410  
FXAK68 PAFC 170105  
AFDAFC  
 
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE ANCHORAGE AK  
505 PM AKDT TUE OCT 16 2018  
   
ANALYSIS AND UPPER LEVELS
 
 
THE LARGE ANCHOR-LOW OVER THE EASTERN BERING SEA REMAINS  
VERTICALLY STACKED TODAY WITH THE 250 MB JET STREAM RUNNING SOUTH  
OF IT AND THEN BENDING NORTHWARD INTO THE EASTERN GULF OF ALASKA.  
THIS JET STREAM HAS MOVED EASTWARD OVER THE PAST DAY AND WAS THE  
MAIN SOURCE OF THE STRONG WINDS AND HEAVY RAINFALL OVER AREAS OF  
SOUTHCENTRAL ALASKA SINCE THEN. AREAS AROUND THE NORTH GULF COAST  
AND PRINCE WILLIAM SOUND REGION SAW 3 TO 5 INCHES OF RAIN IN A 24  
HOUR PERIOD. TODAY THERE ARE JUST SOME SHOWERS THAT NOW PERSIST  
IN THE SOUTHERLY FLOW ALOFT NOW THAT THE JET STREAM HAS MOVED OFF  
TO THE EAST.  
 

 
   
MODEL DISCUSSION
 
 
MODELS ARE IN GOOD AGREEMENT WITH THE LOW PLACEMENT AND INTENSITY  
SITUATED IN THE EASTERN BERING AND SEEM DO BE DOING WELL THROUGH  
TOMORROW NIGHT.  
 
DIFFERENCES ARISE WITH THE NORTH PACIFIC LOW THAT MOVES NORTHWARD  
INTO THE GULF THURSDAY AFTERNOON. THE GFS AND NAM ARE NOT ONLY IN  
GOOD AGREEMENT WITH EACH OTHER, BUT HAVE BEEN MORE CONSISTENT ON  
A RUN-TO-RUN BASIS AS WELL. THE GFS MODEL, IN PARTICULAR, HAS  
BEEN CONSISTENT IN SHOWING THE LOW WITH A STRONGER AND MORE  
NORTHWESTERLY TRACK WHICH FITS INTO THE OVERALL PATTERN THE BEST.  
THE 12Z EC IS STARTING TO CATCH UP WITH THE OTHER MODELS COMPARED  
TO OLDER MODEL RUNS, BUT HAS BEEN THE MOST INCONSISTENT.  
 

 
   
AVIATION
 
 
PANC...GUSTY SOUTHEAST WINDS WILL PERSIST THROUGH THE EVENING AND  
THEN DIMINISH TOWARD MORNING. SHOWERS WILL MOVE THROUGH THE  
REGION THROUGH TOMORROW, BUT SHOULD BECOME LESS NUMEROUS  
THROUGHOUT THE PERIOD. CEILINGS AND VISIBILITIES SHOULD REMAIN VFR  
EVEN DURING THESE SHOWERS, THOUGH THE POSSIBILITY EXISTS FOR A  
BRIEF DROP TO MVFR CONDITIONS IN A SHOWER.  
 

 
 
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (TONIGHT THROUGH  
FRIDAY)...  
 
THE MAIN WEATHER CONCERN THROUGH THE END OF THE WORK WEEK SURROUNDS  
THE RAPIDLY DEEPENING LOW THAT LIFTS NORTH OVER THE GULF THURSDAY  
NIGHT INTO FRIDAY. THIS SYSTEM IS EXPECTED TO BRING STORM FORCE  
WINDS AROUND THE CORE OF THE LOW ALONG WITH MODERATE TO HEAVY RAIN  
ALONG THE COASTAL LOCATIONS.  
 
SHOWERS WILL CONTINUE TO DEVELOP ACROSS SOUTHCENTRAL AND THE GULF  
AS A WEAK TROUGH REMAINS OVER THE REGION THROUGH WEDNESDAY. GUSTY  
SOUTHERLY WINDS PERSIST THROUGH LATE TONIGHT, THEN TAPER DOWN AS  
THE PRESSURE GRADIENT RELAXES ALONG THE DIMINISHING FRONT ACROSS  
THE SOUTHERN MAINLAND. ISOLATED THUNDERSTORMS ARE POSSIBLE ACROSS  
MUCH OF THE GULF AND NEAR THE COASTS WITH GREATER INSTABILITY OVER  
THE AREA WATERS THROUGH WEDNESDAY NIGHT.  
 
THE NEXT FRONT MOVES UP ALONG A STRONG SHORT WAVE ENTERING THE  
SOUTHERN GULF THURSDAY MORNING. THE SURFACE LOW DEEPENS TO 985 MB  
AS IT APPROACHES KODIAK ISLAND THURSDAY AFTERNOON. GALE FORCE  
EASTERLY FLOW ACROSS MUCH OF THE GULF WILL INCREASE TO STORM  
FORCE AS THE ANOTHER LOW QUICKLY FOLLOWS THURSDAY NIGHT. THE  
INITIAL FRONT BRINGS STEADY RAIN BACK TO KODIAK ISLAND THE EASTERN  
KENAI WITH RAIN SPREADING TO THE NORTH COAST BY FRIDAY MORNING.  
SHOWERS WILL MOVE INLAND AHEAD OF THE FRONT, HOWEVER STRONG NORTH  
TO EASTERLY FLOW LIMITS RAINFALL AMOUNTS. THE HEAVIEST RAIN IS  
EXPECTED ACROSS THE EASTERN KENAI AND ALONG PRINCE WILLIAM SOUND.  
 

