Small Craft Advisory 346, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
601 AM AKDT WED MAY 30 2012

.SHORT TERM...COMPLEX LOW OVER THE WESTERN GULF THIS MORNING
WITH VERY AMBIGUOUS OCCLUDED FRONTAL BOUNDARY VISIBLE IN
SATELLITE IMAGERY. RADAR DATA INDICATING PLENTY OF RAIN BUT HOLES
IN THE REFLECTIVITY ARE STARTING TO SHOW UP. SURFACE OBSERVATIONS
SHOWING WIDESPREAD BUT FAIRLY LIGHT PRECIPITATION THIS MORNING
FOR EVERYWHERE EXCEPT SOUTH CENTRAL PANHANDLE. KETCHIKAN HAS BEEN
REPORTING MODERATE RAIN THROUGH THE NIGHT. LIKEWISE FOR A SHIP IN
NORTHERN CLARENCE STRAIT. A POST FRONTAL SHORTWAVE CURRENTLY OVER
THE EASTERN GULF WILL ENHANCE PRECIP RATES BEGINNING THIS
EVENING.

 NO GALES IN THE MORNING FORECAST, BUT HAVE SOLID SMALL CRAFT
CONDITIONS OVER THE COASTAL MARINE WATERS THROUGH TONIGHT WITH
SMALL CRAFT WINDS OVER CROSS SOUND, ICY STRAIT, AND CLARENCE
STRAIT THIS MORNING. SOUTHWEST OUTER COAST DID SEE SOME STRONG
WIND GUSTS IN EXCESS OF 40 MPH LAST NIGHT, BUT WINDS HAVE
DIMINISHED, SO NO STRONG WIND HEADLINES THIS MORNING. PRESSURE
GRADIENT THIS MORNING IS PARALLEL TO THE NORTH-SOUTH INNER
CHANNELS WHICH HAS MADE CHARACTERIZING WIND DIRECTIONS OVER THESE
LOCATIONS PROBLEMATIC. WENT WITH A NORTH WIND BECOMING SOUTH FOR
GLACIER BAY AND SOUTHERN LYNN CANAL. WEAK NORTHERLY PRESSURE
GRADIENT OVER NORTHERN LYNN CANAL IS PRODUCING VARIABLE WINDS.
KEPT A SOUTHERLY FORECAST FOR THIS CHANNEL.

 OPTED TO CHARACTERIZE PRECIP FOR TODAY AND TONIGHT AS STRATIFORM
BASED ON STABILITY PARAMETERS IN 12Z UPPER AIR DATA AS WELL AS
FORECAST UPPER AIR SOUNDINGS. RADAR IS BEGINNING TO SHOW SIGNS OF
A TRANSITION TO CONVECTIVE PRECIPITATION, SO WILL HAVE TO WATCH
THIS TREND AND RE-CHARACTERIZE PRECIPITATION AS SHOWERS LATER
TODAY IF NECESSARY. WHETHER SHOWERS OR RAIN, QPF VALUES NOT
OVERLY HIGH. TOTAL PRECIPITABLE WATER VALUES FROM AMSU SATELLITE
DATA INDICATING MOISTURE PLUME WITH TROPICAL ORIGINS IS NOW SOUTH
OF MOST OF THE PANHANDLE AND MORE OF AN ISSUE FOR WESTERN
WASHINGTON STATE. POSSIBLE EXCEPTION WOULD BE SOUTH CENTRAL
PANHANDLE WHERE MODERATE RAINFALL RATES REFERENCED ABOVE ARE
CONTINUING THIS MORNING.

 MODEL INITIALIZATION - GFS SURFACE WINDS A BETTER MATCH TO
OBSERVATIONS, BUT NAM UPPER LEVEL JET INITIALIZATION BETTER BASED
ON SATELLITE WINDS AND LOCAL AREA PROFILERS. NO SIGNIFICANT
DIFFERENCES BETWEEN MODELS ON SURFACE PRESSURE OVER THE EASTERN
GULF, HOWEVER ONLY NAM AND ECMWF ARE INITIALIZING 2 SEPARATE
PRESSURE CENTERS OVER THE WESTERN GULF AS EVIDENCED IN SATELLITE
IMAGERY. GFS MID LEVEL MOISTURE SLIGHTLY BETTER THAN ECMWF. USED
A BLEND OF 00Z AND 06Z NAM FOR PRESSURE AND WIND. BLENDED HIGH
RESOLUTION NAM AND ECMWF FOR POP AND QPF. TAMPS ADJUSTED USING
GFS40 AND BIAS CORRECTED MOS. FORECAST CONFIDENCE IS AVERAGE.

