080  
FXAK68 PAFC 191332  
AFDAFC  
 
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE ANCHORAGE AK  
432 AM AKST SUN NOV 19 2017  
   
ANALYSIS AND UPPER LEVELS
 
 
A POWERFUL DIGGING UPPER LEVEL LOW CENTERED JUST WEST OF NORTON  
SOUND AND ITS ASSOCIATED INFLUENCE ON THE JET IS DRIVING ALL OF  
THE ACTIVE WEATHER ACROSS SOUTHERN ALASKA THIS MORNING. THE  
PRIMARY JET STREAK LIES TO THE WEST OF THE CENTER OF THE UPPER  
LOW, WHICH IS FURTHER ENHANCING THE NEGATIVE (NORTHWEST TO  
SOUTHEAST) TILT OF THE PRIMARY SHORTWAVE TROUGH AXIS. AS A RESULT,  
A STRONG LOW, ALSO TAKING ADVANTAGE OF EXCELLENT BAROCLINICITY IS  
TRACKING INTO SOUTHWEST ALASKA. BY NOW THE COLD FRONT HAS LARGELY  
SWEPT ACROSS ALL OF SOUTHWEST ALASKA, AND ALL REMAINING LIQUID  
PRECIPITATION IS CHANGING BACK OVER TO SNOW. THE LEADING EDGE OF  
THE PRECIPITATION IS CROSSING THE ALASKA RANGE NOW (A FEAT IN AND  
OF ITSELF), AND WILL BE OVERSPREADING SOUTHCENTRAL OVER THE NEXT  
FEW HOURS. MUCH OF THE HEAVIEST SNOWFALL IS ONGOING ACROSS  
SOUTHWEST ALASKA ON THE WEST SIDE OF THE ALASKA RANGE AND THE  
KUSKOKWIM MOUNTAINS. MEANWHILE FOR THE BERING, A TRANSITION TO  
MUCH COLDER TEMPERATURES ALONG WITH VERY WINDY CONDITIONS IS  
OCCURRING.  
 

 
   
MODEL DISCUSSION
 
 
THE MODELS REMAIN IN EXCELLENT AGREEMENT THROUGH THE SHORT-TERM.  
ALL GENERALLY AGREEING ON THE SYNOPTIC EVOLUTION OF THE ONGOING  
WINTER STORM AND THE TIMING ON THE NEXT FRONT THAT WILL CROSS THE  
BERING AND MOVE INTO SOUTHWEST ALASKA ON TUESDAY. THUS, THE MAIN  
MODEL DIFFERENCE ONCE AGAIN RESIDE IN THE LOCAL EFFECTS, FOR WHICH  
THE HIGH-RESOLUTION MODELS LIKE THE NAMNEST WERE PREFERRED.  
FORECAST CONFIDENCE REMAINS HIGH ON THE BROAD PATTERN AND SOMEWHAT  
LOWER ON THE LOCAL DETAILS.  
 

 
   
AVIATION
 
 
PANC...SNOW HAS BEGUN AND WILL INTENSIFY THROUGH THE MORNING  
BRINGING VISIBILITIES TO MVFR TO OCCASIONAL IFR WITH ANY STRONGER  
BANDS. THE SNOW WILL TAPER TO SNOW SHOWERS LATE MORNING AND END  
COMPLETELY DURING THE AFTERNOON, RESULTING IN IMPROVING CONDITIONS  
BACK TO VFR THROUGH MONDAY MORNING.  
 

 
   
SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 THROUGH 3)
 
 
 
SOUTHCENTRAL MAINLAND...  
A WEAKENING OCCLUDED FRONT IS SPREADING SNOW ACROSS MUCH OF  
SOUTHCENTRAL TODAY. SNOW SHOULD DIMINISH DURING THE AFTERNOON  
INLAND AND THE EVENING TO OVERNIGHT HOURS ALONG THE COASTS. THE  
KENAI PENINSULA WILL GET A FAIR AMOUNT OF SNOW TODAY WITH THE  
WESTERN KENAI PENINSULA EXPECTED TO HIT ADVISORY LEVELS (4 TO 8  
INCHES). GUSTY WINDS DEVELOPING LATER TODAY WILL ALSO REDUCE  
VISIBILITIES IN BLOWING SNOW. ELSEWHERE ACROSS SOUTHCENTRAL SNOW  
AMOUNTS SHOULD NOT EXCEED 2 TO 4 INCHES. OUTFLOW AND GAP  
CONDITIONS ARE EXPECTED TO DEVELOP ACROSS THE NORTH GULF AND THE  
MATANUSKA VALLEY BEGINNING OVERNIGHT. THE STRONGEST OUTFLOW  
CONDITIONS WILL BE ALONG THE NORTH GULF COAST.  
 