 
 
.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 THROUGH 3/TONIGHT  
THROUGH FRIDAY)...  
A LOW SOUTH OF NUNIVAK ISLAND WILL WEAKEN AS IT DRIFTS TO THE  
VICINITY OF CAPE NEWENHAM WEDNESDAY AFTERNOON, THEN REMAIN NEARLY  
STATIONARY AS IT CONTINUES TO DISSIPATE THROUGH THU NIGHT. NUMEROUS  
WEAK WAVES EMBEDDED WITHIN THE FLOW AROUND THE UPPER LOW WILL  
COMBINE WITH BROAD-SCALE ATMOSPHERIC INSTABILITY TO PRODUCE  
SHOWERS. THE LACK OF A STRONG FEATURE MAKES IT DIFFICULT TO  
PINPOINT TIMING AND LOCATION OF SHOWERS. THUS, HAVE LARGELY USED  
A BROAD-BRUSH APPROACH TO THE PRECIP FORECAST WITH SCATTERED  
SHOWERS ACROSS MOST OF SOUTHWEST ALASKA THE NEXT FEW DAYS. SHOWERS  
WILL BEGIN TO DIMINISH FRIDAY AS THE LOW DISSIPATES AND WEAK  
RIDGING BUILDS IN AHEAD OF A DEEP LOW CROSSING THE GULF OF  
ALASKA.  
 
 

 
 
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 THROUGH  
3/TONIGHT THROUGH FRIDAY)...  
A WEAKENING LOW WILL REMAIN PARKED NEAR THE SOUTHWEST ALASKA COAST  
THE NEXT FEW DAYS. WEAK COLD ADVECTION ON THE BACK SIDE OF THIS  
LOW WILL PRODUCE A BAND OF GUSTY GALE FORCE NORTHERLY WINDS  
ACROSS THE CENTRAL BERING SEA ON DOWN TO THE CENTRAL AND EASTERN  
ALEUTIAN ISLANDS. THE COLD ADVECTION WILL HELP TO FOCUS SHOWERS  
THROUGH THIS SAME CORRIDOR. TEMPERATURES MAY BE JUST COLD ENOUGH  
TO SUPPORT SNOW OR A RAIN SNOW MIX OVER THE NORTHERN BERING, BUT  
THE REMAINDER OF THE AREA WILL REMAIN SAFELY ALL RAIN.  
 
THE LOW AND UPPER LEVEL WAVE PATTERN WILL SLOWLY SHIFT EASTWARD,  
WITH A TROUGH MOVING OVERHEAD OF THE WESTERN ALEUTIANS THURSDAY  
NIGHT THROUGH FRIDAY. WITH RIDGING OUT AHEAD OF THIS TROUGH THE  
SURFACE LOW WILL REMAIN WEST OF THE ALEUTIAN CHAIN, THOUGH AN  
OCCLUDED FRONT WILL TRACK EASTWARD ACROSS THE WESTERN ALEUTIANS.  
 

 
   
LONG TERM FORECAST (DAYS 4 THROUGH 7)
 
 
AT THE ONSET OF THE FORECAST PERIOD, THE SYNOPTIC PATTERN  
FEATURES A LOW NEAR KENAI, A SECOND LOW SOUTH OF THE ALEUTIAN  
CHAIN AND A LOW NEAR KAMCHATKA. ANTICIPATE A VERY WET AND PROGRESSIVE  
PATTERN. THERE IS GOOD GENERAL CONSENSUS BETWEEN THE  
GFS/EC/CANADIAN BUT THE BEST PERFORMING MODEL IS THOUGHT TO BE THE  
GFS FOR THIS FORECAST PERIOD. EXPECT BACK TO BACK LOWS TO BRING A  
HEFTY AMOUNT OF PRECIPITATION TO KODIAK, PRINCE WILLIAM SOUND AND  
THE ANCHORAGE BOWL. EVEN THOUGH THE THIRD WEEK OF OCTOBER IS  
CONSIDERED TO BE PART OF THE COLD SEASON FOR ALASKA, THE  
TEMPERATURES WITH BOTH STORMS WILL REMAIN WELL ABOVE FREEZING IN  
THE LOW ELEVATIONS. HIGHER ELEVATIONS ON THE KENAI AND OTHER  
PORTIONS OF SOUTH CENTRAL CAN EXPECT A FRESH BLANKET OF SNOW THIS  
FORECAST PERIOD BUT SIGNIFICANT ACCUMULATIONS NOT EXPECTED. THE  
ENTIRE FORECAST PERIOD, THE GFS HAS ABOVE NORMAL TEMPERATURES AT  
500 MB FROM KENAI TO THE YUKON TERRITORY TO JUNEAU.  
 

 
 
   
AFC WATCHES/WARNINGS/ADVISORIES
 
 
PUBLIC...FLOOD ADVISORY 125.  
MARINE...GALES 173-176 412-413.  
 

 
 

 
 
SYNOPSIS AND MODEL DISCUSSION...EZ  
SOUTHCENTRAL ALASKA...KH  
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...SEB  
LONG TERM...PS  
 
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