Wildfire in Arizona, May 6 to 9, 2017

Area Forecast Discussion
National Weather Service Tucson AZ
917 AM MST Sat May 6 2017

.SYNOPSIS...An unseasonably strong low pressure system will affect
the area through Wednesday. Winds will begin to pick up today with
temperatures well below recent days. The cooling trend and gusty
winds will continue Sunday and Monday, along with increasing
shower and thunderstorm chances by Tuesday. Dry conditions with
much warmer temperatures will return late next week.

&&

.DISCUSSION...The late season amplified pattern that gave us the
early 104 in Tucson will now bring in gusty winds and much cooler
temperatures. The strong ridge that brought the near record
temperatures is east of the area with a deep trough and strong
southern branch split developing behind it. An unseasonably
strong low pressure system will bring gusty winds, much cooler
temperatures and a solid chance of showers by Tuesday. Knock 10
degrees off the temps today, and keep it going with another 15-20
degrees Monday into Tuesday. That means We'll go from 104 Friday
to about 70 Tuesday (and the 70 may be a fight as we try to climb
out of the 60s).

Our current forecast handles this pretty well. Please see the
previous discussion below for additional details.

&&

.AVIATION...Valid through 07/18Z.
Gusty winds developing this afternoon, becoming SW 18-25 kts with
gusts to 35 kts. Surface wind gradually diminishing after 07/03z.
Variable mid to high levels clouds AOA 12k ft with isolated
-SHRA/-TSRA across the White Mountains northeast of KSAD this
afternoon. Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...A Red Flag Warning is in effect today from 10 am
to 7 pm for Fire Weather Zones 150, 151 and most of 152. The
combination of strong and gusty southwest winds, low relative
humidity and a high to very high fire danger will create critical
fire weather conditions.

There will also be a slight chance of showers and thunderstorms in
the mountains mainly north and east of Tucson today. A strong low
pressure system will affect the area this weekend into early next
week. Gusty south to southwest winds will occur each afternoon into
Monday though cooler temperatures and higher relative humidity on
Sunday and Monday should preclude any critical fire weather
conditions. The best chance of wetting rain appears to be Monday
night into Tuesday. Dry conditions are expected to return late next
week with temperatures returning to seasonal normals.

&&

.CLIMATE...The official high temperature forecast at Tucson
International Airport Sunday through Wednesday (May 7-10) is 76, 74,
71 and 77 degrees respectively. The last occurrence of four or more
consecutive days during the month of May with high temperatures
under 80 degrees occurred in 1995 (May 5-8; 78, 73, 66 and 77
degrees respectively).

&&

.PREV DISCUSSION...Latest IR/WV satellite imagery depict the
longwave trough of low pressure aloft now approaching the
California coast. Skies are mostly clear this morning for much of
the forecast area with partly cloudy skies generally across Graham
and Greenlee counties. As the aforementioned trough continues to
dig towards the southeast today /becoming closed off this
afternoon/ the pressure gradient will significantly tighten across
the forecast area resulting in windy conditions later this
morning into early this evening. A wind advisory remains in effect
for the southwestern half or so of our forecast area, generally
from the Tucson area south and westward. Critical fire weather
will be a concern today as well with Red Flag Warnings hoisted.
See fire weather discussion below for additional information on
fire weather concerns. Otherwise, just a bit of mid level moisture
remaining for the White Mountains where a slight chance of
showers and thunderstorms will be possible this afternoon with dry
conditions elsewhere. Temperatures will be about 6 to 12 degrees
cooler than Friday.

Models are now in good agreement on the evolution and timing of the
closed low as it moves from Southern California Sunday into the
northern Gulf of California on Monday, then gradually filling as it
slowly ejects northeast across Southern Arizona on Tuesday and
across the AZ/NM border on Wednesday. As far as sensible weather
impacts for our area, much cooler temperatures will continue to
advect into the region on Sunday with valley highs generally in the
70s. It will still be breezy to windy on Sunday, especially for
eastern Cochise County where winds will be approach wind advisory
thresholds with areas of blowing dust possible. Still generally dry
on Sunday, though a few showers and thunderstorms possible once
again for the White Mountains.

With the core of the low still to our southwest Monday, the best
moisture is expected across the western Deserts where a chance of
showers and thunderstorms is expected with slight chances farther to
the east including Tucson. The best chance of showers and
thunderstorms will be on Tuesday as the core of the upper low moves
across the area. Snow levels will generally be above 7000 feet
Monday night into Tuesday with up to a few inches of snow possible
on the highest mountain peaks. Otherwise, valley QPF's generally
0.25" or less with this event, though some localized areas could see
more. Temperatures on Monday and Tuesday will continue to remain
much below seasonal normals.

As the upper low begins to move away from the area on Wednesday, it
will remain close enough with residual moisture for a continued
chance of a few showers and thunderstorms northeast of Tucson and
especially in the White Mountains. Temperatures will begin to
moderate slightly Wednesday but still remaining at least 10 degrees
below normal. Thereafter, ridging aloft builds in for the end of the
work week with continued warming temperatures and dry conditions.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 7 PM MST this evening for AZZ150>152.

Wind Advisory until 7 PM MST this evening for AZZ501>504-507-508.

&&

Meyer

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