KODIAK AND THE GULF WATERS...  
A DEVELOPING TRIPLE-POINT LOW NEAR KODIAK WILL MOVE SLOWLY EAST  
TODAY AND THEN TRACK SOUTH MONDAY. THIS CENTER WILL PRODUCE  
WIDESPREAD GALES AND STORMS OVER THE NORTHERN AND WESTERN GULF  
WATERS. THESE CONDITIONS WILL HOLD THROUGH TONIGHT BEFORE SLOWLY  
DIMINISHING AND PUSHING SOUTH MONDAY AFTERNOON. SNOW MIXED AT  
TIMES WILL RAIN ALONG WITH STRONG WINDS AND BLOWING SNOW POTENTIAL  
ARE EXPECTED TO CONTINUE OVER KODIAK THROUGH TONIGHT. A SLIGHT  
CHANGE IN THE POSITIONS OF THE TRIPLE COULD MAKE A BIG DIFFERENCE  
IN SNOWFALL POTENTIAL. STAY TUNED FOR UPDATES.  
 

 
   
SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)
 
 
EARLY THIS MORNING, A STRONG COLD FRONT IS STRETCHED FROM JUST  
EAST OF ANIAK TO KING SALMON AT 4 AM. AHEAD OF THIS FRONT,  
WIDESPREAD SNOW HAS DEVELOPED, SOME OF WHICH HAS BEEN HEAVY WITH  
VISIBILITIES REDUCED TO ONE QUARTER OF A MILE. BEHIND THE FRONT,  
THE PRECIPITATION BECOMES MORE SHOWERY IN NATURE WITH MAINLY SNOW  
SHOWERS OBSERVED IN THE KUSKOKWIM DELTA SOUTH TOWARDS BRISTOL BAY,  
BEFORE THINGS CHANGE OVER TO LIQUID FORM. HOWEVER, STRONG  
NORTHWEST WINDS (CURRENTLY PUSHING 55 MPH) HAVE ALREADY PUSHED  
INLAND ALONG THE COAST FROM GOODNEWS BAY NORTH AND THIS WILL  
CONTINUE TO SPREAD SOUTHEAST THROUGH THE REMAINDER OF THE MORNING,  
CHANGING ALL PRECIPITATION BACK TO SNOW SHOWERS. ADDITIONAL  
ACCUMULATIONS OF UP TO 2 INCHES REMAIN POSSIBLE FOR THE BETHEL  
AREA AND POINTS TOWARDS THE COAST, WITH LESS TOWARDS KING SALMON.  
FURTHER INLAND ALONG THE KUSKOKWIM MOUNTAINS AND ALASKA RANGE,  
ANOTHER 3 TO 6 INCHES LOOKS LIKE A GOOD BET BEFORE THE STORM  
GIVING US THE SNOW EXITS THE REGION AS IT HEADS TOWARDS THE GULF  
OF ALASKA. ALTHOUGH THE WINDS WILL GRADUALLY DIMINISH OVER THE  
NEXT 36 HOURS, BLOWING SNOW WILL CONTINUE TO BE A CONCERN THROUGH  
THAT TIME.  
 

 
   
SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)
 
 
WINDS WILL CONTINUE TO INCREASE IN STRENGTH TODAY FOR THE EASTERN  
HALF OF THE BERING SEA AND AKPEN. A STRONG AREA OF LOW PRESSURE  
WILL CONTINUE ITS TREK FROM NOME TOWARDS THE EASTERN KODIAK  
ISLAND VICINITY. A VIGOROUS 125KT MID LEVEL JET ALREADY STRETCHES  
ACROSS THE REGION. HOWEVER, THE LEADING EDGE OF 850 MB COLD  
ADVECTION AND DRYING ALOFT IS LAGGING A FEW HUNDRED MILES BEHIND  
THE SURFACE FRONT. THIS WILL CONTINUE TO DIVE SOUTHEAST HEADING  
THROUGH THE MORNING AND INTO THE AFTERNOON. AS THIS OCCURS,  
VERTICAL MIXING WILL RAPIDLY INCREASE WITH HURRICANE FORCE GUSTS  
LIKELY FOR THE REGION. WESTERN AREAS OF THE ALASKA PENINSULA AND  
EASTERN BERING SEE WILL SEE THE LONGEST DURATION OF SUCH WINDS  
COMPARED TO POINTS FURTHER WEST. WITH THAT IN MIND, THE CURRENT  
HEADLINES LOOK GOOD AND ONLY MINOR TWEAKS TO THE FORECAST WERE  
MADE.  
 
