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FXAK67 PAJK 291441
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
541 AM AKST THU JAN 29 2015
.SHORT TERM...MORNING SURFACE OBSERVATIONS SHOW A FRONTAL BOUNDARY
EXTENDING EWD FROM THE NRN GULF TOWARD AN AREA BETWEEN SITKA AND
JUNEAU. IN ADDITION...IR IMAGERY REVEALS COOLING CLOUD TOPS ALONG
AND N OF THE BOUNDARY...WHICH CORRESPONDS TO A BLOSSOMING ZONE OF
PRECIPITATION THAT WILL IMPACT NRN PORTIONS OF THE CWA THROUGH THE
AFTERNOON. THE BOUNDARY IS FORECAST TO DRIFT SLIGHTLY N DURING THE
MORNING/AFTERNOON BEFORE DISSIPATING...WHICH WILL FAVOR A MODEST
RISE IN TEMPERATURES FROM YAKUTAT TO JUNEAU AND POINTS NWD. THIS
WILL MAKE A TRANSITION TO RAIN INCREASINGLY LIKELY FOR SEA LEVEL
LOCATIONS CURRENTLY EXPERIENCING SNOW. MEANWHILE...SNOW OCCURRING
AT WHITE PASS AND AREAS NEAR HAINES CUSTOMS WILL DIMINISH IN
INTENSITY DURING THE MORNING. THUS...THE WINTER WEATHER ADVISORY
AND WARNING ARE ON TRACK FOR A NOON CANCELLATION...IF NOT SOONER.

OVER THE SRN PANHANDLE...RAIN IS FORECAST TO DISSIPATE BY MIDDAY
AS A DEEP-LAYER OF DRY AIR SPREADS NEWD FROM THE NERN PAC. DRYING
WILL CONTINUE INTO TONIGHT AND SPREAD N INTO THE CNTRL PANHANDLE
AS UPPER-LEVEL SUBSIDENCE INCREASES N OF A WEAK DISTURBANCE
APPROACHING HAIDA GWAII. CLEARING SKIES AND A MOIST BOUNDARY LAYER
MAY AID IN PATCHY FOG DEVELOPMENT FROM PETERSBURG TO ANGOON.
ELSEWHERE...STEEPENING LAPSE RATES AND MODEST ASCENT WILL FAVOR
SHOWERS TONIGHT FROM YAKUTAT TO GUSTAVUS AND HAINES.

AS THE FRONTAL BOUNDARY WAVERS NWD THROUGH THIS AFTERNOON...THE
SURFACE PRESSURE GRADIENT WILL SLACKEN FOR SKAGWAY AND LYNN
CANAL...RESULTING IN WINDS WEAKENING TO AROUND 10 KT AND
OCCASIONALLY BECOMING VARIABLE IN DIRECTION. UPPER-LEVEL
SUBSIDENCE WILL ALSO SUPPORT A WEAK RIDGE OF HIGH PRESSURE
DEVELOPING OVER THE CNTRL PANHANDLE INTO THE ERN GULF FAVORING
WINDS GENERALLY AOB 15 KT FOR MANY OF THE INNER CHANNELS AND
ADJACENT OUTSIDE WATERS. BY LATE TONIGHT...THE PRESSURE GRADIENT
IS FORECAST TO TIGHTEN BACK UP OVER NRN LYNN CANAL SUPPORTING AN
INCREASE IN NLY WINDS TO 20 KT. PRESSURE GRADIENT WILL ALSO
TIGHTEN OVER CLARENCE STRAIT AS A LOW MOVES TOWARD HAIDA
GWAII...WITH 20 KT NLYS ANTICIPATED.

NO CHANGE WAS MADE TO INHERITED PRESSURE GRIDS. POP AND QPF WERE
MODIFIED WITH ECMWF AND HI-RES ARW/NMM. BIGGEST CHANGE TO THESE
FIELDS WAS A REDUCTION IN BOTH OVER THE SRN PANHANDLE TONIGHT.
.LONG TERM...UPPER LEVEL CUT OFF LOW OVER THE NORTHERN PACIFIC
SOUTH OF THE ALASKA PENINSULA, AND THE JET STREAM PASSING THROUGH
THE ALASKA INTERIOR WILL BE THE MAIN PLAYERS IN THE LONG RANGE
FORECAST FOR THE NEXT WEEK. BOTH FEATURES WILL LARGELY REMAIN
UNCHANGED AS FAR AS POSITION BUT THE VARIOUS SMALL WAVES AND
PULSES THAT RIDE ALONG THESE FEATURES AND THEIR INTERACTIONS WITH
EACH OTHER WILL PROVIDE THE FLUCTUATIONS THAT WILL BE SEEN IN THE
FORECAST.

