FXUS66 KMFR 042304
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
304 PM PST FRI DEC 4 2009

.DISCUSSION...CURRENT WATER VAPOR IMAGE CLEARLY SHOWS THE UPPER LEVEL 
TROUGH MOVING INTO WASHINGTON STATE. THE TROUGH WILL MOVE INTO 
OREGON SATURDAY AND WILL BRING A COOLER AIRMASS WITH IT. THE 
RIDGETOPS AND COAST WILL EXPERIENCE THE MOST NOTICEABLE COOLING 
BECAUSE THEY HAVE BEEN WARMER COMPARED TO THE VALLEY LOCATIONS THE 
PAST SEVERAL DAYS. THE TROUGH WILL MOVE SOUTH OF THE AREA SATURDAY 
EVENING USHERING IN A COLDER AIRMASS. THIS WILL RESULT IN 
TEMPERATURES FALLING INTO THE UPPER 20S TO LOW 30S ALONG THE COAST 
WHICH HAS NECESSITATED A FROST ADVISORY FOR TONIGHT AND A FREEZE 
WATCH FOR SATURDAY AND SUNDAY NIGHTS. THE FREEZE WATCH IS LIKELY TO 
BE UPGRADED TO A FREEZE WARNING TONIGHT OR SATURDAY MORNING. 

THE MODELS SHOW ANOTHER AND STRONGER SHORTWAVE REACHING THE CWA 
SATURDAY NIGHT...THEN EVOLVING INTO AND UPPER LOW SUNDAY MORNING. 
THEY ALSO SUGGEST THIS WILL HAVE ENOUGH OVER WATER TRAJECTORY TO 
BRING INCREASING MOISTURE INTO WESTERN SISKIYOU COUNTY LATE SUNDAY 
AFTERNOON...THEN SPREADING INTO EASTERN SISKIYOU AND MODOC COUNTIES 
SUNDAY NIGHT IN THE FORM OF WRAPAROUND MOISTURE.

AT THE SAME TIME COLD AIR WILL ALREADY BE IN PLACE AND THIS COULD 
LEAD TO SOME LIGHT SNOW DOWN TO THE VALLEY FLOORS. RIGHT NOW THIS 
EVENT IS NOT EXPECTED TO BRING HIGH QPF. HOWEVER WITH COLD 
TEMPERATURES IN THE AREA THE SNOW RATIO WILL BE HIGHER THUS LEADING 
TO HIGHER SNOWFALL AMOUNTS. EVEN THEN IT LOOKS LIKE MOUNT SHASTA 
WILL GET MOST OF THE ACCUMULATING SNOW. KEEP IN MIND THAT IF THE 
STORM SHOWS A TRACK FARTHER NORTH...THEN THIS COULD EFFECT HOW MUCH 
AND THE NORTHWARD EXTENT OF ACCUMULATING SNOW. 

THE UPPER LOW MOVES SHIFTS INTO SOUTHEAST OREGON MONDAY AFTERNOON 
WITH PRECIPITATION DECREASING FROM WEST TO EAST. THEREFORE MODOC 
COUNTY WILL BE THE LAST AREA TO SEE IMPROVING CONDITIONS. 

PETRUCELLI 

.LONG TERM...
MONDAY NIGHT THROUGH FRIDAY NIGHT...DECEMBER 7TH THROUGH 11TH...
MODEL GUIDANCE CONTINUES TO STRUGGLE TO COME TO A CONSENSUS FOR THIS 
PERIOD OF TIME...PARTICULARLY FROM TUESDAY NIGHT ONWARD. THE GFS40
KEEPS THE STORM TRACK FURTHEST SOUTH FOR THE PERIOD...THE CANADIAN 
MODEL LESS SO...AND THE ECMWF HAS RETAINED A MORE NORTHWARD STORM 
TRACK WITH ACTIVITY OVER THE AREA...AT TIMES...DURING THE PERIOD.

THE 12Z ECMWF IS THE FAVORED SOLUTION AT THIS TIME...AS IT HAS 
RETAINED CONTINUITY FROM ONE SOLUTION TO THE NEXT...AND THIS IS ALSO 
THE MODEL THAT THE HYDROMETEOROLOGICAL PREDICTION CENTER AND CLIMATE 
PREDICTION CENTER ARE FAVORING. THIS IS IN PART DUE TO THE POOR 
PERFORMANCE OF THE GFS IN REGARD TO THE EVOLUTION OF THE MJO OVER 
THE PACIFIC AND THAT THE ECMWF APPEARS TO BE HANDLING THE REMNANTS 
OF TYPHOON NIDA THE BEST. IT SHOULD BE NOTED THAT THE FORECAST OVER 
THE WEEKEND SHOULD COME TO A BETTER CONSENSUS FOR THE EXTENDED AS 
THE PIECES COME TOGETHER.

THE BOTTOM LINE IS THAT THE STORM TRACK SHOULD PUSH NORTHWARD INTO 
THE AREA WITH TIME. INITIALLY A LOT OF COLD AIR WITH ARCTIC ORIGINS 
WILL BE OVER THE REGION WHICH WILL RESULT IN LOW SNOW LEVEL CONCERNS 
AT THE ONSET OF PRECIPITATION MID NEXT WEEK. THEREAFTER SNOW LEVELS 
ARE EXPECTED TO RISE...ALLOWING FOR MOISTURE IN THE AIR ACROSS THE 
REGION. WILL TRY TO FILL IN MORE DETAILS TOMORROW. 

LUTZ 

&&

.AVIATION...THE MAIN CONCERN AGAIN TONIGHT INTO SATURDAY MORNING 
WILL BE THE POTENTIAL FOR VALLEY FOG IN THE ROGUE AND ILLINOIS 
VALLEYS. HOWEVER COMPARED TO THE LAST FEW NIGHTS THERE IS A CHANCE 
THAT A DRIER AIRMASS ALOFT ALONG WITH INCREASING WIND WILL MOVE INTO 
THE AREA LATE TONIGHT WHICH COULD DELAY THE ONSET AND DURATION OF 
FOG AND LOW VIS. RIGHT NOW WE'LL KEEP FOG AND LOW VIS IN THE TAFS 
WITH LIFR CONDITIONS NEAR KMFR. CIGS WILL LOWER TO LIFT IN THE 
UMPQUA BASIN WITH VIS BETWEEN 2-3 MILES. VFR CONDITIONS ARE EXPECTED 
EAST OF THE CASCADES AND COAST. 

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...FROST ADVISORY FROM MIDNIGHT TONIGHT TO 9 AM PST SATURDAY FOR 
     ORZ021-ORZ022.
     FREEZE WATCH FROM LATE SATURDAY NIGHT THROUGH SUNDAY MORNING FOR 
     ORZ021-ORZ022.
     FREEZE WATCH FROM LATE SUNDAY NIGHT THROUGH MONDAY MORNING FOR 
     ORZ021-ORZ022.
     AIR STAGNATION ADVISORY UNTIL 10 AM PST SATURDAY FOR ORZ024-
     ORZ026-ORZ029-ORZ030-ORZ031.

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR WINDS UNTIL 10 PM 
     PST THIS EVENING FOR PZZ370.
     SMALL CRAFT ADVISORY FOR WINDS FROM 10 AM SATURDAY TO 4 PM PST 
     MONDAY FOR PZZ370.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 10 PM PST MONDAY 
     FOR PZZ350-PZZ356-PZZ370-PZZ376.
     SMALL CRAFT ADVISORY FOR WINDS UNTIL 4 PM PST MONDAY FOR PZZ376.

$$

PETRUCELLI