Small Craft Advisory 238, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
545 AM AKST WED MAR 9 2016

.SHORT TERM...A BROAD LOW PRESSURE REMAINS QUASI-STATIONARY OVER
THE SOUTHERN GULF OF ALASKA. THIS LOW WILL HAVE BANDS OF SHOWERS
AND HIGHER GUSTS MOVING NORTH THROUGH THE PANHANDLE, THEN WEAKEN
OVER THE NORTHEAST GULF. SHOWER ACTIVITIES WILL CONTINUE THROUGH
WEDNESDAY BEFORE DIMINISHING OVERNIGHT.

ON TUESDAY EVENING, AT AROUND 6 PM LOCAL TIME, AS ONE OF THE
STRONGER BAND OF SHOWERS MOVING THROUGH THE SOUTHERN PANHANDLE,
HYDABURG SEAPLANE BASE REPORTED A WIND GUSTS OF 61 MPH.
TEMPERATURES DROPPED 6 DEGREES, FROM 45 DEGREES TO 39 DEGREES IN 20
MINUTES. THE HIGH WIND GUST MAY BE CAUSED BY A WET MICROBURST, AS
THE LOWER PART OF THE ATMOSPHERE WAS RELATIVELY MOIST AND THE
MID-LEVEL WINDS WERE FAIRLY STRONG. THE MELTING OF ICE PARTICLE IN
HEAVIER SHOWERS MAY ALSO HAVE CONTRIBUTED TO THE POTENTIAL WET
MICROBURST.

AS OF EARLY WEDNESDAY MORNING, WE HAVE SHOWERS AND GUSTY WINDS IN
THE SOUTHERN PANHANDLE. THE SHOWER ACTIVITY IS ALSO EVIDENT ON THE
INFRARED SATELLITE IMAGERY. THE SHOWER ACTIVITY WILL SHIFT NORTH
THROUGH TODAY. PATCHY FOG ALSO FORMED IN AREAS WITH BREAKS IN THE
SKY COVER AND SHOWER ACTIVITY.

WITH THE LOW REMAINING IN THE SOUTHERN GULF AND HIGH OVER INTERIOR
BC, A GENERAL EASTERLY FLOW WILL BE ACROSS THE PANHANDLE. BY LATE
TONIGHT, ANOTHER LOW WILL TAKE SHAPE AND MOVE TOWARDS SOUTHERN
PANHANDLE. THE PRESSURE GRADIENT WILL BE REORIENTED SUCH THAT WINDS
WILL BECOME MOSTLY NORTHERLY ACROSS THE PANHANDLE.

UTILIZE ECMWF IN THE FORECAST PACKAGE. FORECAST CONFIDENCE IS ABOUT
AVERAGE. LOWER CONFIDENCE ON THE DETAILS SUCH AS TIMING AND
INTENSITY OF THE SHOWER ACTIVITIES.

.LONG TERM...LOW IN THE CENTRAL GULF ON THURSDAY BECOMES QUASI
STATIONARY IN THE CENTRAL GULF WHILE WEAKENING THROUGH THE EVENING.
AT THE SAME TIME A SECOND LOW MOVES UP FROM THE NE PACIFIC
TRACKING SOUTH OF HAIDA GWAII AND INTO BRITISH COLUMBIA. REMNANTS
OF THE FRONTAL BOUNDARY FROM THE FIRST SYSTEM WILL MOVE OVER THE
NE GULF AND DISSIPATE. THE SECOND LOW WILL MAINLY IMPACT AREAS
SOUTH OF THE PANHANDLE, BUT SECONDARY WRAP JUST HITS THE SOUTHERN
PANHANDLE THURSDAY EVENING. TO THE WEST A THIRD LOW THAT HAS BEEN
TRACKING EAST FROM KAMCHATKA WILL CROSS OVER THE ALEUTIANS THEN
INTO THE WESTERN GULF BY FRIDAY. THE LOW WILL CONTINUE ON A
SOUTHEASTERLY TRACK WITH FIRST FRONTAL BAND HITTING THE PANHANDLE
FRIDAY AND SECOND BANDS HITTING THE FAR SOUTHERN PANHANDLE AS THE
LOW MOVES SOUTH AND WEAKENS. AS THIS LOW MOVES TOWARD HAIDA GWAII
EXPECT A DRYING TREND THROUGH THE WEEKEND DUE TO OFFSHORE FLOW,
ESPECIALLY FOR THE CENTRAL AND NORTHERN PANHANDLE. FOR THE START
OF NEXT WEEK THE NEXT IN A SERIES OF WAVES BEGINS TO MOVE INTO THE
WESTERN GULF.

