899  
FXUS66 KMFR 190436  
AFDMFR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MEDFORD OR  
936 PM PDT MON JUN 18 2018  
   
DISCUSSION
 
THE FORECAST HAS BEEN UPDATED TO ACCOUNT FOR A  
DIMINISHING PROBABILITY OF SHOWERS AND THUNDERSTORMS DURING THE  
REMAINDER OF THIS EVENING. SHOWER AND THUNDERSTORM COVERAGE WAS  
VERY SPARSE THIS EVENING, BUT A COUPLE OF CELLS DID TRACK THROUGH  
KLAMATH FALLS WITH 0.08 INCHES OF RAIN MEASURED AT THE KLAMATH  
FALLS AIRPORT.  
 
THE AIR MASS OVER OUR AREA WILL CONTINUE TO STABILIZE OVERNIGHT  
AS A TROUGH CENTERED OVER IDAHO MOVES INTO MONTANA. RIDGING WILL  
FOLLOW FOR TUESDAY WITH HIGHS GENERALLY 5 TO 10 DEGREES HIGHER  
THAN THEY WERE TODAY...A LITTLE LESS AT THE COAST AND AT THE  
LOWER END OF THAT RANGE IN COASTAL VALLEYS.  
 
THE FOCUS FOR UPDATES WITH THE NEXT ISSUANCE OF THE FORECAST WILL  
BE ON AN SLIGHT CHANCE TO CHANCE OF SHOWERS AND THUNDERSTORMS  
DURING WEDNESDAY AFTERNOON AND EVENING. WITH A PARTIAL DATA SET OF  
NEW DATA, IT STILL SUPPORTS THE CURRENT FORECAST WITH THUNDERSTORMS  
POSSIBLY PRODUCING STRONG WINDS AND HAIL, AND TRACKING NORTH TO  
NORTHEASTWARD AT 10 TO 20 MPH WITH ACTIVITY FOCUSED ON AND NEAR THE  
CASCADES...FROM SISKIYOU COUNTY THROUGH OREGON. SECONDARILY FROM  
NORTHERN KLAMATH AND LAKE COUNTIES INTO EASTERN OREGON. HOT BUT  
DRY CONDITIONS ARE EXPECTED INLAND THROUGH THE REMAINDER OF THE  
WEEK.  
 

 
   
AVIATION...FOR 19/00Z TAFS
 
ISOLATED SHOWERS CONTINUE EAST OF THE  
CASCADES, AND THOUGH THERE HASN'T BEEN ANY LIGHTNING OVER THE LAST  
HOUR, IT'S STILL POSSIBLE TO SEE A STRIKE OR TWO IN A STRONGER STORM  
OVER THE NEXT FEW HOURS. ANY STORM COULD BRING GUSTY OUTFLOW WINDS  
AS WELL. CONDITIONS WEST OF THE CASCADES LOOK TO BE UNEVENTFUL  
THROUGHOUT THE TAF PERIOD, WITH VFR EXPECTED AT ALL INLAND  
TERMINALS. ALONG THE COAST, MOIST ONSHORE FLOW HAS MAINTAINED IFR TO  
LIFR CONDITIONS SOUTH OF BANDON... KOTH CURRENTLY SITS AT VFR BUT  
LOW STRATUS/FOG WILL RETURN TONIGHT. -M&M  
 

 
   
MARINE...UPDATED 800 PM PDT MONDAY 18 JUNE 2018
 
LONG PERIOD  
WEST SWELLS ARE THE DOMINANT SWELL BUT THERE IS STILL A SMALLER  
SHORT PERIOD NORTHWEST SWELL. OVERALL SEAS HAVE BECOME LESS STEEP  
AND RELATIVELY LIGHT WINDS AND SEAS ARE EXPECTED THROUGH THURSDAY.  
A THERMAL TROUGH REDEVELOPS FRIDAY AND CONTINUES THROUGH NEXT  
WEEKEND, AND AS A RESULT, SMALL CRAFT ADVISORY AND HEAVY SEAS WILL  
LIKELY RETURN WITH PART OF THE WATERS SOUTH OF CAPE BLANCO  
POSSIBLY REACHING GALE. -FB  
 

 
   
