Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 022215
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
315 PM PDT THU JUL 2 2015

.DISCUSSION...
TEMPERATURES THIS AFTERNOON ARE ZERO TO 4 DEGREES FAHRENHEIT
HIGHER THAN THEY WERE 24 HOURS AGO. I`VE NUDGED UP FORECAST HIGHS
AT SOME LOCATIONS, TO INCLUDED MEDFORD, WHERE THE HIGH SHOULD END
UP AT ABOUT 110F, GIVE OR TAKE 2 DEGREES. THIS WILL LIKELY BREAK
THE RECORD OF 108F SET IN 1922. MANY RECORD HIGH TEMPERATURES WILL
FALL TODAY. OF NOTE, GUIDANCE INDICATES HIGHS ON FRIDAY WILL BE
ABOUT 5F COOLER THAN TODAY`S DUE TO SOME HIGH CLOUD COVER FOR MOST
AREAS, AND ISOLATED THUNDERSTORMS IN OTHER`S PRIMARILY CALIFORNIA.

THUNDERSTORMS HAVE FORMED IN THE LASSEN NATIONAL PARK ARE THIS
AFTERNOON. WE`VE ALSO SEEN A COUPLE OF CELLS GO UP IN OUR AREA,
ONE OVER MOUNT SHASTA AND THE OTHER WEST OF LAKEVIEW. WITH VERY
WEAK STEERING WINDS, THESE HAVE COLLAPSED BEFORE SUFFICIENT
CHARGES DIFFERENTIAL DEVELOPED TO PRODUCE CLOUD TO GROUND
LIGHTNING STRIKES. WE DO EXPECT ISOLATED THUNDERSTORMS TODAY
ACROSS PORTIONS OF NORTHERN CALIFORNIA AND THE EAST SIDE, THESE
ARE LIKELY TO CONTINUE TO BE THE PULSE TYPE, WHICH MEANS THAT
STEERING FLOW IS WEAK, AND THE STORMS ARE LIKELY TO MOVE VERY
LITTLE AND COLLAPSE WITHIN AND SHORT TIME OF FORMING. SUCH STORMS
CAN PRODUCE BRIEF RAINFALL UNDER THE DOWNDRAFT, BUT ALSO LIGHTNING
AND GUSTY WINDS IN THEIR PERIPHERY AND WHEN COLLAPSING. NEW CELLS
MAY FORM OFF OF THE OUTFLOW OF THE INITIAL ONES.

THE FORECAST FOR ISOLATED THUNDERSTORMS AGAIN ON FRIDAY IN
NORTHERN CALIFORNIA AND PORTIONS OF THE EAST SIDES LOOKS ON
TRACK. WHILE SOME MODEL GUIDANCE HAS INDICATED COVERAGE COULD
EXCEED ISOLATED COVERAGE IN WESTERN SISKIYOU COUNTY AND PORTIONS
OF KLAMATH COUNTY FRIDAY AFTERNOON AND EVENING, OTHER GUIDANCE
INDICATES MORNING CLOUD COVER THERE ON FRIDAY WILL LIMIT SURFACE
HEATING. THUS, WITH MIXED SIGNALS, CONFIDENCE IS CURRENTLY LOW
THAT SCATTERED STORMS WILL OCCUR OVER THE FORECAST AREA ON FRIDAY,
WITH ISOLATED THUNDERSTORMS MORE LIKELY. WE EXPECT STORMS ON
FRIDAY WILL MOVE EAST TO WEST OVER NORTHERN CALIFORNIA, AND
SOUTHEAST TO NORTHWEST OVER EASTERN OREGON AROUND 10 KNOTS. MODEL
CONSENSUS INDICATES THUNDERSTORMS WILL FORM FIRST IN SISKIYOU
AND MODOC COUNTY AND THEN PROPAGATE EAST-NORTHEASTWARD WITH A
MID-LEVEL WAVE INTO KLAMATH AND LAKE COUNTIES.

SATURDAY AND SUNDAY THERE IS A WEAK SHORTWAVE TROUGH THAT WILL
DRIFT ACROSS THE AREA. IT`S A SUBTLE FEATURES, BUT SHOULD BE
ENOUGH TO RESULT IN SCATTERED THUNDERSTORMS OVER PORTIONS OF
NORTHERN CALIFORNIA AND THE EAST SIDE. THERE IS A POSSIBILITY THAT
SOME STORMS COULD REACH THE WEST SIDE ON SUNDAY, BUT MODEL
CONSENSUS INDICATES THE FLOW TO BE A LITTLE TOO WEAK ACROSS THE
SISKIYOUS AND MOISTURE TO BE SUB-PAR FOR THUNDERSTORMS TO REACH
WEST OF THE WESTERN SLOPES OF THE CASCADES.

GUIDANCE, OVERALL, HAS INCREASED THE THUNDERSTORMS THREAT OVER THE
AREA EARLY TO MID NEXT WEEK. THIS IS BECAUSE THE UPPER LEVEL LOW
OFF OF THE COAST PUSHES EASTWARD, PUTTING US IN A MORE FAVORABLE
POSITIONS FOR THUNDERSTORMS AND, POSSIBLY, SOME WITH WETTING
PRECIPITATION. WE EXPECT THAT THIS WILL ALSO BRING ABOUT A
WELCOME COOL DOWN ACROSS THE AREA. THE WEST SIDE DOES RUN THE
RISK OF THUNDERSTORMS NEXT, THOUGH THE GREATEST THREAT WILL
CONTINUE TO BE SOUTH OF THE SISKIYOUS AND FROM THE CASCADES
EASTWARD. BTL

&&

.AVIATION...FOR THE 02/18Z TAF CYCLE...ALONG THE COAST...IFR TO LIFR
CEILINGS AND VISIBILITIES NORTH OF CAPE BLANCO AND THE SOUTH COAST
NEAR BROOKINGS MAY NOT CLEAR UNTIL THIS AFTERNOON...THE LOWER
CONDITIONS ARE EXPECTED TO RETURN TO THE SAME AREAS AGAIN THIS
EVENING. OVER THE REMAINDER OF THE AREA...VFR CONDITIONS WILL
PREVAIL...BUT ISOLATED AFTERNOON AND EVENING THUNDERSTORMS ARE
POSSIBLE OVER THE OREGON CASCADES SOUTH OF CRATER LAKE...OVER
SOUTHERN KLAMATH AND LAKE COUNTIES...AND OVER SISKIYOU AND MODOC
COUNTIES.

