737  
FXAK68 PAFC 210021  
AFDAFC  
 
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE ANCHORAGE AK  
421 PM AKDT SAT JUL 20 2019  
   
ANALYSIS AND UPPER LEVELS
 
 
THE UPPER LEVEL PATTERN OVER THE REGION IS QUITE STAGNANT AT THE  
MOMENT, WITH A COL OVER SOUTHCENTRAL AND A BROAD RIDGE OVER THE  
BERING SEA AND SOUTHWEST ALASKA. CONDITIONS ARE VERY STABLE ACROSS  
THE BERING SEA, ALEUTIANS, AND SOUTHWEST ALASKA. THIS IS PRODUCING  
WIDESPREAD LOW CLOUDS AND PATCHY FOG. FOR SOUTHCENTRAL, THE  
ATMOSPHERE CAN BE CHARACTERIZED AS WEAKLY UNSTABLE. COMPARED TO  
THE LAST FEW DAYS THERE IS MUCH MORE CLOUD COVER WHICH IS LEADING  
TO COOLER TEMPERATURES AND GREATER STABILITY. WITH LESS HEATING  
EXPECT MOST OF THE DIURNAL SHOWER ACTIVITY TO FORM OVER THE  
MOUNTAINS. THE ONLY LOCATION UNSTABLE ENOUGH FOR A FEW  
THUNDERSTORMS IS THE COPPER RIVER BASIN. ASIDE FROM AIR MASS  
INSTABILITY THE ONLY FORCING MECHANISM FOR PRECIPITATION IS A FEW  
UPPER WAVES MOVING THROUGH THE UPPER RIDGE, OUT OF THE YUKON AND  
INTO THE EASTERN COPPER RIVER BASIN. THE LOW WHICH HAS BEEN  
SPINNING OVER THE GULF HAS SUNK SOUTHWARD AND THE PRIMARY IMPACT  
ON THE GULF COAST IS WIDESPREAD CLOUDS.  
 
THE QUIET CONDITIONS IN THE BERING SEA ARE POISED TO CHANGE OVER  
THE NEXT 24 TO 48 HOURS, WITH A STRONG SHORT-WAVE TROUGH DIGGING  
SOUTHEASTWARD ACROSS EASTERN RUSSIA THIS MORNING AND HEADED FOR  
THE BERING SEA.  
 

 
   
MODEL DISCUSSION
 
 
DESPITE THE CHANGING PATTERN, MODELS ARE IN GOOD AGREEMENT WITH  
LARGE SCALE FEATURES THROUGH TUESDAY. WITH A DYNAMIC TROUGH  
MOVING INTO THE BERING SEA, WILL HAVE TO KEEP A CLOSE EYE ON MODELS  
THERE, AS THEY TEND TO STRUGGLE WITH SYSTEMS COMING OUT OF  
RUSSIA. FOR SOUTHCENTRAL, THERE ARE SOME MINOR DIFFERENCES WITH  
THE TRACK OF AN "EASTERLY WAVE" MONDAY NIGHT THROUGH TUESDAY.  
PRECIPITATION WITH THESE WAVES IS OFTEN DIFFICULT TO PINPOINT  
UNTIL ABOUT 12 HOURS PRIOR TO ARRIVAL. FOR NOW, THE FORECAST WILL  
TREND TOWARD MORE CLOUD COVER AND HIGHER CHANCES OF RAIN OR RAIN  
SHOWERS.  
 

 
   
AVIATION
 
 
PANC...VFR CONDITIONS AND LIGHT WINDS WILL PERSIST. WITH STABLE  
CONDITIONS AND LIGHT FLOW, THERE MAY BE SOME MVFR OR LOWER CLOUDS  
IN THE VICINITY. MORE LIKELY, THE VFR CEILING WILL DROP BELOW 5000  
FEET AT TIMES, ESPECIALLY SUNDAY MORNING.  
 

 
   
FIRE WEATHER
 
 
FIRE WEATHER CONCERNS ARE MINIMAL ACROSS SOUTHERN ALASKA THANKS TO  
MORE STABLE CONDITIONS AND EXTENSIVE CLOUD COVER. WILL SEE A BIT  
OF A CHANGE OVER SOUTHCENTRAL ON MONDAY AS A RIDGE NOSES IN AND  
OFFSHORE FLOW HELPS CLEAR OUT SOME OF THE CLOUDS. THIS WILL LEAD  
TO WARMER CONDITIONS, BUT STILL MARGINAL AS FAR AS THUNDERSTORM  
POTENTIAL. TUESDAY LOOKS A LITTLE MORE INTERESTING AS AN EASTERLY  
WAVE CROSSES THROUGH. THE COMBINATION OF INCREASING WARMTH AND  
INSTABILITY COMBINED WITH FORCING FROM THE UPPER WAVE WILL LIKELY  
LEAD TO A MUCH MORE ACTIVE THUNDERSTORM DAY, PARTICULARLY FOR  
INLAND AREAS (COPPER RIVER BASIN/SUSITNA VALLEY).  
 

