Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 222225

Area Forecast Discussion
National Weather Service Tucson AZ
325 PM MST Sun Apr 22 2018

.SYNOPSIS...Expect dry conditions across much of the area and
unseasonably warm daytime temperatures this week. The exceptions are
a few light showers possible southeast of Tucson this afternoon, and
a few afternoon thunderstorms near some eastern mountains the
second half of the week.


.DISCUSSION...As expected, the weak low we`ve been looking at
from the eastern Pacific has opened up as it moves through
northern Mexico and southern Arizona. Lower levels have remained
dry with surface dew points in the teens to 20s and most of the
moisture at 500mb on the 12Z sounding. That same sounding also
showed an increasing trend between 700-500mb though, and current
satellite estimated precipitable water is up to around .65 inches
(from 1/3 of an inch yesterday afternoon and 1/2 inch this
morning). The ACCAS around the area just after sunrise told a
story that has evolved into plenty of virga today, and even some
sprinkles to light showers. Current development is noted southeast
of Tucson in Cochise county where we had good solar insolation.
HRRR trends continue to suggest some enhancement near the
Chiricahua mountains over the next few hours. Still wouldn`t be
surprised by a lightning strike or two there with a small bullseye
of 250 MUCAPE near there.

Otherwise, steady as she goes with the warming trend into early
this week with dirty and long period ridging. Another low has
split from the northeast Pacific and into a position well off the
coast of Baja. As it comes through, this will make Wednesday and
Wednesday evening a lot like today. After Wednesday, we`ll
continue to see enough mid level moisture with weak disturbances
embedded in the flow to bring a few thunderstorms to the eastern
mountains later in the week. Friday looks particularly interesting
with increasing GFS/ECMWF H7 theta-e trends from central through
northwest Mexico.

Model divergence at that point with a more progressive GFS
shunting storm chances east of our area next weekend, while the
ECMWF is less aggressive in reconsolidating the flow south and
southeast of the Gulf of Alaska and is thus slower.


.AVIATION...Valid through 24/00Z.
Isolated -SHRA possible near the New Mexico state line through
23/03Z. Otherwise, FEW-BKN clouds 10k-15k ft AGL with SCT clouds
above 20k ft AGL for the rest of the afternoon before gradually
decreasing in coverage through late evening. Skies will be mostly
SKC by Monday morning. SFC winds will remain light and terrain
driven at generally less than 10 kts for the forecast period.
Aviation discussion not updated for TAF amendments.


.FIRE WEATHER...A few light showers will be possible across
eastern zones this evening, with the main focus being in southern
Cochise County. Dry conditions will return for Monday and Tuesday
before a slight chance of thunderstorms develops across the eastern
mountains during the afternoon hours Wednesday through Saturday. Any
lightning would enhance fire initiation concerns and gusty outflows
may also occur. Above-average temperatures will continue for this
week alongside generally light and terrain driven winds, with a few
afternoon gusts due to daytime heating.






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