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000
FXAK67 PAJK 062340
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
340 PM AKDT WED MAY 6 2015

.SHORT TERM...AN OCCLUDED FRONT WILL MOVE INTO THE NORTHEAST GULF
TONIGHT AND SHOVE A SHARP RIDGE OVER THE EASTERN GULF INTO THE
PANHANDLE TONIGHT. THIS FRONT WILL VEER WINDS SOUTHEAST TO SOLID
SMALL CRAFT ACROSS FOR MOST OF THE OUTSIDE WATERS TONIGHT...
INCREASING TO GALE LATE TONIGHT/EARLY THURSDAY MORNING FOR MARINE
ZONE 52. THE FRONT WEAKENS THURSDAY AFTERNOON AS AN UPPER LEVEL
RIDGE EXTENDS INTO THE NORTHEAST GULF AHEAD OF A NEW SYSTEM
AFFECTING THE LONG TERM FORECAST PERIOD.

THE SURFACE RIDGE USHERED A MARINE STRATUS DECK INLAND INTO
YAKUTAT AND THROUGH CROSS SOUND AND ICY STRAIT LATE TUESDAY
AFTERNOON INTO TUESDAY NIGHT. VISIBLE IMAGERY INDICATES SOME
REMNANTS OF THIS DECK DROPPING SOUTH-SOUTHWEST OFFSHORE, WHICH
INDICATES THE SURFACE RIDGE HAS YET TO CROSS YAKUTAT. WHILE THERE
IS THE POSSIBILITY THAT THE DECK REFORMS THIS EVENING TO MAKE A
WEAK PUSH INLAND AGAIN, WE THINK THE DYNAMICS OF THE OCCLUSION ON
ITS WAY NORTHEAST AND THE MIGRATING RIDGE EASTWARD SHOULD PREVENT
THIS FROM HAPPENING. THE STRATUS DECK PROVED MORE RESILIENT TODAY
OVER SOME ICY STRAIT COMMUNITIES THAN WE ORIGINALLY THOUGHT.
WITH MOISTURE WELL DECOUPLED FROM THE SURFACE AND AN UPPER LEVEL
RIDGE OVERHEAD, OUR ATMOSPHERIC STABILITY HELPED SUSTAIN IT. WITH
SOUTHWEST FLOW AT THE MID-LEVELS INCREASING FROM THE WEST, LAYERS
WILL MOISTEN ACROSS THE PANHANDLE RESULTING IN MIDLEVEL CLOUDS
SLIDING INTO THE PANHANDLE TONIGHT FROM THE GULF. CLOUDS WILL
ENVELOP THE ENTIRE PANHANDLE TOMORROW AS THE WEAKENED OCCLUSION
MOVES ASHORE.

THE FRONT WILL PUSH RAIN INTO THE NORTHEAST GULF WATERS TONIGHT...
MOST LIKELY HOLDING OFF UNTIL THURSDAY MORNING FOR YAKUTAT.
STRONGER DYNAMICS WILL ENSURE THE HIGHEST CONFIDENCE FOR RAIN WILL
REMAIN OVER YAKUTAT DURING THE SHORT-TERM PERIOD, BUT THERE MAY BE
SUFFICIENT ASCENT TRAILING SOUTHEASTWARD FOR A LITTLE RAIN OVER
THE NORTHERN PANHANDLE, PARTICULARLY THE COAST ON THURSDAY. OMEGA
VALUES REPRESENTING UPWARD MOTION ARE WEAKER HERE THAN OVER
YAKUTAT.

THE PERSISTENT MARINE LAYER SEEMS TO HAVE SOFTENED THE EXPECTED
SHARPER THERMAL GRADIENT BETWEEN THE GULF WATERS AND INSIDE
COMMUNITIES...THUS SEA/CHANNEL BREEZES HAVE NOT BEEN AS STRONG.
NORTHERN LYNN CANAL HAS SEEN LIGHT WINDS MOST OF THE MORNING.
STILL THINK THESE WILL RAMP UP THROUGH THE AFTERNOON BEFORE
RELAXING TONIGHT. TO THE SOUTH WHERE CLOUD COVER WAS THINNER,
OCEAN ENTRANCE BREEZES WERE MORE ROBUST. CAPE DECISION PUSHED TO
NEAR 20 KT TODAY FROM THE WEST. AND CLARENCE STRAIT SAW A GOOD
SOUTHERLY. DUE TO CLOUD COVER AND THE FRONTAL TENDENCY FOR WINDS
TO FLIP EASTERLY, WINDS SHOULD FOLLOW THE GREATER SYNOPTIC PATTERN
TOMORROW RATHER THAN ALLOW MESOSCALE PROCESSES TO DICTATE. WE DID
RAISE SOUTHERLY WIND SPEEDS JUST A HAIR THURSDAY AFTERNOON.
DEPENDING ON THE STRENGTH OF THE FRONT, THEY MAY NEED A LITTLE
MORE INCREASING.

USED ECMWF/NAM/ARW/NMM FOR WINDS/POP/QPF. FORECAST CONFIDENCE
GOOD.

