Area Forecast Discussion
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FXAK67 PAJK 212319
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
319 PM AKDT THU AUG 21 2014

.SHORT TERM...WITH UPPER LEVEL RIDGE BUILDING OVER OUR DOMAIN,
SUNNY SKIES SHINE DOWN ON SOUTHEAST. A THIN STRETCH OF FOG LIES
JUST OFFSHORE OF YAKUTAT AND INDICATED BY SATELLITE TO BE SHUNTED
OFF SOUTHWARD AWAY FROM BARANOF AND PRINCE OF WALES AS OFFSHORE
UPPER LEVELS KEEP THE COASTAL FOG AT BAY FOR NOW. THINGS BEGIN TO
SHIFT TONIGHT AS A SHORT-WAVE MOVES ACROSS THE NORTHERN GULF
TURNING WINDS ALOFT BACK ONSHORE. IN ADDITION, THE THERMAL
SURFACE TROUGH EXTENDING NORTHWEST ACROSS THE PANHANDLE IS DUE TO
WEAKEN OVERNIGHT. WITH A SYNOPTIC LEVEL PUSH COMBINED WITH THE
WEAKENING THERMAL TROUGH INLAND, THE MARINE LAYER AND ITS FOG
WILL SPREAD INTO YAKUTAT OVERNIGHT AND EXPAND SOUTHEASTWARD TO
CROSS SOUND LATE TONIGHT. THE CHANCES OF REACHING SITKA ARE NOT AS
GOOD, BUT MOS GUIDANCE DOES INDICATE AN INKLING OF AN ELEVATED
LAYER BY FRIDAY MORNING. ASIDE FROM SOME PATCHY ENCROACHMENT AS
FAR EAST AS GUSTAVUS...FOG SHOULD NOT PENETRATE TOO FAR INLAND.
SOME RADIATIONAL FOG WILL FORM AROUND FREDERICK SOUND AS WELL. A
WEAK SURFACE LOW SHOULD ENTER THE SOUTH CENTRAL GULF BY FRIDAY
AFTERNOON AND LIFT THE FOG INTO AN ELEVATED STRATUS DECK
SO ELECTED NOT TO CONTINUE AREAS OF FOG OVER THE GULF THROUGH THE
DAY, EVEN AS SURFACE RIDGE REMAINS OVER THE EASTERN GULF.

A FEW LIGHTNING STRIKES OVER THE NORTHERN BC MOUNTAINS HAVE RAISED
CONFIDENCE ON THE THREAT OF THUNDERSTORMS OVER HYDER EARLY THIS
EVENING, THUS THIS WAS KEPT IN THE FORECAST. ADDED SOME ISOLATED
SHOWERS IN SKAGWAY EARLY THIS EVENING AS WELL. CONVECTION ON THE
CANADIAN SIDE, ALTHOUGH MAINLY BEHAVED AND REMAINING IN
CANADA, SEEMS TO PREFER WHITE PASS AS AN ENTRY POINT ACROSS OUR
BORDER. SOME SHOWER WORTHY CUMULUS CONFIRMED ON WEBCAMS AROUND
WHITE PASS THIS AFTERNOON.

THE SHORT-WAVE MENTIONED ABOVE WILL SPREAD SOME HIGHER LEVEL
CLOUDINESS OVER THE PANHANDLE TOMORROW JUST AS IT AIDS WITH THE
MARINE PUSH IN THE SURFACE LAYER. SO EVEN AS THE COAST MAY
EXPERIENCE LOW CLOUD DEVELOPMENT, INLAND AREAS SHOULD SEE THE
BLUE SKIES TURN A BIT MORE OF A DIFFUSED MILKY WHITE WITH LESS
DEFINED SHADOWS CAST ON THE GROUND THROUGH THE AFTERNOON. WITH
SLIGHT COOLING FROM THE INCREASING ONSHORE FLOW, TEMPERATURES
WHILE STILL WARMER THAN NORMAL WILL NOT BE AS WARM AS TODAY.
MAINLY UPPER 60S IN SOUTHEAST`S INTERIOR WITH A FEW 70S IN WARM
SPOTS. NORTHERN/CENTRAL COASTAL LOCATIONS IN THE LOWER TO MIDDLE
60S WILL SEE THE MOST COOLING AND COULD BE COOLER THAN
INDICATED...DEPENDENT ON HOW LASTING THE PUSH IS OVERNIGHT.
CONFIDENCE NOT AS CERTAIN HERE.

