Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 050056
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
556 PM PDT FRI SEP 4 2015

.UPDATE...AN UPPER LOW IS BRINGING SHOWERS WITH ISOLATED
THUNDERSTORMS TO THE AREA THIS EVENING. HAVE UPDATED THE FORECAST
TO INCLUDE ISOLATED THUNDERSTORMS IN THE UMPQUA AREA  THIS
EVENING SINCE ISOLATED THUNDERSTORMS ARE STILL OCCURRING OVER
THIS AREA. MODELS INDICATE THAT SHOWER ACTIVITY WILL GRADUALLY
PUSH EASTWARD AS THE UPPER LOW MOVES TO THE EAST TONIGHT.

DURING THE MORNING SATURDAY, EXPECT THE LOW TO BECOME CENTERED
NORTHEAST OF THE AREA. SOME CONTINUED MOISTURE IN NORTHWEST FLOW
AROUND THE BACKSIDE OF UPPER TROUGH, WILL KEEP SOME LINGERING
CLOUDS AND SHOWERS IN PLACE, MAINLY ALONG THE CASCADES AND
SISKIYOUS AND INTO EASTERN AREAS, MAINLY IN EASTERN LAKE COUNTY.
COLD AIR ADVECTION IS EXPECTED TO LOWER THE MORNING TEMPERATURES
IN EAST SIDE AREAS INTO THE MID 30S. THIS COLD AIR COMBINED WITH SOME
PARTIAL CLEARING OF THE SKIES DURING THE EARLY MORNING MAY ALLOW
FOR TEMPERATURES TO LOWER FURTHER DOWN INTO THE LOWER 30S. THE  LOW
TEMPERATURES COMBINED PARTIALLY CLEAR SKIES AND LIGHT WINDS MAY BRING
ANOTHER NIGHT WITH FROST POTENTIAL IN EAST SIDE VALLEYS. WHILE
THERE REMAINS SOME UNCERTAINTY ON HOW COLD CONDITIONS WILL GET
EARLY SATURDAY MORNING, MAINLY DUE TO CLOUD COVER, HAVE OPTED
TO ADD AREAS OF FROST ESPECIALLY GIVEN THAT THE LATEST HRRR HIGH
RESOLUTION MODEL RUN WHICH SUPPORTS CLEARING BETWEEN 10Z-15Z. HAVE
ISSUED A FROST ADVISORY FOR EASTERN VALLEYS.

LATE SATURDAY INTO SUNDAY, EXPECT DRY WEATHER OVER THE AREA WITH
A BROAD UPPER TROUGH TO THE NORTH AND A HIGH PRESSURE RIDGE
OFFSHORE. EXPECT A COOL START TO THE DAY WITH SOME COLD AIR
REMAINING IN PLACE, ESPECIALLY EAST OF THE CASCADES WHERE FREEZING
TEMPERATURES ARE LIKELY. THEN DAYTIME TEMPERATURES WILL WARM UP ON
SUNDAY WITH HIGHS IN THE 70S EAST OF THE CASCADES AND HIGH IN THE
LOWER 80S TO UPPER 70S FOR WEST SIDE VALLEYS.


&&

.AVIATION...FOR THE 05/00Z TAF CYCLE... NUMEROUS SHOWERS AND
ISOLATED THUNDERSTORMS EAST OF THE COASTAL RANGE WILL CONTINUE
THROUGH THIS EVENING. THESE WILL CAUSE PARTIAL TERRAIN OBSCURATIONS
AND ISOLATED MVFR CONDITIONS. OVERNIGHT...AREAS OF MVFR AND LOCAL
IFR CIGS ARE EXPECTED IN LOW CLOUDS ON THE NORTH AND NORTHWEST
SLOPES IN SOUTHWEST OREGON. OTHERWISE, CONDITIONS WILL BE VFR
THROUGH SATURDAY EVENING. /DW

&&

.MARINE...UPDATED 530 PM PDT FRIDAY 4 SEPTEMBER 2015...MODERATE
NORTH WINDS WILL LIKELY CONTINUE THROUGH NEXT WEEK WITH THE
STRONGEST WINDS DURING THE AFTERNOON AND EVENING HOURS AND SOUTH OF
CAPE BLANCO BEYOND 10 NAUTICAL MILES FROM SHORE. WINDS ARE LIKELY TO
BE STRONGEST ON MONDAY WITH GALES POSSIBLE OVER THE OUTER PORTION OF
THE SOUTHERN WATERS ON MONDAY AND TUESDAY.  /DW



