390  
FXAK68 PAFC 211423  
AFDAFC  
 
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE ANCHORAGE AK  
523 AM AKST MON JAN 21 2019  
   
ANALYSIS AND UPPER LEVELS
 
 
AN UPPER LEVEL RIDGE IS RETREATING AS A LOW PRESSURE SYSTEM SOUTH  
OF THE ALEUTIANS IS PUSHING A FRONT NORTH ACROSS THE SOUTHERN  
MAINLAND. SATELLITE IMAGERY SHOWS HIGH AND MID LEVEL CLOUD COVER  
STREAMING NORTH ACROSS THE THE AKPEN AND GULF OF ALASKA AS  
PRECIPITATION IS BEGINNING TO SHOW UP ON THE KING SALMON RADAR  
JUST TO THE SOUTH OF KING SALMON. A WEAK SURFACE LOW IS CURRENTLY  
SPINNING OVER THE GULF BRINGING SNOW SHOWERS TO THE PRICE WILLIAM  
SOUND AND NORTHERN GULF COAST. RADAR IMAGERY ALSO SHOWS SNOW  
SHOWERS PUSHING ACROSS THE WESTERN KENAI PENINSULA AND EVEN ACROSS  
THE ANCHORAGE AREA, THOUGH LOCAL OBSERVATIONS AND WEBCAMS SHOW  
THIS IS MOSTLY EVAPORATING BEFORE REACHING THE GROUND. MEANWHILE,  
THE SURFACE LOW FURTHER WEST OVER THE ALEUTIANS IS BRINGING  
STRONG WINDS AND SNOW SHOWERS TO THE AREA, WITH SCATTEROMETER  
PASSES SHOWING A WIDE SWATH OF GALE FORCE WINDS OVER MOST OF THE  
SOUTHERN BERING SEA.  
 

 
   
MODEL DISCUSSION
 
 
MODELS ARE IN GOOD AGREEMENT THROUGH TUESDAY AS A SERIES OF FRONTS  
PUSHES NORTH ACROSS THE AKPEN AND GULF OF ALASKA. BY WEDNESDAY, A  
SECONDARY LOW MOVES UP FROM THE NORTH PACIFIC AND CROSSES OVER  
THE AKPEN AND INTO BRISTOL BAY. MODELS HAVE RECENTLY BEEN  
STRUGGLING WITH HOW FAR EAST OR WEST THE LOW WOULD TRACK, WHICH  
WOULD HAVE A SIGNIFICANT IMPACT TO WEATHER ACROSS THE SOUTHERN  
MAINLAND. THE NAM HAS BEEN THE OUTLIER TRACKING THE LOW FURTHER  
EAST ACROSS THE SW MAINLAND WHILE THE GFS AND EC HAVE BEEN KEEPING  
THE LOW FURTHER WEST OVER BRISTOL BAY. RECENT NAM RUNS HAVE BEEN  
TRENDING FURTHER WEST TOWARDS THE GFS/EC SOLUTIONS, THUS TRENDED  
TOWARDS THAT SOLUTION AS WELL.  
 

 
   
AVIATION
 
 
PANC...AN APPROACHING FRONT FROM THE SOUTH IS HELPING TO  
DESTABILIZE THE ATMOSPHERE AND HAS ERODED ALL REMAINING FOG AND  
LOW STRATUS IN THE AREA. VFR CONDITIONS AND LIGHT NORTHEASTERLY  
WINDS WILL PREVAIL FOR THE TAF PERIOD WITH JUST A CHANCE OF SOME  
LIGHT SNOW THIS AFTERNOON.  
 

