Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 021149
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
449 AM PDT SUN AUG 2 2015

UPDATED AVIATION DISCUSSION.

.AVIATION...FOR THE 02/12Z TAF CYCLE...LOW LEVEL STREAMLINE
ANALYSIS SUGGESTS THAT THE SMOKE PLUME FROM THE FIRES IN THE
UMPQUA WILL CONTINUE TO AFFECT THE CASCADES AND KLAMATH COUNTY
(INCLUDING KLMT) THIS MORNING, AND THEN GRADUALLY SHIFT TOWARD THE
WEST TO INCLUDE KMFR AS SURFACE WINDS TURN NORTHERLY LATE THIS
MORNING AND THIS AFTERNOON. OUTSIDE THE SMOKE, CONDITIONS WILL BE
VFR. ISOLATED THUNDERSTORMS ARE POSSIBLE OVER MUCH OF THE AREA
INLAND FROM THE COAST THIS MORNING, BUT ARE NOT LIKELY ENOUGH TO
INCLUDE IN THE TAFS. THUNDERSTORM COVERAGE IS EXPECTED TO INCREASE
THIS AFTERNOON, ESPECIALLY CASCADES EASTWARD. STORMS MAY PRODUCE
GUSTY, ERRATIC WINDS AND BRIEF MVFR CIGS/VIS. AT THE COAST, AREAS
IFR STRATUS WILL BURN OFF THIS MORNING, THEN RETURN AGAIN TONIGHT.
-WRIGHT

&&

.PREV DISCUSSION... /ISSUED 329 AM PDT SUN AUG 2 2015/

DISCUSSION...
APPROXIMATELY 400 CLOUD TO GROUND LIGHTNING STRIKES HAVE BEEN
OBSERVED IN THE LAST 24 HOURS ACROSS INLAND AREAS OF THE FORECAST
AREA, WITH OVER 150 CLOUD TO OCEAN STRIKES WITHIN 60 NAUTICAL
MILES OF THE COAST. WHILE SEVERAL STRIKES DID FIND THEIR WAY OUT
INTO THE WEST SIDE VALLEYS OF JACKSON AND JOSEPHINE COUNTIES
SATURDAY, MOST STAYED IN THE MOUNTAINS. AT THIS HOUR, MOST OF THE
LIGHTNING THAT IS OCCURRING IS OVER THE COASTAL WATERS.

THIS MORNING SUBTLE COOLING ALOFT WEST OF AND NEAR THE COAST IN
NORTHWESTERN PORTIONS OF THE FORECAST AREA CONTINUES TO SUPPORT
THUNDERSTORMS THERE AND SHOULD CONTINUE TO DO SO THROUGH THE
MORNING. A SECONDARY AREA OF ELEVATED INSTABILITY EXISTS
SOUTHEASTWARD FROM THERE TO JUST WEST OF MOUNT SHASTA
SOUTHEASTWARD TO THE SIERRAS. THIS IS ASSOCIATED WITH A VORTICITY
MAXIMA AT 500MB THAT NUMERICAL MODELS ARE UNANIMOUS IN SHOWING
STRENGTHENING NORTHWESTWARD THROUGH THE DAY TODAY. THIS 500MB
FEATURE THEN PROPAGATES NORTH AND THEN NORTHEASTWARD ACROSS THE
NORTHEASTERN HALF OF THE FORECAST AREA THIS EVENING THROUGH
TONIGHT. THIS VORTICITY FEATURE IS EXPECTED TO BE THE DRIVING
MECHANISM FOR SCATTERED THUNDERSTORM ACTIVITY OVER MUCH OF THE
FORECAST AREA OVER THE NEXT 24 HOURS. IN SHORT, THE FORECAST AREA
IS CURRENTLY LYING ON THE CUSP OF A MAJOR ROUND OF LIGHTNING AS IS
EVIDENCED BY CURRENT RADAR AND SATELLITE IMAGERY. THIS FEATURE IS
EXPECTED TO PROVIDE THE FORCING MECHANISM NEEDED TO INCREASE
ACTIVITY ACROSS THE AREA. FRUSTRATINGLY, DETAILS IN THE NUMERICAL
MODELS ARE MIXED. THERE IS GOOD AGREEMENT, HOWEVER, IN MORE WEST
SIDE LIGHTING TODAY THAN WE`VE OBSERVED THE LAST COUPLE OF DAYS,
PARTICULARLY IN JOSEPHINE COUNTY. UNCERTAINTIES LIE NORTHEAST OF
THERE, WHERE SMOKE AND SIGNIFICANT CLOUDINESS WILL KEEP
TEMPERATURES ABOUT 10 DEGREES COOLER TODAY THAN YESTERDAY. THE
INCREASE IN UPPER LEVEL DIFFLUENCE AND VORTICITY IS EXPECTED TO
MITIGATE THAT LESSER HEATING, HOWEVER, BRINGING INCREASED
THUNDERSTORM ACTIVITY.

