087  
FXAK68 PAFC 181440  
AFDAFC  
 
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE ANCHORAGE AK  
540 AM AKST MON NOV 18 2024  
 
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 THROUGH 3/TODAY  
THROUGH WEDNESDAY NIGHT)...  
 
KEY MESSAGES:  
 
* WIDESPREAD WINDY CONDITIONS WILL DEVELOP ACROSS SOUTHCENTRAL  
TODAY AND PERSIST INTO TUESDAY. THE STRONGEST WINDS ARE EXPECTED  
IN THE MATANUSKA VALLEY, AND THOMPSON PASS/VALDEZ AREAS. AREAS  
OF BLOWING AND DRIFTING SNOW ARE ALSO LIKELY ALONG AREA  
ROADWAYS.  
 
* AIR TEMPERATURES AND WIND CHILLS WILL CONTINUE TO TREND LOWER,  
BRINGING THE COLDEST AIR OF THE WINTER SO FAR TO SOUTHCENTRAL.  
 
* THE COLD AIR OUTBREAK WILL NOT BE LONG-LIVED, WITH WARMING  
TEMPERATURES DURING THE LATTER HALF OF THE WEEK. DRY CONDITIONS  
WILL PERSIST THROUGH THE END OF THE WEEK AND PERHAPS BEYOND.  
 
THE UPPER LEVEL FLOW OVER ALASKA HAS BECOME HIGHLY AMPLIFIED OVER  
THE PAST 24 HOURS, WITH A BUILDING RIDGE OVER THE BERING SEA AND  
A TROUGH EXTENDING FROM MAINLAND ALASKA SOUTHWARD TO THE NORTHEAST  
PACIFIC. THE UPPER LOW WHICH HAD BEEN OVER WESTERN AK THE PAST  
SEVERAL DAYS IS NOW AN OPEN TROUGH TRACKING SOUTH OF KODIAK ISLAND  
INTO THE NORTH PACIFIC. THIS IS THE LATEST FEATURE TO PROVIDE  
ANOTHER SURGE IN WINDS ACROSS THE WESTERN GULF AND KODIAK ISLAND,  
WITH THE STRONGEST WINDS THOUGH BAYS AND PASSES ALONG THE SOUTH  
SIDE OF THE ALASKA PENINSULA. WITH THE APPROACH OF THE UPPER RIDGE  
FROM THE WEST, DEEP NORTHERLY FLOW IS DEVELOPING OVER MAINLAND  
ALASKA WITH COLD AIR ADVECTING SOUTHWARD ACROSS SOUTHCENTRAL AND  
INTO THE GULF. THIS IS LEADING TO GUSTY GAP WINDS THOUGH MOUNTAIN  
PASSES AS WELL AS BAYS ALONG THE COAST. THE SURFACE LOW IN THE  
GULF IS SLOWLY EXITING SOUTHWARD, BUT PRESSURE GRADIENTS ACROSS  
SOUTHCENTRAL ARE STRENGTHENING AS HIGH PRESSURE BUILDS OVER  
INTERIOR ALASKA. LAST, BUT NOT LEAST, A SHORT-WAVE TROUGH IS  
DIGGING SOUTHWARD ACROSS THE EASTERN INTERIOR TOWARD THE COPPER  
RIVER BASIN. ALL OF THIS IS SETTING THE TABLE FOR WIDESPREAD WINDY  
CONDITIONS AND SUB-ZERO WIND CHILL TEMPERATURES THE NEXT 24 TO 36  
HOURS.  
 