LIKE YESTERDAY THE RIDGE HAS PROVEN TO BE A BIT STRONGER AND
PERHAPS BLUNT...HITTING THE COAST. STILL WAITING FOR A MAX IN
CLARENCE STRAIT. POSSIBLY THE ECMWF OVERDID THE GRADIENT JUST AS
NAM IS UNDERREPRESENTING IT. MIDDLE GEM SUGGESTING 15 KT WILL DO
IT. MEANWHILE...ELDRED ROCK STUBBORNLY FLIRTED WITH NORTHERLY 20
KT, THUS WILL BE BEGINNING ZONE 12 AS N 10 KT INSTEAD OF LIGHT.
JUNEAU`S WINDS...ALWAYS COMPLEX SEEMS TO INDICATE THE GASTINEAU
CONVERGENCE ZONE TO BE SOUTH OF DOWNTOWN NOW, SO GENERALLY
NORTHWEST WINDS WILL DO...ALTHOUGH DOUGLAS STILL SHOWING
SOUTHEAST. AS AFTERNOON HEATING SUBSIDES, THE ENTIRE CHANNEL SEEMS
TO GIVE IN TO THE SYNOPTIC FLOW. GRADIENTS WILL WEAKLY FLIP FRIDAY
ALLOWING MOST CHANNELS EXCEPT SOUTH OF FREDERICK TO SWITCH TO A
SOUTHERLY DIRECTION.

CONFINED MOST UPDATES TO FRIDAY PERIOD WITH ECMWF AND GFS USED AS
GUIDANCE. FORECAST CONFIDENCE GOOD.


.LONG TERM...THE FORECAST FOR THE PANHANDLE IS TURNING DAMP AGAIN
AS THE UPPER RIDGE THAT HAS BEEN KEEPING US DRY RECENTLY FLATTENS
OUT OVER THE WEEKEND BEFORE GETTING REPLACED BY A UPPER TROUGH
EARLY NEXT WEEK. LATER NEXT WEEK DOES NOT LOOK MUCH IMPROVED AS
MOST MODELS ARE TRENDING TOWARD A BROAD UPPER TROUGH OVER ALASKA
WITH STRONG ZONAL FLOW OVER THE GULF AND ALEUTIANS ISLANDS.

AT THE SURFACE, A WEAK LOW WILL BE MOVING ACROSS THE SOUTHERN GULF
ON SAT AS A WEAK UPPER TROUGH TRIES TO MOVE THROUGH THE RIDGE. IT
WILL NOT BE THAT SUCCESSFUL BUT I CAN`T COMPLETELY RULE OUT SOME
SHOWERS FOR SAT FOR THE PANHANDLE AS WHAT IS LEFT OF IT MOVES
THROUGH. ONLY HAVE SLIGHT CHANCE TO CHANCE POPS FOR AREAS FROM ICE
STRAIT SOUTHWARD FOR THIS FEATURE. LITTLE IN THE WAY OF WIND AS
THIS FEATURE IS SO WEAK.

AFTER THIS THE RIDGE POPS BACK UP JUST A BIT FOR SUN BEFORE IT
GETS FLATTENED AGAIN AND PUSHED EAST BY THE NEXT APPROACHING SYSTEM.
THIS ONE HAS A LOT MORE SUPPORT BEHIND IT AS THE PARENT LOW HAS A
RATHER DECENT STRENGTH UPPER LOW OVER TOP OF IT. THE ASSOCIATED
FRONT ON THE OTHER HAND WILL BE FIGHTING THE SURFACE RIDGE AS IT
MOVES EAST SUN NIGHT INTO MON. THERE IS ALSO NOT MUCH TROPICAL
MOISTURE AVAILABLE FOR IT TO PLAY WITH AND THE FRONT IS NOT
STALLING OVER THE AREA SO EXPECTED RAINFALL AMOUNTS ARE EXPECTED
TO BE IN THE QUARTER TO HALF INCH RANGE THROUGH TUE. AS FOR WIND,
NOT MUCH OUT OF THIS ONE AS THE PARENT LOW IS WELL WEST OVER
BRISTOL BAY AT THAT TIME SO ONLY SMALL CRAFT WINDS ARE EXPECTED AT
THE MOST DURING FRONTAL PASSAGE. THAT REMAINS TRUE EVEN AS THE
SURFACE LOW CROSSES THE NORTHERN GULF MID WEEK BUT BY THAT TIME IT
WILL BE WEAKENING RATHER FAST. MODELS ARE STILL FIGHTING OVER THE
DETAILS AS THE ECMWF AND GEM HAVE RAIN STARTING UP ACROSS THE
PANHANDLE SUN EVENING WHILE THE NAM AND GFS HOLD OFF UNTIL LATE
THAT NIGHT. AT THE MOMENT HAVE CHANCE POPS FOR MOST OF THE
PANHANDLE SUN EVENING THEN LIKELY POPS FOR LATER IN THE NIGHT.

FARTHER OUT STILL SOME DISAGREEMENT ON HOW THE BROAD UPPER TROUGH
WILL SHAPE UP LATE WEEK. LONG RANGE MODELS ARE AT ODDS ON WHEN
VARIOUS PIECES OF ENERGY WILL BE MOVING THROUGH THE GULF AND HOW
FAR SOUTH THEY WILL BE SO DECIDED TO STICK WITH A MORE ENSEMBLE
APPROACH FOR THE EXTENDED PERIOD.


&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.

&&

$$

JWA/EAL

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