SMOKE TODAY WILL BE PUSHED ALONG MAINLY EAST AND SOUTHEAST OF
EXISTING FIRES. SUSPECT THAT MIXING AND LIFT FROM THE SHORTWAVE
TROUGH MOVING THROUGH TODAY WILL LIFT OUT A GOOD BIT OF THE SMOKE
THROUGH THE DAY. HOWEVER, CONTINUED SMOKE GENERATION FROM FIRES IN
THE AREA MEANS IT`S VERY UNLIKELY SMOKE WILL CEASE TO BE AN ISSUE
FOR AT LEAST SEVERAL DAYS, ESPECIALLY NEAR AND EAST OF THE STOUTS
CREEK FIRE.

MODELS HAVE TRENDED SLOWER WITH MOVING THUNDERSTORM ACTIVITY
EASTWARD FOR MONDAY. IN FACT, THERE IS PLENTY OF LINGERING
INSTABILITY FOR THUNDERSTORMS MONDAY AFTERNOON AND EVENING, EVEN
ON THE WEST SIDE, AND ESPECIALLY FROM THE CASCADES EASTWARD UNDER
A GENERAL SOUTHWEST FLOW AS MORE PRONOUNCED COOLING OCCURS AT
500MB. LIMITED MOISTURE, HOWEVER, IS EXPECTED TO KEEP STORMS
MOSTLY FROM THE MARBLE MOUNTAINS, SISKIYOUS, AND CASCADES
EASTWARD. GUSTY AFTERNOON AND EVENING WINDS SHOULD BE EXPECTED
MONDAY AFTERNOON AND EVENING, ESPECIALLY NEAR ACTIVE WILDFIRES.
THERE WILL BE LINGERING THUNDERSTORM CHANCES FOR SIMILAR AREAS,
DIMINISHING FROM THE WEST WITH TIME, TUESDAY INTO WEDNESDAY.

TEMPERATURES WILL COOL THROUGH THURSDAY MORNING BEFORE COMING UP
AGAIN THURSDAY AND FRIDAY UNTIL ANOTHER UPPER LEVEL TROUGH DIVES
IN FOR NEXT WEEKEND. THIS TROUGH WILL BRING A NEW THREAT FOR SHOWERS
AND THUNDERSTORMS. BTL

MARINE...UPDATED 200 AM PDT SUNDAY 2 AUGUST 2015...OFFSHORE HIGH
PRESSURE AND WEAK LOW PRESSURE OVER THE WATERS WILL RESULT IN
CONTINUED LIGHT NORTH WINDS AND SMALL SEAS THROUGH TUESDAY
MORNING. OFFSHORE HIGH PRESSURE WILL STRENGTHEN AND A THERMAL
TROUGH WILL REDEVELOP ALONG THE COAST TUESDAY AFTERNOON LEADING TO
STRONGER NORTH WINDS AND CHOPPY SEAS THAT WILL LAST INTO THURSDAY.
-WRIGHT

