FXUS66 KMFR 101713
AFDMFR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
913 AM PST THU DEC 10 2009
.DISCUSSION...THERE WILL BE ONE MORE DAY AND NIGHT OF WIDESPREAD BELOW
NORMAL TEMPERATURES ACROSS THE CWA. TEMPERATURES WILL BE SLOWER TO
MODERATE OVER THE EAST SIDE AND WILL REMAIN BELOW FREEZING THERE
TOMORROW. VALLEYS ON THE WEST SIDE WILL DROP INTO THE 20S TONIGHT
AND WARM TO ABOVE FREEZING DURING THE DAY. LIGHT PRECIPITATION
ARRIVES FRIDAY AND THE BIG FORECAST CHALLENGE IS DETERMINING WHAT
SURFACE TEMPERATURES WILL BE...THE TIMING OF PRECIPITATION...AND
TYPE OF PRECIPITATION. CURRENT MODEL RUNS BRING LIGHT SNOW TO
NORTHERN CALIFORNIA BY FRIDAY MORNING. WILL BE ISSUING A WINTER
WEATHER ADVISORY FOR WESTERN SISKIYOU COUNTY FOR SOME SNOW AND
POSSIBLE FREEZING RAIN IN THE VALLEYS. RIGHT NOW NAM INDICATES
ENTIRE COLUMN OF AIR ABOVE FREEZING FOR ROGUE VALLEY ON
FRIDAY...BUT CONFIDENCE IN THE MODEL IS NOT HIGH GIVEN POOR
INITIALIZATION THIS MORNING PER THE MFR SOUNDING. WILL FOCUS ON
ROGUE AND ILLINOIS VALLEYS TO DETERMINE WHETHER AN ADVISORY IS
NECESSARY.
&&
.AVIATION...VFR CONDITIONS WILL CONTINUE OVER ALL TERMINALS TODAY
WITH SOME MID CLOUDS MOVING IN TONIGHT AND TOMORROW MORNING...AND
POSSIBLE LIGHT PRECIPITATION OVER NORTHERN CALIFORNIA AND EXTREME
SOUTHERN OREGON LATE FRIDAY MORNING.
&&
.PREV DISCUSSION... /ISSUED 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.
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...FREEZE WARNING FROM 11 PM THIS EVENING TO 9 AM PST FRIDAY
FOR ORZ021-ORZ022.
CA...NONE.
PACIFIC COASTAL WATERS...NONE.
$$
NK
