Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 260410

Area Forecast Discussion
National Weather Service Tucson AZ
910 PM MST Thu May 25 2017

.SYNOPSIS...Gusty winds and slightly below normal daytime
temperatures will occur Friday. A warming trend with less wind will
then prevail Saturday into Monday. A weak low pressure system will
bring a chance of showers and thunderstorms especially east of
Tucson Monday into next Thursday.


.DISCUSSION...IR satellite imagery has indicated a gradual decrease
in cirriform clouds across southeast Arizona during the past 2-3
hours. The back edge of these mostly high-level clouds extended from
just east of Phoenix southwestward into the northern Gulf of
California. Thus, mostly clear skies were across western Pima County
as of 9 pm MST, and partly cloudy skies prevailed elsewhere across
the area. Surface wind speeds valid 9 pm MST had diminished to less
than 10 mph for most locales, although 15-20 mph speeds were
observed mainly across southern Cochise County.

The 26/00Z NAM/GFS were very similar with depicting the bulk of 500-
300 mb moisture of significance to be east of this forecast area by
daybreak Friday. Thus, sunny skies will likely be the rule for much
of southeast Arizona Friday. The lack of clouds may produce higher
wind speeds Friday versus today. However, wind speeds are expected
to remain below Wind Advisory criteria. High temperatures Friday are
forecast to be about 2-5 degrees cooler versus temperatures achieved
this afternoon. Expect a degree-or-two of warming Saturday.

Please refer to the additional sections for further detail.


.AVIATION...Valid thru 27/06Z.
SCT-BKN clouds mostly above 20k ft AGL then decreasing clouds from
west-to-east overnight. Clear skies or a FEW clouds above 20k ft AGL
will prevail Friday into Friday evening. Surface wind decreasing to
mainly less than 12 kts by daybreak Friday. Surface wind 15Z-18Z
Friday and into Friday evening swly/wly 12-25 kts with gusts to near
35 kts. The strongest speeds will be east of KTUS. Aviation
discussion not updated for TAF amendments.


.FIRE WEATHER...A Red Flag Warning is in effect from 10 am to 8 pm
MST Friday for portions of Fire Weather Zones 151 and 152, mainly
south-to-southeast of Tucson. The combination of strong and gusty
winds, low relative humidity values and a very high fire danger will
create critical fire weather conditions.

Less wind will prevail this weekend and next week. Some increase in
moisture will result in a slight chance of mainly afternoon and
evening thunderstorms near higher terrain Monday into next
Wednesday. Expect erratic and gusty winds due to thunderstorm


.PREV DISCUSSION /237 PM MST/...Height and thickness decreases will
continue the cooling trend into Friday, with nearly steady daytime
temperatures Saturday. Overall, afternoon temperatures will be 1-3
degrees below normal Friday and Saturday, warming to slightly above
normal on Sunday.

A highly amplified ridge of high pressure will build across the
western United States late in the weekend into the middle of next
week. The high will be centered over northwest Nevada Sunday,
gradually shifting east into central Utah by Wednesday. Weaknesses
in the flow under this ridge will allow moisture to push westward
into the southern Arizona Monday through Thursday of next week. The
bulk of this moisture will remain east of the Tucson Metro area
across Cochise, Graham and Greenlee counties.

The models indicate a weak upper low will develop off the Baja
Peninsula late Monday into early Tuesday, shifting east across
Sonora Tuesday into Wednesday. Flow around this feature may
contribute to the westward push of moisture across southern Arizona.
The latest numerical guidance figures have fairly robust numbers for
this time of year, with 20/30 pops for eastern portions of the
forecast area on Tuesday and Wednesday of next week. As a result,
have bumped up pops for the valley locations across eastern portions
of the forecast area next week into the slight chance category (and
a good chance in the White Mountains).

However, have not gone quite as aggressive as the guidance values
just yet. Still plenty of time between now and then to evaluate
additional model runs and make any pop adjustments. Daytime
temperatures are expected to peak on Monday, with a gradual cooling
trend through the rest of the week as clouds and moisture moderate
daytime heating.


    Red Flag Warning from 10 AM to 8 PM MST Friday for AZZ151-152.



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