Gale Warning 171, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
346 PM AKDT TUE APR 15 2014

.SHORT TERM...A WEAK MID LEVEL CIRCULATION IS LOCATED OVER THE
CENTRAL PANHANDLE AS OF EARLY THIS AFTERNOON. THIS LOW HAS BEEN
PRODUCING PRECIPITATION OVER THE SOUTHERN ZONES ALL MORNING WHICH
THEN SPREAD INTO SITKA SHORTLY AFTER NOON. AROUND THE SAME TIME,
RAIN OVER KETCHIKAN ENDED. BELIEVE PRECIP WILL FOR THE MOST PART
DRY UP THIS EVENING WITH GREATEST CHANCE FOR RAIN REMAINING ALONG
THE OUTER COAST AND OVER THE COAST MOUNTAINS. NO STRONG SIGNALS
IN THE 700 MB OMEGA FIELD OR THE MID LEVEL VORTICITY PATTERNS,
THOUGH, SO CONFIDENCE IN THIS ASPECT OF THE AFTERNOON FORECAST IS
NOT VERY HIGH. SITUATION MUCH THE SAME TOMORROW MORNING. BY
TOMORROW AFTERNOON, A FRONT ASSOCIATED WITH A DEVELOPING GALE
FORCE LOW WILL APPROACH THE PANHANDLE FROM THE SOUTHWEST AND
SPREAD RAIN INLAND. AS OF THIS AFTERNOON, NO HEAVY PRECIP
EXPECTED.

 A VERY WEAK PRESSURE GRADIENT REMAINS OVER SOUTHEAST ALASKA AS
OF THIS AFTERNOON. WINDS HAVE BEEN GENERALLY 10 MPH OR LESS OVER
LAND AND 20 KTS OR LESS OVER THE INNER CHANNELS WITH WEAK SEA
BREEZES OCCURRING UNDER MOSTLY CLOUDY SKIES. A NORTHERLY/EASTERLY
PRESSURE GRADIENT WILL SET UP THROUGH THE DAY TOMORROW AS THE
FRONT AND ITS ASSOCIATED LOW DRAWS NEAR. BY THE END OF THE DAY,
AM EXPECTING EASTERLY 30 KT SMALL CRAFT WINDS OVER THE SOUTHERN
COASTAL MARINE ZONES WITH 25 KT SMALL CRAFT WINDS OVER THE
REMAINDER OF THE COASTAL ZONES AS WELL AS CLARENCE STRAIT.
ELSEWHERE OVER THE INNER CHANNELS, 15 TO 20 KTS.

 USED A BLEND OF 12Z NAM AND GEM FOR ADJUSTMENTS TO PRESSURE AND
WIND. POP AND QPF FROM A BLEND OF GFS, GEM, AND ECMWF WITH MIDDLE
POP VALUES REMOVED. TEMPS ADJUSTED PER BIAS CORRECTED SREF.
OVERALL CONFIDENCE IS AVERAGE.

 .LONG TERM...ABNORMALLY ACTIVE WEATHER PATTERN CONTINUES. FIRST
STORM SYSTEM TO IMPACT THE AREA FROM WEDNESDAY NIGHT INTO
THURSDAY. THEN A STRONGER SECOND SYSTEM FOR THE WEEKEND.

