306  
FXUS66 KMFR 211723  
AFDMFR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MEDFORD OR  
923 AM PST TUE NOV 21 2017  
   
DISCUSSION
 
MOST, IF NOT ALL OF THE SIGNIFICANT RAINFALL HAS  
SHIFTED NORTH OF THE AREA THIS MORNING. THE RADAR IS STILL PICKING  
UP ON SOME LIGHT RETURNS, SO STILL CANNOT RULE OUT A OFF/ON LIGHT  
RAIN THE REST OF THE MORNING. THIS AFTERNOON ODDS ARE WE'LL SEE  
MORE DRY TIME THAN NOT. STILL A SHOWER OR TWO COULD NOT BE RULED  
OUT. MADE SOME ADJUSTMENTS TO THE FORECAST TO REFLECT THIS AND  
HAVE ADJUSTED POPS AND RAINFALL AMOUNTS LOWER FOR THIS AFTERNOON.  
AN UPPER RIDGE CENTERED IN SOUTHERN CALIFORNIA SHOULD BE STRONG  
ENOUGH TO DEFLECT MOST OF THE RAINFALL NORTH OF OUR AREA THE REST  
OF TODAY THROUGH TONIGHT. HOWEVER OCCASIONAL RAIN IS STILL  
EXPECTED ALONG THE COAST AND NORTHWEST DOUGLAS COUNTY.  
 
SNOW LEVELS WILL REMAIN HIGH FOR THE REST OF THE WEEK. THIS WILL  
BE GOOD NEWS FOR THOSE WHO PLAN ON TRAVELING TODAY OR TOMORROW.  
-PETRUCELLI  
 

 
   
PREV DISCUSSION
 
/ISSUED 420 AM PST TUE NOV 21 2017/  
 
DISCUSSION...THE WARM FRONTAL PRECIP HAS MOVED TO THE NORTH OF  
THE REGION. THE COLD FRONT APPROACHES THE COAST THIS AFTERNOON,  
WITH WINDS INCREASING THROUGH THE DAY. THE PRESSURE GRADIENT IN  
THE SHASTA VALLEY CONTINUES TO INDICATE ADVISORY WINDS LATER THIS  
MORNING INTO THE EVENING, AND STRONG SOUTHWEST 700 MB WINDS OVER  
THE EAST SIDE SHOULD BRING WINDS AT THE HIGHER ELEVATIONS UP TO  
ADVISORY STRENGTH. WITH THE STRONG SOUTHERLY FLOW UP THE SHASTA  
VALLEY SPILLING DOWN INTO THE ROGUE VALLEY TEMPERATURES TAKEN  
DOWN DRY ADIABATICALLY FROM 850 MB WOULD INDICATE HIGH  
TEMPERATURES IN THE UPPER 60S. HOWEVER, THE LOW FOG AND STRATUS  
UNDERNEATH THE STRONG SURFACE INVERSION WILL SLOW THE HEATING AND  
THE DECOUPLED FLOW ALOFT WILL TAKE A WHILE TO FINALLY REACH THE  
SURFACE AND HAVE HEDGED DOWN THE HIGH TEMPERATURES A BIT TO  
ACCOUNT FOR THIS. IF THE SKIES CLEAR AND WINDS MIX DOWN BY MID TO  
LATE MORNING, THEN WE COULD SEE A HIGH TEMPERATURE NEAR 70 THIS  
AFTERNOON AT THE MEDFORD AIRPORT. THE FRONT STALLS OFFSHORE AND  
THE BULK OF THE PRECIP FALLS NEAR THE COAST AS THIS SYSTEM IS  
SHUNTED THE NORTH AS IT HITS THE UPPER LEVEL RIDGE OVER THE PAC  
NW.  
 