FURTHER WEST, A RIDGE OF HIGH PRESSURE STRETCHED ACROSS THE  
WESTERN ALEUTIANS AND THIS RIDGE WILL SHIFT EASTWARD THROUGH THIS  
EVENING BEFORE DE-AMPLIFYING OVERNIGHT. HEADING INTO MONDAY, A  
STRONG LOW MOVING ACROSS EASTERN SIBERIA WILL SEND YET ANOTHER  
COLD FRONT EASTWARD ACROSS THE BERING SEA MONDAY INTO TUESDAY,  
WITH STRONG WINDS DEVELOPING ACROSS THE NORTHERN HALF OF THE  
REGION.  
 
ANOTHER LOW WILL MOVE INTO THE WESTERN BERING BY WEDNESDAY  
MORNING, WITH AN ATTENDANT WARM FRONT SWEEPING NORTHEAST.  
WIDESPREAD PRECIPITATION WILL DEVELOP ALONG THIS FEATURE AND WE  
WERE TEMPTED TO ADD IN A MENTION OF FOG BUT DECIDED TO HOLD OFF  
FOR ANOTHER FORECAST CYCLE OR TWO, AS SOME MODELS DIFFER ON THE  
STRENGTH OF THE WARM AIR ALOFT MOVING INTO THE AREA. THIS LOW  
WILL RAPIDLY DEEPEN AS IT HEADS TOWARDS THE KUSKOKWIM DELTA BY  
LATE WEDNESDAY EVENING, DEEPENING 26 MB AS IT DOES SO. AS SUCH,  
YOU GUESSED IT, MORE STRONG WINDS ARE LIKELY, POSSIBLY REACHING  
STORM FORCE.  
 

 
   
LONG TERM FORECAST (DAYS 3 THROUGH 7)
 
 
AFTER TUESDAY'S SYSTEM MOVES OUT OF ALASKA, A SHORTWAVE RIDGE WILL  
ONCE AGAIN MOVE IN OVER MOST OF THE STATE. THIS WILL BRING A  
PERIOD OF CLEAR SKIES AND SEASONABLY COLD TO BELOW NORMAL  
TEMPERATURES IN SOME VALLEYS THROUGH WEDNESDAY EVENING. YET  
ANOTHER SYSTEM WILL APPROACH ALASKA FROM THE WEST BEGINNING  
WEDNESDAY NIGHT, TRAVERSING THE BERING SEA ON A VERY SIMILAR PATH  
TO THE PREVIOUS TWO SYSTEMS. THIS WILL BRING A REPEAT OF STRONG  
WESTERLY WINDS FOLLOWED BY STRONG NORTHWESTERLY WINDS FOR THE  
BERING COAST AND THE AK PEN. PRECIPITATION TYPE LOOKS LIKE IT WILL  
BE LESS OF A CHALLENGE WITH THIS SYSTEM, AS IT HAS COLDER AIR  
ALOFT THAN THE CURRENT SYSTEMS. CURRENT THINKING IS THAT IT WILL  
REMAIN ALL SNOW FOR THE WEST COAST ON THURSDAY, BUT THAT MAY  
CHANGE AS THE SYSTEM GETS CLOSER.  
 
THIS SYSTEM IS CURRENTLY EXPECTED TO BOTTOM OUT AT 970 MB AS IT  
APPROACHES THE WEST COAST. AS IT CROSSES THE AK PEN, IT DEVELOPS A  
SECONDARY LOW IN THE GULF OF ALASKA WHICH SHOULD HELP TO DRAW  
SOME COLDER AIR DOWN FROM THE INTERIOR. AS A RESULT, OUTFLOW WINDS  
ARE EXPECTED TO PICK UP ON THE SOUTHERN SIDE OF THE AK PEN AND IN  
THE USUAL CHANNELED AREAS THROUGHOUT SOUTHCENTRAL. IF THE SYSTEM  
REMAINS AS STRONG AS FORECAST, THE WEATHER CHALLENGE FOR THE END  
OF NEXT WEEK WILL BE STRONG NORTHERLY WINDS FOR BOTH EAST AND  
WEST.  
 

 
 
   
AFC WATCHES/WARNINGS/ADVISORIES
 
 
PUBLIC...HIGH WIND WARNING: 181 185 195.  
WINTER WEATHER ADVISORY: 121 152 161 171.  
 
MARINE...  
STORM WARNING: 119 120 131 132 136 137 155 165 170-172 179-181  
185 352 412 414.  
GALE WARNING: 127 130 138 139 150 160 173 174 178 351 411 413.  
 

 
 

 
 
SYNOPSIS AND MODEL DISCUSSION...JPW  
SOUTHCENTRAL ALASKA...RMC  
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD  
LONG TERM...LF  
 
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