640  
FXUS66 KMFR 151556  
AFDMFR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MEDFORD OR  
856 AM PDT WED AUG 15 2018  
   
DISCUSSION
 
ELEVATED CONVECTION SPREAD NORTH THROUGH OUR  
FORECAST AREA AS EXPECTED LAST NIGHT AND THIS MORNING. WE'VE  
DODGED THE LIGHTNING BULLET IN MANY AREAS, BUT THERE HAVE BEEN 9  
CLOUD TO GROUND STRIKES, 6 OF WHICH OCCURRED IN MODOC COUNTY, 2 IN  
CENTRAL SISKIYOU COUNTY, AND ONE STRIKE JUST NORTH OF KLAMATH  
FALLS. WHILE THERE MAY BE SOME RAINDROPS REACHING THE GROUND IN  
PLACES, NO MEASUREABLE RAIN CAN BE FOUND ON ANY OBSERVATIONS, SO  
THESE STORMS ARE EASILY CLASSIFIED AS DRY.  
 
THE FORECAST FOR THE REMAINDER OF THE DAY IS VERY COMPLICATED.  
GUIDANCE GENERALLY SHOWS THIS ACTIVITY LIFTING NORTH OF US THROUGH  
THE MORNING WITH A BRIEF BREAK IN ACTIVITY THIS AFTERNOON. THEN  
MODELS SHOW CONVECTION REDEVELOPING, MAINLY CASCADES AND EASTWARD  
LATER THIS AFTERNOON AND CONTINUING INTO THE EVENING. HOWEVER,  
JUST AS HAS BEEN THE CASE ALL ALONG, THE GFS WON'T GIVE UP ON THE  
IDEA OF WEST SIDE THUNDERSTORMS THIS AFTERNOON. WEST SIDE  
CONVECTION IS LOOKING MORE DOUBTFUL FOR 3 REASONS: 1. NONE OF THE  
OTHER GUIDANCE, INCLUDING THE CONVECTION ALLOWING MODELS, SHOWS  
THIS, 2. THE GFS WAS WRONG ABOUT THAT SAME THING OVERNIGHT AND  
THIS MORNING, AND 3. SURFACE INSTABILITY WILL BE LIMITED BY SMOKE,  
AND WE'D NEED SOME HELP FROM THE SURFACE TO BREAK THROUGH THE MID  
LEVEL CAP SHOWN ON FORECAST SOUNDINGS THIS AFTERNOON. WE WILL BE  
LAUNCHING A SPECIAL 18Z SOUNDING, AND HOPEFULLY THIS WILL SHED  
SOME LIGHT ON THE SITUATION. ALL THIS SAID, WE'RE LEANING TOWARD  
DROPPING THE FIRE WEATHER WATCH FOR THE WEST SIDE LOCATIONS.  
 
ISOLATED TO SCATTERED CONVECTION OVER THE REST OF THE AREA  
(CASCADES AND EAST SIDE) STILL LOOKS REASONABLE, SO THE RED FLAG  
WARNING FOR THESE LOCATIONS IS ON TRACK. THE FOCUS SHOULD BE FROM  
THE CASCADES NEAR CRATER ACROSS THE NORTHERN KLAMATH, WHICH IS ONE  
OF THE MORE LIGHTNING-PRONE AREAS AROUND. THE ONE CAVEAT IS THAT  
MID LEVEL CLOUDS THAT ARE ALREADY IN PLACE WILL LIMIT SURFACE  
INSTABILITY IN THESE LOCATIONS EARLY ON, BUT IT WILL CLEAR OUT  
FROM THE SOUTH THIS AFTERNOON.  
 
NO UPDATES ARE PLANNED AT THE MOMENT, BUT SOME COULD CERTAINLY BE  
FORTHCOMING LATER DEPENDING ON HOW CONVECTION DEVELOPS (OR  
DOESN'T). -WRIGHT  
 

 
   
AVIATION...FOR THE 15/12Z TAFS
 
ALONG THE COAST WIDESPREAD  
IFR/LIFR CIGS AND MVFR/IFR VISIBILITIES WILL PERSIST THROUGH TODAY  
WITH GRADUAL EROSION OF COVERAGE IN THE COASTAL VALLEYS DURING THE  
LATE MORNING AND AFTERNOON.MVFR/IFR WILL RETURN IN FORCE TONIGHT.  
 
INLAND, FOR THE UMPQUA BASIN, VFR CONDITIONS ARE EXPECTED THROUGHOUT  
THE TAF PERIOD. ELSEWHERE INLAND, WIDESPREAD SMOKE FROM AREA  
WILDFIRES IS RESULTING IN REDUCED VISIBILITIES. MVFR VSBYS WITH  
LOCAL IFR VSBYS WILL PERSIST THROUGH THE TAF PERIOD.  
 