WITH A STRONG ATMOSPHERIC RIVER EVENT INDICATED PRECIP WILL  
CONTINUE ON AND OFF NEAR THE COAST AHEAD OF THE NEXT SYSTEM THAT  
MOVES IN WEDNESDAY. THIS FRONT WILL BRING PRECIP MUCH FARTHER  
INLAND AS THE UPPER LEVEL RIDGE SHIFTS TO THE EAST AND FLATTENS  
AS WE HEAD TOWARDS THE END OF THE WEEK, BRINGING PRECIP ACROSS THE  
EAST SIDE INTO FRIDAY MORNING. THIS ACTIVE PATTERN REMAINS AND  
INTENSIFIES THROUGH THE WEEKEND AS AN UPPER LEVEL TROUGH MOVES  
THROUGH, WITH SNOW LEVEL REMAINING HIGH UNTIL MONDAY WHEN A COOLER  
AIR MASS MOVES IN BEHIND A FRONT MONDAY. SVEN  
 
AVIATION...21/12Z TAF CYCLE... A WARM FRONTAL WAVE MOVING ACROSS  
THE FORECAST AREA FROM THE SOUTH TONIGHT WILL CONTINUE TO BRING  
CIG/VIS REDUCTIONS THROUGH THIS MORNING, BUT WINDS WILL ALSO BE  
INCREASING ALOFT. THIS WILL RESULT IN CONCERNS FOR LOW LEVEL WIND  
SHEAR AT ALL TAF SITES CENTERED ON, BUT NOT CONFINED TO, THIS  
MORNING. MOST VALLEY LOCATIONS WILL EXPERIENCE IFR TO MVFR  
CONDITIONS EARLY MORNING, BUT LOCAL VFR AND LIFR WILL ALSO OCCUR  
DUE TO FLUCTUATIONS IN WIND AND PRECIPITATION. EXPECT WIDESPREAD  
MOUNTAIN OBSCURATIONS DECREASING THIS AFTERNOON, AND THEN  
INCREASING AGAIN IN THE EVENING. TUESDAY AFTERNOON CEILINGS AND  
VISIBILITIES ARE EXPECTED TO IMPROVE TO VFR AT ALL VALLEY  
LOCATIONS. THIS EVENING THE NEXT FRONTAL WAVE IS LIKELY TO BRING  
ANOTHER ROUND OF DETERIORATING CONDITIONS TO THE COASTAL MOUNTAINS  
WESTWARD. BTL/SVEN  
 
MARINE...UPDATED 300 AM PST TUESDAY, 21 NOVEMBER 2017...  
A PROLONGED PERIOD OF ADVISORY TO GALE FORCE SOUTHERLY WINDS AND  
BUILDING SEAS IS EXPECTED TODAY INTO THURSDAY YIELDING STEEP TO VERY  
STEEP SEAS. REMAINING NORTHWEST SWELL AND SOUTHERLY FRESH SWELL FROM  
YESTERDAY'S FRONTAL SYSTEM WILL COMBINE WITH SOUTH WIND SEAS TO  
RESULT IN VERY STEEP AND CHAOTIC SEAS OVER MUCH OF THE AREA. SOUTH  
WINDS ARE LIKELY TO PEAK AROUND MIDDAY TODAY, AND SEAS ARE EXPECTED  
TO PEAK THIS EVENING THROUGH WEDNESDAY MORNING. SEAS WILL THEN  
REMAIN HAZARDOUS INTO THURSDAY. A BRIEF BREAK IS EXPECTED FRIDAY  
BEFORE THE NEXT FRONTAL SYSTEM ARRIVES THIS WEEKEND. BTL/SPILDE  
 

 
   
MFR WATCHES/WARNINGS/ADVISORIES
 
 
OR...WIND ADVISORY UNTIL 10 PM PST THIS EVENING FOR ORZ030-031.  
 
CA...WIND ADVISORY UNTIL 10 PM PST THIS EVENING FOR CAZ085.  
WIND ADVISORY UNTIL 10 PM PST THIS EVENING FOR CAZ081.  
 
PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY UNTIL 4 AM PST WEDNESDAY FOR  
PZZ350-356-376.  
GALE WARNING UNTIL 4 AM PST WEDNESDAY FOR PZZ350-356-370-376.  
 

 
 
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