Weather

742 
fxus65 ktwc 060335 rra 
afdtwc 


Area forecast discussion 
National Weather Service Tucson Arizona 
835 PM MST Monday Jan 5 2009 


Synopsis...clouds lingering through around the middle of the night 
before partial clearing begins. Cold with patchy frost tonight in 
eastern areas and patchy fog in central locations. Colder Tuesday 
night...then high pressure aloft will bring dry and warmer 
conditions the rest of the week. 


&& 


Discussion...WV and infrared satellite imagery show an impulse on the 
back side of the exiting system currently dropping south across 
southern Utah and northern Arizona. Infrared imagery shows colder cloud 
tops across northwest New Mexico and across NE Arizona...but beginning to 
extend into the NE fringes (white mountains) of my forecast area as 
well. 


Surface observations show several locations over the higher terrain 
of northern Arizona...mainly north of the Mogollon Rim...reporting 
snow. With that said the day shift kept chance category probability of precipitation going 
for my portion of zone 19 overnight...and this still looks 
reasonable...given that the precipitation is moving to the southeast. 


Infrared imagery also shows an extensive area of middle level clouds moving 
in from the north and west. Some of this cloud deck has already made 
its way into Pinal...Graham and Greenlee counties. These clouds are 
moving fairly quickly and based on timing of these clouds they 
should affect my forecast area from around now through about 09z or 
so. With that said...temperatures should not cool very much with the cloud 
deck overhead...but once they clear expect temperatures to fall. Given the 
uncertainty of how much these clouds will affect temperatures...will just 
leave the inherited lows as is. As of 03z...temperatures seem to be on 
track for expected lows. 


Day shift also included a mention of patchy frost and fog overnight 
given the residual moisture still in place and expected cooler temperatures. 


&& 


Aviation...precipitation continuing to decrease in coverage through the 
evening hours. Isolated MVFR conditions still possible through 
06/03z. Scattered shsn overnight in the White Mountains well NE of ktus. 
Few-scattered clouds at or above 10k feet above ground level Tuesday. Seasonal diurnally 
driven surface winds into Tuesday as ridge starts to build in from 
the west. Aviation discussion not amended for taf amendments. 


&& 


Previous discussion...a secondary system from the northwest will brush 
by to our northeast tonight...should keep some snow showers going in 
the far eastern mountains this evening...but not expecting 
significant snowfall. Advisories did well with snow reports ranging 
from 5 to 9 inches above 6000 feet. Cooler tonight with near 
freezing west of Tucson below freezing near to east of Tucson. Could 
see some patchy frost with that as well...mainly east...with patchy 
fog possible in central areas that are not quite as cold. Feature 
bringing snow showers to far eastern mountains may be accompanied by 
periods of cloudiness overnight further south and west...so colder 
temperature trend may be moderated somewhat. With more clearing and 
less residual boundary layer moisture...Tuesday night into Wednesday 
morning will be colder in most locations. 


Strong eastern Pacific Ridge will nose into the area for Tuesday 
through Thursday. A secondary shortwave ridge will amplify through 
on Thursday as a piece of energy digs into the northern and central 
West Coast. May come close to a cut-off resolution which would 
greatly complicate the weekend. Right now going with a more 
progressive trajectory. 


&& 


Twc watches/warnings/advisories...none. 


$$ 


Weather.Gov/Tucson