Frost Advisory 39, NWS Medford, OR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
905 AM PDT SAT OCT 10 2009

.DISCUSSION...
A VERY MINOR COSMETIC TYPE OF UPDATE WAS ISSUED TO THE SKY
CONDITION FORECAST ACROSS THE AREA FOR TODAY. THIS WAS MAINLY TO
DEPICT CONDITIONS BETTER IN NORTHERN LAKE AND KLAMATH COUNTIES AND
THE DENSE BUT SHALLOW FOG THIS MORNING IN COOS AND WESTERN DOUGLAS
COUNTIES.

THE FORECAST FROM OVERNIGHT LOOKS VERY MUCH ON TRACK AT THIS TIME.
THERE ARE STILL SOME MODEL DIFFERENCES SHOWING UP WITH THE TIMING
AND INTENSITY DETAILS WITH THE STORM SYSTEMS NEXT WEEK. EXPECT TO
DELVE INTO THESE DETAILS A BIT MORE THIS AFTERNOON.

&&

.AVIATION...
LIFR DENSE BUT SHALLOW FOG EXISTS IN MANY OF THE LOWER VALLEYS OF
COOS AND DOUGLAS COUNTIES THIS MORNING. THIS WILL BURN OF MID TO
LATE MORNING. THEREAFTER...VFR CONDITIONS ARE EXPECTED IN ALL
AREAS.

&&

.PREV DISCUSSION... /ISSUED 404 AM PDT SAT OCT 10 2009/

DISCUSSION...COMPARED TO 24 HOURS AGO...IT IS NOW APPARENT THAT
IT WILL BE A LITTLE COOLER THIS WEEKEND DUE TO THE FARTHER
WESTWARD PROGRESSION OF A BACKDOOR COLD FRONT ASSOCIATED WITH AN
UPPER LEVEL TROUGH DROPPING SOUTHWEST FROM ALBERTA THIS WEEKEND
ACROSS WESTERN MONTANA INTO IDAHO. THERE MAY BE A FEW PATCHES OF
FROST IN WEST SIDE VALLEYS SUNDAY MORNING...BUT PERHAPS AREAS OF
FROST MONDAY MORNING.

THERE IS LITTLE CHANGE FROM THE PREVIOUS FORECAST THROUGH THURSDAY.
THE ECMWF AND GFS ARE IN GOOD AGREEMENT WITH THE NEXT UPPER TROUGH
OVER WESTERN CANADA RETROGRADING INTO THE GULF OF ALASKA BY
TUESDAY WHILE A MUCH WARMER AND MORE MOIST PACIFIC TROUGH MOVES
EAST TOWARD NORTHERN CALIFORNIA. THIS SOUTHERN BRANCH WILL BE THE
MAIN DRIVER OF WET AND WINDY CONDITIONS FROM MONDAY EVENING
THROUGH WEDNESDAY WITH SNOW LEVELS ABOVE 7000 FEET. FOR OUR AREA...
SOUTHWEST FLOW WILL RESULT IN THE HEAVIEST RAINFALL FALLING IN
CURRY COUNTY AND WESTERN AND SOUTHERN PORTIONS OF SISKIYOU COUNTY
BUT HEAVY RAIN AND HIGH ELEVATION SNOW IS EXPECTED ACROSS NORTHERN
AND CENTRAL CALIFORNIA.

BEYOND WEDNESDAY...MODEL SOLUTIONS DIVERGE. THE 00Z GFS IS MUCH
MORE PROGRESSIVE THAN ITS EARLIER RUNS AND CONTINUES A SERIES OF
WEAKER DISTURBANCES THROUGH NEXT WEEKEND WHILE THE ECMWF DEVELOPS
A BAROCLINIC BAND WITH A SLOW MOVING FRONT OVER OREGON AT THE END
OF THE WEEK. DESPITE THE UNCERTAINTY...I HAVE ADDED MENTION OF A
SLIGHT CHANCE TO CHANCE OF SHOWERS FOR FRIDAY AND SATURDAY WITH
BOTH MODELS SHOWING A FRONT NEARBY.

AVIATION...VFR CONDITIONS UNDER CLEAR SKIES OVER THE NEXT 24
HOURS EXCEPT IFR ALONG THE COAST EARLY THIS MORNING.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR WINDS UNTIL 2 AM
     PDT SUNDAY FOR PZZ356.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 2 AM PDT SUNDAY
     FOR PZZ356.
     SMALL CRAFT ADVISORY FOR WINDS UNTIL 5 AM PDT SUNDAY FOR PZZ376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 5 AM PDT SUNDAY
     FOR PZZ376.

BTL/DW