THERE IS A SLIGHT CHANCE OF THUNDERSTORMS FROM THE CASCADES EASTWARD  
THIS MORNING THROUGH THIS AFTERNOON AND INTO THE EVENING. THIS  
SLIGHT CHANCE WILL EXPAND WEST OF THE CASCADES ACROSS SISKIYOU,  
JACKSON, AND EASTERN DOUGLAS COUNTIES LATER IN THE DAY. -DW/BPN  
 

 
   
MARINE...UPDATED 800 AM PDT TUESDAY, 15 AUGUST 2018
 
RELATIVELY  
LIGHT WINDS AND SEAS, ALONG WITH COASTAL FOG AND LOW CLOUDS, ARE  
EXPECTED THIS MORNING. BUILDING NORTHWEST SWELL IS EXPECTED TODAY,  
BUT CONDITIONS SHOULD STAY BELOW SMALL CRAFT ADVISORY LEVELS. A  
THERMAL TROUGH WILL REDEVELOP ALONG THE COAST ON THURSDAY, PRODUCING  
GUSTY NORTH WINDS AND STEEP SEAS INTO THIS WEEKEND. SMALL CRAFT  
ADVISORY CONDITIONS ARE LIKELY, WITH AFTERNOON AND EVENING GALES  
POSSIBLE FRIDAY AND SATURDAY SOUTH OF CAPE BLANCO. CONDITIONS ARE  
EXPECTED TO IMPROVE EARLY NEXT WEEK. -CC  
 

 
   
PREV DISCUSSION
 
/ISSUED 322 AM PDT WED AUG 15 2018/  
 
DISCUSSION...SMOKE COVERAGE AND INTENSITY TODAY IS SHOWN BY  
MODEL GUIDANCE TO BE VERY SIMILAR TO YESTERDAY, SO WON'T GET INTO  
A LOT OF DETAIL HERE. TODAY WE'LL BE FOCUSED ON THUNDERSTORM  
POTENTIAL. MOISTURE BEING SQUEEZED NORTHWARD BETWEEN AN UPPER  
TROUGH OFFSHORE AND THE UPPER HIGH OVER THE FOUR CORNERS IS  
ARRIVING FROM THE SOUTH EARLY THIS MORNING. RADAR IS SHOWING SOME  
MOSTLY WEAK ECHOES LIFTING NORTHWARD INTO MODOC, EASTERN SISKIYOU,  
SOUTHERN KLAMATH AND LAKE COUNTIES, BUT IN THE LAST HOUR OR SO,  
SEVERAL CLOUD TO GROUND LIGHTNING STRIKES HAVE BEEN OBSERVED FROM  
A CELL ABOUT HALF WAY BETWEEN TIONESTA AND CANBY SOUTH OF HIGHWAY  
139 IN MODOC COUNTY. ANOTHER NICE CLUSTER OF CELLS THAT COULD  
CRACK OUT SOME LIGHTNING APPEARS TO BE HEADED INTO EASTERN  
SISKIYOU COUNTY. MODEL SOUNDINGS ARE SHOWING CLOUD BASES IN THESE  
AREAS UP AROUND 10000 FEET AGL, SO LITTLE OR NO RAIN IS OCCURRING  
WITH ANY OF THESE CELLS. THIS WILL CONTINUE TO BE THE CASE THIS  
MORNING AS THE MOISTURE AXIS ALOFT SHIFTS NORTHWARD FROM ABOUT THE  
CASCADE CREST EASTWARD. A RED FLAG WARNING IS OUT FOR THESE AREAS  
FOR ISOLATED DRY THUNDERSTORMS ON VERY DRY FUELS AND THIS IS IN  
EFFECT UNTIL 11 PM THIS EVENING.  
 
