FXUS66 KMFR 101108
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
308 AM PST THU DEC 10 2009

.DISCUSSION...A COLD DRY AIRMASS REMAINS IN PLACE TODAY. CURRENT IR 
IMAGE SHOWS CLEAR SKIES OVER THE CWA AND A SYSTEM NEAR 40 N AND 130 
W THAT IS SHOWING SIGNS OF STRETCHING AND WEAKENING. AT THE SAME 
TIME A NORTHWEST FLOW WILL REMAIN OVER THE AREA THROUGH TONIGHT 
WHICH IS CONTRIBUTING TO THE STRETCHING. TEMPERATURES THIS AFTERNOON 
WILL END UP SIMILAR TO WEDNESDAY. 

THE MAIN CHALLENGE AHEAD WILL BE THE ONSET OF PRECIPITATION. THE 0Z 
GFS AND CANADIAN CONTINUE TO SHOW MOISTURE MOVING INTO SOUTHWEST 
OREGON AND NORTHERN CALIFORNIA LATE TONIGHT. THE 0Z NAM WAS MORE IN 
LINE WITH THE 0Z ECMWF...NOW THE 6Z RUN IS SPREADING PRECIPITATION 
IN QUICKER INTO NORTHERN CALIFORNIA AND SOUTHWEST OREGON BY EARLY 
FRIDAY MORNING. THE ECMWF IS SLOWER AND WEAKER WITH THE ONSET OF 
PRECIPITATION UNTIL AROUND 18Z IN SOUTHWEST OREGON...THEN SLOWLY 
SPREADING NORTH FRIDAY AFTERNOON.
 
WITH THAT SAID...IF THE PRECIPITATION ARRIVES IN THE MORNING...IT 
COULD START OUT AS FLURRIES OR VERY LIGHT SNOW. THE  FORECAST 
SOUNDING FOR MEDFORD SUGGEST THAT PRECIPITATION STARTS OUT AS 
LIGHT SNOW...THEN TURNING OVER TO LIGHT RAIN IN THE AFTERNOON. THIS 
IS A SCENARIO THAT WILL HAVE TO ME MONITORED CLOSELY DUE TO 
UNCERTAINTY OF THE MODEL GUIDANCE. IF THE MODELS REMAIN CONSISTENT 
LATER THIS MORNING...THEN A WINTER WEATHER ADVISORY MAY HAVE TO BE 
CONSIDERED FOR JACKSON AND JOSEPHINE COUNTIES. WE'LL DEFER TO THE 
DAY SHIFT IN THE EVENT THE MODELS CHANGE. 

PRECIPITATION CONTINUES TO SPREAD INTO THE AREA FRIDAY NIGHT ALONG 
WITH SNOW LEVELS SLOWLY RISING. AT THIS TIME NOT EXPECTING A HIGH 
QPF EVENT. 

MOST OF THE JET ENERGY THIS WEEKEND WILL BE DIRECTED SOUTH INTO 
CALIFORNIA WHICH WILL LIMIT THE AMOUNT OF PRECIPITATION IN OREGON. 
SHOWERS WILL CONTINUE SATURDAY AND SUNDAY WITH SNOW LEVELS BETWEEN 
3500 AND 4500 FEET. 

500 MB HEIGHTS RISE NEXT MONDAY AS SHORTWAVE RIDGING BUILDS OVER THE 
CWA. THIS WILL BRING A BREAK IN THE WEATHER. A WET AND MILD PATTERN 
IS IN THE WORKS THE REST OF NEXT WEEK WITH HIGH SNOW LEVELS. THE 
MAIN QUESTION WILL BE THE TIMING OF EACH STORM...BUT IT LOOKS LIKE 
MOST DAYS WILL BE WET WITH WINDY CONDITIONS ALONG THE COAST.

&&

.AVIATION...VFR CONDITIONS CONTINUE TODAY AND TONIGHT. HIGH TO MID 
LEVEL CLOUDS WILL INCREASE FROM THE SOUTHWEST THIS AFTERNOON. CIGS 
WILL LOWER TO MVFR LEVELS AS A WEAK SURFACE LOW MOVES TOWARDS 
SOUTHWEST OREGON. 

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...FREEZE WARNING UNTIL 9 AM PST THIS MORNING FOR ORZ021-ORZ022.
     FREEZE WARNING FROM 11 PM THIS EVENING TO 9 AM PST FRIDAY FOR 
     ORZ021-ORZ022.

CA...NONE.

PACIFIC COASTAL WATERS...NONE.

$$

PETRUCELLI