312
FXAK67 PAJK 191547 CCA
AFDAJK
SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
510 AM AKST WED FEB 19 2020
SHORT TERM
THE EASTWARD MOVING COLD FRONT JUST OFF SHORE THE
PANHANDLE COAST WEDNESDAY MORNING, IS TRACKING A TOUCH SLOWER
THAN EARLIER FORECASTED. IT WILL MOVE IN DURING THE DAY AND WILL
BE WEAKENING. SHOWERY ACTIVITY WRAPPING IN BEHIND THE FRONT,
MAINLY TO IMPACT THE NORTHEAST GULF AND NORTHERN PANHANDLE, AND TO
A LESSER EXTEND THE SOUTHERN PANHANDLE.
A BETTER THAN EXPECTED WARM PUSH THROUGH LYNN CANAL, HAS HAINES
AND SKAGWAY IN THE UPPER 30S THIS MORNING AND THIS PERMEATED ALL
THE WAY TO THE BORDER ON THE HAINES HIGHWAY. WITH SUCH A WARM AIR
MASS, THE WINTER STORM WARNING WAS CANCELLED. THE WHITE PASS AREA IS
STILL BELOW FREEZING SO HAVE KEPT THAT ONE.
MODELS A LITTLE BETTER WITH TIMING FOR THURSDAY SYSTEM, BUT STILL
SOME TIMING AND STRENGTH DIFFERENCES. WE KEPT A SLIGHTLY SLOWER
SPEED FACTOR BETWEEN THE SOLUTIONS, AND HAVE A PREFERENCE FOR THE
GFS MOISTURE COMING ACROSS.
THE AIR MASS MOVING ACROSS THE BEHIND THE THURSDAY SYSTEM LOOKS
MUCH COOLER THAN THAT ONE BETWEEN THE WED AND THURSDAY EVENT. WE
TRENDED AWAY FROM SEA LEVEL ACCUMULATIONS THURSDAY, A MIX IS
POSSIBLE IT WAS JUST LOOKING THAT WE WERE NOT GOING TO HAVE THE
COOLER SURFACE TEMPERATURES TO ACCUMULATE THE SNOW.
WIND WISE THE LARGEST ISSUE IS THE GUSTY AND STRONG WINDS IN THE
SKAGWAY AREA INTO THURSDAY, ALTHOUGH SOME LOCATIONS WILL SEE THE
REALLY GUSTY WINDS RETURN THURSDAY AFTERNOON WITH THE NEXT FEATURE
ARRIVING.
LONG TERM
THE CHALLENGES OF WINTER-TIME SPLIT FLOW PERSIST IN
THE MID- RANGE INTO EARLY NEXT WEEK, AS MOIST PACIFIC SYSTEMS
RAIL ACROSS 50 N AND OCCASIONALLY FROM LATITUDES SOUTHWARD AND
INTERACT WITH PERSISTENT AND COLDER BERING SEA SYSTEMS THAT
PERIODICALLY REPLANT THEMSELVES IN THE GULF OF ALASKA. THIS
INTRODUCES MANY COMPLICATIONS THAT FRANKLY MODELS (AND
FORECASTERS) OFTEN STRUGGLE WITH. WITH TEMPERATURES MARGINALLY
HOVERING IN THE METEOROLOGICALLY SCARY NEIGHBORHOOD OF THE
MYTHICALLY WELL-MARKED RAIN/SNOW LINE, SMALL ERROR POTENTIAL CAN
SPAN THE IMPACT SCALE FROM LITTLE TO GREAT.
AFTER A VIGOROUS FRONT CLEARS THE PANHANDLE A MARITIME, A
RELATIVELY COOL AIR MASS SPREADS ACROSS SOUTHEAST ALASKA,
SUPPORTING SHOWERS. THESE SHOWERS WILL FALL AS MAINLY RAIN FOR
THE SOUTH AND A MIX FOR THE NORTH. POORLY RESOLVED SHORT- WAVES
COULD ENHANCE SOME ACCUMULATIONS DURING THIS TIME, ESPECIALLY AS
THICKNESSES AND TEMPERATURES DROP INTO FRIDAY NIGHT.
SATURDAY, IT INCREASINGLY LOOKS AS THOUGH THE SOUTHERN STREAM
ENERGY BECOMES EVEN MORE ACTIVE AS A STORM LOOKS TO BARREL INTO
THE BC COAST. THIS HELPS SPEED COOLING ACROSS SOUTHEAST AND
PROBABLY INCREASES FRONTOGENESIS SOMEWHERE ACROSS EITHER THE
EASTERN GULF OF ALASKA OR THE COASTAL PANHANDLE. MUCH OF THIS
PRECIPITATION COULD FALL AS SNOW, GIVEN LOW THICKNESSES AND
COOLING 850 MB TEMPERATURES. WHILE IT IS STILL AN EVOLVING STORY,
WE LOWERED QPF DURING THE WEEKEND, AS UNCERTAINTY IS UNCOMFORTABLY
HIGH. YET IT IS CERTAINLY PLAUSIBLE THAT A FEW COMMUNITIES COULD
GET SIGNIFICANT SNOW FROM THIS SCENARIO. EVENTUALLY, EITHER
SUNDAY OR SUNDAY NIGHT THE STEERING FLOW TURNS WESTERLY AND
POTENTIALLY SETS UP ANOTHER OVERRUNNING EVENT LATE IN THE WEEKEND
OR EARLY NEXT WEEK. BUT SHOULD THE SOUTHERN TRACK ROB THE NORTH OF
MOISTURE, THIS SETUP MAY BE MUCH ADO ABOUT NOTHING.
ENSEMBLES AND OPERATIONAL RUNS THEN HINT AT A MORE DEEPLY
SUBTROPICAL SYSTEM PERHAPS BEGINNING AS SNOW AND ENDING AS RAIN
FOR MUCH OF THE PANHANDLE MID NEXT WEEK. WHEN EXACTLY THIS
HAPPENS, WE ARE STILL MERELY WAGERING. BUT AS WE HINTED EARLIER,
THERE IS CONFIDENCE THAT SOUTHEAST ALASKA REGION-WIDE WILL
EXPERIENCE A COOL-DOWN THIS WEEKEND INTO AT LEAST MONDAY BEFORE
WARMING INTO MID NEXT WEEK. THIS PROBABLY MEANS MORE SNOW FOR
SOME.
WESTERLY WINDS FRIDAY WILL BE RELATIVELY HIGH IN THE GULF WITH
WIDESPREAD 30 KT AND EVEN SOME GALE FORCE WINDS. BUT AS THE SYSTEM
TO THE SOUTH NEARS THE BC COAST, WINDS LARGELY DIMINISH ACROSS THE
PANHANDLE EVEN AS THE INNER CHANNELS FLIP NORTH SATURDAY. WINDS
LOOK TO HAVE LITTLE IMPACT THIS WEEKEND UNTIL AN ANTICIPATED
FRONT ARRIVES MID NEXT WEEK WITH STRONG SOUTHEASTERLIES.
AJK WATCHES/WARNINGS/ADVISORIES
PUBLIC...WINTER STORM WARNING UNTIL 9 AM AKST THIS MORNING FOR
AKZ018.
STRONG WIND THROUGH LATE TONIGHT FOR AKZ018.
STRONG WIND UNTIL 9 AM AKST THIS MORNING FOR AKZ028.
MARINE...GALE WARNING FOR PKZ041-052.
SMALL CRAFT ADVISORY FOR PKZ012-013-022-031>036-042-043-051-053.
BEZENEK/JWA
VISIT US AT HTTP://WWW.WEATHER.GOV/JUNEAU
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page