712  
FXUS66 KMFR 210540  
AFDMFR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MEDFORD OR  
1040 PM PDT SAT JUL 20 2019  
 
UPDATED AVIATION SECTION  
   
UPDATE
 
A FEW CHANGES WERE NECESSARY THIS EVENING TO BRING THE  
SKY COVER FORECAST IN LINE WITH THE CURRENT SATELLITE AND STATION  
OBSERVATIONS. A THIN LINE OF CLOUDS HAS DEVELOPED JUST INLAND OF  
THE COAST FROM BANDON TO NORTH BEND AND UP TO REEDSPORT.  
MEANWHILE, SOME RESIDUAL CUMULUS CLOUDS REMAIN OVER THE HIGHER  
TERRAIN OF SISKIYOU, MODOC, AND LAKE COUNTIES. OTHERWISE, CLEAR  
SKIES ARE THE RULE, ALTHOUGH FURTHER CLOUD DEVELOPMENT IS POSSIBLE  
THIS EVENING AND TONIGHT ALONG THE COAST NORTH OF CAPE BLANCO.  
 
FOR MORE INFORMATION ON THE REST OF THE FORECAST, SEE THE PREVIOUS  
DISCUSSION BELOW. -BPN  
 

 
   
AVIATION...FOR THE 21/06Z TAFS
 
FOR INLAND AREAS, VFR CONDITIONS  
ARE EXPECTED TO CONTINUE TONIGHT THROUGH MOST OF SUNDAY. HOWEVER,  
ISOLATED THUNDERSTORMS MAY FORM OVER THE HIGHER TERRAIN OF THE EAST  
SIDE (GENERALLY EAST OF KLAMATH FALLS) SUNDAY AFTERNOON/EVENING.  
THERE IS A VERY SLIGHT CHANCE OF A THUNDERSTORM NEAR THE  
SCOTT/SALMON MOUNTAINS OF SOUTHERN SISKIYOU COUNTY.  
 
ALONG THE COAST, ESPECIALLY FROM CAPE BLANCO NORTHWARD AND ALSO FROM  
GOLD BEACH SOUTHWARD, EXPECT AREAS OF IFR/LIFR LOW CLOUDS AND PATCHY  
FOG TONIGHT INTO SUNDAY. SOME CLOUDS/FOG WILL SPREAD INTO THE  
COASTAL VALLEYS AND ALSO THE LOWER UMPQUA BASIN NORTH AND WEST OF  
ROSEBURG. EXPECT CONDITIONS TO IMPROVE TO VFR IN MOST AREAS BY  
SUNDAY AFTERNOON, BUT LOW CLOUDS/FOG LIKELY RETURN TO THE SAME AREAS  
SUNDAY EVENING. -SPILDE  
 

 
   
MARINE...UPDATED 830 PM PDT SATURDAY 20 JULY 2019
 
THE THERMAL  
TROUGH ALONG THE COAST WILL CONTINUE TO WEAKEN TONIGHT INTO SUNDAY.  
SEAS HAZARDOUS TO SMALL CRAFT OVER ALL THE WATERS TONIGHT WILL EASE  
BELOW ADVISORY LEVELS NORTH OF CAPE BLANCO ON SUNDAY. HOWEVER, WINDS  
AND SEAS WILL REMAIN HAZARDOUS TO SMALL CRAFT SOUTH OF CAPE BLANCO  
THROUGH SUNDAY EVENING. CALMER WINDS AND SEAS WILL COVER ALL WATERS  
BY MONDAY MORNING AND CONTINUE THROUGH TUESDAY NIGHT.  
 
