Area Forecast Discussion
Issued by NWS Flagstaff, AZ

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FXUS65 KFGZ 200353

Area Forecast Discussion
National Weather Service Flagstaff AZ
853 PM MST Fri Oct 19 2018

.SYNOPSIS...For the weekend, expect increasing cloud cover and
chances for showers and thunderstorms as a low pressure system
impacts the area. Daytime temperatures will be near normal, and
snowfall will be confined to the highest mountain peaks. Chances
for showers and thunderstorms continue Monday and Tuesday, with a
return of dry weather by Wednesday.


.DISCUSSION...Sat imagery and sfc obs indicates the moisture is
delayed moving into the area and thus decreased the POPs through
18Z. There are some low clouds moving into SE AZ as far as Tucson
and expect them to continuing advecting to the NW. Otherwise, the
current forecast agrees with the latest models runs through the
weekend. Still looking for slight chance of showers along and
south of the Mogollon Rim after 12Z with scattered showers
developing from the White Mountains west through Yavapai and
southern Coconino Counties in the afternoon.


.PREV DISCUSSION /249 PM MST/...Current water vapor imagery shows
a developing cutoff low centered off the coast of Southern
California. This low will deepen overnight, before it begins to
draw moisture into northern Arizona from the southeast on
Saturday. Some shower and thunderstorm activity is expected as the
atmosphere destabilizes, however uncertainty is high with regards
to the amount of convection. The GFS model predicts the most
activity, with lesser amounts forecast by the ECMWF, NAM and
various hi-res guidance. As a result, have opted to keep chances
for storms around 40% or less, with the best chances along and
south of the Mogollon Rim through much of the day. Saturday
evening and Saturday night, chances for showers continue, with
Coconino and Yavapai Counties favored as synoptic scale forcing
associated with the cutoff low strengthens over the area.

On Sunday, chances for showers and thunderstorms increases
further with the passage of a shortwave trough rotating around the
low. In fact, Sunday afternoon looks to have the best combination
of forcing and instability, with the greatest model agreement
across Coconino and Yavapai counties. 0-6 km bulk shear would
support organized convection, but instability is a tad bit low.
At this point, there looks to be only a slight risk of localized
flash flooding along the Coconino and Kaiabab Plateaus. Snowlevels
will remain high during this event, so any snowfall will be
confined to the highest mountain peaks. Daytime temperatures will
be near seasonal averages.

The low continues to impact northern Arizona on Monday and Tuesday
as it slowly lifts to the northeast. As it does so, chances for
showers and thunderstorms expand eastward. By Wednesday, the low
exits as an open wave and a dry, zonal wind flow pattern sets up
in it`s wake.


.AVIATION...For the 06Z package...Expect VFR conditions and breezy
conditions tonight. There is a slight chance for showers developing
after 12Z Saturday, generally south of a KPRC-KFLG-KSJN line, then
spreading NW through the day. Aviation discussion not updated for
TAF amendments.


.FIRE WEATHER....A broad trough near the California Coast will bring
an increase in moisture over the Northland this weekend. Expect
showers and a few thunderstorms to develop Saturday and Sunday, with
higher relative humidity and lower wind speeds.

Monday through Wednesday...Showers will continue across the area
Monday and Tuesday, with dry and warmer conditions Wednesday through
the rest of the week.






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