 
   
SHORT TERM FORECAST SOUTHCENTRAL ALASKA (THROUGH TUESDAY)
 
 
LOOKS LIKE A COUPLE NICE DAYS ARE ON TAP FOR SOUTHERN ALASKA. THE  
AREA WILL REMAIN BETWEEN MAJOR SYNOPTIC WEATHER SYSTEMS, WITH  
RELATIVELY WEAK FLOW ALOFT. THE LOW-LEVEL AIR MASS IS QUITE WARM,  
RESULTING IN A COUPLE DAYS OF ABOVE-AVERAGE TEMPERATURES FOR THIS  
TIME OF YEAR ON MONDAY AND TUESDAY. THE ONLY CHANCE FOR SHOWERS  
OR THUNDERSTORMS WILL BE OVER THE MOUNTAINS IN THE LATE AFTERNOON  
AND EVENING. LOOK FOR HIGH TEMPERATURES IN THE 70S WITH MOSTLY  
CLEAR CONDITIONS, SAVE FOR SOME LOW CLOUDS AROUND COOK INLET IN  
THE MORNINGS. ON LATE MONDAY INTO TUESDAY, AN EASTERLY WAVE ALOFT  
WILL MOVE ALONG THE COASTAL MOUNTAINS, LIKELY SPARKING SHOWERS AND  
THUNDERSTORMS ALONG WITH IT. THESE EASTERLY WAVE EVENTS ARE  
USUALLY POORLY MODELED AND CAN COME IN MUCH FASTER/SLOWER THAN  
PROGGED. AT THE VERY LEAST, EXPECT AN INCREASE IN MID AND HIGH  
LEVEL CLOUD COVER, ALONG WITH AN INCREASE IN SHOWERS AND  
THUNDERSTORMS.  
 

 
 
.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 THROUGH 3; TONIGHT  
THROUGH TUESDAY EVENING)...  
 
A RIDGE WILL SLOWLY TRACK EASTWARD ACROSS THE BERING THROUGH  
MONDAY BRINGING MOSTLY CLOUDY SKIES AND POSSIBLE MORNING FOG TO  
SOUTHWEST. BRIEF ONSHORE SHOWERS ARE POSSIBLE ALONG COASTAL AREAS.  
THE ONSHORE FLOW WILL WEAKEN BY TUESDAY, POTENTIALLY LEADING TO  
PARTIAL CLEARING OVER THE REGION.  
 

 
 
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 THROUGH 3; TONIGHT  
THROUGH TUESDAY EVENING)...  
 
A FRONT DESCENDING SOUTHWARD FROM SIBERIA WILL LIKELY BRING GALES  
TO THE WESTERN BERING ON SUNDAY BEFORE DEPARTING BACK NORTHWARD. A  
WEAK NORTH PACIFIC LOW WILL APPROACH ADAK ON SUNDAY AS WELL,  
LEADING TO WIDESPREAD RAIN AND GUSTY SOUTHEASTERLY WINDS TO AREAS  
GENERALLY WEST OF UNIMAK ISLAND THROUGH MONDAY AFTERNOON. FURTHER  
EAST, A RIDGE WILL SLOWLY TRACK OVER THE REGION BRINGING MARINE  
STRATUS AND FOG TO THE AKPEN AND EASTERN ALEUTIANS. THOUGH THE  
RIDGE WILL WEAKEN BY TUESDAY, WEAK ONSHORE FLOW WILL CAUSE THE  
CLOUD COVER TO PERSIST.  
 

 
   
MARINE (DAYS 3 THROUGH 5/TUESDAY THROUGH THURSDAY)
 
 
A SERIES OF FAIRLY STRONG STORM SYSTEMS (FOR THIS TIME OF YEAR)  
WILL CROSS THE BERING SEA TUESDAY THROUGH THURSDAY. THERE IS HIGH  
PROBABILITY OF SMALL CRAFT WINDS WITH EACH OF THESE SYSTEMS, WITH  
SOME POTENTIAL FOR GALES AS WELL. BASED ON THE EXPECTED STORM  
TRACK ACROSS THE NORTHERN BERING SEA, THE STRONGEST WINDS WILL  
BE MOST LIKELY ACROSS THE HEART OF THE BERING SEA ON OVER TO THE  
WESTERN ALASKA COASTAL WATERS.  
 

 
   
LONG TERM FORECAST (DAYS 4 THROUGH 7/WEDNESDAY THROUGH SATURDAY)
 
 
THERE IS QUITE A BIT OF SPREAD IN MODEL SOLUTIONS, WHICH GROWS  
SIGNIFICANTLY AS WE HEAD THROUGH THE EXTENDED FORECAST PERIOD.  
THUS, FORECAST CONFIDENCE IS LOW. A DEEP TROUGH WILL BE SITTING  
OVER THE BERING SEA, WITH ACTIVE WEATHER LIKELY AS SHORT-  
WAVES/LOWS MOVE THROUGH THE TROUGH. THE BIG QUESTION IS HOW FAR  
EAST DOES THE LONG-WAVE TROUGH EXTEND, WITH SOME SOLUTIONS DRIVING  
THE TROUGH ACROSS MUCH OF MAINLAND ALASKA. THIS WOULD REPRESENT A  
CHANGE FROM THE TYPICAL SUMMER-TIME DIURNAL CONVECTION TO MORE  
ORGANIZED DYNAMICALLY INDUCED PRECIPITATION WITH COOLER/CLOUDIER  
CONDITIONS. FOR NOW, THE FORECAST WILL CONTINUE TO REFLECT AN IN-  
BETWEEN SOLUTION, WITH THE TROUGH REACHING SOUTHWEST ALASKA AND  
UPPER RIDGING (WITH ASSOCIATED WARMER TEMPERATURES AND INSTABILITY  
INDUCED CONVECTION) HOLDING ACROSS SOUTHCENTRAL ALASKA.  
 

 
 
   
AFC WATCHES/WARNINGS/ADVISORIES
 
 
PUBLIC...NONE.  
MARINE...GALE 185 411.  
FIRE WEATHER...NONE.  
 

 
 

 
 
SYNOPSIS AND MODEL DISCUSSION...SEB  
SOUTHCENTRAL ALASKA...MTL  
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AP  
MARINE/LONG TERM...SEB  
 
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