 THE START OF THE LONG TERM FORECAST PERIOD WILL FEATURE AN
INTENSIFYING GALE FORCE LOW MOVING FROM THE NORTH PACIFIC TOWARDS
THE OUTER COAST. COMPARED TO PREVIOUS FORECAST PACKAGE, THE
CURRENT FORECAST IS THAT THIS LOW WILL BE STRONGER AND CLOSER TO
THE OUTER COAST, WHICH TRANSLATE TO A TIGHTER PRESSURE GRADIENT
OVER THE SOUTHERN PANHANDLE. FOR WEDNESDAY NIGHT INTO THURSDAY,
BUMP UP THE WINDS FOR SOUTHERN BARANOF ISLAND, PRINCE OF WALES
ISLAND, AND KETCHIKAN AREA TO STRONG WIND LEVEL, AND PUT IN GALE
FORCE WINDS FOR CLARENCE STRAIT. WITH A STRONGER LOW OFFSHORE,
THERE WILL ALSO BE A TIGHT NORTHERLY PRESSURE GRADIENT OVER THE
NORTHERN PANHANDLE. DO EXPECT NORTHERLY WINDS OF 10 TO 20 MPH IN
SKAGWAY, HAINES, AND LYNN CANAL. THERE WILL BE STRONGER MOUNTAIN
OUTFLOW WIND NEAR DOWNTOWN JUNEAU AND DOUGLAS, RESULTING IN SOME
HIGHER NORTHEASTERLY GUSTS. WITH STRONGER NORTHERLY WINDS
BRINGING IN DRIER CONTINENTAL AIR OVER THE AREA, THE NORTHERN
PANHANDLE SHOULD BE VOID OF PRECIPITATION FOR WEDNESDAY NIGHT. AS
THE LOW CONTINUES TO TRACK NORTH ON THURSDAY, THE PRESSURE
GRADIENT SHOULD BECOME SOUTHERLY AND PRECIPITATION WILL QUICKLY
SPREAD INTO THE NORTHERN PANHANDLE.

 FROM THURSDAY NIGHT INTO FRIDAY, SOUTHERLY PRESSURE GRADIENT
WILL REESTABLISH ACROSS THE PANHANDLE. THIS WILL BE THE BREAK
BEFORE THE STRONGER SYSTEM IMPACT THE PANHANDLE FOR THE WEEKEND.
THIS STRONGER SYSTEM IS CURRENTLY SOUTHEAST OF JAPAN, DRAWING DRY
AND COOL POLAR CONTINENTAL AIR FROM NORTHEAST ASIA WHILE ALSO
PULLING IN WARM AND MOIST MARITIME TROPICAL AIR FROM A
EX-TROPICAL SYSTEM OVER THE WESTERN PACIFIC OCEAN. IN ADDITION,
THIS LOW IS COUPLED WITH A 130-KT JET STREAM. THIS STORM SYSTEM
IS EXPECTED TO MOVE RAPIDLY EASTWARD ACROSS THE NORTH PACIFIC,
AND SHOULD REACH SOUTHERN GULF OF ALASKA BY FRIDAY NIGHT. THIS
SYSTEM IS DYNAMIC DUE TO ITS FAST FORWARD MOTION. IT IS LIKELY TO
BRING IN STRONG WIND FOR A WIDE AREA OF PANHANDLE THIS WEEKEND.

 FORECAST CONFIDENCE IS ABOUT AVERAGE FOR THE SYNOPTIC PATTERN OF
LOW PRESSURE SYSTEMS TRACKING ACROSS THE GULF TOWARDS THE
PANHANDLE. HOWEVER, DETAILS OF THESE STORM SYSTEMS STILL NEED TO
BE REFINED. NUMERICAL WEATHER MODELS ARE IN TWO DIFFERENT CAMPS
TODAY. ECMWF/NAM SUGGEST THE WEDNESDAY NIGHT LOW TO BE FURTHER
EAST, WHILE GFS/GEM SUGGEST THE SYSTEM TO BE FURTHER WEST. DECIDE
TO GO WITH A BLEND OF ECMWF/NAM AS THEY TEND TO PRODUCE A MORE
REALISTIC PRESSURE GRADIENT OVER SOUTHEAST ALASKA. THE NEWEST 18Z
GFS JOINS THE CAMP OF ECMWF/NAM, WHICH BOOSTS CONFIDENCE FOR THE
FIRST SYSTEM. MODELS ARE STILL STRUGGLING WITH THE DETAILS OF THE
STRONGER SYSTEM THIS WEEKEND, THUS GO WITH WPC GUIDANCE, WHICH IS
HEAVILY BASED ON THE 50-MEMBER ECMWF ENSEMBLE.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ036-041>043-051-052.

&&

FRITSCH/RCL