 
 
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2/TODAY  
THROUGH TUESDAY NIGHT)...  
BROAD SOUTHERLY FLOW ABOVE THE SURFACE COMBINED WITH A WEAK UPPER  
LEVEL WAVE WILL PRODUCE AREAS OF VERY LIGHT SNOW ACROSS  
SOUTHCENTRAL TODAY. GENERALLY EXPECT FLURRIES OR A DUSTING INLAND.  
LOW LEVEL INSTABILITY AND UPSLOPE FLOW ALONG THE COAST AND PRINCE  
WILLIAM SOUND WILL LEAD TO SNOW SHOWERS AND SOME MINOR SNOW  
ACCUMULATION. FURTHER SOUTH, A WEAKENING OCCLUDED FRONT EXTENDING  
FROM A DEEP LOW ALONG THE ALEUTIANS WILL SLOWLY LIFT NORTHWARD  
TOWARD KODIAK ISLAND TODAY, THEN FALL APART BEFORE REACHING THE  
NORTHERN GULF TONIGHT. ANOTHER UPPER LEVEL SHORT-WAVE WILL LIFT  
NORTHWARD, BUT WILL WEAKEN AS IT CROSSES SOUTHCENTRAL DUE TO  
RAPIDLY RISING HEIGHTS ALOFT AS THE UPPER LEVEL FLOW AMPLIFIES.  
THUS, EXPECT LITTLE IN THE WAY OF PRECIPITATION WITH IT. LOW LEVEL  
SOUTHEAST FLOW WILL FAVOR UPSLOPE PRECIPITATION IN WESTERN PRINCE  
WILLIAM SOUND AS WELL AS THE WEST SIDE OF COOK INLET AND THE  
WESTERN SUSITNA VALLEY.  
 
ANOTHER OCCLUDED FRONT WILL MAKE ITS WAY TO KODIAK ISLAND ON  
TUESDAY, WITH TEMPERATURES WARM ENOUGH TO PRODUCE ALL RAIN. THIS  
FRONT WILL ALSO DISSIPATE AS IT LIFTS NORTHWARD TOWARD SOUTHCENTRAL.  
A MUCH MORE SIGNIFICANT STORM SYSTEM IS SHAPING UP FOR TUESDAY  
NIGHT INTO WEDNESDAY. WHILE THERE IS UNCERTAINTY IN THE STORM  
TRACK, THERE IS HIGH CONFIDENCE THIS SYSTEM WILL TRACK INTO THE  
BERING SEA. DEEP SOUTHERLY FLOW WILL PUMP UP WARM AIR FROM THE  
PACIFIC TO SOUTHCENTRAL, SO AS PRECIPITATION SPREADS TO THE GULF  
COAST ON WEDNESDAY IT WILL FALL AS MOSTLY RAIN. STRONG LOW LEVEL  
SOUTHEAST FLOW WILL LEAD TO DOWNSLOPE DRYING FOR THE POPULATION  
CENTERS, FROM THE WESTERN KENAI TO ANCHORAGE AND THE MATANUSKA  
VALLEY. THE EXACT TRACK OF THE STORM WILL ULTIMATELY DETERMINE HOW  
SIGNIFICANT OF A WARM-UP THESE AREAS SEE.  
 

 
   
SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2
 
TODAY AND  
TUESDAY)... AN OCCLUDED FRONT ASSOCIATED WITH A NORTH PACIFIC LOW  
NEARING THE CENTRAL ALEUTIANS WILL BRING PRECIPITATION TO MUCH OF  
SOUTHWEST OVER THE NEXT TWO DAYS AND, IN ITS WAKE, A SHIFT TO  
WARMER WEATHER.  
 