MOISTURE WILL CONTINUE TO EXPAND WEST AND NORTHWESTWARD THIS  
AFTERNOON AND EVENING AND SOME MODEL GUIDANCE CONTINUES TO  
INDICATE THUNDERSTORM POTENTIAL DURING THIS TIME FRAME OVER THE  
INTERIOR WEST SIDE. THIS INCLUDES AREAS FROM ABOUT THE NORTHERN  
HALF OF WESTERN SISKIYOU COUNTY NORTH-NORTHEASTWARD ACROSS THE  
SISKIYOU MOUNTAINS TO THE CASCADE FOOTHILLS. OF COURSE, THERE HAS  
BEEN A TREMENDOUS AMOUNT OF SMOKE FROM THE WILDFIRES ACROSS THE  
REGION. RECENT HISTORY HAS SHOWN THAT CONVECTION HAS BEEN  
SIGNIFICANTLY SUPPRESSED DUE TO THE SHADING EFFECTS OF THE SMOKE  
(WHICH THE MODEL MIGHT NOT OTHERWISE KNOW IS THERE AND THIS  
EFFECTIVELY LIMITS INSTABILITY). CONVECTION ALLOWING MODELS  
(HRRR, NAMNEST, HIRES ARW/NMM) ALL KEEP ACTIVITY FROM ABOUT THE  
CASCADE CREST EASTWARD THIS AFTERNOON/EVENING. BUT, THE 00Z GFS  
MAINTAINS THERE COULD BE SOME CELLS THAT DEVELOP OVER THE SISKIYOU  
MOUNTAINS AND ALSO EASTERN PORTIONS OF THE UMPQUA DIVIDE, THEN  
PROPAGATE NORTHWARD. CONFIDENCE ISN'T HIGH ENOUGH HERE TO UPGRADE  
THE FIRE WEATHER WATCH, BUT WE HAVE PUSHED BACK THE START TIME TO  
21Z SINCE IT DOESN'T LOOK LIKE THERE IS ANY THREAT BEFORE THEN.  
THIS WILL ALLOW THE DAY SHIFT TO TAKE A LOOK AT THE 12Z GUIDANCE  
AND SEE IF WE NEED TO MAKE ANY LAST MINUTE UPGRADES OR JUST  
CANCEL IT.  
 
THE UPPER TROUGH WILL BEGIN TO MOVE EASTWARD TONIGHT IN RESPONSE  
TO A POTENT SHORT WAVE ROUNDING ITS BASE NEAR 40 N AND 130 W. THE  
TROUGH AND ASSOCIATED SHORT WAVE DISTURBANCE WILL MOVE ONSHORE AND  
THROUGH THE AREA THURSDAY. THIS WILL LIKELY GENERATE ANOTHER  
ROUND OF THUNDERSTORMS WITH THE BEST ACTIVITY FROM THE CASCADE  
CREST EASTWARD ACROSS NORTHERN KLAMATH AND LAKE COUNTIES. EVEN  
THOUGH THOSE AREAS WILL STAND THE BEST CHANCE AT SEEING  
THUNDERSTORMS, A SLIGHT CHANCE ALSO EXISTS BACK ACROSS THE UMPQUA  
DIVIDE AND JACKSON COUNTY TO THE SISKIYOU MOUNTAINS. WHILE  
THUNDERSTORMS AREN'T EXPECTED FARTHER SOUTH AND EAST, GUSTY WEST  
TO SOUTHWEST WINDS ARE EXPECTED TO DEVELOP AHEAD OF THE TROUGH  
OVER PORTIONS OF THE EAST SIDE AND NORTHERN CALIFORNIA. -SPILDE  
 
BEYOND THAT FROM TUESDAY AFTERNOON'S AFD, AS THE TROUGH MOVES  
OVER AND THEN EAST OF US FRIDAY, CONDITIONS SHOULD STABILIZE, AND  
WE'VE KEPT THE FORECAST DRY FOR FRIDAY. HOWEVER, A TROUGH MOVING  
THROUGH WILL PROBABLY BRING GUSTY WEST WINDS, ESPECIALLY TO EAST  
SIDE LOCATIONS. THUS, WE LOSE ONE THREAT (LIGHTNING) AND ADD  
ANOTHER (WIND).  
 
FEW CHANGES WERE MADE TO THE EXTENDED FORECAST. A RIDGE MOVES IN  
BEHIND THE TROUGH THIS WEEKEND AND THAT WILL BRING HOTTER, DRIER  
WEATHER AGAIN. THIS ALSO LOOKS LIKE A THERMAL TROUGH SETUP WHICH  
MEANS OFFSHORE (NORTHEAST) WINDS AND POOR NIGHT TIME HUMIDITY  
RECOVERIES IN THE COASTAL MOUNTAINS. MODELS THEN SHOW ANOTHER  
UPPER LOW COMING IN EARLY NEXT WEEK, BUT THIS ONE WILL PROBABLY BE  
TO OUR NORTH, WHICH IS A DRY, ALBEIT COOLER, WEATHER PATTERN FOR  
OUR AREA. -WRIGHT  
 