A STRONG THERMAL TROUGH WILL BEGIN TO BUILD TOWARDS THE END OF NEXT  
WEEK. GALE FORCE WINDS AND HAZARDOUS SEAS WILL PROBABLY OCCUR  
TOWARDS THE END OF THE WEEK WHEN THIS STRONG THERMAL TROUGH IS IN  
PLACE. -SARGEANT/SPILDE  
 

 
   
PREV DISCUSSION
 
/ISSUED 505 PM PDT SAT JUL 20 2019/  
 
DISCUSSION...  
IT'S ANOTHER QUIET AFTERNOON WITH TEMPERATURES CURRENTLY RUNNING  
1 TO 3 DEGREES WARMER THAN THIS TIME YESTERDAY, EXCEPT IN  
BROOKINGS, WHERE TEMPERATURES LAST HOUR WERE 15 DEGREES COOLER  
THAN YESTERDAY AT THIS TIME.  
 
ONE ITEM TO NOTE THIS AFTERNOON IS A BIT OF STRATUS THAT HAS  
DEVELOPED IN THE CHARLESTON AND CAPE ARAGO AREAS, AND TO A LESSER  
DEGREE, IN A SMALL AREA SOUTHWEST OF REEDSPORT ALONG THE COAST  
AND BETWEEN DENMARK AND CAPE BLANCO. IN THESE AREAS, A BREEZY TO  
WINDY NORTHERLY FLOW IS PROVIDING ENOUGH LIFT ON THE TERRAIN TO  
RESULT IN SOME CLOUDINESS. THIS IS LIKELY TO EBB AND FLOW THROUGH  
THIS AFTERNOON, BEFORE THE MARINE LAYER INCREASES ALONG AND NEAR  
THE COAST AND INTO THE UMPQUA BASIN THIS EVENING THROUGH SUNDAY  
MORNING.  
 
ANOTHER ITEM OF NOTE IS SOME CUMULUS DEVELOPMENT ACROSS NORCAL  
AND FROM THE CASCADES EAST. THIS IS ASSOCIATED WITH INCREASING  
MOISTURE IN THE MID-LEVELS, MAINLY AT THE 700MB LEVEL. THIS IS A  
SIGN OF THINGS TO COME FOR SUNDAY, POSSIBLY LINGERING INTO MONDAY  
AND TUESDAY, AS A SHOWER AND THUNDERSTORM THREAT MOVES NORTHWARD  
INTO THE AREA.  
 
MORE SPECIFICALLY, WE'RE EXPECTING ISOLATED THUNDERSTORMS SUNDAY  
AFTERNOON AND EVENING ACROSS PORTIONS OF MODOC, LAKE, AND KLAMATH  
COUNTIES, AND A SLIGHT CHANCE OF THUNDERSTORMS ACROSS PART OF  
SISKIYOU COUNTY FROM THE TRINITY ALPS, SCOTT MOUNTAINS, AND SCOTT  
VALLEY AREAS. THE FEATURE TO WATCH SHOWS UP WELL AS A LOW  
PRESSURE SWIRL ON THE GOES15 AND GOES17 WATER VAPOR CHANNELS THIS  
AFTERNOON WEST OF BAJA CALIFORNIA AND THE SOUTHERN CALIFORNIA  
COAST WEST OF LA AND SAN DIEGO. MODEL GUIDANCE SUGGESTS THAT A  
SHORTWAVE TROUGH AT 500MB ON THE FRONT SIDE OF THIS FEATURE,  
RELATED VORTICITY ADVECTION, AND INCREASING ATMOSPHERIC MOISTURE  
SHOULD BE ENOUGH TO RESULT IN ISOLATED THUNDERSTORMS IN THE  
MENTIONED AREAS TOMORROW AFTERNOON AND EVENING.  
 
WHAT NEEDS TO BE WATCHED IS MODEL TRENDS WITH THIS FEATURE, AS  
THERE ISN'T AS MUCH DATA COMING IN FROM THAT AREA AS THERE IS  
FROM OVERLAND AREAS. IN OTHER WORDS, THE MODELS MIGHT NOT HAVE THE  
BEST READ ON THIS FEATURE AT THE CURRENT TIME, AND THE EVOLUTION  
OF IT IN THE MODEL FIELDS IN THE NEXT 24 HOURS WILL BE TELLING. AS  
OF NOW IT APPEARS THAT SUNDAY WILL BRING A RELATIVELY MINOR  
AMOUNT OF LIGHTNING, ON THE ORDER OF 20 TO 200 STRIKES, BUT THE  
VORTICITY MAXIMUM MOVES ACROSS OUR AREA SUNDAY NIGHT INTO MONDAY  
MORNING. THUS, WHILE THE CHANCE IS CURRENTLY SMALL (<10%), IT'S  
NOT IMPOSSIBLE THAT THERE COULD BE SOME LINGERING THUNDERSTORM  
ACTIVITY THEN EAST OF THE CASCADES.  
 
