366 
FXUS65 KTWC 100429
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
929 PM MST Tue Oct 9 2018

.SYNOPSIS...Dry with below average temperatures into Thursday. 
Increasing moisture from tropical system Sergio and a Pacific 
storm system will bring showers and thunderstorms to much of the 
region Thursday night into early next week.

&&

.DISCUSSION...The latest info on Sergio includes an official NHC
track that is slightly further southeast than previous iterations 
with the 00Z GFS now focusing the heaviest impacts on Sonora and 
northwest Chihuahua Friday and into southern New Mexico Saturday.
Our busiest areas will likely be southeast of Tucson closer to the
track of the storm remnants and deepest moisture shearing quickly
into the main downstream flow. That would include areas around
Bisbee, Tombstone and Douglas. The proximity of an Eastern 
Pacific low as it pushes in from the west will keep shower 
activity through the weekend. Ultimately the Sunday to Tuesday 
timeframe may actually end up with more areas impacted by precip.

Otherwise steady as she goes with dry conditions and below average
temperatures to end the week. Please see the previous discussion
below for additional details.

&&

.AVIATION...Valid through 11/06Z.
Mostly clear. Surface wind until 10/01z wly/nwly 8-15 kts with 
gusts near 20 kts. Surface wind variable in direction mainly less 
than 12 kts rest of valid period. Aviation discussion not updated 
for TAF amendments.

&&

.FIRE WEATHER...Dry conditions are expected into Thursday with 
daytime temperatures remaining several degrees below normal. 
Increasing moisture associated with tropical system Sergio is 
expected to result in areas of showers and thunderstorms late 
Thursday night through Saturday, with an emphasis on locations
southeast of Tucson through Friday. 20-foot winds will be terrain
driven and generally less than 15 mph much of this week.

&&

.PREV DISCUSSION...A few decorative cumulus clouds were about the
area this afternoon with a shower or two over the White 
mountains. This convective activity will shut down around or 
shortly after sunset this evening with skies clearing, setting us 
up for another cool night. Wednesday morning low temperatures will
be similar to what they were this morning with a few low 30s 
possible in the coldest areas of Cochise, Graham and Greenlee 
counties. 

Wednesday we will be under the influence of dry westerly flow as we
transition from post trough to pre-Sergio/next trough. Highs will
warm about 6 degrees from today which is still cooler than average. 

Temperatures will be similar Thursday with cloud cover on the 
increase in advance of the next weather system to head our way. 
We should squeak out another dry day with deep moisture holding off 
until Thursday night and Friday. 

Current trends for Sergio are to take its remains just south of the 
state as it passes by Friday and Friday night. Given that the heavy 
rainfall with these systems is generally concentrated very near the 
core of the system (even when decayed) small shifts in the path 
result in significant differences in total rainfall amounts over any 
given location. The greatest threat for heavy rains continues to be 
over the SE corner of the state at this time with the absolute 
heaviest of the system remaining over Mexico. For this afternoon's
update I adjusted our QPF down a touch mainly across central and 
western parts of the forecast area. 

Beyond that, models continue to struggle a bit with the closed low
that looks to impact the area potentially well into next week in 
some fashion. Cutoff upper lows that are still fairly close to the 
main westerlies are difficult to deal with and I would expect to see 
plenty of shifting around in the models over the next several days.
Suffice to say current solutions and many ensemble members have this
low in the area through Friday, October 19th. If that comes to pass 
the below normal temperatures will continue with a threat of showers 
here and there at times through the entire period of time. 

&&

.TWC WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

Meyer/Cerniglia

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