255 
fxus65 ktwc 210427 
afdtwc 


Area forecast discussion 
National Weather Service Tucson Arizona 
927 PM MST Sat Mar 20 2010 


Synopsis...high pressure aloft will bring dry and warm conditions 
through Monday. A low pressure system may bring a few showers to the 
area late Tuesday into Wednesday along with cooler daytime 
temperatures. Dry conditions to occur Thursday and Friday as high 
pressure aloft returns. 


&& 


Discussion...latest infrared satellite trends depict scattered middle-high level 
clouds spilling over ridge into western Arizona. Modest moisture 
advection in the upper levels will allow a few high clouds to work 
in overnight...but not enough to knock forecasted low temperatures 
off track. Northwesterly flow aloft will continue to dominate 
overnight and tomorrow morning as upper level ridge axis stays west. 
Inherited forecast package looks good...so no updates or changes 
made. 


&& 


Aviation...some increase in cirrus clouds from northwest expected 
during 06z-18z period Sunday...then mostly clear. Surface winds 
Ely/southeasterly 5-15 kts through Sunday morning. Aviation discussion not 
updated for taf amendments. 


&& 


Fire weather...high pressure aloft will bring dry conditions with 
warmer daytime temperatures Sunday into Monday. No wind concerns are 
expected both days. A low pressure system will then bring a slight 
chance of showers mainly to areas east of Tucson late Tuesday into 
Wednesday. Dry with diurnal wind trends Thursday and Friday as high 
pressure aloft returns. 


&& 


Previous discussion...flow aloft to become westerly Monday as ridge flattens 
and moves eastward. Focus of attention to then toward trough over the 
Pacific northwest late Monday...as well as upper low in the southern stream off the 
Baja California coast. Systems attempt to phase over the southwestern Continental U.S. Tuesday. Some 
differences were noted between the 20/12z GFS/European model (ecmwf) solutions with 
regard to precipitation potential...with the GFS drier versus the European model (ecmwf). 
Will maintain a slight chance of showers across the White Mountains 
Tuesday. Have opted to increase probability of precipitation about 5 percent or so versus the 
previous forecast from Tucson eastward Tuesday night and Wednesday. At any rate 
probability of precipitation are still mainly in the slight chance category from Tucson eastward 
Tuesday night-Wed. Upper trough prognosticated to be east of the area by Thursday. 
Dry conditions to occur Thursday-Sat as low amplitude ridge prevails. 
Warmer sun with maximum temperatures Monday forecast to be about 10 degrees f or so 
above normal. Cooler Tuesday and Wednesday with high temperatures a few degrees below 
normal. Warmer Thursday due to influence of upper ridge. 


&& 


Twc watches/warnings/advisories...none. 


$$ 


Minnick/jd 
previous discussion...bf 


Weather.Gov/Tucson