&&

.PREV DISCUSSION... /ISSUED 1258 PM PDT FRI SEP 4 2015/

DISCUSSION...THE UPPER LOW IS NOW CENTERED OVER WESTERN WASHINGTON
AND WILL CONTINUE TO MOVE SOUTH OVER THE AREA LATE THIS AFTERNOON.
SHOWERS AND ISOLATED THUNDERSTORMS WILL INCREASE OVER TIME AS THE
UPPER LOW AND COLD AIR ALOFT (-25C AT 500MB) MOVES OVERHEAD, THUS
INCREASING INSTABILITY. THE LATEST HRRR MODEL RUN SHOWS MOST OF THE
SHOWERS AND ISOLATED THUNDERSTORMS ALONG AND EAST OF THE CASCADES,
BUT SUSPECT IT MAY BE UNDERESTIMATING THE CONVECTIVE ACTIVITY WEST
OF THE CASCADES. THEREFORE WE`LL CONTINUE TO KEEP POPS HIGHER WEST
OF THE CASCADES INTO THIS EVENING. IN ADDITION THERE`S A CHANCE SOME
THUNDERSTORMS COULD PRODUCE GUSTY WINDS AND SMALL HAIL.

THE 12Z NAM AND GFS SHOW THE TROUGH AXIS MOVING EAST OF THE CASCADES
LATE TONIGHT AT WHICH POINT THE BULK OF THE PRECIPITATION WILL SHIFT
INTO LAKE, MODOC AND EASTERN KLAMATH COUNTY. A COLDER AIR MASS WILL
SETTLE INTO THE AREA TONIGHT, BUT THERE MAY A SUFFICIENT AMOUNT OF
CLOUD COVER REMAINING IN THE AREA, SO NIGHTTIME LOWS MAY NOT DROP AS
LOW AS WOULD BE EXPECTED. WE`LL KEEP PATCHY FROST TO THE FORECAST,
BUT GIVEN THE CLOUD COVER, DO NOT THINK THAT THIS WOULD BE A
WIDESPREAD EVENT. EVEN THE NEAR FREEZING TEMPERATURES MAY ONLY
LAST FOR AN HOUR OR TWO NEAR DAYBREAK. SO WILL NOT ISSUE ANY
HEADLINES AT THIS TIME.

THE UPPER TROUGH WILL MOVE EAST SATURDAY MORNING AND WEAK RIDGING
BUILDS IN FROM THE SOUTHWEST. THE DEFORMATION ZONE WILL BE CONFINED
TO EASTERN LAKE AND MODOC COUNTY WITH RAIN AND HIGHER ELEVATION
RAIN/WET SNOW MIX EARLY IN THE MORNING, THEN PLAIN RAIN. THE MODELS
HAVE TRENDED FASTER WITH THE PROGRESSION OF THE UPPER LOW SATURDAY,
SO WE COULD SEE CONDITIONS DRY OUT IN THE AFTERNOON IN EASTERN LAKE
AND MODOC COUNTY. ELSEWHERE IT WILL BE DRY WITH MILDER TEMPERATURES.

CONDITIONS WILL BE DRY SATURDAY NIGHT AND THERE WILL BE LITTLE OR NO
CLOUD COVER. THIS WILL ALLOW RADIATIONAL COOLING TO TAKE PLACE AND
WERE MORE LIKELY TO HAVE WIDESPREAD FREEZING TEMPERATURES EAST OF
THE CASCADES. THEREFORE A FREEZE WATCH WILL BE IN EFFECT FOR
SATURDAY NIGHT INTO EARLY SUNDAY MORNING.

THE COOLER THAN NORMAL TEMPERATURES WILL NOT LAST LONG. THE MODELS
REMAIN IN GOOD AGREEMENT DRY AND WARMER WEATHER RETURNING SUNDAY AND
LASTING INTO MOST OF NEXT WEEK WITH THE THERMAL TROUGH SETTING UP
SUNDAY AND REMAINING A FIXTURE FOR MOST OF NEXT WEEK. IN FACT 850 MB
TEMPERATURES ARE PROJECTED TO INCREASE OVER TIME AND PEAK OUT
BETWEEN 24-26 C NEXT THURSDAY WHICH IF CORRECT COULD RESULT IN
TEMPERATURES IN THE MID TO UPPER 90S FOR THE ROGUE VALLEY.
-PETRUCELLI


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...FROST ADVISORY FROM 3 AM TO 8 AM PDT SATURDAY FOR ORZ029>031.
     FREEZE WATCH FROM LATE SATURDAY NIGHT THROUGH SUNDAY MORNING FOR
     ORZ029>031.

CA...FROST ADVISORY FROM 3 AM TO 8 AM PDT SATURDAY FOR CAZ084-085.
     FREEZE WATCH FROM LATE SATURDAY NIGHT THROUGH SUNDAY MORNING FOR
     CAZ084-085.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY UNTIL 11 PM PDT THIS EVENING FOR PZZ376.
     SMALL CRAFT ADVISORY FROM 2 PM SATURDAY TO 11 PM PDT SUNDAY FOR
     PZZ376.
     SMALL CRAFT ADVISORY FROM 2 PM TO 11 PM PDT SATURDAY FOR PZZ356.

$$

CC


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