Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 301617
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
917 AM PDT THU JUL 30 2015

.DISCUSSION...VERY WARM TEMPERATURES WILL CONTINUE TODAY AND
TOMORROW. WE ARE FORECASTING HIGHS FOR MEDFORD AT 109. THIS MAY BE
A DEGREE OR TWO TOO HIGH GIVEN THE LATEST MODEL RUN BUT EVEN THE
NEW NUMBERS ARE IN THE 105-110 RANGE. SATELLITE IMAGERY SHOWS LOW
CLOUDS IN THE COASTAL WATERS SPREADING NORTH TO NEAR POINT ST
GEORGE CALIFORNIA.

OUR NEXT CONCERN IS THUNDERSTORM POTENTIAL. THE LATEST GUIDANCE
STILL KEEPS MOST OF THE MOISTURE SOUTH OF OF SISKIYOU COUNTY
FRIDAY, BUT BOTH THE NAM12 AND GFS20 ARE BRINGING A SHORT WAVE
DISTURBANCE INTO NORTHERN CALIFORNIA FRIDAY EVENING THEN TAKING
THIS SHORT WAVE NORTH FRIDAY NIGHT INTO SATURDAY MORNING. WE ARE
LEANING TOWARD HAVING THUNDERSTORM POTENTIAL EXTENDING INTO FRIDAY
NIGHT. /FB


&&

.AVIATION...FOR THE 30/12Z TAF CYCLE...ALONG THE COAST AND
OVER THE COASTAL WATERS...AREAS OF IFR CIGS/VSBYS NORTH OF CAPE
BLANCO WILL CLEAR BY MID-MORNING. AREAS OF IFR CIGS/VSBYS WILL MOVE
NORTH ALONG THE SOUTH COAST TODAY...THEN CONTINUE TO SPREAD NORTH OF
CAPE BLANCO TONIGHT. INLAND...VFR CONDITIONS WILL PREVAIL THROUGH
THURSDAY NIGHT.

&&

.MARINE...UPDATED 200 AM PDT THURSDAY 30 JULY 2015...A THERMAL
TROUGH NEAR THE COAST WILL CONTINUE TO WEAKEN THROUGH FRIDAY WHEN IT
WILL MOVE INLAND. NORTH WINDS AND WIND-DRIVEN SEAS WILL GRADUALLY
DIMINISH.  MARGINAL SMALL CRAFT ADVISORY CONDITIONS MAY AFFECT THE
OUTER WATERS THIS WEEKEND.

&&

.FIRE WEATHER...UPDATED 200 AM PDT THURSDAY 30 JULY 2015...VERY
HOT AND DRY CONDITIONS CONTINUE THROUGH THE END OF THE WEEK...WITH
HAINES 6 DRY AND UNSTABLE CONDITIONS AFFECTING SOME INLAND AREAS
THURSDAY AND FRIDAY...INCLUDING THE CABLE CROSSING FIRE. POOR TO
MODERATE RECOVERIES WILL CONTINUE THROUGH FRIDAY MORNING...WITH
LOWER OVERNIGHT WIND SPEEDS. TEMPERATURES WILL REMAIN ABOUT 10 TO 15
DEGREES ABOVE NORMAL THROUGH FRIDAY. TEMPERATURES WILL LOWER
GRADUALLY SATURDAY INTO NEXT WEEK WITH INCREASING CLOUD COVER AND A
COOLING AIR MASS. THUS...HUMIDITIES WILL ALSO GRADUALLY INCREASE
OVER THE WEEKEND AND INTO NEXT WEEK.

THUNDERSTORMS MAY DEVELOP OVER THE FORECAST AREA AS EARLY AS FRIDAY
AFTERNOON...BUT MODELS HAVE BEEN TRENDING WEAKER WITH AN IMPULSE
THAT IS NOW EXPECTED TO STAY SOUTH AND WEST OF THE FORECAST AREA.
THEREFORE...CONFIDENCE ON ANY THUNDERSTORM ACTIVITY FOR FRIDAY IS
LOW. THAT SAID...ANY THUNDERSTORMS THAT FORM FRIDAY WILL FEATURE
VERY LITTLE RAIN WITH THEM. BETTER TRIGGERS FOR THUNDERSTORMS...AND
MORE UNSTABLE CONDITIONS...EXIST SUNDAY AND MONDAY.  ANY LIGHTNING
THAT OCCURS THIS WEEKEND OR EARLY NEXT WEEK WILL BE ON THE HEELS OF
EXTREMELY DRY AND HOT CONDITIONS...SO THE POTENTIAL FOR FIRE STARTS
WILL BE ENHANCED.