FIRE WEATHER...AS EXPECTED, MOISTURE IS ARRIVING IN THE SOUTHERLY  
FLOW ALOFT AT THE MID AND UPPER LEVELS EARLY THIS MORNING WITH  
ISOLATED CELLS PRODUCING CLOUD TO GROUND LIGHTNING IN FIRE ZONE  
285 (MODOC) AND 284 (EASTERN SISKIYOU COUNTY). THESE WILL LIFT  
NORTHWARD INTO PORTIONS OF KLAMATH AND LAKE COUNTIES THIS MORNING  
AND MAY REACH AS FAR WEST AS THE CASCADE CREST. THE RFW FOR THESE  
AREAS CONTINUES AND IS IN EFFECT UNTIL 11 PM FOR DRY  
THUNDERSTORMS/ABUNDANT LIGHTNING ON VERY DRY FUELS. EXPECT THE  
MOIST AXIS ALOFT TO EXPAND NORTH AND WESTWARD THIS AFTERNOON AND  
EVENING AND THIS MAY RESULT IN SOME THUNDERSTORM ACTIVITY OVER THE  
INTERIOR WEST SIDE TOO. CONFIDENCE IN THUNDERSTORMS IN THESE  
AREAS IS LOWER DUE TO MULTIPLE FACTORS, ONE BEING DIFFERING MODEL  
SOLUTIONS, BUT ALSO COVERAGE OF WILDFIRE SMOKE, WHICH TENDS TO  
INHIBIT CONVECTION. THE CONVECTION ALLOWING MODELS ALL KEEP THE  
ACTIVITY FROM ABOUT THE CASCADE CREST EASTWARD THIS AFTERNOON, BUT  
THE 00Z GFS INSISTS AT LEAST SOME ISOLATED CELLS WILL FORM NEAR  
THE SISKIYOU MOUNTAINS/UMPQUA DIVIDE AND PROPAGATE NORTHWARD. WE  
STILL HAVE A FIRE WEATHER WATCH IN EFFECT, BUT HAVE PUSHED BACK  
THE START TIME TO 21Z (2 PM PDT) SINCE IT DOESN'T LOOK LIKE MUCH  
WILL OCCUR BEFORE THEN. THIS WILL GIVE THE DAY SHIFT A CHANCE TO  
LOOK AT THE 12Z GUIDANCE AND MAKE ANY LAST MINUTE  
UPGRADES/CANCELLATIONS. EXPECT ANOTHER ROUND OF GUSTY SOUTH WINDS  
IN THE SOUTHERN PORTION OF THE SHASTA VALLEY NEAR WEED THIS  
AFTERNOON/EVENING, BUT HUMIDITY SHOULD BE UP A BIT COMPARED TO  
YESTERDAY.  
 
WE'LL BE TAKING A CLOSER LOOK TODAY WHETHER OR NOT WE'LL NEED  
ANOTHER FIRE WEATHER WATCH FOR THURSDAY'S CONVECTION. MODELS ARE  
STILL PINNING THE BEST CHANCES FROM ABOUT THE CASCADE CREST  
EASTWARD ACROSS NORTHERN KLAMATH AND LAKE COUNTIES, THOUGH A SLIGHT  
CHANCE FOR THUNDER ALSO EXISTS BACK ACROSS THE UMPQUA DIVIDE TO  
THE SISKIYOU MOUNTAINS. THE UPPER TROUGH WILL INCREASE THE  
PRESSURE GRADIENT AND WIND ALOFT ALSO INCREASE THURSDAY, SO GUSTY  
WEST TO SOUTHWEST WINDS WILL DEVELOP IN THE AFTERNOON/EVENING IN  
NE CALIFORNIA AND OVER THE EAST SIDE.  
 
DRY WEATHER WILL MOVE IN LATE THIS WEEK INTO THE WEEKEND WITH A  
PERIOD OF OFFSHORE NE WINDS EXPECTED IN THE SISKIYOUS AND COAST  
RANGES FRIDAY THROUGH SATURDAY NIGHT AS A THERMAL TROUGH DEVELOPS  
IN NORTHERN CALIFORNIA. THIS WILL LEAD TO SIGNIFICANT RIDGETOP  
DRYING WITH POOR TO MODERATE OVERNIGHT HUMIDITY RECOVERIES FOR  
MANY OF THOSE AREAS, INCLUDING AT LEAST TO SOME DEGREE, THE  
KLONDIKE/TAYLOR FIRE IN WESTERN JOSEPHINE COUNTY. -SPILDE  
 

 
   
MFR WATCHES/WARNINGS/ADVISORIES
 
 
OR...RED FLAG WARNING UNTIL 11 PM PDT THIS EVENING FOR  
ORZ617-623>625.  
FIRE WEATHER WATCH FROM 2 PM PDT THIS AFTERNOON THROUGH THIS  
EVENING FOR ORZ617-621>623.  
 
CA...FIRE WEATHER WATCH FROM 2 PM PDT THIS AFTERNOON THROUGH THIS  
EVENING FOR CAZ280-281.  
RED FLAG WARNING UNTIL 11 PM PDT THIS EVENING FOR CAZ284-285.  
 
PACIFIC COASTAL WATERS...GALE WATCH FROM FRIDAY MORNING THROUGH SATURDAY EVENING FOR  
PZZ356-376.  
SMALL CRAFT ADVISORY FROM 11 AM THURSDAY TO 11 PM PDT SATURDAY  
FOR PZZ350-356-370-376.  
 

 
 
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