fxus65 ktwc 141554 

Area forecast discussion 
National Weather Service Tucson Arizona 
854 am MST Thu Dec 14 2017 

Synopsis...a fast moving trough will push through The Four Corners 
today, bringing an increase in clouds, some breeziness and a slight 
chance of showers to far Southeast Arizona. Sunny and dry conditions 
will then prevail Friday and Saturday. Another weather system may 
affect the area by Sunday, with cooler temperatures and a slight 
chance of valley rain and mountain snow showers. 


Discussion...upper trough moving across SW states is bringing 
some clouds across eastern portions of Arizona. Clouds were accounted 
for in current forecast and high temperature forecast also looks 
on track for today. Winds will develop a northerly component late 
today then becoming easterly this evening, again as in current 
forecast. Mid level moisture present in far southeast corner of 
state as indicated by 10k ft cloud deck at kdug could be enough 
for a few sprinkles or light showers as trough acts on it into 
this evening. 

12z NAM and 06z GFS pretty similar to 00z European model (ecmwf) in depiction of 
systems impinging on Southeast Arizona through 12z Sunday. No need for changes 
to the short term forecast at this time and will continue to 
delve into the latest models for the forecast for Sunday and 
beyond for the afternoon update. 


Aviation...valid thru 15/18z. 
An increase in clouds will occur this afternoon leading to few- 
scattered clouds at 10k-14k ft above ground level mainly along a line from ksad to 
kols. Isold -shra possible near kdug this afternoon and evening 
as a weak trough passes through. Surface winds will follow diurnal 
trends ahead of the trough today before increasing out of the NE- 
southeast at 12-15 kts after 15/03z. Aviation discussion not updated for 
taf amendments. 


Fire weather...except for a possible shower in the far 
southeast corner of the state this afternoon as a weak trough passes 
by, expect dry conditions through Saturday. Winds ahead of the 
trough will increase out of the northeast-southeast late this 
evening into Friday morning for eastern locales and in gap wind 
areas. Another system will pass through Sunday into Monday 
bringing with it cooler temperatures, increased wind speeds and 
the potential for a more widespread chance of light 
precipitation. Drier air and warmer temperatures will then return 
into the middle of next week. 


Previous discussion...infrared satellite imagery indicated clear skies 
across Southeast Arizona this morning, though clouds associated with 
a fast moving trough were streaming across the northeast portion of 
the state. A lack of deeper moisture will generally mean just an 
increase in cloud cover for our area as the trough progresses 
southward. That said, cannot totally rule out a stray sprinkle or 
shower across far southeast portions of Cochise County this 
afternoon and evening as the system attempts to draw additional 
moisture northward toward the states once it's made it to Mexico. 
Temperatures this afternoon will be noticeably cooler compared to 
Wednesday due to cloud cover and falling heights. 

Temperatures remain near average through Saturday as the above- 
mentioned trough moves east into Texas and we watch another 
potential weather maker pinch off from the mean flow along the 
California coast. As a result, both the GFS and European model (ecmwf) develop a 
closed low somewhere off the western coast of the baja Saturday 
afternoon and evening. At the same time, the main trough from which 
this low split off, is progged to dive south through the Great Basin 
towards The Four Corners region. There has been a slight improvement 
in the agreement between the 14/00z operational GFS and European model (ecmwf) with 
how these systems evolve, but considerable differences still exist. 
The million dollar questions is whether these disturbances will 
remain independent of each other, or if the "four corners trough" 
will subsequently re-absorb the "baja low" over/near Arizona. With 
the thought that either outcome will increase moisture levels in 
conjunction with some favorable upper level dynamics, went ahead and 
increased pops Sunday and Sunday night, but kept them in the slight 
chance category. 

Thankfully, model solutions return to agreement Monday night as 
this(these) system(s) depart the region. Cooler northwest flow will become 
zonal, then give way to slight ridging for Tuesday and Wednesday as 
temperatures rebound back to slightly above average values. We'll 
then watch for another trough to dig out of the pac northwest by the end of 
next week, but that is currently beyond the purview of this forecast 
package, as there's plenty to speculate on between now and then. 


Twc watches/warnings/advisories...none. 



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