Area Forecast Discussion
Issued by NWS Flagstaff, AZ

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FXUS65 KFGZ 171630

Area Forecast Discussion
National Weather Service Flagstaff AZ
930 AM MST Wed Jul 17 2019

.SYNOPSIS...Expect another warm and breezy day across northern
Arizona. Thunderstorm chances will be limited to along and south
of the Mogollon Rim today, with any storms producing very little
rainfall. Similar conditions are forecast through the week, with
increasing moisture and storm chances possible over the weekend.


.DISCUSSION...Mesoanalysis this morning indicates a decent low
level moisture surge from overnight convection in northern Mexico.
Dewpoints across southern Yavapai County have risen into the low
50s, with dewpoints along the Rim rising into the mid-upper 40s. Model
instability parameters indicate the potential for 250-500 J/kg of
CAPE across Yavapai County this afternoon as well. Based on this,
opted to expand the slight chance of thunderstorms into this
area. Slight chances for the Rim still look good, with higher
probabilities over the White Mountains. The primary threat with
any of these storms will be gusty outflow winds and dry lightning.

While RH values have increased some since yesterday, another round
of breezy southwest winds will keep a heightened fire danger
across the region. Daytime temperatures will be a degree or two
cooler than Tuesday.


.PREV DISCUSSION /330 AM MST/...A slight increase in moisture in
underway this morning, thanks to impressive overnight convection
in northern Mexico and northward moving outflow. Thunderstorm
chances today will favor the White Mountains region, but forecast
soundings and hi resolution model runs support just enough
instability along the Mogollon Rim to include the possibility of
a few showers or storms this far west. Storms that develop today
will produce little rainfall and gusty winds. Hot daytime
temperatures will continue, though they should be slightly below
Tuesday`s high temperatures. The lowest elevations of Yavapai
county and the bottom of the Grand Canyon will reach 105 to 110F.

Similar weather conditions are expected through the week as the
synoptic scale weather pattern changes very little. An active
northern stream flow across the northern U.S. is suppressing
subtropical high pressure further south than is typical this time
of year. This is a less favorable pattern for monsoonal moisture.
For now, we will maintain a persistence forecast of thunderstorm
chances favoring the White Mountains with low chances each
afternoon across the Mogollon Rim. However, active convection is
anticipated each day across northern Mexico, and a strong enough
push of moisture northward could lead to higher storms chances. Be
sure to stay up to date with the forecast through the week.

A much more favorable monsoonal pattern is possible by late this
weekend or early next week, when the high pressure circulation
builds northward and opens the door to increasing moisture. Expect
increasing thunderstorm chances during this period along with
moderating temperatures as cloud cover increases.


.AVIATION...For the 18Z package...VFR conditions are expected over
northern Arizona for the next 24 hours. Southwest winds 10-20 kts
gusting 25-30 kts until 02Z Thurs. The best chance of showers and
thunderstorms will be east of a line from KSOW to KRQE between
18Z and 03Z Thurs, but an influx of moisture from the south this
morning indicated by sfc stations is giving a slight chance for
thunderstorms south of I-40 through 02Z. Aviation discussion not
updated for TAF amendments.


.FIRE WEATHER...Southwest winds will remain breezy today, with
a slight increase in RH values. Wind speeds will be lighter on
Thursday. Thunderstorm chances will remain highest in the White
Mountains both days. There is a a slight chance of thunderstorms
south of I-40 today and along the Mogollon Rim up to Flagstaff

Friday through Sunday...Thunderstorm chances will increase each day
as monsoonal moisture pushes farther north and west. The highest
Haines values will be near the Four Corners region on Friday.






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