377  
FXUS66 KMFR 232351  
AFDMFR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MEDFORD OR  
350 PM PST FRI FEB 23 2018  
 
UPDATED AVIATION DISCUSSION.  
   
DISCUSSION
 
A COUPLE OF SYSTEMS WILL MOVE IN FROM THE NORTHWEST  
THIS WEEKEND BRINGING MODERATE TO HEAVY SNOW ALONG THE CASCADES AND  
A CHANCE FOR LOWER ELEVATION SNOW WEST OF THE CASCADES.  
 
THE LATEST VISIBLE IMAGE SHOWS HIGH AND MID LEVEL CLOUDS ALREADY  
MOVING INTO THE AREA AHEAD OF THE FIRST DISTURBANCE. THE DIFFERENCE  
WITH THIS ONE COMPARED TO WEDNESDAY NIGHT/THURSDAY MORNING IS THERE  
IS NOT AS MUCH OVER WATER TRAJECTORY. THEREFORE PRECIPITATION  
AMOUNTS SHOULD BE KEPT IN CHECK SOMEWHAT. DESPITE THIS, IT WILL  
STILL BE A TRICKY FORECAST IN THAT WE COULD SEE SNOW LEVELS GET  
CLOSE TO THE VALLEY FLOOR LATE TONIGHT INTO SATURDAY MORNING, COME  
UP BRIEFLY TO 1500 TO 2000 FEET SATURDAY AFTERNOON, THEN LOWER AGAIN  
SATURDAY EVENING. RIGHT NOW WE THINK THE HEAVIEST PRECIPITATION WILL  
BE SATURDAY MORNING, POSSIBLY INTO EARLY SATURDAY AFTERNOON, THEN  
DECREASING SATURDAY EVENING. MEANWHILE THERE IS INCREASING CONCERN  
FOR SNOW TO ACCUMULATE ALONG HIGHWAY 97 NORTH OF CHILOQUIN. GIVEN  
THE ABOVE MENTIONED REASONING, MADE SOME ADJUSTMENTS TO THE CURRENT  
SNOW ADVISORY TO INCLUDE PORTIONS OF HIGHWAY 199 JUST SOUTH OF SELMA  
AND HIGHWAY 97 NORTH OF CHILOQUIN. PLEASE SEE WSWMFR FOR MORE  
DETAILS.  
 
WINDS WILL BE ANOTHER CONCERN SATURDAY WITH 700 MB WINDS BETWEEN 45-  
55 KTS AND A WIND ADVISORY REMAINS IN AFFECT. PLEASE SEE NPWMFR FOR  
MORE DETAILS.  
 
WE'LL CATCH A BRIEF BREAK IN THE ACTION SATURDAY EVENING, THEN OUR  
NEXT FOCUS OF CONCERN WILL BE AROUND LATE SUNDAY MORNING THROUGH  
SUNDAY NIGHT. ANOTHER UPPER TROUGH WILL DIVE SOUTHWARD AND THIS ONE  
IS EXPECTED TO HAVE MORE OVER WATER TRAJECTORY WHICH COULD SPELL  
TROUBLE FOR THE CASCADES AND SISKIYOUS. THESE AREAS COULD GET  
HAMMERED WITH HEAVY SNOW FROM SUNDAY MORNING THROUGH SUNDAY EVENING  
WITH 1-2 FEET POSSIBLE ALONG THE CASCADES AND UP TO A FOOT POSSIBLE  
OVER THE SISKIYOUS, INCLUDING MOUNT ASHLAND. THE HEAVIEST  
PRECIPITATION IS EXPECTED TO BE FROM SUNDAY MORNING INTO SUNDAY  
EVENING, THEN GRADUALLY DECREASING SUNDAY NIGHT AS THE FRONT PUSHES  
SOUTH. THERE IS ALSO CONCERN FOR LOWER ELEVATION SNOW WEST OF THE  
CASCADES, ESPECIALLY SUNDAY MORNING, THEN AGAIN SUNDAY EVENING AS  
COLDER AIR MOVES OVERHEAD. RIGHT NOW, WE THINK SNOW LEVELS WILL  
START OUT BETWEEN 2000 AND 3000 FEET, THEN FALLING SUNDAY NIGHT TO  
SOMEWHERE BETWEEN 1000 AND 2000 FEET. ITS LIKELY ANOTHER WINTER  
WEATHER ADVISORY WILL BE ISSUED AFTER THE CURRENT ONE FOR TONIGHT  
INTO SATURDAY EXPIRES.  
 
