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Forecast Discussion for MFR NWS Office 
000
FXUS66 KMFR 300348
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
848 PM PDT THU JUL 29 2010

.DISCUSSION...AIR MASS IS STABILIZING THIS EVENING. HAVE UPDATED
THE GRIDS TO REMOVE THUNDERSTORMS THIS EVENING. NEW MODEL RUN
CONTINUES THE SLIGHT COOLING TREND IN THE NEAR TERM WITH THE
UPPER LEVEL TROUGH GRADUALLY SAGGING INTO OUR FORECAST AREA. THIS
WILL ENHANCE ONSHORE FLOW INTO SOUTHWEST OREGON. HOWEVER AHEAD OF
THIS TROUGH WINDS IN THE EAST COULD ALSO INCREASE..ESPECIALLY IN
MODOC AN EASTERN LAKE COUNTIES. SLIGHT INSTABILITY IN THE AIR
MASS IS EXPECTED ON FRIDAY OVER THE CASCADES FROM CRATER LAKE
NORTH AND NORTHERN KLAMATH/LAKE COUNTIES.

&&

.AVIATION...LOW CLOUDS AND FOG ARE HANGING JUST INLAND FROM THE
COASTLINE...EXCEPT FROM ABOUT CAPE BLANCO TO GOLD BEACH THIS
EVENING. EXPECT IFR TO LIFR CONDITIONS TO FILL BACK IN ALONG THE
COAST OVERNIGHT AND THEN MIGRATE INLAND TO AREAS SIMILAR OR A BIT
FARTHER INLAND BY FRIDAY MORNING. SLIGHT COOLING ABOVE THE MARINE
LAYER IS LIKELY TO ALLOW THE LAYER TO DEEPEN BY ABOUT 500 FEET
TONIGHT. THIS WILL RESULT IN CLOUDS HANGING ALONG THE COAST FRIDAY
SIMILAR TO TODAY...THOUGH CLOUD BASES ARE LIKELY TO BE 500-1000
FEET HIGHER THAN TODAY. ELSEWHERE VFR CONTINUES OVERNIGHT. A FEW
CB CLOUDS ARE POSSIBLE NEAR CRATER LAKE AND NORTHERN KLAMATH
COUNTY FRIDAY AFTERNOON.

&&

.PREV DISCUSSION... /ISSUED 311 PM PDT THU JUL 29 2010/

DISCUSSION...
FORECAST MODEL BUFFER SOUNDINGS THAT INITIALIZED WELL THIS MORNING
AS COMPARED TO THE MEDFORD MORNING SOUNDING INDICATE A DRY LAYER
ABOVE AN INVERSION AT 600MB MOISTENING AND WEAKENING THIS
AFTERNOON. IF THIS WERE TO OCCUR ISOLATED SHOWERS AND
THUNDERSTORMS WOULD OCCUR LATER THIS AFTERNOON AND EVENING IN
AREAS AROUND AND NEAR WHERE CUMULUS HAS DEVELOPED THIS
AFTERNOON...MAINLY IN THE CASCADES AND SISKIYOUS.
HOWEVER...SATELLITE TRENDS AND A VISUAL ON THE CLOUDS FROM WALKING
OUT THE DOOR INDICATE THAT ACTIVITY IS MORE LIKELY TO BE SIMILAR
TO YESTERDAY...WHERE A FEW BRIEF RAIN SHOWERS OCCURRED AND NO
LIGHTNING. HAVE LEFT ISOLATED THUNDER IN THE CRATER LAKE AREA FOR
THIS AFTERNOON THROUGH 5 PM PDT...BUT THEN SCALED BACK COVERAGE
AND WORDING TO SLIGHT CHANCES OF SHOWERS AND THUNDERSTORMS FOR THE
EVENING. ALTOGETHER...CONFIDENCE IS LOW THAT WE WILL SEE ANY
LIGHTNING TODAY.

