 PM AKDT THU AUG 18 2011

.SHORT TERM...A WEAK SURFACE RIDGE OVER THE PANHANDLE TODAY WILL
CONTINUING MOVING EAST AND WILL BE EAST OF THE AREA BY FRIDAY
MORNING. UPPER LEVEL FLOW REMAINS ZONAL BUT IS EXPECTED TO GAIN A
LITTLE AMPLITUDE THIS EVENING BUT OPENS UP INTO A LONG FETCH OF
SW FLOW BY LATER TONIGHT. A LOW IS BEGINNING TO DEVELOP NEAR
KODIAK THAT IS EXPECTED TO DEEPEN TO AROUND 983 MB BY FRIDAY
AFTERNOON. A WARM FRONT IS MOVING INTO THE SOUTHEAST GULF THAT
WILL MOVE NE AND ACROSS SOUTHEAST ALASKA THROUGH FRIDAY.

 SATELLITE SHOWS MAINLY CLOUDY SKIES ACROSS THE REGION TODAY.
THERE AREA A FEW BREAKS IN THE CLOUDS IN LEE OF HIGHER WESTERLY
RIDGES. AN ENHANCED AREA OF MARINE CLOUDS IS CURRENTLY PUSHING
INTO SOUTHERN ZONES THAT WILL SPREAD ACROSS ALL OF SOUTHEAST
ALASKA BY FRIDAY MORNING. INCREASING MID AND HIGH CLOUDS ARE ALSO
MOVING OVER THE NORTHERN PANHANDLE. A VERY MOIST AIR MASS WILL
SPREAD ACROSS THE AREA LATE TONIGHT THROUGH FRIDAY WITH
PERCEPTIBLE WATER VALUES INCREASING TO BETWEEN 1.0 AND 1.5 INCHES
BY FRIDAY AFTERNOON.

 HAVE ONLY ISOLATED SHOWERS ALONG THE MOUNTAINS THIS AFTERNOON
AND EVENING. RADAR INDICATING LEAD PRECIP AHEAD OF WARM FRONT
ALREADY INTO COASTAL WATERS AT THIS TIME. RAIN WILL SPREAD INTO
SOUTHERN COASTAL AREAS THIS EVENING AND WILL BE LIKELY FOR ALL
PANHANDLE BY FRIDAY MORNING. CATEGORICAL RAIN IS IN STORE FOR ALL
PANHANDLE ON FRIDAY AS WARM FRONT PUSHES INLAND. RAINFALL RATES
COULD BE MODERATE ALONG COAST MOUNTAINS IN THE MORNING.

 SE WINDS WILL BE ON THE INCREASE IN COASTAL WATERS TONIGHT AND
THROUGH SOUTHERN TWO THIRDS OF INNER CHANNELS FRIDAY. SE WINDS
INCREASE TO SMCR THIS EVENING AND TO GALE FORCE WITH BARRIER
EFFECTS FOR PKZ51 BY FRIDAY MORNING. A SOLID SMCR REMAINDER OF
COASTAL WATERS. FAVORABLE GRADIENT ORIENTATION WITH FRONTAL
TROUGH EXPECTED TO PUSH SE WINDS TO 25 KT FOR MUCH OF SOUTHERN
AND CENTRAL INNER CHANNELS ON FRIDAY. IN THE NORTH HAVE A SMCR
SLY IN LYNN CANAL NOW THAT WILL DIMINISH IN ADVANCE OF FRONTAL
TROUGH TONIGHT INTO EARLY FRIDAY. WILL SEE SUSTAINED WIND OF
15 TO 25 MPH WITH GUSTS PUSHING 35 MPH FOR PUBLIC ZONES ON
FRIDAY. SEAS WILL BE ON THE RISE AND FORECAST TO BE 7-10 FEET BY
FRIDAY AFTERNOON.

