154  
FXUS66 KMFR 272231  
AFDMFR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MEDFORD OR  
331 PM PDT SUN MAY 27 2018  
   
SHORT TERM
 
TONIGHT THROUGH WEDNESDAY NIGHT.  
THERE IS LITTLE CHANGE IN THE FORECAST FOR THE REMAINDER OF THE  
MEMORIAL DAY WEEKEND. HIGH PRESSURE HAS BROUGHT WARMING AND DRYING  
AND THAT TREND WILL CONTINUE ON MONDAY WITH HIGHS A FEW DEGREES  
WARMER THAN TODAY...AT 5 TO 10 DEGREES ABOVE NORMAL. COASTAL  
TEMPERATURES WILL BE NEAR NORMAL, EXCEPT NEAR BROOKINGS. A WEAK TO  
MODERATELY STRONG CHETCO EFFECT HAS ALLOWED THE HIGH SO FAR TO  
REACH THE MID 70S, ABOUT A DOZEN DEGREES ABOVE NORMAL. THE  
DOWNSLOPE WARMING FOR BROOKINGS WAS LIKELY AT A PEAK EARLY THIS  
AFTERNOON, BUT OVERNIGHT AND MORNING NORTHEAST WINDS WILL CONTINUE  
AT LEAST A WEAK EFFECT WITH HIGHS SEVERAL DEGREES WARMER THAN  
OTHER COASTAL SITES THROUGH WEDNESDAY.  
 
THE AMPLITUDE OF THE UPPER HIGH WILL FLATTEN ON MEMORIAL DAY AS A  
WEAK SHORTWAVE (ASSOCIATED WITH A TROUGH IN THE GULF OF ALASKA)  
MOVES INTO THE PACIFIC NORTHWEST. THIS WILL PUSH A THERMAL TROUGH  
INLAND AND RESULT IN THE WARMEST DAY OF THE WEEK THERE. THE  
TROUGH WILL SEND A MOISTURE-LIMITED TROUGH ACROSS OUR AREA TUESDAY  
INTO TUESDAY NIGHT. THE MAIN EFFECTS OF THIS TROUGH WILL BE  
INCREASING MID AND HIGH CLOUDS, BREEZY WEST TO NORTHWEST WINDS,  
AND THE START OF A COOLING TREND. BUT, THERE WILL BE WEAK  
INSTABILITY...ASSURING THAT A PORTION OF THE INCREASED CLOUD  
COVERAGE WILL BE IN THE FORM OF CUMULUS. THERE IS A SLIGHT CHANCE  
OF SHOWERS OR THUNDERSTORMS IN THE FAR EAST SIDE...OVER THE  
WARNER MOUNTAINS.  
 
ANOTHER STRONGER, THOUGH NOT STRONG, SHORTWAVE WILL FOLLOW TUESDAY  
NIGHT INTO WEDNESDAY WITH THE MAJORITY OF ITS INCREASED MOISTURE  
ABOVE 12K TO 15K FEET. INSTABILITY IS SUCH THAT THERE IS A DECENT  
CHANCE OF PRECIPITATION OUT OF THE CLOUDS, ESPECIALLY DURING  
WEDNESDAY AFTERNOON AND EVENING, BUT MUCH WILL BE VIRGA. THUS, THE  
PROBABILITY OF SHOWERS AND THUNDERSTORMS WAS LIMITED TO A SLIGHT  
CHANCE. THE MAJOR UNCERTAINTY IN THE SHORT TERM RELATES TO THE  
POSITION OF ANY SHOWERS AND THUNDERSTORMS ON WEDNESDAY. A  
RELATIVELY SMALL CHANGE IN POSITION OR TIMING COULD ALTER WHICH  
AREA HAS THE HIGHEST PROBABILITY. FOR NOW, THERE IS GOOD  
AGREEMENT BETWEEN THE GFS AND ECMWF THAT THE MAIN REGION AFFECTED  
WILL BE FROM SOUTHERN SISKIYOU COUNTY EXTENDING EAST AND NORTHEASTWARD  
ACROSS THE REGION EAST OF THE CASCADES. YET ANOTHER DISTURBANCE  
AS THE UPPER TROUGH MOVES INLAND WILL BRING A HIGHER PROBABILITY  
OF SHOWERS OVERNIGHT WEDNESDAY NIGHT. THIS PROBABILITY STILL LOOKS  
TO BE HIGHEST ON THE EAST SIDE BUT POSSIBLY ACROSS MUCH OF THE  
AREA.  
   