FOR THURSDAY MODELS INDICATE A COUPLE OF DEGREES OF COOLING MOST
AREAS WHICH IS LIKELY TO COUNTERACT A SLIGHT BIT OF COOLING ALOFT
AS A 700 MB LOW NEAR THE OREGON CALIFORNIA BORDER WEST OF THE
COAST BACKS THE FLOW A BIT AT 700MB. HAVE CONTINUED WITH THUNDER
SLIGHT CHANCES AND ENTERED CHANCE FOR THE AREA AT AND AROUND CRATER
LAKE. REFRAINED FROM GOING WITH MORE THAN PROBABILITY WORDING AS
CONFIDENCE IS LOW. TRENDS FROM THE LAST TWO DAYS WOULD INDICATE THAT
THE MODELS ARE OVERDOING MOISTURE AND INSTABILITY AND FAILING TO
CAPTURE DRIER MORE STABLE AIR BETWEEN 500-600MB. IF NOTHING HAPPENS
TODAY IN TERMS OF LIGHTNING I WOULD SUGGEST THAT THE NIGHT SHIFT
SCALE POPS AND THUNDER CHANCES DOWN BY AT LEAST 10 PERCENT FOR
TOMORROW.

TEMPERATURES THIS WEEKEND ARE EXPECTED TO BE A LITTLE BELOW NORMAL
DUE TO A COOLER AIR MASS HANGING OVER THE AREA. EARLY TO MID NEXT
WEEK THE GFS40 HOVERS TEMPERATURES CLOSE TO NORMAL...BUT THE ECMWF
TRENDS THEM TO 5 TO 10 DEGREES ABOVE NORMAL BY MIDWEEK. FOR NOW
STUCK WITH THE GOING FORECAST BEYOND ABOUT TUESDAY AS IT SPLITS
THE DIFFERENCE AND SIDES MORE WITH THE GFS40...WHICH HAS DONE
FAIRLY WELL OF LATE. LUTZ

AVIATION...
LOW CLOUDS AND FOG ARE HANGING JUST INLAND FROM THE
COASTLINE...EXCEPT FROM ABOUT PORT ORFORD TO GOLD BEACH THIS
AFTERNOON. EXPECT IFR TO LIFR CONDITIONS TO FILL BACK IN ALONG THE
COAST THIS EVENING AND THEN MIGRATE INLAND TO AREAS SIMILAR OR A BIT
FARTHER INLAND THAN THIS MORNING BY TOMORROW MORNING. SLIGHT
COOLING ABOVE THE MARINE LAYER IS LIKELY TO ALLOW THE LAYER TO
DEEPEN BY ABOUT 500 FEET TONIGHT. THIS WILL RESULT IN CLOUDS HANGING
ALONG THE COAST TOMORROW SIMILAR TO TODAY...THOUGH DECKS ARE
LIKELY TO BE 500-1000 FEET HIGHER THAN TODAY. ELSEWHERE VFR EXCEPT
MVFR TO IFR IN ISOLATED SHOWERS AND THUNDERSTORMS AT AND NEAR
CRATER LAKE NATIONAL PARK THIS AFTERNOON. A SLIGHT CHANCE OF
ISOLATED SHOWERS AND STORMS EXISTS IN THE CASCADES AND SISKIYOUS
AND FAR NORTHERN KLAMATH AND LAKE COUNTIES THIS AFTERNOON AND
EVENING WHERE MVFR TO IFR CONDITIONS WOULD LIKELY OCCUR WITH ANY
ACTIVITY.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...FIRE WEATHER WATCH FROM FRIDAY AFTERNOON THROUGH FRIDAY EVENING
     FOR ORZ027-030.

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR WINDS UNTIL 5 AM PDT TUESDAY FOR
     PZZ376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 5 AM PDT TUESDAY
     FOR PZZ376.

$$

08/99/99

NWS MFR Office Area Forecast Discussion