Area Forecast Discussion
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FXAK67 PAJK 271359
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
559 AM AKDT WED MAY 27 2015

.SHORT TERM...AN UPPER LEVEL LOW HAS FORMED AND IS MOVING ACROSS
THE NORTHERN PANHANDLE AS OF EARLY THIS MORNING AND PERIODS OF
LIGHT RAIN HAVE BEEN REPORTED OVER MOST NORTHERN LOCATIONS
OVERNIGHT. WRAP AROUND MID TO UPPER LEVEL CLOUD COVER HAS ALREADY
MOVED OVER ZONE 17 WHERE CLOUD TRAJECTORIES HAVE GONE FROM
EASTERLY TO NORTHERLY OVERNIGHT. ON WATER VAPOR IMAGERY, A DRY
SLOT PUSHED IN OVER THE PANHANDLE EARLY IN THE NIGHT, BUT A PLUME
OF MORE MOIST AIR HAS ADVECTED IN BEHIND AND HORIZONTAL MIXING
ASSOCIATED WITH THE UPPER LEVEL CIRCULATION IS PROVIDING A LITTLE
MORE MOISTURE. PWAT VALUES RANGING FROM SLIGHTLY BELOW NORMAL OVER
THE GULF TO SLIGHTLY ABOVE NORMAL OVER LAND, SO QPF VALUES ARE ON
THE LOW SIDE IN SPITE OF SOME FAIRLY STRONG VORTICITY ADVECTION.
PERIODS OF LIGHT RAIN WILL CONTINUE THROUGH THE DAY TODAY, BUT
WILL BE CONFINED PRIMARILY TO THE NORTHERN TWO THIRDS OF THE
PANHANDLE. BY THIS AFTERNOON, WRAP AROUND PRECIP WILL BE
CONCENTRATED OVER THE NORTHERN INNER CHANNELS, BUT THEN WORK ITS
WAY WEST AND SOUTH AS THE UPPER LOW BEGINS TO TRACK MORE TO THE
SOUTHEAST WITH AN OVERALL DIMINISHING TREND OVERNIGHT.

A COLD POOL ALOFT ASSOCIATED WITH THE LOW WITH TEMPERATURES DOWN
TO -26C PROMPTED CLOSE SCRUTINY WITH REGARD TO CALLING THIS PRECIP
RAIN OR SHOWERS. IN THE END, LOW LEVEL STABILITY IS SUCH THAT A
DECOUPLING OF THE NEAR SURFACE ENVIRONMENT FROM THE COLDER AIR
ALOFT IS GOING TO BE STRONG ENOUGH THAT THE ENTIRE EVENT WILL
MANIFEST AS STRATIFORM RAIN.

AT THE SURFACE, HIGH PRESSURE IS ONCE AGAIN BUILDING OVER THE
GULF. AT THE SAME TIME, AN INVERTED TROUGH OVER WESTERN CANADA IS
BECOMING MORE SHARPLY DEFINED. RESULTING PRESSURE GRADIENT OVER
THE EASTERN GULF WILL GENERATE SMALL CRAFT WINDS OVER PORTIONS OF
THE COASTAL MARINE ZONES AS WELL AS NORTHERN PORTIONS OF OFFSHORE
ZONE 310 THROUGH THE SHORT TERM FORECAST PERIOD. ON THE INSIDE,
SMALL CRAFT NORTH WESTERLIES HAVE BEEN OCCURRING IN CROSS SOUND
SINCE BEFORE DAWN AND ARE EXPECTED TO LAST UNTIL THE AFTERNOON.
SMALL CRAFT SOUTHERLIES OVER LYNN CANAL HAVE RELAXED AS OF EARLY
THIS MORNING, BUT ARE EXPECTED TO PICK UP ONCE AGAIN AROUND NOON
TODAY. THIS EVENING WILL SEE WINDS OVER THE INNER CHANNELS RELAX
AND THEN SHIFT TO THE NORTH LATE TONIGHT AS THE INVERTED TROUGH
MOVE WEST OVER THE PANHANDLE.

CLOUD COVER TODAY WILL BE MORE EXTENSIVE THAN IN RECENT DAYS, SO
DAYTIME HIGHS WILL BE DIMINISHED SOMEWHAT. LOOK FOR HIGHS IN THE
UPPER 50S TO LOW 60S. OVERNIGHT LOWS TONIGHT WILL GET DOWN TO THE
MID 40S.

