730  
FXAK67 PAJK 221509  
AFDAJK  
 
SOUTHEAST ALASKA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE JUNEAU AK  
609 AM AKST MON JAN 22 2018  
   
SHORT TERM
 
/THROUGH TUESDAY NIGHT/ LARGE SCALE UPPER TROF WILL  
REMAIN OVER THE GULF THROUGH TUE NIGHT. BASE OF UPPER TROF WILL  
CLOSE OFF TO AN UPPER LOW OVER THE FAR S GULF TODAY, AND THIS LOW  
WILL SHIFT E TO THE S OF HAIDA GWAII BY LATE TUE NIGHT. SEVERAL  
SHORTWAVES WILL MOVE ACROSS THE AREA THROUGH TUE. A SERIES OF LOW  
PRESSURE TROFS ASSOCIATED WITH THE SHORTWAVES WILL MOVE ACROSS THE  
AREA THROUGH TUE. A LOW PRESSURE AREA WILL DEVELOP OVER THE NE  
PACIFIC TONIGHT AND MOVE N TO NEAR HAIDA GWAII BY LATE TUE  
AFTERNOON. AN OCCLUDED FRONT WILL MOVE INTO THE FAR S PANHANDLE  
BY TUE EVENING. USED NAM/EC BLEND FOR PRESSURES AND WINDS. NAMNEST  
WAS INCORPORATED IN THE WIND BLEND FOR TUE AND TUE NIGHT TO SHOW  
MORE DEFINED OUTFLOW THEN.  
 
MAIN FORECAST CONCERNS WILL BE PRECIP POTENTIAL/TYPE/AMOUNTS AND  
WINDS. FIRST MAIN SHORTWAVE AND SFC TROF WILL MOVE N ACROSS THE  
AREA TODAY. EXPECT A WELL ORGANIZED BAND OF SHOWERS WITH THIS  
FEATURE AS IT MOVES THROUGH. THERE IS A NARROW WARM SLOT JUST  
AHEAD OF THE TROF WHICH WILL KEEP SOME RAIN MIXING IN OVER THE S  
HALF OF THE AREA. AS THE TROF MOVES THROUGH, COLDER AIR ALOFT  
SHOULD TRANSITION MUCH OF THE PRECIP TO SNOW SHOWERS. CURRENTLY  
THINK THE CENTRAL AND N WILL SEE 1-3 INCHES OF SNOW WITH THIS  
TROF TODAY.  
 
TRICKIER SITUATION WILL DEVELOP FOR TONIGHT. ANOTHER SHORTWAVE  
WILL MOVE NE INTO THE AREA, AND A BAND OF SHOWERS WILL COME IN  
WITH IT. THIS BAND MAY SET UP MORE PARALLEL TO THE DEEP LAYER FLOW  
WHICH COULD LEAD TO TRAINING CELLS OVER A NARROW AREA. MODELS HINT  
AT THIS BUT DIFFER ON PLACEMENT OF THE BAND. AT THIS POINT,  
KEEPING A GENERAL 1-3 INCHES OF SNOW WITH THIS FEATURE FOR TONIGHT  
OVER THE N, BUT LATER SHIFTS WILL NEED TO MONITOR FOR HIGHER  
AMOUNTS WHERE THIS BAND SETS UP. EXPECT THE S TO SEE MAINLY  
SCATTERED SNOW SHOWERS ALTHOUGH THE OUTER COAST COULD SEE MORE.  
 
AS LOW MOVES N TOWARD HAIDA GWAII TUE, SHOWERS WILL BE PUSHED BACK  
TO THE W OVER THE GULF AS FLOW BECOMES INCREASINGLY OFFSHORE. HOWEVER,  
PRECIP WITH THE LOW AND ITS FRONT WILL BE MOVING INTO THE FAR S  
AREA LATE IN THE AFTERNOON. SOME OF THIS PRECIP WILL REACH THE  
CENTRAL AREA TUE NIGHT. THINK MOST OF THE PRECIP WILL BE SNOW OR A  
RAIN/SNOW MIX TO START, BUT LIKELY TRANSITION TO RAIN OVER THE  
FAR S TUE NIGHT. SNOWFALL AMOUNTS WILL BE TRICKY AS THEY WILL  
DEPEND ON IF AND WHEN PRECIP CHANGES TO RAIN. BEST CHANCE FOR  
ACCUMULATING SNOW WILL BE OVER THE S-CENTRAL AREA TUE NIGHT WHERE  
THE PRECIP SHOULD REMAIN MAINLY SNOW. COULD BE 2-4 INCHES IN THE  
S-CENTRAL AREA BY DAYBREAK WED BASED ON CURRENT TIMING OF FRONT  
MOVING IN.  
 