PREV DISCUSSION
 
/ISSUED 247 PM PDT MON JUN 18 2018/  
 
DISCUSSION...THE UPPER LOW IS NOW IN SOUTHWEST IDAHO. WERE STILL ON  
THE BACK EDGE OF THE LOW WITH SOME WRAP AROUND MOISTURE. THE CLOUD  
COVER THAT WAS EXTENSIVE EAST OF THE CASCADES THIS MORNING IS  
BREAKING UP AS THE ATMOSPHERE BECOMES UNSTABLE. THE POTENTIAL FOR  
SHOWERS STILL EXIST MAINLY ALONG AND EAST OF THE CASCADES INTO THIS  
EVENING. A FEW LIGHTNING STRIKES HAVE SHOWN UP EAST OF OUR AREA, BUT  
STILL CANNOT RULE OUT A FEW ISOLATED STORMS LATER THIS AFTERNOON AND  
EVENING, EXCEPT FOR NORTHERN KLAMATH AND MOST OF LAKE COUNTY BECAUSE  
IT'S MORE STABLE. MEANWHILE WEST OF THE CASCADES SHOULD BE IN THE  
CLEAR OF ANY THUNDERSTORMS. THIS IS BECAUSE THE STEERING FLOW IS  
FROM THE NORTH TO NORTHWEST, SO ANY STORMS THAT DEVELOP WILL MOVE  
SOUTH TO SOUTHEAST, AND IT'S MORE STABLE. CUMULUS CLOUDS WILL BUILD  
IN SOME AREAS WEST OF THE CASCADES INLAND FROM THE COAST, BUT THEY  
SHOULD NOT HAVE MUCH VERTICAL EXTENT TO THEM.  
 
TUESDAY WILL BE DRY AND MUCH WARMER FOR MOST LOCATIONS INLAND FROM  
THE COAST AS SHORT WAVE RIDGING BUILDS IN. IT NOW LOOKS LIKE THE  
BEST INSTABILITY WILL BE EAST OF OUR AREA, THEREFORE WENT WITH DRY  
CONDITIONS ACROSS THE BOARD. AT THE COAST, THE MARINE STRATUS  
REMAINS IN PLACE, SO WE'LL ONCE AGAIN BE DEALING WITH OVERCAST SKIES  
IN SIMILAR LOCATIONS AS THIS MORNING THEN RETREATING AT OR JUST OFF  
THE COAST IN THE AFTERNOON.  
 
OUR NEXT FOCUS OF ATTENTION WILL BE WEDNESDAY AFTERNOON AND NIGHT.  
ALL OF THE INGREDIENTS ARE STARTING TO COME TOGETHER FOR AN OUTBREAK  
OF THUNDERSTORMS, SOME OF WHICH COULD BE STRONG TO SEVERE WEDNESDAY  
AFTERNOON THROUGH AT LEAST WEDNESDAY EVENING. THE INGREDIENTS  
NECESSARY FOR THUNDERSTORMS ARE: MOISTURE, TRIGGER (SHORTWAVE) AND  
INSTABILITY. WE'LL HAVE OF THESE AND THE INDICATIONS FOR ALL THREE  
ARE SIGNIFICANT. EACH OF THESE WILL BE DISCUSSED BELOW.  
 
TRIGGER: THERE IS GOOD AGREEMENT AMONG THE MODELS THAT A SHORTWAVE  
TROUGH WILL APPROACH THE OREGON COAST WEDNESDAY AFTERNOON. AT THE  
SAME TIME IT'S EXPECTED TO BECOME NEGATIVELY TILTED WITH PLENTY OF  
STRONG SHORTWAVES (TRIGGER) OUT AHEAD OF IT. A NEGATIVELY TILTED  
TROUGH IS TYPICALLY AN INDICATION OF A SYSTEM STRENGTHENING.  
 
MOISTURE: THIS WILL BE IN ABUNDANCE ON WEDNESDAY. MODELS ARE SHOWING  
PRECIPITABLE WATER VALUES JUST OVER A HALF INCH WEDNESDAY MORNING,  
INCREASING TO TO ALMOST AN INCH OR SLIGHTLY MORE, ESPECIALLY ALONG  
AND WEST OF THE CASCADES LATE WEDNESDAY AFTERNOON.  
 
INSTABILITY: PLENTY OF THIS EXIST, ESPECIALLY IN THE AFTERNOON. THE  
GENERAL CONSENSUS IS FOR VERY UNSTABLE CONDITIONS WEDNESDAY  
AFTERNOON AND EVENING. FOR EXAMPLE, THE GFS SHOWS LI'S BETWEEN -3  
AND -5 C. THE NAM IS EVEN LOWER WITH VALUES BETWEEN -5 AND -7C. IN  
ADDITION CAPE VALUES WELL OVER 1000 J/KG. ALL OF THIS WILL BE COMING  
DURING NEAR OR MAX HEATING OF THE DAY WHICH WILL ONLY ADD TO THE  
INSTABILITY.  
 