EXISTING PRESSURE AND WIND FORECAST REMAINED MOSTLY ON TRACK, SO
VERY LITTLE CHANGE THERE. UPDATED POP AND QPF USING A BLEND OF GEM
AND ECMWF. TEMPS ADJUSTED USING BIAS CORRECTED GFS40 AND BIAS
CORRECTED MOS. OVERALL FORECAST CONFIDENCE IS AVERAGE TO SLIGHTLY
ABOVE AVERAGE.

.LONG TERM...AT THE START OF THE LONG TERM PERIOD THE UPPER LEVEL
LOW MENTIONED IN THE SHORT TERM SECTION WILL STILL BE LINGERING
AROUND OVER THE SOUTHERN THIRD OF THE FORECAST AREA. THIS UPPER
LEVEL FEATURE WILL KEEP A CHANCE OF SHOWERS FROM FREDRICK SOUND
SOUTHWARD WITH CHANCES DIMINISHING THROUGH THURSDAY AS THE UPPER
LOW DRIFTS SOUTHEAST. THE HYDER AREA WILL CONTINUE TO SEE A CHANCE OF
SHOWERS INTO THURSDAY NIGHT NIGHT WITH SOME VORT LOBES DRIFTING
AROUND THE DEPARTING UPPER LEVEL LOW.

OFFSHORE FLOW WILL INCREASE FROM NORTH TO SOUTH THROUGH THURSDAY
WITH THE SUN RETURNING FOR THE NORTHERN HALF OF THE PANHANDLE BY
THE AFTERNOON. THERE WILL BE WAA OVER THE AREA AND WITH SUNNY
SKIES TEMPS WILL RISE INTO THE UPPER 60S TO LOWER 70S ON THURSDAY.
FRIDAY AND SATURDAY THE ENTIRE FORECAST AREA SHOULD BE MOST SUNNY AND
WITH 850MB TEMPS RANGING FROM +13 TO +11 TEMPS WILL BE IN THE MID
70S. AFTERNOON SEA BREEZES MIGHT LIMIT HIGH TEMPERATURES AT
LOCATIONS ALONG THE WATER ALONG WITH POSSIBLE FORMATION OF SEA
STRATUS ALONG THE GULF COAST.

THESE WARM AND SUNNY CONDITIONS WILL PERSIST INTO THE WEEKEND AS
THE UPPER RIDGE WILL REBUILD OVER THE GULF TO KEEP ANY LARGE
WEATHER SYSTEM FROM COMING INTO THE EASTERN GULF. SO TEMPS WILL
REMAIN ABOVE NORMAL AND THE CONTINUED DRY CONDITIONS. A UPPER
LEVEL TROF IS FORECASTED TO DROP SOUTH FROM THE YUKON LATE
SATURDAY INTO SUNDAY. THE EC IS MORE AGGRESSIVE WITH THIS FEATURE
THAN THE GFS WITH CLOUD COVER AND PRECIP OVER THE NORTHERN THIRD.
THERE IS LOW CONFIDENCE IN THIS ATTM TIME. LOOKING INTO EARLY NEXT
WEEK THE UPPER AND MID LEVEL FLOW IS TRYING TO SHIFT MORE ONSHORE
WITH THE UPPER RIDGE OVER THE GULF FLATTENING OUT. THERE IS NOT
PRECIP FORECASTED RIGHT NOW BUT WITH THE ONSHORE FLOW THIS WILL
INCREASE THE THREAT OF CLOUDS NEXT WEEK.

WIND WISE...THERE IS NOT MUCH WIND TO SPEAK OF FROM THURSDAY
THROUGH THE WEEKEND WITH VERY WEAK PRESSURE GRADIENT. SO WITH THAT
SAID MARINE WINDS WILL BE LESS THAN 15KT OVER MOST LOCATIONS WITH
THE EXCEPTION TO COASTAL LOCATIONS WHERE NW WINDS MAY INCREASE
FROM DAYTIME HEATING TO 20 KT FROM THE NORTHWEST. OVER LAND THERE
WILL BE AFTERNOON SEA BREEZES BUT LIGHT WINDS OVERNIGHT.

THERE IS AVERAGE FORECASTER CONFIDENCE FOR THE LONG TERM PORTION
AND USED A BLEND OF THE NAM/EC THROUGH DAY 4 AND THEY WPC FOR THE
EXTENDED PORTION.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ012-022-041>043-051-052.

&&

$$

FRITSCH/ABJ

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