THE FIRST MAJOR SHIFT SHOWS UP FRI INTO SAT AS A TROUGH ALONG THE
JET BRINGS IN SOME COLD AIR INTO THE SOUTHERN YUKON. SURFACE
PRESSURES ARE EXPECTED TO HIT 1045 MB BY FRI NIGHT ACROSS THE
SOUTHERN YUKON WITH PRESSURE GRADIENTS ALONG THE COAST MOUNTAINS
REACHING 10 TO 15 MB. OUTFLOW WINDS WILL BE BLOWING THROUGH MANY
MOUNTAIN PASSES WITH STORM FORCE WINDS EXPECTED SAT IN LYNN CANAL
AND STRONG WIND GUSTS IN SKAGWAY, HAINES, THE PASSES EAST OF
YAKUTAT, DISENCHANTMENT BAY, AND TAKU INLET. MOUNTAIN WAVE WINDS
IN DOWNTOWN JUNEAU AND DOUGLAS ARE A GOOD POSSIBILITY AS WELL WITH CROSS
BARRIER FLOW INCREASING TO 40 TO 50 KT. AN INVERSION ABOVE RIDGE
TOP IS ALSO EXPECTED WITH THE COLD AIR OUTFLOW. THE CRUCIAL LEVEL
MIGHT BE THE LIMITING FACTOR AS WHILE THERE IS A DEFINITE WIND
SHIFT IT IS ONLY AT AROUND 600 TO 700 MB RATHER THEN THE IDEAL
500 MB. STILL GUSTS TO 50 MPH ARE EXPECTED FOR DOWNTOWN JUNEAU AND
DOUGLAS LATE FRI NIGHT THROUGH SAT NIGHT.

MEANWHILE THE SOUTHERN PANHANDLE WILL BE DEALING WITH WHAT THE CUT
OFF UPPER LOW HAS TO THROW AT US. IT COMES IN THE FORM OF A
WEAKENING FRONT OVER THE WEEKEND. WINDS OUT IN THE GULF WILL BE
INCREASING TO GALE FORCE ON FRI NIGHT AND SAT AS A RESULT BUT WILL
BE GRADUALLY DIMINISHING AS THE FRONT SHEARS APART UNDER DIFLUENT
FLOW. THE PRECIP SHIELD WILL ALSO NOT MAKE IT THAT FAR NORTH AS A
RESULT OF THE SAME DIFLUENT FLOW AND THE DRY NORTHERLY OUTFLOW
FARTHER NORTH. LIKELY POPS ONLY MAKE IT AS FAR NORTH AS FREDERICK
SOUND AT MOST AND EVEN THEN EXPECTED AMOUNTS WILL BE LIGHT AS THE
FRONT SHEARS APART.

THE COLD AIR LOOKS TO BE IN A LOSING BATTLE WITH THE WARM AIR BY
EARLY NEXT WEEK AS THE MAIN PUSH OF COLD AIR MOVES OFF TO THE
EAST. NEW MODEL RUNS ARE INCREASING SOUTHERLY FLOW ACROSS THE AREA
INTO EARLY NEXT WEEK, BUT WITH FEW, IF ANY, STRONG STORMS COMING
IN THERE WILL BE VERY LITTLE TO KICK THE COLD AIR OUT OF THE INNER
CHANNELS. THUS TEMPERATURES WILL REMAIN COOL BUT NOT BITTERLY COLD
EARLY NEXT WEEK. NEXT MAJOR STORM LOOKS TO COMES MID TO LATE NEXT
WEEK AS MORE COLD AIR GETS INJECTED INTO THE WESTERN HALF OF THE
UPPER LOW THOUGH MODELS ARE GETTING REALLY SPREAD OUT AT THIS
POINT.

OVERALL MODELS WERE IN DECENT AGREEMENT WITH MOST FEATURES THROUGH
EARLY NEXT WEEK DECENTLY REPRESENTED. NOT MANY CHANGES OVERALL AS
MODELS KEPT THE MAIN IDEA OVER THE LAST 24 HOURS. THROUGH DID
SPEED UP THE FRONT OVER THE SOUTHERN GULF OVER THE WEEKEND. MAIN
GUIDANCE USED WAS NAM/EC/GEM FOR MOST OF THE PERIOD.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER STORM WARNING UNTIL NOON AKST TODAY FOR AKZ019.
         WINTER WEATHER ADVISORY UNTIL NOON AKST TODAY FOR AKZ018.
MARINE...SMALL CRAFT ADVISORY FOR PKZ036-051. 
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ041>043-052. 

&&

$$

GARNER/EAL

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