Wildfire in Arizona, April 13 to 30, 2018

Area Forecast Discussion
National Weather Service Tucson AZ
945 AM MST Fri Apr 13 2018

.SYNOPSIS...A system exiting the region will bring another
round of strong winds today, resulting in areas of blowing dust and
critical fire conditions. Freezing temperatures are likely late
tonight and Saturday morning for the coldest eastern and southern
valleys. These conditions will be followed by a strong warming trend
this weekend and early next week.

&&

.DISCUSSION...With the cold front east of the area, our
temperature trends are down 15-20 degrees compared to yesterday.
Dew point changes are even more impressive; down between 20 and
40 degrees into single digits (on both sides of the zero line).
Winds are not as strong in most locations, but strong enough when
added to the very dry air mass to yield critical fire weather
conditions. We're already hitting Red Flag levels in multiple
locations in Cochise, Graham and Pima counties.

Next up is the overnight low temperature forecast for tonight.
It's not a temperature forecast as much as it is a wind forecast.
The potential of the dry and cool airmass is a freeze to hard
freeze in colder valley locations primarily east and south of
Tucson. Winds will diminish significantly overnight, but could
still be strong enough in some valley locations to keep the
atmosphere mixed, which would moderate overnight lows. A look at
latest model trends suggests Sulphur Springs Valley and San Pedro
River Valley (including much of Cochise and portions of Graham
county) will manage to establish inversions in the early morning
hours and drop below freezing. We'll fine tune this forecast as we
contemplate areas that will transition from a watch to a warning.

&&

.AVIATION...Valid through 14/18Z.
Mostly clear. SFC wind wly/nwly at 15-25 kts and gusts between
35-40 kts in most locations from the late morning thru the early
evening hours tonight. Stronger SFC winds are expected in the
upper Gila river valley near KSAD today, with nwly SFC winds at
25-35 kts and gusts to near 45 kts. SFC wind slowly diminishing
aft 14/03Z. Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Strong winds will continue across the area today on
the backside of an exiting system. Even though it will be much
cooler, the air mass will be extremely dry with dewpoints dropping
to near zero in many areas. That combined with gusty winds for most
areas will result in critical fire weather conditions. A Red Flag
Warning remains in effect through 7 pm MST this evening.

Saturday and Sunday will be relatively quiet wind-wise as an
upper level ridge builds over the area. The air mass will remain
very dry with minimum RHs in the single digits and poor overnight
recoveries.

Another storm system will likely bring areas of critical fire
weather conditions to portions of southeast Arizona Monday, followed
by lighter, but still breezy winds Tuesday and Wednesday. Yet
another storm system is possible during the Thursday and Friday time
frame of next week.

&&

.PREV DISCUSSION...Another round of strong winds will result in
areas of blowing dust and critical fire weather conditions today.
This will especially be the case east of Tucson, with the
strongest wind speeds in the upper Gila River Valley around
Safford. A Red Flag Warning and Public Wind Advisory have been
posted for parts of southeast Arizona today. The storm system
responsible for these windy conditions will track into the Plains
by tonight. A colder air mass and lighter winds in the wake of
this system will set the stage for a possible freeze Saturday
morning in the valleys of Cochise and Santa Cruz counties. A
Freeze Watch has been posted for late tonight and Saturday morning
for these valleys. Thereafter, models showed a ridge of high
pressure aloft building over the region this weekend for a rapid
warm up in daytime temperatures. The ridge axis will shift east of
the region Monday as a couple of weather system enter the West
Coast next week. Models continued to keep the track of these
systems north of the area, so mainly looking a more wind and
continued dry conditions.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 7 PM MST this evening for AZZ150>153.

Freeze Watch from late tonight through Saturday morning for
AZZ503-506>509.

Wind Advisory until 7 PM MST this evening for AZZ507>509.

&&

Meyer

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