Area Forecast Discussion
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FXAK67 PAJK 032353
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
253 PM AKST TUE MAR 3 2015

.SHORT TERM...SHORT RANGE FORECAST BECOMING A BIT MORE ACTIVE AS
TWO WEAK SYSTEMS MOVE THROUGH OVER THE NEXT 24 HOURS. SYSTEM
NUMBER ONE IS OVER THE PANHANDLE RIGHT NOW AND SO FAR IT DOES NOT
HAVE MUCH TO SHOW FOR IT. YAKUTAT IS THE ONLY PLACE THAT HAS SEEN
ANY RAIN SO FAR WITH AROUND A TENTH OF AN INCH COLLECTED AS OF
11 AM. THE REST OF THE PANHANDLE HAS JUST SEEN AN INCREASE IN
CLOUD COVER OVERNIGHT AS AN UPPER LEVEL RIDGE OVER THE PANHANDLE
HAS SUPPRESSED MOST OF THE PRECIP WITH THIS FRONT. THOUGH SOME
LIGHT RAIN SHOWERS ALONG THE OUTER COAST ARE NOT OUT OF THE
QUESTION AS BIORKA ISLAND RADAR DOES SHOW SOME VERY LIGHT PRECIP
JUST OFFSHORE AND SITKA HAS OBSERVED SOME LIGHT RAIN THIS
AFTERNOON. AS FOR WIND, THE 25 KT BARRIER JET NEAR CAPE SUCKLING
THIS MORNING IS THE HIGHEST WINDS ANYWHERE IN THE FORECAST AREA
WITH EVERY PLACE ELSE RUNNING 15 KT OR LESS.

FOR TONIGHT NOT MUCH CHANGE FROM WHAT IS CURRENTLY GOING ON.
ONSHORE FLOW WILL CONTINUE TO BRING LIGHT RAIN TO THE YAKUTAT
AREA WITH THE REST OF THE PANHANDLE CONTINUING TO DEAL WITH CLOUD
COVER. I CAN NOT COMPLETELY RULE OUT SOME LIGHT PRECIP OVER THE
NORTHERN PANHANDLE WITH THE ONGOING LIGHT ONSHORE FLOW OVERNIGHT.
SO HAVE KEPT A CHANCE OF LIGHT RAIN (AND CHANCE OF LIGHT RAIN AND
SNOW FOR AREAS THAT GET COLD ENOUGH OVERNIGHT. I.E. SKAGWAY, AND
HAINES) FOR NORTHERN AREAS WITH SOME LIKELY AND CATEGORICAL POPS
FOR THE OUTER COAST DUE TO THE SHOWERS SEEN ON RADAR. WITH THE
CONTINUING CLOUD COVER OVERNIGHT LOWS WERE RAISED A FEW DEGREES
WITH SOME NORTHERN AREAS NOW ABOVE FREEZING FOR LOWS AS THERE IS
NOT AS MUCH CHANCE FOR AREAS TO RADIATE OUT OVERNIGHT.

FOR TOMORROW THE TREND IS WETTER AS A SECOND SLIGHTLY STRONGER
FRONT MOVES IN FROM THE WEST SPREADING MORE SIGNIFICANT RAIN
ACROSS THE PANHANDLE AS IT COMES. YAKUTAT WILL SEE IT FIRST WITH
RAIN RATES INCREASING LATE TONIGHT OR EARLY TOMORROW. THE REST OF
THE PANHANDLE WILL SEE RAIN START UP THROUGHOUT WED MORNING.
LITTLE IN THE WAY OF MOISTURE ASSOCIATED WITH THIS FEATURE AS
CURRENT PRECIPITABLE WATER RETRIEVALS SHOW ONLY AROUND A QUARTER TO
HALF INCH OF PRECIPITABLE WATER AT MOST. SO RAINFALL AMOUNTS
THROUGH TOMORROW AFTERNOON ARE EXPECTED TO ONLY BE IN THE QUARTER
INCH RANGE.

AS FOR WIND, NO SIGNIFICANT CHANGE ACROSS THE PANHANDLE AS
PRESSURE GRADIENTS REMAIN WEAK. MOST WINDS REMAIN AT 15 KT OR LESS
THROUGH TOMORROW AFTERNOON. EVEN THE WINDS IN THE NORTHERN GULF WILL BE
DIMINISHING THIS EVENING AS THE INITIAL WEAK SURFACE FRONT MOVES
ONSHORE. THE GULF WILL BE LEFT WITH 15 KT WINDS THROUGH TOMORROW
EVEN WITH THE NEXT WEAK FRONT MOVING THROUGH.

SHORT RANGE MODELS WERE IN GOOD AGREEMENT THOUGH THERE WERE SOME
MINOR DISAGREEMENTS ON HOW WIDESPREAD THE LIGHT RAIN WOULD BE
TONIGHT AND ON STRENGTH OF THE WEAK LOW IN THE NW GULF TOMORROW.
ELECTED TO USE NAM AND ECMWF FOR GUIDANCE TODAY AS BOTH SEEMED TO
HAVE DECENT CONSISTENCY WITH SHORT RANGE FEATURES.