MODELS ARE IN MUCH BETTER AGREEMENT THAN THEY WERE 24 HOURS AGO  
WITH THE TRACK OF THE UPPER LEVEL SHORT-WAVE DIGGING SOUTHWARD  
ACROSS THE STATE. THEY DIG IT SOUTHEASTWARD TOWARD THE ALCAN  
BORDER THIS AFTERNOON, WITH THE WEAKER TAIL END CONTINUING  
SOUTHWARD ACROSS THE VALDEZ/CORDOVA AREAS INTO THE GULF. MODEL  
GUIDANCE THEN INDICATES DEVELOPMENT OF AN UPPER LOW NEAR THE ALCAN  
BORDER, WITH THE LOW THEN PROCEEDING TO DROP DUE SOUTH INTO THE  
GULF LATE TONIGHT/EARLY TUESDAY. THE PASSAGE OF THE TROUGH WILL  
ENHANCE WINDS ACROSS THE REGION, WITH STRONG NORTHERLY FLOW, COLD  
AIR ADVECTION, AND SUBSIDENCE BEHIND THE TROUGH. HOWEVER, IT WILL  
NOT BE NEARLY AS IMPACTFUL AS IF IT HAD DUG DUE SOUTH ACROSS  
SOUTHCENTRAL. ALSO, THE FORCING MECHANISMS FOR WINDS ARE NOT  
QUITE IN SYNC TIMING-WISE. THUS, EXPECT STRONG GUSTY WINDS, BUT  
NOT DAMAGING WINDS. WITH THE LATEST FORECAST UPDATES THIS  
MORNING, UPGRADED TO A HIGH WIND WARNING FOR THOMPSON PASS (75 MPH  
GUSTS), BUT KEPT WINDS BELOW THIS LEVEL FOR VALDEZ. GENERALLY  
UPPED WINDS ACROSS INLAND VALLEYS, INCLUDING THE SUSITNA VALLEY  
AND COPPER RIVER VALLEY, AS UPPER LEVEL FORCING STRENGTHENS LATER  
TODAY. THE FORECAST FOR STRONG WINDS ACROSS THE MATANUSKA VALLEY  
AND DOWN KNIK ARM TOWARD NORTH ANCHORAGE IS ON TRACK. THE BIG  
WILD-CARD HERE AND FOR OTHER AREAS EXPECTING STRONG WINDS, IS  
WHAT THE EXTENT OF BLOWING SNOW WILL BE. OPTED TO CONTINUE WITH A  
SPECIAL WEATHER STATEMENT TO HIGHLIGHT THE LIKELIHOOD OF BLOWING  
AND DRIFTING SNOW ACROSS ROADWAYS. THIS IS NOT AN OBVIOUS BLIZZARD  
SET-UP, BUT EXPECT THERE WILL BE SOME REDUCTION IN VISIBILITY,  
ESPECIALLY AS WINDS FIRST DEVELOP TODAY AND BLOW THE FRESH SNOW  
FROM THE PAST COUPLE DAYS.  
 
WINDS AND SUB-ZERO WIND CHILLS WILL LINGER INTO TUESDAY. THE UPPER  
RIDGE WILL THEN BUILD IN FROM THE WEST TUESDAY THROUGH TUESDAY  
NIGHT, LEADING TO LIGHTENING OF WINDS FOR MUCH OF THE REGION. AS  
ALWAYS, THE ONE EXCEPTION WILL BE COASTAL GAP WINDS WHICH WILL  
LINGER THROUGH AT LEAST MID WEEK AS PRESSURE AND THERMAL GRADIENTS  
REMAIN IN PLACE (BETWEEN HIGHER PRESSURE AND COLDER AIR INLAND  
AND LOWER PRESSURE AND WARMER AIR OVER THE GULF). THE COLDEST  
MORNING OF THE WEEK WILL LIKELY BE WEDNESDAY MORNING, WITH CALM  
WINDS INLAND ALLOWING FOR OPTIMAL RADIATIONAL COOLING. WARMER AIR  
WILL THEN MOVE IN ALOFT WITH THE RIDGE AS WE CONTINUE THROUGH THE  
WEEK. TEMPERATURES WILL GRADUALLY WARM EVERYWHERE, BUT ESPECIALLY  
IN THE MOUNTAINS.  
 
-SEB  
 
 
 
.SHORT TERM FORECAST SOUTHWEST ALASKA AND THE BERING  
SEA/ALEUTIANS (DAYS 1 THROUGH 3)...  
 