THE FRONT IS CURRENTLY STRETCHED FROM THE AKPEN TO THE CENTRAL  
ALEUTIANS. HIGH PRESSURE OVER EASTERN SIBERIA AND AN ARCTIC UPPER  
LOW OVER NORTHERN AK HAVE MAINTAINED OFFSHORE FLOW AND VERY COLD,  
DRY CONDITIONS IN THE LOWER KUSKOKWIM VALLEY/KUSKOKWIM DELTA,  
HOWEVER FARTHER SOUTH ALONG THE AKPEN TEMPERATURES HAVE STARTED TO  
INCREASE IN SOUTHERLY FLOW BEHIND THE FRONT. EXPECT BLOWING SNOW  
IN THE BRISTOL BAY AREA LATER TODAY, THEN A TRANSITION TO RAIN AND  
TEMPERATURES ABOVE FREEZING TUESDAY. LOOKING FARTHER NORTH, THE  
LOWER KUSKOKWIM VALLEY AND KUSKOKWIM DELTA WILL HANG ON TO  
NORTHEAST FLOW AT THE SURFACE UNTIL LATER TONIGHT, AND EXPECT  
BLOWING SNOW ALONG THE KUSKO DELTA COAST TONIGHT. THESE AREAS WILL  
LIKELY HANG ON TO COLD AIR A BIT LONGER THAN FARTHER SOUTH, BUT  
EVEN INLAND VALLEYS WILL WARM TO ABOVE FREEZING BY MIDWEEK.  
 

 
   
SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2
 
TODAY AND  
TUESDAY)... A GALE FORCE NORTH PACIFIC LOW IS SLOWLY SHIFTING  
NORTH/NORTHWEST TOWARD THE CENTRAL ALEUTIANS. THIS LOW WILL  
CONTINUE TO BRING AREAS OF GALES TO THE WESTERN ALEUTIANS AND  
WIDESPREAD GALES TO MUCH OF THE BERING, INCLUDING THE PRIBILOFS,  
THROUGHOUT THE DAY. OVER THE EASTERN ALEUTIANS, WINDS WILL SLOWLY  
DIMINISH TODAY AS THE LOW GRADUALLY SHIFTS WESTWARD.  
 
AN OCCLUDED FRONT ASSOCIATED WITH THE LOW CURRENTLY STRETCHES  
FROM THE AKPEN TO THE CENTRAL ALEUTIANS, AND PTYPES OVER THE  
CENTRAL AND EASTERN ALEUTIANS HAVE CHANGED OVER TO RAIN.  
TEMPERATURES IN THE UPPER 30S TO LOW 40S WILL PERSIST INTO  
TUESDAY. THE WESTERN ALEUTIANS REMAIN ON THE COLD SIDE OF THE LOW,  
THUS WILL CONTINUE SNOW OR RAIN/SNOW MIX. A DEFORMATION BAND  
NEARING THE PRIBILOFS IS EVIDENT ON WATER VAPOR SATELLITE WHICH  
WILL ENHANCE PRECIPITATION RATES. WITH NORTHEAST GALES AT THE  
SURFACE, EXPECT BLOWING SNOW TODAY INTO TONIGHT. AS THE FRONT  
LIFTS NORTH OF THE AREA, WINDS WILL VEER TO SOUTHERLY AND  
PRECIPITATION WILL TRANSITION TO RAIN.  
 

 
   
MARINE (DAYS 3 THROUGH 5)
 
 
(WEDNESDAY THROUGH FRIDAY)  
 
THE MARINE OUTLOOK REMAINS CHALLENGING AS MODEL CONTINUITY REMAINS  
MODEST. THE GENERAL TREND OVER THE LAST 24 HOURS HAS BEEN FOR A  
NORTHWESTWARD SHIFT IN THE SURFACE AND UPPER AIR PATTERN, AS A  
RIDGE OF HIGH PRESSURE BUILD NORTHWEST ACROSS THE EAST CENTRAL  
GULF, THEN ACROSS SOUTHCENTRAL ALASKA INTO THE NORTH SLOPE. THIS  
WILL ALSO ALLOW A SERIES OF LOWS LIFTING ACROSS THE WESTERN AND  
CENTRAL ALEUTIANS ON WEDNESDAY TO RETROGRADE TOWARDS THE WESTERN  
ALEUTIANS AND KAMCHATKA PENINSULA BY FRIDAY. HOW FAST THIS OCCURS  
AND WHERE THE LOW PRESSURE CENTERS WILL BE IS YET TO BE  
DETERMINED.  
 
