Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 041339
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
639 AM PDT FRI SEP 4 2015

.UPDATE...PUT OUT A QUICK UPDATE JUST NOW TO INCREASE POPS ON THE
EAST SIDE AND ALLOW FOR THUNDERSTORMS OVER ALL AREAS THIS MORNING.
AIRMASS IS ALREADY DESTABILIZING QUICKLY AND WE`VE SEEN SIX
LIGHTNING STRIKES ALONG THE SISKIYOU/MODOC BORDER, AND THIS IS
WITH THE MAJORITY OF THE COLD POOL AND INSTABILITY YET TO COME
TODAY. IT ALSO WOULDN`T BE OUT OF THE QUESTION TO SEE A FEW
SNOWFLAKES OVER LAKE AND MODOC COUNTIES THIS MORNING AS SURFACE
TEMPERATURES ARE NEAR OR BELOW FREEZING. TEMP/DEWPOINT SPREAD ARE
FAIRLY HIGH, THOUGH, SO IT MAY BE JUST VIRGA OUT THERE. -WRIGHT

&&

.PREV DISCUSSION... /ISSUED 511 AM PDT FRI SEP 4 2015/

AVIATION...FOR THE 04/12Z TAF CYCLE...VFR CONDITIONS WILL
CONTINUE FOR MOST TAF SITES EARLY THIS MORNING. CLOUDS AND
SHOWERS WILL INCREASE AND CIGS WILL LOWER THROUGH THIS MORNING,
ESPECIALLY EAST OF THE CASCADES WHERE SHOWERS WILL BE MOST
NUMEROUS. THUNDERSTORMS WILL ALSO BE POSSIBLE THIS AFTERNOON. MVFR
CIGS AND VIS ARE EXPECTED IN HEAVIER SHOWERS. ALSO EXPECT MOUNTAIN
OBSCURATIONS, ESPECIALLY OVER AND EAST OF THE CASCADES. THESE
CONDITIONS WILL PERSIST INTO THIS EVENING. -WRIGHT

PREV DISCUSSION... /ISSUED 325 AM PDT FRI SEP 4 2015/

DISCUSSION...TEMPERATURES THIS MORNING HAVE BEEN QUITE COLD
RELATIVE TO NORMAL FOR THIS TIME OF YEAR, WITH TEMPERATURES EVEN
DROPPING TO THE MID 20S IN THE GENERAL REGION NEAR CHEMULT. WITH
SEVERAL MORE HOURS OF COOLING TO GO, AND CLOUDS NOT QUITE IN THE
AREA YET, THE CURRENT FROST ADVISORY SEEMS TO BE ON TRACK FOR THE
EAST SIDE. WILL THEREFORE LET THIS RIDE THROUGH THE MORNING.
TEMPERATURES WILL REMAIN MUCH COOLER THAN NORMAL TODAY, AS AMPLE
CLOUDS AND RAIN SHOULD KEEP SOLAR HEATING TO A MINIMUM.

AN UPPER LEVEL LOW, CURRENTLY LOCATED OVER THE SEATTLE AREA, WILL
DROP SOUTH TODAY, AND TAKE POSITION OVER OREGON BY THIS AFTERNOON.
AS IT DROPS SOUTH, A VERY POTENT SHORTWAVE ORBITING THE LOW WILL
PASS OVERHEAD, AND WITH THE LOWERING TEMPERATURES ALOFT, ENOUGH
INSTABILITY AND DYNAMICS SHOULD BE PRESENT TO PRODUCE SHOWERS AND
ISOLATED THUNDERSTORMS OVER THE BULK OF THE FORECAST AREA LATE
THIS MORNING INTO THIS EVENING. WHILE MOST RAINFALL AMOUNTS WILL
BE LIGHT, THERE IS A GOOD CHANCE THAT MANY LOCATIONS COULD SEE
WETTING RAINS. THIS IS PARTICULARLY TRUE EAST OF THE CASCADES,
WHERE FORCING WILL BE STRONGEST DURING THE PEAK OF DAYTIME
HEATING. OVERNIGHT, THE COLD AIR MASS WILL BEGIN TO SETTLE IN.
HOWEVER, THERE SHOULD BE AMPLE CLOUDS REMAINING IN THE AREA, SO
NIGHTTIME LOWS MAY NOT DROP AS LOW AS WOULD BE EXPECTED. HAVE
ADDED PATCHY FROST TO THE FORECAST, BUT GIVEN THE CLOUD COVER, DO
NOT THINK THAT THIS WOULD BE A WIDESPREAD EVENT, SO WILL NOT ISSUE
ANY HEADLINES AT THIS TIME.

THE LOW WILL BEGIN MOVING EAST SATURDAY MORNING, AND GRADUALLY,
SHOWERS AND CLOUDS WILL MOVE OUT OF THE FORECAST AREA AS WELL. EXPECT
THAT THE SKIES WILL BE MOSTLY CLEAR BY SATURDAY NIGHT, AIDED IN PART
TO DEVELOPING OFFSHORE FLOW DRYING OUT THE MID LEVELS. WITH THE COLD
AIR STILL AT THE SURFACE, AND NO CLOUDS TO ACT AS A BLANKET, SUSPECT
THAT THIS WILL BE THE COOLEST NIGHT OF THE WEEK. IN FACT, WIDESPREAD
FROST AND FREEZE IS LIKELY FOR THE EAST SIDE.

THESE COLD TEMPERATURES WILL NOT LAST, HOWEVER, AS UPPER LEVEL
RIDGING WILL BUILD INTO THE AREA, AND THE THERMAL TROUGH WILL RETURN
TO OUR SOUTH. OFFSHORE FLOW SHOULD KEEP THE AREA CLEAR OF CLOUDS,
AND TEMPERATURES WILL RISE TO VALUES AROUND 5 DEGREES ABOVE NORMAL
FOR THIS TIME OF YEAR BY THE MIDDLE OF NEXT WEEK. SEVERAL WAVES WILL
APPROACH THE WEST COAST DURING THIS TIME, BUT THE RIDGE SHOULD KEEP
THE TRACK OF ANY PRECIPITATION MAKING SYSTEMS WELL NORTH OF THE
FORECAST AREA. THEREFORE, FOR THE REMAINDER OF THE FORECAST TERM,
EXPECT GRADUALLY WARMING TEMPERATURES AND DRY CONDITIONS. -BPN

MARINE...UPDATED 230 AM PDT FRIDAY 4 SEPTEMBER 2015...NORTH WINDS
WILL CONTINUE THROUGH THE FORECAST PERIOD. A PERIOD OF SMALL CRAFT
ADVISORY LEVEL WINDS IS EXPECTED THIS AFTERNOON AND EVENING SOUTH
OF CAPE BLANCO. WINDS THEN STRENGTHEN AGAIN SUNDAY AS A THERMAL
TROUGH FORMS OVER NORTHERN CALIFORNIA. GALES WILL BE POSSIBLE OVER
THE SOUTHERN WATERS MONDAY AND TUESDAY. SEAS WILL BE PRIMARILY
WIND DRIVEN THROUGH EARLY NEXT WEEK. -WRIGHT

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...FROST ADVISORY UNTIL 7 AM PDT THIS MORNING FOR ORZ029>031.

CA...FROST ADVISORY UNTIL 7 AM PDT THIS MORNING FOR CAZ084-085.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FROM 11 AM THIS MORNING
     TO 11 PM PDT THIS EVENING FOR PZZ376.

$$



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