KEY POINTS THROUGH MID-WEEK:  
 
* STRONG WINDS THROUGH THE GAPS AND PASSES FROM COLD BAY TO PORT  
HEIDEN ARE EXPECTED TODAY.  
 
* THE FIRST ARCTIC AIR MASS MOVES OVER SOUTHWEST ALASKA THIS  
EVENING.  
 
* STRONG HIGH PRESSURE BRINGS WARM AIR TO THE ALEUTIANS, BERING  
SEA AND MOST OF SOUTHWEST ALASKA LATE TOMORROW THROUGH MID-  
WEEK.  
 
NIGHTTIME MICROPHYSICS SHOWS A SHARP TROUGH OVER THE EASTERN  
ALEUTIANS. THIS TROUGH CONTINUES TO CAUSE SNOW SHOWERS FROM COLD  
BAY EAST TO PORT HEIDEN. THESE CONVECTIVE SNOW SHOWERS HAVE  
FREQUENTLY REDUCED VISIBILITIES IN THE AREA TO ONE HALF OF A MILE  
THOUGH ACCUMULATIONS HAVE BEEN A TRACE AS OF 4:00 AM. SURFACE  
OBSERVATIONS HAVE REPORTED WIND GUSTS FROM 30 TO 45 MPH. THESE  
SNOW SHOWERS AND RAPID CHANGES IN VISIBILITY WILL CONTINUE THROUGH  
THIS EVENING. ADDITIONALLY AS THE TROUGH MOVES EASTWARD AND A  
WAVE OF ENERGY MOVES THROUGH BRISTOL BAY, STORM FORCE GAP WINDS  
OUT OF THE BAYS AND PASSES FROM COLD BAY TO PORT HEIDEN ARE  
EXPECTED WITH THE POSSIBILITY OF REACHING HURRICANE FORCE LATER  
THIS MORNING.  
 
ARCTIC AIR FLOWS OVER THE INTERIOR THIS EVENING THROUGH TUESDAY  
MORNING. GUIDANCE CONTINUES TO SHOW THE COLDEST AIR WILL IS  
EXPECTED FROM LATE THIS EVENING THROUGH LATE TOMORROW MORNING.  
TOMORROW MORNING'S LOWS RANGING FROM THE MIDDLE 20S TO THE MIDDLE  
TEENS BELOW ZERO WILL BE WIDE SPREAD FROM ANIAK TO LIME VILLAGE  
NORTHWARD. WIND CHILLS RANGING FROM THE MIDDLE -20S TO THE MIDDLE  
-30S ARE ALSO EXPECTED DURING THIS TIME, TOO. SOUTH AND WEST OF  
THIS LINE TO THE COAST, LOWS WILL BE IN THE SINGLE DIGITS ABOVE  
TO A FEW DEGREES BELOW ZERO WITH WIND CHILLS IN THE TEENS BELOW  
ZERO.  
 
A RIDGE OF HIGH PRESSURE OVER THE WESTERN ALEUTIANS CONTINUES  
TO MOVE SLOWLY EAST BRINGING WARM AIR TO LOCATIONS FROM DUTCH  
HARBOR WESTWARD. THOUGH SURFACE WINDS IN DUTCH HARBOR OVERNIGHT  
RANGED FROM 20 TO 30 MPH, CALMER WINDS ARE EXPECTED LATER THIS  
MORNING AS THE AFOREMENTIONED TROUGH SLIDES EAST. THIS RIDGE WILL  
BRING WARM AIR TO THE BERING SEA, ALASKA PENINSULA AND MOST OF  
SOUTHWEST ALASKA TOMORROW RESULTING IN WIDESPREAD FOG FOR MANY  
PLACES. THOUGH A WAVE OF SNOW MOVES OVER THE AREA FROM GOODNEWS  
BAY NORTHEASTWARD TOWARD ANIAK AND WEST TO NEWTOK THOUGH QPF  
AMOUNTS RANGE FROM A TRACE TO A FEW HUNDREDTHS OF AN INCH. WITH  
THE WARM AIR WORKING ITS WAY INTO THE AREA SIMULTANEOUSLY, POCKETS  
OF FREEZING DRIZZLE ARE POSSIBLE DURING THIS TIME.  
 
