Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 280436
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
935 PM MST Mon Mar 27 2017

.SYNOPSIS...A low pressure system will bring a chance of showers
mainly east of Tucson through Tuesday night. Expect strong gusty
winds Tuesday and cooler temperatures. Dry conditions with a warming
trend will occur Wednesday into Thursday. The next system will bring
another chance of showers mainly northeast of Tucson Friday through
Sunday.

&&

.DISCUSSION...IR satellite imagery depicted clear skies west of the
Tucson metro area at this time. Meanwhile, partly cloudy skies
prevailed across eastern sections. A deepening upper trough was over
the Intermountain west this evening, and the 28/00Z GFS depicted a
554 dm low to be centered near the White Mountains around daybreak
Tuesday.

The various 27/12Z NWP solutions trended deeper/wetter with this
upper trough/closed low pressure system versus NWP solutions from
this time Sunday evening. The dayshift opted to increase PoPs for
tonight into Tuesday, especially for locales east of Tucson, and
this adjustment seems quite reasonable based on the 28/00Z NAM/GFS
and several HRRR solutions.

Thus, the official forecast continues with a chance of showers
northeast of Tucson mostly northeast of Tucson the rest of tonight.
Based on the NAM/GFS and several HRRR solutions, opted to insert a
slight chance of sprinkles for the Tucson metro area late tonight
(06Z-12Z Tuesday). A chance of showers and higher elevation snow
showers continues Tuesday across northern Greenlee/Graham Counties,
and a slight chance of showers further south across the eastern
portion of Cochise County.

The upper low is progged to move eastward into central New Mexico by
Tuesday evening. A very tight mid-level gradient on the western
periphery of this system will lead to strong and gusty westerly and
northwesterly winds Tuesday. Thus, a Wind Advisory is in effect from
11 AM to 7 PM MST Tuesday east-to-south of Tucson. Meanwhile, a Red
Flag Warning is also in effect from 11 AM to 7 PM MST Tuesday south-
to-southeast of Tucson. The combination of strong and gusty winds,
low relative humidity and a high fire danger rating will likely
produce critical fire weather conditions.

Please refer to the additional sections for further detail.

&&

.AVIATION...Valid through 29/06Z.
Isolated to scattered -SHRA will occur mainly east of a KCGZ-KTUS-
KFHU line into Tuesday afternoon, then scattered -SHSN mainly NE of
KSAD Tuesday evening. Otherwise, west of KTUS expect SKC to SCT
clouds around 10k-15k ft AGL. KTUS vicinity eastward, expect a FEW
to BKN clouds around 8k-12k ft AGL into Tuesday afternoon followed
by decreasing clouds Tuesday evening. Surface wind rest of tonight
generally wly 5-15 kts with gusts to 20 kts. Surface wind Tuesday
into Tuesday evening wly/nwly 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...There is a chance of showers into Tuesday night,
especially across Graham and Greenlee counties. Farther south in
southern fire weather zones 151 and 152, windy conditions and low
humidities will result in critical fire weather conditions Tuesday.
Therefore, a Red Flag Warning has been issued from 11 am to 7 pm for
the southern portions of fire weather zones 151 and 152. Afternoon
breezes will continue Wednesday and Thursday along with warmer
temperatures. Another weather system will then move in late Friday
with gusty winds. This system will also bring a chance of showers
mainly northeast of Tucson Friday through Sunday.

&&

.PREV DISCUSSION /258 PM MST/...A low pressure system over southern
Nevada will continue to move southeast/east into the state tonight.
The latest satellite trends and models runs show this system will
track a little further southward and faster than previous model
runs, with the low centered over northeast Arizona by 12Z Tuesday.
Therefore, have bumped up precipitation chances this evening/tonight
for areas north/northeast of Tucson over far eastern Pinal, Graham
and Greenlee counties. Slight chance pops exist as far south/
southwest as Oracle and Mount Lemmon, as well as the northern half
of Cochise county. This system will also generate strong and gusty
winds across the forecast area.

The strongest winds will be over eastern Santa Cruz, Cochise and
Graham counties, where a wind advisory is now in effect (has been
issued) from 11 am to 7 pm mst Tuesday. Expect cooler temperatures
on Tuesday, with below normal temperatures and daytime temperatures
lowering 7-10 degrees (versus today`s highs). By Tuesday evening,
precipitation chances will be confined mainly to the northern half
of Graham and Greenlee counties, ending by early Wednesday morning.
The highest elevations in the White Mountains, such as Hannagan
Meadow, could pick up 1-3 inches of snowfall with this system.

Short wave ridging will transition across the area Wednesday and
Thursday, with near normal daytime temperatures on Wednesday and
temperatures warming to 5-8 degrees above normal Thursday. Although
winds will be down substantially from Tuesday`s levels, expect some
breeziness during the afternoon and early evening hours on both
Wednesday and Thursday.

Another storm system is then expected to move into the region late
Friday, lingering into early Sunday. This system is progged to be
stronger than the one moving through the region tonight and Tuesday.
However, models differences are quite large in respect to the track
of this system, with the GFS tracking the system through the eastern
half of Arizona, while the ECMWF moves the system through the Four
Corners region. Given this large difference, did not make many
changes to the current pop grids for Friday through Sunday, with
slight chance/chance pops primarily in Graham and Greenlee counties.
If the track of the GFS ends up verifying, then precipitation
chances will need to be upped significantly for eastern areas and
introduced as far west as Tucson. Breezy to windy conditions are
expected on Friday as the system moves into the region, with cooler
daytime temperatures in the Friday through Sunday time frame.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
    Red Flag Warning from 11 AM to 7 PM MST Tuesday for the southern
      portions of AZZ151-152.

    Wind Advisory from 11 AM to 7 PM MST Tuesday for AZZ507>509-511>
     513.

&&

$$

Francis
PREVIOUS DISCUSSION...Zell

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