&&

.MARINE...UPDATED 300 AM PDT THURSDAY 2 JULY 2015...A THERMAL TROUGH
NEAR THE COAST WILL WEAKEN INTO THURSDAY...BUT PERSIST INTO
SATURDAY. SMALL CRAFT ADVISORY LEVEL NORTH WINDS AND STEEP TO VERY
STEEP SEAS WILL PERSIST FOR THE NEXT SEVERAL DAYS. WINDS AND WAVES
WILL SUBSIDE THIS WEEKEND.

&&

.FIRE WEATHER...UPDATED 200 PM PDT THURSDAY 2 JULY 2015...HOT AND
DRY WEATHER WILL PERSIST INTO THIS WEEKEND...BUT THE HOTTEST DAY
WILL BE TODAY. AN INVERSION WILL BRING CONTINUED MODERATE TO LOCALLY
POOR RECOVERIES TO MANY RIDGES OVER THE AREA TONIGHT AND FRIDAY
NIGHT.  MOISTURE ALOFT IS INCREASING TODAY AND WILL INCREASE FURTHER
ON  FRIDAY WITH ISOLATED AFTERNOON AND EVENING THUNDERSTORMS
EXPECTED DURING THIS PERIOD OVER NORTHERN CALIFORNIA AND EAST OF THE
CASCADES. TODAY, THE MAIN THREAT FOR STORMS IS OVER MODOC BUT
EXTENDS TO THE WEST INTO SISKIYOU COUNTY AND NORTH INTO SOUTHERN
KLAMATH AND LAKE COUNTIES. ON FRIDAY, EXPECT A MOISTURE PLUME TO MOVE
INTO NORTHERN CALIFORNIA BY MORNING. THIS WILL BRING A SLIGHT CHANCE
OF MORNING SHOWERS AND THUNDERSTORMS DURING THE MORNING HOURS. THEN
EXPECTED ISOLATED SHOWERS AND THUNDERSTORMS TO DEVELOP INTO THE
AFTERNOON IN NORTHERN CALIFORNIA AND FROM THE CASCADES EAST. EXPECT
THE BEST CHANCE FOR THUNDERSTORMS TO EXTEND FROM SOUTH CENTRAL AND
EASTERN SISKIYOU COUNTY NORTHEAST INTO MODOC COUNTY AND INTO
SOUTHEASTERN KLAMATH AND SOUTHERN LAKE COUNTIES.  ON SATURDAY,
EXPECT A SIMILAR AREA FOR THUNDERSTORMS DEVELOPMENT IN THE AFTERNOON
AND EVENING. HOWEVER CONFIDENCE IS INCREASING THAT STORMS MAY BE
SCATTERED, MAINLY IN MODOC AND NORTHWARD INTO SOUTHEASTERN KLAMATH
AND SOUTHERN LAKE COUNTIES. HAVE HEADLINED FOR THESE STORMS AND WILL
CONSIDER THE POTENTIAL FOR FIRE WEATHER WATCHES FOR THE SATURDAY
EVENT WITH THE NEXT FORECAST CYCLE. THROUGH SATURDAY, GIVEN A
RELATIVELY SLOW STORM MOTION, EXPECT STORMS TO HAVE WETTING RAINS,
MAINLY IN THE CORE OF THE STORM.

THUNDERSTORM CHANCES WILL INCREASE OVER THE AREA ON SUNDAY WITH
CONTINUING CHANCES MONDAY AND TUESDAY. BEST CHANCES FOR
THUNDERSTORMS DURING THIS PERIOD ARE EXPECTED FROM THE CASCADES EAST
IN OREGON AND OVER NORTHERN CALIFORNIA. HOWEVER, STORMS ARE ALSO
POSSIBLE WEST OF THE CASCADES,  MAINLY FOR JACKSON COUNTY AND
EASTERN DOUGLAS COUNTY DURING THIS PERIOD AS WELL WITH MODELS SHOW
PERIODS OF SOUTH FLOW BRINGING STORMS INTO WESTERN AREAS. /CC

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...HEAT ADVISORY UNTIL 11 PM PDT FRIDAY FOR ORZ023.
     HEAT ADVISORY UNTIL 11 PM PDT SATURDAY FOR ORZ024-026.

CA...HEAT ADVISORY UNTIL 11 PM PDT SATURDAY FOR CAZ080-081.

PACIFIC COASTAL WATERS...
- SMALL CRAFT ADVISORY FOR WINDS UNTIL 2 AM PDT FRIDAY FOR
  PZZ350-356-370.
- SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 5 AM PDT SUNDAY
  FOR PZZ350-356-370-376.
- SMALL CRAFT ADVISORY FOR WINDS UNTIL 5 AM PDT SATURDAY FOR
  PZZ376.
- HAZARDOUS SEAS WARNING UNTIL 2 AM PDT FRIDAY FOR PZZ376.

$$

BTL/CC/BPN


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