575  
FXUS66 KMFR 280536  
AFDMFR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MEDFORD OR  
1035 PM PDT THU APR 27 2017  
 
.UPDATED AVIATION DISCUSSION  
   
DISCUSSION
 
THE MAIN UPDATE THIS EVENING WAS TO LOWER  
TEMPERATURES WEST OF THE CASCADES. AFTER ASSESSING CLOUD COVER  
TRENDS AND LATEST MOS GUIDANCE COMPARED TO OBSERVATIONS, WE THINK  
THERE IS A GOOD CHANCE THAT TEMPERATURES WILL DIP TO FREEZING IN  
COLDER PORTIONS OF JOSEPHINE AND JACKSON COUNTY VALLEYS TONIGHT.  
SINCE WE THINK THAT READINGS WILL BOTTOM OUT AT 32F AND NOT LOWER  
AND THUS LIKELY ONLY FOR A FEW HOURS AT MOST, WE ARE NOT ISSUING A  
FREEZE WARNING. STILL, THE GOAL OF THE FORECAST UPDATE AND  
ADDITION OF GRAPHICS TO OUR WEBSITE IS TO BRING ATTENTION TO THE  
POTENTIAL OF BRIEF FREEZING CONDITIONS TONIGHT, AND AGRICULTURAL  
INTERESTS CAN TAKE NECESSARY PRECAUTIONS.  
 
PLEASE SEE THE PREVIOUS DISCUSSION BELOW FOR DETAILS ON THE  
TRANSITION TO DRIER AND WARMER CONDITIONS EARLY THIS WEEKEND AND  
AGAIN NEXT WEEK.  
 

 
   
AVIATION...28/06Z TAF CYCLE
 
MOISTURE IN NORTHWEST LOW LEVEL FLOW  
TONIGHT IS BANKING UP AGAINST HIGHER TERRAIN, ESPECIALLY NORTHWEST-  
FACING SLOPES. CEILINGS HAVE SCATTERED OUT AT THE COAST AND SHOULD  
REMAIN GENERALLY VFR THROUGH THE NIGHT. MVFR CONDITIONS ARE EXPECTED  
IN AND AROUND ROSEBURG EARLY FRIDAY MORNING AS MOISTURE POOLS THERE  
OVERNIGHT. ELSEWHERE, MOSTLY VFR CONDITIONS ARE EXPECTED. AGAIN,  
PARTIAL MOUNTAIN OBSCURATION IS EXPECTED ESPECIALLY IN THE CASCADES,  
UMPQUA DIVIDE, AND SISKIYOUS. BY TOMORROW AFTERNOON, ALL LOCATIONS  
SHOULD BE VFR UNDER A DRYING AIR MASS. SK  
 

 
   
MARINE...UPDATED 200 PM PDT THURSDAY, 27 APRIL 2017
 
WEAK HIGH  
PRESSURE WILL PERSIST OVER THE WATERS INTO EARLY FRIDAY WITH  
SLOWLY DIMINISHING MODERATE SEAS. THE MODELS ARE IN GOOD AGREEMENT  
SHOWING SMALL CRAFT CONDITIONS PRIMARILY FOR THE SOUTHERN WATERS.  
HOWEVER IT'S POSSIBLE PORTIONS OF THE NORTHERN WATERS SOUTH OF  
BANDON COULD EXPERIENCE SMALL CRAFT CONDITIONS. CONFIDENCE WAS NOT  
HIGH ENOUGH TO INCLUDE THE SOUTHERN PORTION OF THE NORTHERN  
WATERS, BUT LATER SHIFTS WILL NEED TO TAKE ANOTHER LOOK AT THIS.  
GUSTY NORTH WINDS WILL INCREASE FRIDAY AFTERNOON AS HIGH PRESSURE  
STRENGTHENS OFFSHORE WHILE A THERMAL TROUGH DEVELOPS ALONG THE  
COAST. WINDS WILL BE STRONGEST FROM 8 TO 30 NM FROM SHORE IN THE  
WATERS SOUTH OF GOLD BEACH. THE PATTERN WILL WEAKEN SLIGHTLY ON  
SATURDAY BUT STRENGTHEN AGAIN EARLY NEXT WEEK WITH ADVISORY  
STRENGTH NORTHERLY WINDS LIKELY TO DEVELOP. -PETRUCELLI  
 

 
   
PREV DISCUSSION
 
/ISSUED 230 PM PDT THU APR 27 2017/  
 
DISCUSSION...  
 