ADDITIONALLY, A SIGNIFICANT SOUTHERLY WIND FIELD YIELDS 0-6KM BULK  
SHEAR OF 40KT, AND UPPER LEVEL DEFORMATION IS HIGH. IF ALL THIS  
COMES TO PASS, SEVERE THUNDERSTORMS ARE POSSIBLE WITH THE PRIMARY  
THREAT BEING DAMAGING WINDS, BUT SMALL HAIL COULD NOT BE RULED  
OUT. THERE'S STILL SOME UNCERTAINTY WITH THIS FORECAST, BUT  
THERE'S FAIRLY GOOD AGREEMENT MOST OF THE ACTION COULD BE CENTERED  
FROM WESTERN AND CENTRAL SIKSYOU COUNTY NORTH ALONG THE CASCADES  
AND PORTIONS OF THE WESTSIDE, THIS WOULD INCLUDE THE ROGUE VALLEY.  
 
IT REMAINS TO BE SEEN IF THE DETAILS ON THE LOCATIONS AND TIMING AND  
EXPECTED THUNDERSTORM PARAMETERS AND PLACEMENT/TIMING OF THE  
SHORTWAVE WILL CHANGE. THEREFORE WATCH FOR UPDATES. RIGHT NOW, WE  
THINK THE THE BEST CHANCE FOR SIGNIFICANT THUNDERSTORMS IS LATE  
WEDNESDAY AFTERNOON AND EVENING WHEN THE BEST DYNAMICS ARRIVE.  
 
THE AXIS OF THE SHORTWAVE TROUGH WILL SWING NORTHEAST AND CENTERED  
EAST OF THE CASCADES LATER WEDNESDAY EVENING. THE BEST CHANCE FOR  
THUNDERSTORMS WILL ALSO BEGIN TO SHIFT EAST AS THE STEERING WINDS  
BECOME WESTERLY AND BEST DYNAMICS ARE CONFINED TO NORTHERN KLAMATH  
AND LAKE COUNTY.  
 
SLIGHT COOLING IS EXPECTED THURSDAY AND FRIDAY WITH A WEAK WEST TO  
NORTHWEST FLOW AND LIGHT TO MODERATE ONSHORE FLOW. ANOTHER SHORTWAVE  
WILL SWING NORTH OF OUR AREA FRIDAY NIGHT INTO SATURDAY. WE'LL STAY  
DRY, BUT THE RAPID WARM UP MAY NOT MATERIALIZE. WE'LL STILL BE ABOVE  
NORMAL THOUGH.  
 
WE'LL HEAT UP SOME SUNDAY AS RIDGING BUILDS OVER THE AREA. THIS  
WON'T LAST LONG AS AN UPPER TROUGH APPROACHES THE AREA MONDAY WITH  
INCREASING ONSHORE FLOW. -PETRUCELLI  
 
FIRE WEATHER...THE UPPER LOW THAT HAS BEEN FEED MOIST UNSTABLE AIR  
TO THE REGION CONTINUES TO SLOWLY WOBBLE EAST TODAY WITH  
THUNDERSTORMS OVER CASCADES AND THE EAST SIDE. AN UPPER RIDGE WILL  
BUILD IN BEHIND THE EXITING UPPER LOW TUESDAY, BRINGING A DRAMATIC  
WARMUP AND A DRYING PATTERN INTO MID WEEK. MOIST UNSTABLE AIR FEEDS  
INTO THE REGION AGAIN ON WEDNESDAY, WITH STRONG INSTABILITY OVER THE  
CASCADES. THIS AREA HAS A CHANCE OF SEEING HAIL AND DAMAGING WINDS  
WEDNESDAY AFTERNOON INTO THE EVENING. A WARMING AND DRYING  
PATTERN RETURNS THURSDAY INTO THE WEEKEND. SVEN  
 

 
   
MFR WATCHES/WARNINGS/ADVISORIES
 
 
OR...NONE.  
 
CA...NONE.  
 
PACIFIC COASTAL WATERS...NONE.  
 

 
 
DW/MAP/M&M  
 
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