HOWEVER, THERE HAS BEEN SOME IMPROVEMENT WITH THIS SINCE  
YESTERDAY. THE GFS AND CANADIAN MODELS HAVE SIMILAR FORECAST  
SOLUTIONS, WHERE AS THE EUROPEAN MODEL (ECMWF) SEEMS SOMEWHAT IN  
AGREEMENT, BUT TO A MUCH LESSER EXTENT. THIS CAUSES SURFACE LOW  
STRENGTH DIFFERENCES OF UP TO 20 MB. OVERALL, THE MOST LIKELY  
SCENARIO AT THIS POINT IS FOR EACH SYSTEM AND THEIR ASSOCIATED  
FRONTS TO BRING SUSTAINED GALE FORCE WINDS WITH SOME GUSTS PERHAPS  
APPROACHING LOWER-END STORM FORCE. SOME OF THESE FRONTS MAY REACH  
THE WESTERN GULF BEFORE WEAKENING AS THE BUMP INTO THE DOWNSTREAM  
RIDGE.  
 

 
   
LONG TERM FORECAST (DAYS 3 THROUGH 7)
 
 
MODEL UNCERTAINTY REMAINS MODERATE IN THE WEDNESDAY THROUGH FRIDAY  
TIME FRAME, BEFORE THE NUMERICAL FORECASTS CONTINUITY DEGRADES  
MORE TOWARDS THE WEEKEND. IN GENERAL THE SURFACE AND UPPER PATTERN  
FAVORS A RIDGE OF HIGH PRESSURE GRADUALLY BUILDING NORTHWESTWARD  
FROM THE EASTERN PACIFIC, INTO THE EAST CENTRAL GULF, CONTINUING  
TOWARDS THE NORTH SLOPE AND EASTERN SIBERIA. THIS WOULD ALLOW FOR  
MODERATING TEMPERATURES AS WE HEAD THROUGH THE PERIOD WITH SOME  
PRECIPITATION TYPE ISSUES FOR SOUTHCENTRAL POSSIBLY DEVELOPING,  
DUE TO WARMER AIR ALOFT ADVECTING OVER THE COLDER SURFACE  
CONDITIONS, AS A WEAKENING FRONT FROM THE BERING LOWS TRIES TO  
PUSH INTO THE REGION BEFORE WEAKENING SOMEWHAT WHILE SLOWING DOWN.  
SHOULD THIS OCCUR, THE OVER-RUNNING WARM AIR AROUND 850 MB WOULD  
CAUSE AT LEAST SOME PRECIPITATION TYPE CONCERNS, MOST LIKELY TO  
DEVELOP IN THE LATE WEDNESDAY THROUGH THURSDAY TIME FRAME.  
 
MEANWHILE, A SERIES OF LOWS WILL CONTINUE TO LIFT NORTH ACROSS  
THE CENTRAL ALEUTIANS BEFORE STALLING AS THEY BUILD INTO THE  
BUILDING RIDGE, CAUSING EACH LOW TO ROTATE AROUND EACH OTHER IN A  
FUJIWHARA-LIKE FASHION EARLY ON. AS THE RIDGE CONTINUES TO BUILD  
TOWARDS THE WEEKEND, ITS ASSOCIATED EFFECT WILL BE TO SHIFT THIS  
AREA OF DISTURBED WEATHER FURTHER WEST TOWARDS THE WESTERN  
ALEUTIANS, EXTENDING NORTHWESTWARD TOWARDS THE KAMCHATKA  
PENINSULA.  
 

 
 
   
AFC WATCHES/WARNINGS/ADVISORIES
 
 
PUBLIC...NONE.  
MARINE...GALES 130 139 172 173 174 175 176 177 179 185 411 412 413 414  
HEAVY FREEZING SPRAY 160 185 412 414.  
FIRE WEATHER...NONE.  
 

 
 

 
 
SYNOPSIS AND MODEL DISCUSSION...KVP  
SOUTHCENTRAL ALASKA...SEB  
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA/MM  
MARINE/LONG TERM...PD  
 
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