THIS MUCH IS CERTAIN, WINTER TRAVEL CONDITIONS ARE LIKELY WITH  
HAZARDOUS ROAD CONDITIONS OVER THE HIGHER MOUNTAIN PASSES AND  
POSSIBLY OVER THE PASSES ALONG I-5, ESPECIALLY SUNDAY EVENING.  
THEREFORE HAVE ISSUED A WINTER STORM WATCH TO ADDRESS THIS CONCERN.  
PLEASE SEE WSWMFR FOR MORE DETAILS.  
   
LONG TERM DISCUSSION...TUESDAY THROUGH FRIDAY
 
MODELS SHOW GOOD  
AGREEMENT WITH AN ACTIVE PATTERN OVER THE PACIFIC NORTHWEST NEXT  
WEEK. THE UPPER RIDGE IS FORECAST TO SHIFT FURTHER WEST AND AN UPPER  
TROUGH WILL BE LOCATED OVER THE REGION WITH AN ACTIVE JET STREAM  
ALOFT. THIS WILL OPEN THE DOOR FOR SEVERAL WEATHER SYSTEMS TO MOVE  
DOWN FROM THE NORTHWEST AND IMPACT THE AREA TUESDAY THROUGH FRIDAY.  
ONE OF THESE FRONTS, WHICH IS FORECAST TO MOVE INTO THE AREA  
WEDNESDAY NIGHT INTO THURSDAY, MAY BE STRONG AND BRING A POTENTIAL  
FOR MODERATE HEAVY RAIN OR SNOW AND STRONG GUSTY WINDS.  
 
THE DISTURBANCE WHICH MOVES INTO THE AREA ON TUESDAY, MAY BE  
RELATIVELY WEAK WITH ONLY LIGHT TO MODERATE PRECIPITATION. THE  
POSITION OF THE RIDGE AND TRACK OF THIS DISTURBANCE WILL BE FACTORS  
IN HOW STRONG AND MOIST THIS FRONT IS AS IT MOVES INLAND. OVERALL,  
MODELS SUPPORT GENERALLY LIGHT TO LOCALLY MODERATE PRECIPITATION AS  
THIS SYSTEM MOVES INTO THE AREA TUESDAY INTO WEDNESDAY.  
 
A SURFACE LOW IS THEN FORECAST TO APPROACH THE REGION AND BRING A  
STRONG FRONT INLAND WEDNESDAY NIGHT AND THURSDAY. MODELS INDICATE  
THAT THIS SYSTEM WILL HAVE ABUNDANT MOISTURE WITH IT AND THERE IS A  
POTENTIAL FOR MODERATE TO HEAVY PRECIPITATION TO DEVELOP OVER THE  
AREA, ESPECIALLY FROM THE CASCADES WEST. SOME OF THIS MAY FALL AS  
HEAVY SNOW ON AREA PASSES WITH SNOW LEVELS FORECAST AROUND 2500 TO  
3000 FEET. ALSO WITH THE SURFACE LOW DEEPENING AS IT NEARS THE  
PACIFIC NORTHWEST COAST ON THURSDAY, STRONG GUSTY WINDS MAY DEVELOP  
OVER PORTIONS OF THE AREA. OF NOTE, THERE IS VARIABILITY IN MODEL  
FORECASTS ON THE TRACK AND STRENGTH OF THE LOW; SO CONFIDENCE IS LOW  
ON THE IMPACTS WITH THIS STORM. WILL NEED TO MONITOR THIS SYSTEM  
WITH ADDITIONAL MODEL RUNS.  
 