SHORT TERM...TONIGHT THROUGH SUNDAY NIGHT...ALTHOUGH SATELLITE  
IMAGERY DOESN'T SHOW IT ALL TOO WELL, SATELLITE AND SURFACE  
OBSERVATIONS SHOW NUMEROUS LIGHT SHOWERS MOVING ACROSS THE  
FORECAST AREA THIS AFTERNOON. THESE WILL DIMINISH THROUGH THE  
EVENING AS THE JET STREAM AXIS AND UPPER LEVEL TROUGH SLIDE TO THE  
EAST. HIGH PRESSURE AND UPPER LEVEL RIDGING WILL THEN BUILD IN  
OVER THE EASTERN PACIFIC, AND THIS WILL BE THE PRIMARY DRIVER OF  
OUR WEATHER FOR THE NEXT SEVERAL DAYS. ALSO OF NOTE, THE CLEAR  
SKIES AND RESIDUAL COOL AIR IN THE AREA MAY PRODUCE SOME ISOLATED  
AREAS OF FROST IN THE ROGUE, APPLEGATE, AND ILLINOIS VALLEYS  
OVERNIGHT TONIGHT INTO EARLY TOMORROW MORNING.  
 
WITH THE RIDGE PLACED TO OUR WEST, AND A GENERAL TROUGH OVER THE  
CENTRAL UNITED STATES, WE WILL RESIDE UNDER SWIFT NORTHWEST FLOW  
ALOFT FOR THE DURATION OF THE TERM. THE RIDGE WILL DEFLECT MOST  
ENERGY AND PRECIPITATION PRODUCING SYSTEMS TO OUR NORTH, LEAVING  
THE AREA DRY AND WARMER. HOWEVER, THE TRAILING EDGE OF A FRONT  
PASSING TO OUR NORTH ON SATURDAY NIGHT INTO SUNDAY WILL SKIRT THE  
NORTHERN HALF OF THE FORECAST AREA, PRODUCING SHOWERS AND  
SLIGHTLY COOLER TEMPERATURES, AND ALSO DISRUPT THE THERMAL TROUGH  
PATTERN THAT WILL PERIODICALLY PRODUCE MUCH WARMER TEMPERATURES  
OVER THE RIDGES AND ALONG THE SOUTHWEST OREGON COAST NEAR  
BROOKINGS. THE MODELS HAVE NOT BEEN CONSISTENT ON THE STRENGTH OF  
THE FRONT AS THEY PASS TO OUR NORTH, NOR HAVE THEY AGREED ON WHERE  
THE BEST CHANCES FOR SHOWERS WILL BE. SO, HAVE KEPT A SLIGHT  
CHANCE TO A CHANCE OF SHOWERS IN SOME AREAS AND EXPANDED COVERAGE  
TO OTHERS IN AN EFFORT TO MORE CLOSELY ALIGN WITH THE LATEST  
GUIDANCE, BUT SUSPECT THIS MAY CHANGE IN LATER FORECAST CYCLES.  
OTHERWISE, EXPECT GRADUALLY WARMING TEMPERATURES THROUGH THE WEEK.  
-BPN  
 
LONG TERM...MONDAY THROUGH THURSDAY...THE AREA WILL BE UNDER THE  
INFLUENCE OF AN UPPER RIDGE MONDAY THROUGH WEDNESDAY WITH MAINLY  
WARM AND DRY CONDITIONS. A WEAK DISTURBANCE IS EXPECTED TO MOVE OVER  
THE RIDGE ON TUESDAY, AND WILL BRING A SLIGHT CHANCE FOR LIGHT  
PRECIPITATION TO NORTHERN PORTIONS OF THE AREA.  
 
WEDNESDAY, MODELS AND ENSEMBLES CONTINUE TO SHOW THE UPPER RIDGE  
WILL BUILD INLAND OVER THE AREA AND BRING DRY AND VERY WARM  
CONDITIONS TO THE AREA. HIGHS IN THE UPPER 70S TO LOW 80S ARE  
EXPECTED IN WESTERN VALLEYS WITH IN THE LOW 70S POSSIBLE FOR EASTERN  
VALLEYS.  
 
THURSDAY, THE UPPER RIDGE IS FORECAST TO SHIFT EASTWARD WHILE A  
SHORTWAVE TROUGH MOVES INTO THE REGION. THIS TROUGH COMBINED WITH  
SOUTHERLY MOISTURE AND INSTABLITY WILL BRING A SLIGHT CHANCE OF  
SHOWERS AND THUNDERSTORMS TO INLAND LOCATIONS. -CC  
 

 
   
MFR WATCHES/WARNINGS/ADVISORIES
 
 
OR...NONE.  
 
CA...NONE.  
 
PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FROM 11 AM FRIDAY TO 5  
AM PDT SATURDAY FOR PZZ356-376.  
 

 
 
NSK/CC/MAP  
 
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