FIRE WEATHER...UPDATED 250 AM PDT SUNDAY 2 AUGUST 2015...FEW
CHANGES HAVE BEEN MADE THE FIRE WEATHER FORECAST THIS MORNING AS
THINGS REMAIN ON TRACK. RED FLAG WARNINGS REMAIN IN PLACE FOR MOST
OF OUR AREA INLAND FROM THE IMMEDIATE COASTLINE. THEY ARE IN EFFECT
THROUGH THIS EVENING ON THE WEST SIDE AND THROUGH TONIGHT INTO
MONDAY MORNING ROUGHLY FROM THE CASCADES EAST. WE`VE SEEN A FAIR
AMOUNT OF LOW TOPPED CONVECTION OVER THE AREA THROUGH THE NIGHT, BUT
WE HAVEN`T SEEN MUCH LIGHTNING OUT OF THEM, SO FAR. THERE ARE SOME
FAIRLY SIGNIFICANT DISTURBANCES SEEN ON WATER VAPOR IMAGERY ROTATING
NORTHWARD THROUGH CALIFORNIA, AND ALL GUIDANCE SUGGESTS THESE WILL
BRING ISOLATED TO SCATTERED THUNDERSTORMS TO OUR AREA TODAY. SEVERAL
OF THE MODELS SHOW THUNDERSTORMS DEVELOPING AROUND DAWN THROUGH MID
MORNING FROM CENTRAL SISKIYOU COUNTY UP THROUGH OUR WEST SIDE OREGON
ZONES. THE LOW LEVELS REMAIN VERY DRY, SO IF THIS HAPPENS, STORMS
WILL LIKELY BE ON THE DRY SIDE. CONFIDENCE IN THIS IS LOW, BUT THE
POTENTIAL IMPACT IS HIGH.

CONFIDENCE IS HIGHER IN A MUCH MORE SIGNIFICANT OUTBREAK OF STORMS
LATER TODAY THROUGH THIS EVENING AS A STRONG SHORTWAVE CURRENTLY
AROUND THE CENTRAL CA/NV BORDER MOVES NORTH. ALL THE MODELS AGREE ON
THIS, BUT PLACEMENT OF THE GREATEST IMPACT VARIES. AS USUAL, THE
MOST LIKELY AREAS FOR THUNDERSTORMS WILL BE THE MOUNTAINS AND EAST
SIDE. NEVERTHELESS, ALL OUR AREA IS POTENTIALLY UNDER THE GUN FOR
ABUNDANT LIGHTNING THIS AFTERNOON AND EVENING. THE ONLY POSITIVE IS
THAT PRECIPITABLE WATER INCREASES AS THE COLUMN MOISTENS AND BASES
LOWER THROUGH THE DAY, SO STORMS SHOULD BE TRENDING WETTER THE LATER
IN THE DAY WE GET. THE ACTIVITY WILL CARRY ON LONGER FROM THE
CASCADES EAST, SO RED FLAG WARNINGS HAVE BEEN EXTENDED THROUGH
TONIGHT FOR THESE AREAS. -WRIGHT

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...     RED FLAG WARNING FROM 11 AM THIS MORNING TO 5 AM PDT MONDAY FOR
     ORZ625.
     RED FLAG WARNING UNTIL 5 AM PDT MONDAY FOR ORZ624.
     RED FLAG WARNING UNTIL 11 PM PDT THIS EVENING FOR
     ORZ615-616-619-620-622.
     RED FLAG WARNING UNTIL 5 AM PDT MONDAY FOR ORZ617-621-623.

CA...     RED FLAG WARNING UNTIL 11 PM PDT THIS EVENING FOR
     CAZ280-281-284.
     RED FLAG WARNING UNTIL 5 AM PDT MONDAY FOR CAZ285.

PACIFIC COASTAL WATERS...NONE.

$$



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