LONG TERM
 
THURSDAY THROUGH SUNDAY.  
ISOLATED SHOWERS WILL LINGER ACROSS MOST OF OUR FORECAST AREA ON  
THURSDAY WITH THE EXCEPTION OF THE COASTAL COUNTIES AND THE UMPQUA  
BASIN WHERE THE ATHMOSPHERE WILL BE MORE STABLE UNDER NORTHERLY  
FLOW. THE TROUGH IS EXPECTED TO FINALLY LIFT OUT OF THE AREA  
FRIDAY. BOTH THE GFS AND THE ECMWF BRING A DEEP LOW AND TROUGH TO  
THE COASTAL WATERS FRIDAY. WHILE MOST OF OUR FORECAST AREA WILL BE  
DRY, THE COAST AND ROSEBURG COULD SEE ONSHORE WITH LOW CLOUDS  
BLANKETING THE VALLEYS FRIDAY NIGHT INTO SATURDAY MORNING.  
CONFIDENCE IS NOT VERY HIGH ON THE STRENGTH OF THIS LOW AND MOST  
AREAS EXCEPT THE COAST SHOULD BE DRY NEXT WEEKEND. -FB  
 

 
   
AVIATION...BASED ON 27/18Z TAFS
 
BREEZY TO GUSTY NORTH WINDS  
WILL CONTINUE THIS AFTERNOON INTO EARLY EVENING. VFR CONDITIONS  
WILL CONTINUE THROUGH THE TAF PERIOD, WITH ONE EXCEPTION. STRATUS  
LOW CLOUDS ARE EXPECTED AT THE COOS COUNTY COAST AGAIN SHORTLY  
AFTER SUNSET THIS EVENING WITH IFR CIGS AROUND MIDNIGHT INTO EARLY  
MONDAY MORNING. OFFSHORE FLOW WILL KEEP THE COAST CLEAR FROM CAPE  
BLANCO SOUTH THROUGH BROOKINGS. -FB  
 

 
   
MARINE...UPDATED 130 PM PDT SUNDAY 27 MAY 2018
 
THE THERMAL  
TROUGH WILL CONTINUE TO STRENGTHEN OVER THE NEXT SEVERAL DAYS. GUSTY  
NORTH WINDS AND STEEP SEAS SOUTH OF CAPE BLANCO WILL STEADILY SPREAD  
NORTH UNTIL NEARLY ALL AREAS ARE AFFECTED BY THIS EVENING. SEAS  
SOUTH OF CAPE BLANCO WILL BECOME VERY STEEP AND HAZARDOUS BY  
TONIGHT.  
 
BY MONDAY, PRESSURE GRADIENTS ARE EXPECTED TO STRENGTHEN FURTHER,  
AND AS A RESULT, NORTH GALES ARE EXPECTED SOUTH OF PORT ORFORD, AND  
VERY STEEP SEAS WILL SPREAD TO AREAS NORTH OF CAPE BLANCO. THESE  
CONDITIONS WILL LIKELY PERSIST THROUGH WEDNESDAY NIGHT, WITH WINDS  
AND SEAS DIMINISHING SLIGHTLY OVERNIGHT AND EVEN MORE SO THURSDAY.  
 
CONDITIONS WILL BE RELATIVELY CALM THROUGH FRIDAY AS AN UPPER LEVEL  
TROUGH AND SURFACE LOW APPROACH FORM THE NORTHWEST. GUIDANCE IS  
KEEPING THIS PATTERN AROUND LONGER THAN PREVIOUSLY FORECAST AND THIS  
WILL DELAY THE REDEVELOPMENT OF THE THERMAL TROUGH UNTIL EARLY NEXT  
WEEK. THIS PATTERN WILL ALSO LEAD TO BUILDING SEAS NEXT WEEKEND AS A  
RESULT OF INCREASING SWELL VERSUS CHOPPY WIND DRIVEN SEAS. BR-Y/BPN  
 

 
   
MFR WATCHES/WARNINGS/ADVISORIES
 
 
OR...NONE.  
 
CA...NONE.  
 
PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY UNTIL 11 AM PDT  
THURSDAY FOR PZZ350-356-370-376.  
GALE WARNING FROM 11 AM MONDAY TO 11 AM PDT THURSDAY FOR  
PZZ356-376.  
HAZARDOUS SEAS WARNING UNTIL 11 AM PDT THURSDAY FOR PZZ356-376.  
HAZARDOUS SEAS WARNING FROM 5 AM TUESDAY TO 11 AM PDT THURSDAY  
FOR PZZ350-370.  
 

 
 
DW/FJB/BR-Y  
 
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