.LONG TERM...THE SYNOPTIC PATTERN THROUGH THE WEEKEND REMAIN UNSETTLED
WITH A UPPER LEVEL LOW SPINNING OVER THE GULF. UPPER TROFS OF LOW
PRESSURE WILL ROTATE OVER THE PANHANDLE ONE ON THURSDAY THEN
ANOTHER AND STRONGER ONE FRIDAY NIGHT THROUGH SAT. A SURFACE RIDGE
OF HIGH PRESSURE WILL PERSIST OVER THE FORECAST AREA THROUGH
THURSDAY NIGHT THEN A WEAKENING LOW PRESSURE SYSTEM WILL DRIFT OUT
OF THE NORTH PACIFIC AND OVER THE SOUTHERN PANHANDLE FRIDAY. WINDS
OVER THE INNER CHANNELS WILL BE 10 TO 20 KT FROM THE SOUTH ON
THURSDAY WITH THE SURFACE RIDGE OVER THE SE AK. THIS RIDGE WILL
WEAKEN ALONG WITH THE WINDS THROUGH THURSDAY NIGHT AS THE LOW
MOVES OVER THE SOUTHERN AREAS. THIS WILL TURN THE WINDS AROUND TO
THE NORTH BUT WILL BE ON THE LIGHT SIDE WITH A WEAK PRESSURE
GRADIENT. AS THE LOW LIFTS OVER THE CENTRAL AREAS FRIDAY THE WINDS
WILL INCREASE FROM THE SOUTH TO BE NEAR 15 KT BUT AGAIN THE WINDS
WILL RELAX THROUGH SAT.

RAIN SHOWERS WILL PERSIST OVER THE MOST OF THE FORECAST AREA EARLY
THURSDAY BUT BECOME SCATTERED BY THURSDAY NIGHT. THERE WILL BE A
LITTLE BREAK IN THE SHOWERS ON FRIDAY OVER THE NORTHERN AREA BUT
THE SOUTHERN AREAS WILL SEE SHOWERS LIKELY WITH THE LOW MOVING
OVER THE AREA.

FOR THE REST OF THE WEEKEND INTO EARLY NEXT WEEK WITH THE UPPER LOW
REMAINING OVER THE GULF. THERE WILL BE A CHANCE OF SHOWERS WITH
SOME BREAKS DEVELOPING SUN/MON WITH INCREASING OFFSHORE FLOW.
THERE IS SOME INDICATION THAT THERE WILL BE ENOUGH MOISTURE OVER
CANADA THAT A THE THREAT OF PRECIP WILL INCREASE.

TEMPS WILL REMAIN BELOW NORMAL FOR THIS TIME OF YEAR WITH 850 MB
TEMPS RANGING FROM 0C TO -2C. THERE WILL SOME WARMING ON
FRIDAY...SO I INCREASED THE HIGHS BUT FOR THE MOST PART LOWER THE
HIGHS ACROSS THE AREA AND RAISED THE LOWS SOME.

THERE LOOKS TO BE GOOD MODEL AGREEMENT THROUGH THE WEEKEND SO THERE
IS AVERAGE FORECASTER CONFIDENCE. THERE WAS NOT MUCH CHANGE TO
THE OVERALL FORECAST FROM THE PREVIOUS PACKAGE. JUST SOME MINOR
TWEAKS WERE MADE. WITH THE SAID USED A BLEND OF THE INHERITED
FORECAST WITH THE LATEST GFS IN THE MID RANGE.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING FOR PKZ052.
         SMALL CRAFT ADVISORY FOR PKZ021-022-035-036-041>043-051.

&&

FRITSCH/ABJ