MONDAY INTO TUESDAY THIS FEATURE EDGES EASTWARD LEAVING A SLIGHT  
CHANCE OF THUNDERSTORMS ACROSS THE EAST SIDE, MAINLY OVER  
SOUTHEASTERN LAKE AND MODOC COUNTIES.  
 
A SLIGHT COOL DOWN TUESDAY IS LIKELY TO BE FOLLOWED BY ANOTHER  
WARMING TREND FOR THE REMAINDER OF NEXT WEEK. THERE MAY BE A  
THREAT OF THUNDER AGAIN FROM THE CASCADES EAST BY NEXT WEEKEND.  
BTL  
 

 
 
FIRE WEATHER...UPDATED 200 PM PDT SATURDAY 20 JULY 2019...NORTH TO  
NORTHEAST WINDS WILL DEVELOP TONIGHT AND PERSIST THROUGH MONDAY,  
BRINGING MODERATE RH RECOVERIES TO THE WEST SIDE RIDGES. INLAND  
TEMPERATURES WILL WARM TO FIVE DEGREES ABOVE NORMAL VALUES SUNDAY  
AND HUMIDITIES WILL DROP. THE THUNDERSTORM FORECAST IS INTERESTING  
AS WE FEEL CONFIDENT WITH THE FORECAST FOR ISOLATED THUNDERSTORMS  
EAST OF THE CASCADES ON SUNDAY. WESTERN SISKIYOU COUNTY IS A LITTLE  
MORE UNCERTAIN, BUT WE DECIDED TO KEEP ISOLATED THUNDERSTORMS IN THE  
FORECAST FOR THAT AREA SUNDAY EVENING. THE THUNDERSTORMS EAST OF  
THE CASCADES AND IN SISKIYOU COUNTY WILL PROBABLY BE DRY. THERE IS  
ALSO A FAIR AMOUNT OF POTENTIAL INSTABILITY THAT PERSISTS SUNDAY  
NIGHT JUST WEST OF THE CASCADES. ONE MODEL CONTINUES THE TREND OF  
KEEPING THE CASCADE CREST AND AREAS JUST WEST OF THE CREST DRY FOR  
SUNDAY NIGHT. WE CONTINUE TO SEE INGREDIENTS SUPPORTING  
THUNDERSTORM DEVELOPMENT IN THAT AREA SUNDAY NIGHT, BUT THE WEATHER  
MODELS JUST DON'T WANT TO BRING THUNDERSTORMS INTO THE FORECAST.  
 
OTHERWISE, THE SLIGHT CHANCE FOR THUNDERSTORMS IN LAKE AND KLAMATH  
CONTINUES MONDAY AFTERNOON AND MONDAY EVENING AS UPPER LEVEL ENERGY  
KEEPS MOVING THROUGH THE AREA. WE ALSO HAVE HIGH CONFIDENCE IN A  
WARMING AND DRYING TREND NEXT WEEKEND AS MODELS SUGGEST HIGH  
PRESSURE WILL BUILD INTO THE PACIFIC NORTHWEST. -SMITH  
 

 
   
MFR WATCHES/WARNINGS/ADVISORIES
 
 
OR...NONE.  
 
CA...NONE.  
 
PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY UNTIL 11 PM PDT SUNDAY FOR PZZ356-376.  
HAZARDOUS SEAS WARNING UNTIL 11 PM PDT THIS EVENING FOR  
PZZ356-376.  
SMALL CRAFT ADVISORY UNTIL 11 AM PDT SUNDAY FOR PZZ350-370.  
 

 
 
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