FXUS65 KTWC 241610
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
908 AM MST THU DEC 24 2009

.SYNOPSIS...HIGH PRESSURE ALOFT ALONG THE WEST COAST WILL BRING 
GENERALLY CLEAR SKIES THROUGH CHRISTMAS DAY. REMAINING COOL TODAY 
AND FRIDAY AS WELL AS WIDESPREAD FREEZING TEMPERATURES TONIGHT AND 
FRIDAY NIGHT. DRY WEATHER WILL CONTINUE THIS WEEKEND BUT WITH 
VARIABLE HIGH CLOUDS AS THE HIGH PRESSURE SYSTEM WEAKENS. ANOTHER 
LOW PRESSURE SYSTEM WILL THEN BRING A SLIGHT CHANCE OF VALLEY RAIN 
AND MOUNTAIN SNOW MONDAY NIGHT INTO TUESDAY.

&&

.DISCUSSION...HIGH PRESSURE RIDGE ALOFT ALONG THE WEST COAST 
WILL KEEP STORMS AWAY FROM THE REGION THE NEXT SEVERAL DAYS. THE 
ONLY EXCEPTION TO THIS WAS A WEAK UPPER LOW WELL OFF THE WEST COAST 
OF NORTHERN BAJA THIS MORNING. THIS FEATURE WILL TRACK EASTWARD 
UNDER THE HIGH PRESSURE RIDGE AND BRING MAINLY HIGH LEVEL CLOUDINESS 
TO THE AREA AS EARLY AS LATER THIS EVENING. OTHERWISE...STILL 
LOOKING AT DRY WEATHER WITH COOLER THAN NORMAL HIGH TEMPERATURES 
THROUGH SATURDAY. PLEASE REFER TO THE PREVIOUS DISCUSSION BELOW FOR 
MORE DETAILS.   

&&

.AVIATION...MOSTLY CLEAR SKIES WITH SURFACE WINDS GENERALLY LESS 
THAN 10 KTS WILL PREVAIL INTO FRIDAY MORNING. AVIATION DISCUSSION 
NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...NO FIRE WEATHER CONCERNS AT THIS TIME.
 
&&

.PREV DISCUSSION...UPPER RIDGE TO REMAIN ALONG THE WEST COAST THRU 
TONIGHT THEN SHIFT EWD FRI. RESULTANT NWLY FLOW WILL PROVIDE 
GENERALLY CLEAR SKIES THRU CHRISTMAS DAY. WIDESPREAD FREEZING TEMPS 
ON TAP BOTH TONIGHT AND FRI NIGHT. AT THIS TIME BELIEVE THAT A HARD 
FREEZE WILL BE AVOIDED FROM THE TUCSON METRO AREA WWD...AND DAILY 
RECORD MIN TEMPS SHOULD NOT BE SET AS WELL. UPPER RIDGE TO THEN 
BREAK DOWN THIS WEEKEND. MOISTURE MAINLY ABOVE 500 MB SHOULD BE 
SUFFICIENT FOR AT LEAST PARTLY CLOUDY SKIES SAT NIGHT AND SUN. 
THEREAFTER...THE NEXT ERN PACIFIC TROUGH IS PROGGED TO APPROACH THE 
SRN CALIFORNIA/NRN BAJA COASTS EARLY MON...THEN MOVE EWD ACROSS THE 
SWRN CONUS MON-TUE. LOW-GRADE POPS MERITED MON NORTH AND WEST OF 
TUCSON WITH DRY CONDITIONS CONTINUING FROM THE TUCSON METRO AREA 
SEWD. APPEARS THE BEST CHANCE OF MEASURABLE PRECIP WILL BE MON 
NIGHT-TUE. FOR NOW WILL DEPICT JUST A SLIGHT CHANCE OF VALLEY RAIN 
AND MOUNTAIN SNOW SHOWERS MOST SECTIONS...BUT ENOUGH TIME TO REFINE 
THE TIMING AND ADJUST PRECIP CHANCES WITH THIS SYSTEM. TROUGH SHOULD 
BE WELL EAST OF THIS AREA WED. WILL MAINTAIN A SLIGHT CHANCE OF RAIN 
AND SNOW SHOWERS NEXT WED ACROSS NRN GREENLEE/GRAHAM COUNTIES WITH 
DRY CONDITIONS ELSEWHERE. WARMER TODAY THOUGH HIGH TEMPS REMAINING 
ABOUT 6-10 DEGS OR SO BELOW NORMAL. GRADUALLY WARMER FRI-SUN THEN 
COOLER NEXT TUE-WED DUE TO INFLUENCE FROM PACIFIC SYSTEM.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...NONE.

$$

WEATHER.GOV/TUCSON