.LONG TERM...FIRST FRONT IN THE OVERALL STRONG S FLOW ALOFT
DEVELOPING CURRENTLY IN THE GULF WILL BE EXITING THE FAR NORTHERN
PANHANDLE (MOSTLY YAKUTAT) AT 03Z FRI. NEXT FRONT IS MORE
ORGANIZED AND STEMS FROM A TIGHT CLOSED LOW THAT DEVELOPS AS IT
MOVES INTO THE SOUTHERN GULF LATE THURS. TRACKS NORTHWARD RIGHT THRU
THE CENTRAL GULF AND NORTHWESTWARD TOWARDS A POSITION WEST OF
YAKUTAT BY 00Z SAT AT THE SURFACE WITH THE UPPER CLOSED LOW JUST BEHIND.
THIS PUTS YAK IN THE PRECIP BULLSEYE AND TAKES A MOVING FRONT
THROUGH ALL OF THE PANHANDLE. ABOUT 12 HRS OF PRECIP EXPECTED OVER
THE LATTER BUT YAKUTAT GETS A DIRECT HIT AND MORE WINDS. NAM RUN
HAS UPWARDS OF 3" QPF THROUGH 84 HRS...GFS IS AT 2.3 WHILE EC JUST
ABOUT 2". ADDITIONAL RAINS WILL FALL AFTER SUN 00Z AT YAK BUT FOR
NOW THE PREDICTIONS ARE RELATIVELY LIGHT, A QUARTER TO A HALF INCH
BY MON 12Z. THUS WITH CURRENT LOW LEVELS OF THE SITUK (65.5 FEET)
FLOOD THREAT BEARS WATCHING BUT CURRENTLY IS LOW. LATEST RFC
PREDICTION HAS THE SITUK AT ONLY 65.7 FEET AT 07Z ON OR SO ON SAT
BUT THAT IS PRIOR TO A PORTION OF THE MAIN PUSH OF THE 2ND FRONT.
INHERITED PRESSURE/WIND GRIDS WERE FINE ON THIS SCENARIO THRU FRI.
THIS FRONT SHOULD ALSO BRING GALES TO THE MARINE ZONE 52 AS WELL
AS 30KT+ TO 310 AND THE REST OF THE NORTHERN OFFSHORE ZONES FRIDAY
AND SATURDAY. GRADIENTS CONCENTRATED OFFSHORE AS WE ARE MISSING A
CONTINENTAL HIGH TO CONCENTRATE THE PRESSURE DIFFERENCE INSHORE.
THUS MAIN WIND IMPACT INSHORE WILL BE AT CROSS SOUND. FOR THE
GRIDS LATER FRI AND SAT. WENT WITH A EC/NAM COMBO ON BOTH DYNAMIC
AND T/D FIELDS. MOS NUMBERS DICTATED A WARMUP ON FRI WITH THE
SOUTHERLY FLOW AHEAD OF THE FRONT. SAME WITH MIN TEMPS SAT
MORNING. INTO SUN CHOSE EC/NAM PRESSURE FIELDS WITH TPRES WINDS
ALONG WITH TWEAKS. SHOULD BE NOTED THAT 18Z NAM HAS SIGNIFICANTLY
LESS QPF THAN THE 12Z RUN OVER THE SOUTHERN 2/3 OF THE PANHANDLE
WITH THE SATURDAY FRONT.

CHALLENGE FOR NEXT WEEK IS CHOOSING AN ACCURATE MODEL/OR COMBO. AT
96 HOURS MODEL AGREEMENT IS RELATIVELY STRONG...IN FACT GFS/EC/GEM
COMPARISON IS FAVORABLE THRU MID- MONDAY. BUT AT TIME THE 12Z GFS
WEAKENED THE TIGHT REMNANT OF THE WEEKEND LOW AND KEPT IT STATIONARY
AS ANOTHER CLOSED LOW PHASES IN FROM THE WEST AND REINFORCES THE NORTHERN
GULF TROUGHING. THIS WAS IN CONTRAST TO THE 12Z EC/GEM WHICH
KICKED THE OLD LOW SOUTHEASTWARD AS A STRONG UPPER RIDGE BUILT
INTO THE WESTERN GULF BY TUES/WED, SPREADING EASTWARD. THEN THE
18Z GFS ARRIVED AND ITS AGREEMENT WITH THE 12Z EC/GEM IS STRONG.
WPC (PARTLY MEETING ITS DEADLINES) WENT WITH THE GFS THROUGH
MONDAY OR SO, PRIOR TO THE NEW EC AND GFS RUNS WITHOUT MUCH
CONFIDENCE. HOWEVER TUES ONWARD THEY WENT WITH THE EC ENSEMBLE/GEM
SOLUTION...FORTUNATELY. 18Z MODEL UPDATE BOOSTS CONFIDENCE IN THE
APPROACH WITH THE GRIDS CHOSEN TO GO HERE...WITH THE EC/GEM IN THE
MID- RANGE AND EVOLVING TO WPC AFTER DAY 5 OR SO. IN HINDSIGHT
WOULD HAVE IGNORED THE GFS RUNS COMPLETELY THROUGH 12Z THIS
MORNING. AT ANY RATE...THE RESULT IS PRECIP-FREE ZONES IN THE
EXTENDED FOR THE TUES-WED PERIODS, WITH UPPER RIDGING DOMINATING
AND WEAK GRADIENTS. FORECAST CONFIDENCE ENDS UP BEING ABOVE
AVERAGE FOR THIS SCENARIO THROUGH THE MIDDLE OF NEXT WEEK.


&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING FOR PKZ052.
         SMALL CRAFT ADVISORY FOR PKZ043-051.

&&

$$

JWA/WESLEY

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