.LONG TERM...MERIDIONAL FLOW PATTERN MOVING A SERIES OF
SHORTWAVES OVER THE AK GULF THIS WEEK WILL TRANSITION TO A MORE
ZONAL FLOW PATTERN FOR THE WEEKEND THEN TRANSITION BACK TO MORE
AMPLIFIED WAVE FOR THE START OF NEXT WEEK. THE SHORTWAVE IN THE
GULF THIS WEEK HAVE BEEN ON THE WEAK SIDE WITH WINDS GENERALLY
LESS THAN 20 KT AND LOW QPF VALUES. THE WAVE MOVING INTO THE GULF
AND ASSOCIATED FRONT WILL MOVE OVER THE PANHANDLE WEDNESDAY NIGHT
INTO THURSDAY. ANOTHER WAVE OVER THE NORTHERN GULF WILL TRACK OVER
THE AREA FRIDAY WHILE INTERACTING WITH A WAVE EXTENDING FROM A
CLOSED LOW IN THE NORTH PACIFIC. MEANWHILE A CLOSED LOW IS
TRACKING FROM THE BERING SEA, MOVING ACROSS THE AK INTERIOR THEN
DROPPING DOWN TOWARD THE PANHANDLE SUNDAY INTO MONDAY THEN EXITING
TO THE SOUTH THROUGH TUESDAY.

MODELS WERE SHOWING MESOSCALE DIFFERENCES WITH THE WEAKER WAVES
WITH MAIN DIFFERENCES IN POP FIELDS. DECIDED THAT WITH ONSHORE
FLOW TO KEEP WITH A GENERAL BLEND WITH POPS AT CHANCE OR LIKELY.
HOWEVER NOT COUNTING OUT A FEW BREAKS DEVELOPING BEHIND THE WAVES.
WITH WEAK PRESSURE GRADIENT NO SIGNIFICANT WINDS EXPECTED THROUGH
THE WEEK. THE SATURDAY INTO SUNDAY SYSTEM IS SHOWING A MORE
ORGANIZED LOW CENTER WITH HIGHER QPF AND WINDS. GULF WINDS WILL
PICK UP TO SMALL CRAFT LEVELS ALONG THE FRONT WITH INNER CHANNEL
WINDS, ESPECIALLY OVER THE NORTHERN PANHANDLE, PICKING UP TO SMALL
CRAFT AS SOUTHERLY PRESSURE GRADIENT TIGHTENS.

TEMPERATURES KEEPING IN THE LOW TO MID 40S DURING THE DAY AND LOW
TO MID 30S OVERNIGHT. PRECIP SHOULD BE MOSTLY RAIN THROUGH THE
WEEK, WITH SOME POSSIBLE SNOW MIXED OVER THE NORTHERN REGIONS AND
AT HIGHER ELEVATIONS AT 850 MB TEMPS DO DROP INTO THE -2 TO -4 C
RANGE. THE PRECIP/CLOUD COVER SHOULD LIMIT MUCH OF A DIURNAL
TEMPERATURE SWING. BY THE START OF NEXT WEEK THERE IS INDICATION OF
A DEEP MID LEVEL TROUGH DIGGING FROM THE AK INTERIOR AS THE NEXT
SURFACE LOW MOVES TOWARD THE PANHANDLE. 850 MB TEMPS WITH THIS
TROUGH DROPPING INTO THE -10 TO -20 C RANGE. CONTINUED THE TREND
OF COOLING OFF TEMPERATURES WITH THIS NEXT WAVE AND AS OF NOW THIS
IS SETTING UP FOR A POTENTIAL SNOW EVENT. WHILE THERE WAS MORE
MODEL SPREAD WITH THE WEAK WAVE DETAILS MODELS BEGAN TO FALL IN
LINE WITH THIS LARGER/STRONGER SYSTEM. POTENTIAL FOR SNOW IS STILL
TOWARD THEN END OF THE FORECAST RANGE SO EXPECT CHANGES FROM NOW
TO THEN TO OCCUR, BUT FOR NOW THE SNOW POTENTIAL IS THERE.

THE 12Z ECMWF BEGAN TO SHOW SOME SHIFTS FROM PREVIOUS RUN AND
OTHER MODELS EARLY ON. NUDGED GRIDS EARLY ON WITH SOME NAM THEN
WENT WITH A ECMWF/GFS BLEND THEN TRANSITIONED TO NEW WPC. CHANGES
WERE VERY MINOR WITH AT MOST 5 KT WIND SPEED CHANGES AND A COUPLE
OF DEGREES TEMP CHANGE. FORECAST OVERALL IS AVERAGE WITH HIGHER
CONFIDENCE IN A WET PATTERN THROUGH THE WEEK BUT LOWER CONFIDENCE
IS TIMING OF PRECIP DUE TO THE MODEL SPREAD.

&&

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

&&

$$

EAL/PRB

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