-DJ  
 
 
.LONG TERM FORECAST (DAYS 4 THROUGH 7: THURSDAY THROUGH  
SUNDAY)...  
 
BY THURSDAY, A HIGH PRESSURE RIDGE WILL BE THE DOMINATE FEATURE  
ACROSS MOST OF THE STATE, WITH A NORTH-SOUTH ORIENTED AXIS RUNNING  
THROUGH SOUTHWEST ALASKA. THIS WILL BRING NORTHERLY FLOW TO THE  
SOUTHERN MAINLAND AND SOUTHERLY FLOW TO THE CENTRAL AND WESTERN  
ALEUTIANS. WARMER AIR ALOFT IS ASSOCIATED WITH THIS FEATURE, SO WE  
ARE EXPECTING THE COLD TEMPERATURES FROM THE FIRST HALF OF THE  
WEEK TO GIVE WAY TO MORE MODERATE TEMPS IN BOTH SOUTHWEST AND  
SOUTHCENTRAL. THE COPPER RIVER BASIN COULD BE THE EXCEPTION HERE  
AND STAY COLDER.  
 
TIGHTENING PRESSURE GRADIENTS COULD BRING MODERATELY STRONG  
SOUTHERLY WINDS OVER THE WESTERN ALEUTIANS AND CENTRAL BERING SEA  
ON THURSDAY AHEAD OF A NORTH PACIFIC LOW THAT LOOKS TO ENTER THE  
BERING SEA THURSDAY NIGHT. THIS SYSTEM WILL BE PUSHED TO THE  
NORTHEAST AS IT MOVES THROUGH THE TOP EDGE OF THE AMPLIFIED RIDGE.  
THE LOW SHOULD STAY IN NORTHERN ALASKA, BUT THERE IS SOME MODEL  
DISAGREEMENT HERE ABOUT HOW MUCH IT WILL FLATTEN OUT THE RIDGE.  
THIS WILL BE SOMETHING TO KEEP AN EYE ON GOING FORWARD AS A COUPLE  
SOLUTIONS HAVE THIS WAVE BRINGING ITS ENERGY SOUTH OF THE ALASKA  
RANGE ON SATURDAY NIGHT AND DIGGING THROUGH SOUTHCENTRAL.  
 
LIGHTER WINDS AND LITTLE PRECIPITATION ARE EXPECTED THROUGHOUT  
THE LONG TERM OUTLOOK FOR MOST OF SOUTHCENTRAL AND SOUTHWEST  
ALASKA.  
 
.AVIATION...  
 
PANC...VFR CONDITIONS WILL PERSIST. DEEP NORTHERLY FLOW AND COLD  
AIR ADVECTION WILL LEAD TO DEVELOPMENT OF GUSTY NORTHERLY WINDS BY  
MIDDAY. THERE IS COME UNCERTAINTY IN EXACT TIMING OF WINDS, BUT  
ONCE THEY DEVELOP EXPECT WINDS TO STEADILY STRENGTHEN THROUGH THE  
AFTERNOON HOURS AND PEAK THIS EVENING INTO THE OVERNIGHT HOURS.  
THE STRONGEST CORE OF WINDS WILL COME OUT OF THE MATANUSKA VALLEY  
AND DOWN KNIK ARM. HOWEVER, THERE IS NOTHING TO DRIVE THESE WINDS  
ALL THE WAY SOUTH TO PANC. THUS, EXPECT WIND GUSTS WILL PEAK  
RIGHT AROUND 30 KTS. WINDS WILL THEN QUICKLY DIMINISH DURING THE  
DAY TUESDAY AS A RIDGE BUILDS IN FROM THE WEST.  
 
 
 
 
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