&&

.PREV DISCUSSION... /ISSUED 251 AM PDT THU JUL 30 2015/

DISCUSSION...CURRENT SURFACE ANALYSIS SHOWS THE THERMAL TROUGH ALONG
THE COAST. MEANWHILE OFFSHORE FLOW HAS WEAKENED ALONG THE COAST,
SOUTH OF CAPE BLANCO AND NOW THERE IS A WEAK ONSHORE FLOW. THIS HAS
ALLOWED BROOKINGS TO COOL DOWN TO 64 DEGREES. AS IS TYPICAL WITH
THIS TYPE OF PATTERN THE THERMAL TROUGH WILL SHIFT INLAND THIS
AFTERNOON WITH TEMPERATURES BETWEEN 105-110 FOR MANY WEST SIDE
VALLEY LOCATIONS. TEMPERATURES EAST OF THE CASCADES WILL ALSO END
UP HIGHER AS THE THERMAL TROUGH SHIFTS EAST OF THE CASCADES LATE
IN THE AFTERNOON. AT THE COAST WEAK ONSHORE FLOW IS EXPECTED TO
CONTINUE AND AS A RESULT AREAS SOUTH OF CAPE BLANCO WILL END UP
MUCH COOLER COMPARED TO THE LAST COUPLE OF DAYS, THUS WE`LL CANCEL
THE HEAT ADVISORY FOR THE SOUTH COAST.

CONDITIONS WILL REMAIN DRY AND HOT AGAIN TODAY. THE LATEST WATER
VAPOR IMAGE SHOWS PLENTY IF DRY AIR ALOFT OVER OUR AREA, BUT
MONSOONAL MOISTURE IS ON THE INCREASE AND IS MOVING NORTHWARD
TOWARDS CENTRAL CAL AHEAD OF A WEAK UPPER LOW NEAR 33N/133W. THE
LEADING EDGE OF THIS SHOULD MAKE IT INTO NORTHERN CAL LATE THIS
AFTERNOON, BUT THE BULK OF THE MOISTURE WILL BE NEAR 500MB (MID
LEVEL MOISTURE). THEREFORE WERE ONLY EXPECTING SOME MID LEVEL
CLOUDINESS IN NORTHERN CAL. ITS POSSIBLE CUMULUS COULD DEVELOP
OVER THE HIGHER TERRAIN IN WESTERN SISKIYOU COUNTY AND JUST EAST
OF MOUNT SHASTA.

THE NAM SHOWS A STRONGER SHORTWAVE MOVING INTO NORTHERN CAL LATE IN
THE AFTERNOON, BUT THE GFS SHOWS LITTLE OR NO SHORTWAVES. IN
ADDITION ITS NOT LOOKING AS UNSTABLE COMPARED TO THE PAST COUPLE OF
DAYS. MODELS SHOW MOST OF THE MID LEVEL MOISTURE CONFINED TO THE
CASCADES AND HIGHER TERRAIN IN SISKIYOU COUNTY. EVEN THEN ITS MOSTLY
A RESULT OF HIGHER MOISTURE AT 500 MB. GIVEN THE ABOVE MENTIONED
SCENARIOS HAVE REDUCED THE COVERAGE OF THUNDERSTORMS TO THE
CASCADES, SISKIYOUS AND HIGHER TERRAIN IN SISKIYOU COUNTY FOR
LATE FRIDAY AFTERNOON AND EVENING. DEPENDING ON THE AMOUNT OF
CLOUD COVER, TEMPERATURES IN A RELATIVE SENSE COULD END UP A FEW
DEGREES LOWER ON AVERAGE COMPARED TO TODAY, BUT IT WILL STILL BE
HOT.

CONFIDENCE OF THE COVERAGE AND AMOUNT OF THUNDERSTORMS REMAINS LOW
THIS WEEKEND INTO THE START OF NEXT WEEK. MID LEVEL MOISTURE IS
PRESENT, BUT THE MODELS DON`T SHOW MUCH IF ANY TRIGGER AND THE BULK
OF THE MID LEVEL MOISTURE DEPICTED IS MOSTLY AROUND 500MB. HOWEVER
THEY SHOW A STRONGER SHORTWAVE MOVING INTO MODOC COUNTY ON SUNDAY
WHICH COULD RESULT IN A GREATER COVERAGE OF THUNDERSTORMS EAST OF
THE CASCADES.

BEYOND MONDAY THE GFS SHOWS A TROUGH DIGGING SOUTH TOWARDS THE AREAS
BRINGING A RELIEF TO THE HEAT WITH THE BEST CHANCE FOR STORMS EAST
OF THE CASCADES. THE EC SHOWS A DIFFERENT SOLUTION WITH A WEAK RIDGE
OVER THE AREA, A WEAK UPPER LOW NEAR 35N/130W AND A STRONGER UPPER
TROUGH/LOW CENTERED NEAR 52N/140W. GIVEN THE DIFFERENT MODEL
SOLUTIONS, DID NOT MAKE ANY CHANGES IN THE FORECAST BEYOND MONDAY
-PETRUCELLI



&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...RED FLAG WARNING UNTIL 8 PM PDT THIS EVENING FOR ORZ616.
     HEAT ADVISORY UNTIL 11 PM PDT SATURDAY 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 HAZARDOUS SEAS UNTIL 11 AM PDT THIS
     MORNING FOR PZZ370-376.

$$

FJB/FJB/JRS


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