fxus65 ktwc 241627 

Area forecast discussion 
National Weather Service Tucson Arizona 
927 am MST Sat Mar 24 2018 

Synopsis...seasonal temperatures and gusty afternoon winds will 
prevail this weekend. A weak disturbance could bring a few light 
rain showers to portions of Cochise County this afternoon, 
otherwise dry conditions through the weekend. A low pressure 
system will bring cooler temperatures during first part of the new 
work week and a slight chance of mainly mountain snow showers 
east of Tucson Tuesday and Wednesday. Warmer temperatures will 
return to close out the work week. 


Discussion...satellite imagery shows mid and high level moisture 
streaming into Southeast Arizona. Thicker patches of clouds will hold 
afternoon temps a shade below yesterday's Max temperatures, but 
today will end up right around normal. Marginal mid level 
instability exists upstream as seen by vertical enhancements to 
cloud features. Forecast models show this instability late this 
afternoon over southeast Cochise County although the best moisture 
appears to have been shifted a bit farther southeast into nm and 
Mexico. Current forecast for a slight chance of showers in that 
general area looks reasonable although any amounts will be very 

Biggest weather story today remains the strong southwest winds 
which will be developing. Sustained winds will be close to 
advisory levels of 30 mph at times south and east of Tucson. 
Currently, a red flag warning is in effect. See fire weather 
section for more details. 

In summary, current forecast looks on track for today. 


Aviation...valid through 25/18z. 
Scattered-broken clouds above 20k ft above ground level will thicken this afternoon with 
cloud bases lowering to 8-10k ft agl, especially in the southeast corner 
of the state where isolated showers may develop. Surface winds 
strengthening to southwesterly 20-25 kts with gusts approaching 35 kts at 
times, easing to less than 12 kts after sunset. Aviation 
discussion not updated for taf amendments. 


Fire weather...a red flag warning is in effect beginning late this 
morning through the afternoon across eastern Santa Cruz County 
stretching east over a large portion of Cochise County. 20-ft winds 
peak at 20-30 mph with stronger gusts possible, decreasing after 
sunset. However, relative humidities don't completely bottom out, 
running roughly 15-25% with a slight chance of showers developing in 
the far southeast corner of the state. 

Expect breezy conditions to redevelop both Sunday and Monday 
afternoons. Winds will be slightly weaker Sunday than today, then 
a bit stronger again Monday. Humidities will be the lowest 
Sunday compared to today and Monday. Thus, winds will be the 
limiting factor for critical fire weather conditions Sunday. A 
Fire Weather Watch remains in in effect for southeast Cochise 
County on Sunday. 

On Monday, cooler temps and resultant higher humidities will be 
the limiting factor for critical fire weather condition despite 
windy conditions in Cochise County. Winds will be substantially 
reduced Tuesday as low pressure passes near, and high terrain 
snow showers will be possible. 

A return to warmer temperatures is expected for the latter half of 
the work week with a fairly normal diurnal wind pattern. 


Previous discussion...latest infrared/WV satellite imagery shows southwesterly 
flow aloft across Southeast Arizona with mostly cloudy skies across 
most of the forecast area as an area of cirroform cloudiness moves 
through. Under the southwesterly flow aloft, we're going to be 
watching a jet streak that will move across the forecast area this 
afternoon. Model guidance is in good agreement in depicting the 
possibility of a few showers mainly over Cochise County this 
afternoon into early this evening with considerable mid/upper level 
clouds across much of the remainder of the forecast area. Given the 
fairly dry sub cloud layer, any precipitation that makes it to the 
ground will be minimal with no more than perhaps a couple 
hundredths of an inch across southern and eastern Cochise County. 
Meanwhile, a fairly tight pressure gradient will result in breezy 
to locally windy conditions this afternoon especially south and 
east of Tucson. Wind speeds should remain below advisory 
thresholds with patchy blowing dust possible across eastern 
Cochise County. The winds will be strong enough that combined with 
low relative humidity there will be critical fire conditions, 
thus a red flag warning is in effect today for portions of 
Cochise, Santa Cruz and extreme southeast Pima County. See fire weather 
discussion below for additional information. 

Continued southwesterly flow aloft is expected on Sunday, though 
with dry conditions areawide. Winds will remain gusty, especially 
for eastern Cochise County where a Fire Weather Watch remains in 
effect. Seasonal temperatures are expected through Sunday. 

During the upcoming work week, our attention will turn to a trough 
and associated upper level low that will close off as it drops into 
Arizona on Tuesday. The latest ensemble and deterministic guidance 
have trended to keep the trajectory of the low generally just to the 
north and east of Tucson. Given that this is a moisture starved 
system, we're not expecting more than mainly a few snow showers 
across the mountains from Tucson north and eastward Tuesday into 
Wednesday with generally dry conditions in the valleys. The most 
noticeable change will be the cooler temperatures especially on 
Tuesday with highs in the mid 60's in Tucson which is about 10 
degrees cooler than normal. 

As the upper level low moves to the east of our area starting on 
Wednesday, heights and thicknesses will rapidly increase as ridging 
builds in from the west. This will result in a warming trend with 
highs back above normal to end the work week. 


Twc watches/warnings/advisories... 
red flag warning until 6 PM MST this evening for azz151-152. 

Fire Weather Watch from Sunday morning through Sunday afternoon 
for azz152. 


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