WINDS WILL BE STRONGEST NEAR THE TROFS MOVING ACROSS THE AREA. SCA  
LEVEL WINDS ARE LIKELY OVER THE GULF WITH EACH TROF, AND SOME OF  
THE INNER CHANNELS WILL ALSO SEE SCA LEVEL WINDS THROUGH TONIGHT.  
THE LOW/FRONT MOVING N TOWARD HAIDA GWAII WILL INCREASE OFFSHORE  
WINDS TUE AND TUE NIGHT. COULD SEE GALES FOR LYNN CANAL AND CROSS  
SOUND BY TUE EVENING...WITH SCA LEVEL WINDS OVER MUCH OF THE  
REMAINING INNER CHANNELS AND GULF AREAS BY TUE NIGHT. THE FAR SE  
GULF COULD SEE GALES TUE INTO TUE EVENING AHEAD OF THE FRONT  
MOVING INTO THE AREA.  
   
LONG TERM.../WEDNESDAY THROUGH MONDAY/
 
LONG RANGE PERIOD  
BEGINS WITH AN UPPER LOW SOUTH AND EAST OF THE GULF OF ALASKA  
MOVING EAST TOWARDS WASHINGTON. ANOTHER UPPER LOW LOCATED OVER  
THE NORTHERN INTERIOR WILL BE TRACKING SOUTH AND BE OVER THE  
NORTHWEST GULF BY THURSDAY MORNING. UPSTREAM, A BUILDING UPPER  
RIDGE WILL BE SITUATED OVER THE BERING SEA. THE UPPER LOW WILL  
SLOWLY TRACK SOUTH AND DOMINATE THE GULF BY FRIDAY MORNING. BY  
THIS TIME, THE UPSTREAM RIDGE WILL HAVE STRENGTHENED INTO AN  
OMEGA BLOCK, WITH ANOTHER UPPER LOW OVER THE SEA OF OKHOTSK. BY  
THE END OF NEXT WEEKEND, THE OMEGA BLOCK REMAINS STRONG AND IN  
PLACE WHILE THE UPPER LOW WILL HAVE CONTINUED A SLOW TRACK SOUTH  
OF THE GULF OF ALASKA.  
 
THE COMBINED EFFECT OF THE UPPER LOW OVER THE GULF AND THE  
BUILDING UPPER RIDGE TO THE WEST WILL BE TO ADVECT IN COLDER LOW  
LEVEL AIR OVER THE PANHANDLE. SOME MODIFICATION OF THIS AIRMASS  
WILL OCCUR AS IT CROSSES A CONSIDERABLE DISTANCE OVER THE OPEN  
OCEAN, BUT THE RIDGE WILL PREVENT ANY WARMER AIR FROM THE WEST  
FROM MIXING IN. 850H TEMPERATURES FAVORING RAIN ON WEDNESDAY AND  
THURSDAY DURING THE DAY SOUTH OF FREDERICK SOUND, BUT THEN BECOME  
MORE SUPPORTIVE OF SNOW ALL THE WAY SOUTH TO THE DIXON ENTRANCE  
OVERNIGHT BOTH NIGHTS AND THEN THROUGH AT LEAST SATURDAY.  
1000-500 AND 1000-850 THICKNESSES SHOWING A SIMILAR PATTERN.  
DAYTIME HIGHS OVER THE SOUTHERN HALF OF THE PANHANDLE FROM  
FREDERICK SOUND SOUTH INDICATING THAT THERE IS A GOOD CHANCE THAT  
AT LEAST SOME OF THE PRECIPITATION FOR THIS COMING WEEK WILL BE IN  
THE FORM OF RAIN. OTHERWISE, WHAT PRECIP WE DO SEE MAY BE MOSTLY  
IN THE FORM OF SNOW. NO WELL DEFINED FRONTS CURRENTLY BEING  
DEPICTED IN MEDIUM TO LONG RANGE MODELS, SO CONVECTIVE PRECIP  
(SHOWERS) IS ANTICIPATED THROUGH AT LEAST WEDNESDAY NIGHT. 12  
HOUR SNOW TOTALS CURRENTLY INDICATING POSSIBLY ADVISORY LEVEL  
SNOWFALL WEDNESDAY FOR CENTRAL ZONES AND WEDNESDAY NIGHT FOR  
NORTHERN ZONES SOUTH OF BERNERS BAY. CONVECTIVE NATURE OF THIS  
PRECIPITATION WILL CAUSE THE SNOW TOTALS TO BE A CONSTANTLY MOVING  
TARGET EVEN AS THE EVENT UNFOLDS, SO STAY TUNED FOR UPDATES AS THE  
WEEK PROGRESSES.  
 
NO SIGNIFICANT CHANGES TO PRESSURE OR WINDS. POP AND QPF PRIMARILY  
FROM NAM WEDNESDAY AND WEDNESDAY NIGHT WITH LITTLE CHANGE FOR THE  
REMAINDER OF THE LONG RANGE FORECAST. DAYTIME HIGHS AND OVERNIGHT  
LOWS GENERALLY NUDGED DOWN SLIGHTLY FOR THE SECOND HALF OF THE  
WEEK BASED ON CURRENT MODEL SPECTRUM PLOTS. OVERALL FORECAST  
CONFIDENCE IS AVERAGE, BUT BELOW AVERAGE FOR SNOW TOTALS.  
 

 
   
AJK WATCHES/WARNINGS/ADVISORIES
 
 
PUBLIC...NONE.  
MARINE...SMALL CRAFT ADVISORY FOR PKZ012-013-022-033-036-041>043-051-052.  
 

 
 

 
 
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