Area Forecast Discussion
Issued by NWS Tucson, AZ

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262
FXUS65 KTWC 190420
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
920 PM MST Wed Apr 18 2018

.SYNOPSIS...Stronger winds will return Thursday into Friday as a
storm system moves north of the area. Cooler temperatures and a
few showers possible near the mountains northeast of Tucson
Friday. Warmer this weekend into early next week.

&&

.DISCUSSION...Southwesterly flow is increasing between high
pressure east of the area and a trough digging into the region
down the west coast. Locally windy by tomorrow afternoon as a low
pressure center remains engaged to higher latitude flow and
consolidates near southern Nevada. The main story will be wind
this far south with some dust and critical fire weather
conditions. A quick look at 00Z analysis and model output trends
lends confidence to the current forecast. No updates this evening.

One caveat; watch that low embedded in the stream of moisture
well off the central Baja coast (easy to pick out on water vapor
imagery). H7 theta-e fields increase through Sonora and Chihuahua
over the weekend. It wouldn`t take much to shift this a little
further north for a few light showers near the mountains Saturday
night or Sunday.

Please see the sections below for additional details.

&&

.AVIATION...Valid through 20/06Z.
SCT-BKN cirrus clouds above 20k ft. SFC winds below 10 kts
overnight, increasing Thursday during the late morning,
continuing into the afternoon SWLY 20-25 kts gusting to 35 kts.
Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...A deep trough will produce critical fire weather
conditions areawide on Thursday from the late morning into the
early evening. Southwesterly 20-ft winds ramp up through the day
peaking in the afternoon 20-30 mph with gusts to 40-45 mph. A Red
Flag warning has been issued for all of southeast Arizona Thursday
from 11 am to 8 pm. As the weather system exits east on Friday,
relative humidities increase slightly but strong winds still
remain along the Arizona/New Mexico border. This could produce
small isolated areas of near critical fire conditions, albeit not
widespread enough to justify the issuance of any products. Winds
then become predominantly light and terrain driven over the
weekend and beyond.

&&

.PREV DISCUSSION...Beautiful chamber of commerce day across
southeast Arizona under abundant sunshine, near normal high
temperatures and some localized breezy conditions. Satellite
imagery this afternoon showed the leading edge of mainly high
level clouds over central Baja CA. These clouds will be along the
border between 6-7 pm and continue to spread NE across the eastern
half of the forecast this evening. As fast as these clouds come
in tonight, they will be out of here with mostly clear condition
by sunrise Thursday.

Our next storm system, currently off the northern CA coast, will
move through the Great Basin on Thursday and bring strong gusty
winds area wide. Combined with low afternoon relative humidity
values and high fire danger, a Red Flag Warning has been posted
for all of SE AZ for Thursday afternoon. Wind speeds, for the most
part, will stay below advisory criteria. However can`t rule out a
few spots hitting criteria for an hour or two. Blowing dust also a
concern tomorrow. Outside of western Pima county, most of the area
will be warmer tomorrow versus today.

Much cooler Friday as the upper low moves into Colorado. Gusty NW
winds across the far eastern areas may bring a brief period of Red
Flag conditions being met. Otherwise highs will run around 6-14
degrees cooler than Thursday. The exception will be far western
Pima county where there will be little change. A weak disturbance
on back side of upper low will move across NE and E-cntrl AZ
Friday night bring a slight chance of rain or snow showers to far
northern Greenlee county. Can`t rule out a lightning strike or
two. Cooler overnight lows into Saturday morning for the eastern
areas with a few spots in the Sulphur Springs Valley briefly
touching freezing.

The weekend looks great with temperatures rebounding to above
normal levels under building high pressure. May see an increase
in high cloud cover late Saturday night into Sunday as a weak
upper level low approaches from the SW. Both the GFS and ECMWF
produce very light QPF along the international border on Sunday.
Confidence to low to add to forecast but something to watch.

Above normal highs to continue in the Monday thru Wednesady time
frame. Moisture moving west across New Mexico next week could
bring a few buildups along the AZ/NM border Tuesday and Wednesday.
Will have to watch model trends in case dry lighting needs to be
added to the forecast in this area.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from 11 AM to 8 PM MST Thursday for AZZ150>153.

&&

$$

Meyer

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