850 MB TEMPERATURES NOT SHOWING MUCH VARIATION COMPARED TO CURRENT
AIRMASS, SO WHILE A BASE LINE HIGH AND LOW STILL IN THE MID 40S
TO MID 30S REMAINS THE SAME DIURNAL VARIATION WILL BE MORE
IMPACTED BY CLOUD COVER. THE CLEARER NIGHTS FOR FRIDAY NIGHT AND
THE WEEKEND TO THE NORTH WITH RADIATIONAL COOLING WILL DROPS TEMPS
INTO THE 20S WHILE DAY TIME HIGHS MAY NUDGE BIT CLOSER TO 50.
AFTER A DRY THURSDAY THE COMBINATION FOR FRONTAL BANDS MOVING UP
FROM THE SOUTH AND WEST WILL MOVE IN PRECIP LATE THURSDAY NIGHT
INTO FRIDAY BUT DUE TO THE SPEED OF THE PARENT LOWS AND THE
SOUTHERLY TRACK WILL HAVE DRY WEATHER FOR THE NORTHERN HALF OF
PANHANDLE WIT CHANCE PRECIP TO THE SOUTH THROUGH MONDAY. THE DRY
PERIOD EXPECTED TO COME TO AN END MONDAY NIGHT INTO TUESDAY. NOT
MUCH IN WAY OF QPF WITH THESE WAVES THROUGH THE WEEKEND, ONLY A
FEW TENTHS.

MAIN IMPACT FROM THESE SYSTEMS WILL BE WINDS OVER THE GULF FROM
THE FRONTS AND OVER THE PANHANDLE AND INNER CHANNELS MAINLY DUE TO
PRESSURE GRADIENT. OVER THE GULF WINDS INCREASE AGAIN TO SMALL
CRAFT THURSDAY NIGHT WITH POTENTIAL GALE FORCE BARRIER JET BY
FRIDAY IN THE NE GULF. THESE WINDS DROP OVER THE COASTAL WATERS
BUT THE PICK UP AGAIN OVER THE SE GULF DUE TO THE LOW TRACKING
FROM THE ALEUTIANS TO THE SOUTHEAST. WINDS DROP OFF BY THE END OF
THE WEEKEND. INVERTED TROUGH OVER THE PANHANDLE ON THURSDAY AND
RESULTING PRESSURE GRADIENT PRODUCES NORTHERLY SMALL CRAFT WINDS,
MAINLY TO THE NORTH. OUTFLOW GRADIENT AND CROSS BARRIER FLOW
SETTING UP JUNEAU FOR MOUNTAIN WAVE ON THURSDAY. INVERSION MAY BE
A BIT LOW BUT CRITICAL LEVEL LOOKS FAVORABLE IN THE MORNING. FOR
NOW THINK HIGHER WINDS ARE ELEVATION BUT NO TRUE TAKU EVENT.
AFTER A SHIFT TO THE SOUTH THURSDAY NIGHT WINDS FLIP BACK TO THE
NORTH BETWEEN HIGH OVER YUKON THE THE HAIDA GWAII LOW WHILE
SOUTHERN AREAS WILL BE SOUTHEASTERLY DUE TO GEOSTROPHIC FLOW.

EARLY ON 00Z GFS/ECMWF WILL MORE IN LINE. NAM WAS CLOSE BUT WAS
BIT FASTER MOVING SYSTEMS IN AND OUT. UPDATED GRIDS TO DAY 4
USING THE GFS/ECMWF BLEND THEN KEPT WITH WPC. HOWEVER NEWER
GFS/ECMWF WERE SHOWING A MORE CONSOLIDATED LOW CENTER THAN WPC AND
BIT FURTHER EAST. WILL HAVE TO SEE IF NEXT RUNS STILL HAVE THIS
SAME SOLUTION. FORECAST CONFIDENCE IS BIT ABOVE AVERAGE.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING FOR PKZ043-051.
     SMALL CRAFT ADVISORY FOR PKZ012-013-021-022-031>033-035-036-041-
     042-052.
&&

RCL/PRB

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