 NO MODEL ISSUES IN SHORT TERM WITH GOOD AGREEMENT. USED 12Z
NAM12 TO UPDATE GRIDS WHICH WAS A BIT FASTER WITH THE ONSET OF
PRECIP TONIGHT.

.LONG TERM...A VERY WET AND WINDY PERIOD IS IN STORE FOR THE AREA
FRI NIGHT INTO SAT NIGHT...AS A STRONG AND JUICY FRONTAL SYSTEM
MOVES SLOWLY ACROSS THE AREA. A LOW PRESSURE WAVE WILL DEVELOP ON
THE FRONT AND MOVE NE ACROSS THE CENTRAL PANHANDLE SAT EVENING.
THE FRONT SHOULD FINALLY MOVE E OF THE AREA BY LATE SAT NIGHT.
OLD PARENT LOW WILL SWING INTO THE SW GULF SAT...THEN WEAKEN TO A
TROF AS IT MOVES INTO THE ERN GULF SUN. WILL ALSO HAVE A LOW
REMAIN OVER THE NW GULF THROUGH SUN AT LEAST. ENDED UP USING A
BLEND OF THE 12Z NAM AND 00Z ECMWF 00Z SAT TO 00Z MON...THEN WENT
WITH HPC PRESSURE AND WINDS FOR 12Z MON ON OUT.

WINDS WILL BE STRONGEST OVER THE GULF AHEAD OF THE FRONT FRI NIGHT
AND SAT...WITH INNER CHANNEL WINDS STRONGEST DURING LATE FRI NIGHT
THRU SAT EVENING ESPECIALLY OVER THE SRN AREA. WIND GUSTS MAY GET
TO 40-50 MPH OVER THE SRN AND COASTAL AREAS LATE FRI NIGHT THRU
LATE SAT EVENING. CLARENCE STRAIT WINDS WILL GET RATHER STRONG SAT
INTO SAT EVENING...WITH 40-45 KT SE WINDS LIKELY THERE. WINDS
SHOULD SETTLE DOWN IN MOST AREAS ONCE FRONT MOVES THRU THE AREA
SAT NIGHT.

FOR SUN ON OUT...ONSHORE FLOW WILL PERSIST AND WILL SEE SEVERAL
SHORTWAVES MOVE THRU THE AREA SUN INTO MIDWEEK. WILL KEEP POPS ON
THE HIGH SIDE FOR THIS PERIOD BUT INDICATE A GRADUAL DECREASE THRU
THE PERIOD AS TIMING OF THE SHORTWAVES BECOMES TRICKY FURTHER
OUT.

.HYDROLOGY...LOOKING LIKE VERY HEAVY RAINFALL ESPECIALLY OVER THE
SRN HALF OF THE AREA FRI NIGHT INTO SAT NIGHT. SHOULD SEE A
GENERAL 1-3 INCH RAINFALL OVER THE N AND 3 TO 6 INCHES OVER THE S
DURING THIS TIME...WITH LOCALIZED AMOUNTS OVER 8 INCHES POSSIBLE
ESPECIALLY ALONG S-SW FACING SLOPES...WITH PRECIP WATER VALUES OVER
1.5 INCHES ALONG AND AHEAD OF THE SLOW MOVING FRONT. AFTER COORD
WITH APRFC...AM ISSUING A FLOOD WATCH FOR THE ZONES S OF FREDERICK
SOUND FROM 12Z SAT TO 12Z SUN. IT IS POSSIBLE THAT ZONE 25 MAY
NEED AN URBAN/SMALL STREAM FLOOD ADVY FOR FRI NIGHT AND SAT
ALSO...BUT THIS IS A LOWER CONFIDENCE FORECAST THAN FOR AREAS
FURTHER S.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...FLOOD WATCH FROM LATE FRIDAY NIGHT THROUGH LATE SATURDAY NIGHT
     FOR AKZ026>029.
MARINE...GALE WARNING FOR PKZ052.
         SMALL CRAFT ADVISORY FOR PKZ012-021-022-033>036-041>043-051.

&&

MM/RWT