Area Forecast Discussion
Issued by NWS Tucson, AZ
FXUS65 KTWC 240426
Area Forecast Discussion
National Weather Service Tucson AZ
925 PM MST FRI SEP 23 2016
.SYNOPSIS...Mostly dry conditions will then prevail this weekend.
Moisture and a slight chance of showers returns to the area early
next week as an upper level low moves west across Sonora Mexico.
.DISCUSSION...The cold front that was responsible for the spotty
rain and cooler temperatures today had moved east of the area this
evening. Satellite imagery was showing mostly clear skies in the
wake of this front which will continue overnight. The current
forecast looked on track, so no updates necessary this evening.
Please refer to the additional sections for more details.
.AVIATION...Valid through 25/06Z.
Surface wind will be terrain driven less than 10 kts overnight. FEW-
SCT clouds Saturday around 10-15k ft AGL mainly SE of KTUS with sfc
wind WLY/NWLY around 10 kts. Aviation discussion not updated for TAF
.FIRE WEATHER...Mainly light winds will occur Saturday, with elevated
easterly breezes Sunday through Wednesday of next week. After some
drying this weekend, moisture will return to the area starting
Sunday afternoon as an upper level low begins to affect Arizona. A
chance of showers and thunderstorms will then persist across the
area into the middle of next week.
.PREV DISCUSSION...Models indicate the upper low will continue
to move east into the weekend, reaching the front range of the
northern Rockies and northern Plains by Saturday with the associated
trough axis trailing the low into eastern Arizona and western New
By late in the day Saturday, a vort max will dive down the back side
of this trough over eastern Arizona and eventually form a cutoff low
over northern Sonora/Chihuahua Mexico by late in the day Sunday.
This will result in a northeast to easterly flow across my forecast
area, which will pull moisture from our east into Arizona. This low
will then move slowly west and eventually northwest toward the
Colorado river valley by late Tuesday into early Wednesday. As this
occurs we will see a moisture increase from the east with an
increase in rain chances beginning late in the day Sunday, with a
continued small threat through late Wednesday. There are significant
differences among the models with regard to rain chances, with the
GFS just showing isolated activity for Tucson throughout all of next
week, although the best chance will be Monday through Wednesday. The
ECMWF shows scattered activity Monday and Tuesday, with isolated
activity Wednesday through Friday. For now, my POP forecast is lower
than GFS MOS numbers (just slight chances through the middle of the
week and single digit POPs late next week), so if it continues to
look like this low will materialize as the models advertise, then we
have plenty of room to nudge POP numbers higher.
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