THE ACTIVE PATTERN MAY THEN CONTINUE FRIDAY AS AN UPPER TROUGH  
REMAINS IN PLACE OVER THE REGION AND ANOTHER DISTURBANCE MOVES DOWN  
INTO THE AREA FROM THE NORTHWEST. -CMC  
 

 
   
AVIATION...24/00Z TAF CYCLE
 
A WEAK FRONT TONIGHT WILL BRING  
INCREASING CLOUD COVER THIS EVENING INTO TONIGHT WITH AREAS OF MVFR  
CIGS/VIS AND LOCAL IFR CIGS AND RAIN/SNOW SPREADING INTO THE COAST  
AROUND 03-06Z AND INLAND FROM THE CASCADES WEST BETWEEN 06-10Z. SNOW  
MAY FALL DOWN TO LOWER VALLEYS, INCLUDING AT KMFR LATE TONIGHT AND  
EARLY SATURDAY MORNING. DURING THE EARLY MORNING HOURS, BETWEEN 10-  
15Z, EXPECT AREAS OF MVFR CIGS AND LIGHT SNOW TO SPREAD EAST OF THE  
CASCADES AND INTO NORTHERN CALIFORNIA. WIDESPREAD TERRAIN  
OBSCURATIONS ARE EXPECTED BY TONIGHT INTO SATURDAY MORNING. -CC  
 

 
   
MARINE...UPDATED 245 PM PST FRIDAY 23 FEB 2018
 
SEAS WILL REMAIN  
STEEP TO VERY STEEP THROUGH SATURDAY. WINDS WILL SHIFT TO SOUTHERLY  
LATER THIS AFTERNOON, THEN A WEAK FRONT WILL MOVE ONSHORE THIS  
EVENING, BRINGING INCREASED WEST WINDS AND A STEEP NORTHWEST SWELL.  
A STRONGER FRONT WILL MOVE ONSHORE EARLY SUNDAY, AND IT WILL BRING  
STEEP, HEAVY NORTHWEST SWELL WITH IT. EVEN HEAVIER SWELL WILL MOVE  
IN MONDAY. YET ANOTHER WEAK FRONT WILL APPROACH THE AREA TUESDAY  
WITH ANOTHER ROUND OF HIGH AND VERY LONG PERIOD SWELL POSSIBLE  
WEDNESDAY. -SVEN  
 

 
   
MFR WATCHES/WARNINGS/ADVISORIES
 
 
OR...WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 4 PM PST  
SATURDAY FOR ORZ029-030.  
WIND ADVISORY FROM 10 AM TO 10 PM PST SATURDAY FOR ORZ029>031.  
WINTER STORM WATCH FROM SUNDAY MORNING THROUGH LATE SUNDAY NIGHT  
FOR ORZ029-030.  
WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 4 PM PST  
SATURDAY FOR ORZ021-023>026.  
WINTER STORM WARNING FROM 10 PM THIS EVENING TO 4 PM PST  
SATURDAY FOR ORZ025.  
WINTER STORM WATCH FROM SUNDAY MORNING THROUGH LATE SUNDAY NIGHT  
FOR ORZ025-027-028.  
WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 4 PM PST  
SATURDAY FOR ORZ027-028.  
 
CA...WIND ADVISORY FROM 10 AM TO 10 PM PST SATURDAY FOR CAZ084-085.  
 
PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FROM 4 AM TO 4 PM PST  
SATURDAY FOR PZZ350-356-370-376. HAZARDOUS SEAS WARNING  
FROM 4 PM SATURDAY TO 1 AM PST SUNDAY FOR PZZ350-356-370-376.  
 

 
 
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