Area Forecast Discussion
Issued by NWS Flagstaff, AZ

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FXUS65 KFGZ 122110

Area Forecast Discussion
National Weather Service Flagstaff AZ
210 PM MST Wed Aug 12 2020

.SYNOPSIS...An increase in monsoon activity will continue into
Thursday afternoon. Strong high pressure will rebuild over the
region later this week and lasting at least through Monday. This
means more hot and dry conditons, with some record high
temperatures possible.


.DISCUSSION...The two-fold weather story is the slight uptick in
monsoonal activity today and again Thursday before very hot
temperatures once again setup over central and northern Arizona
on Friday.

Haze that swept across western and northern Arizona earlier today
continues to spread across northern Navajo Nation and the Four
Corners region this afternoon. The smoke can be traced back to an
ongoing fire in the Baja Peninsula area of Mexico. Haze remains in
the forecast through 8 PM this evening.

Scattered showers and thunderstorms are occurring along the
eastern Mogollon Rim and southeastward into the White Mountains
region this afternoon. General storm motion has been east-
northeastward at 10 - 15 mph. Cloud to ground lightning continues
to be observed, along with a few areas receiving measurable
rainfall. Gusty outflow winds remain possible with gusts up to
30-40 mph in the strongest outflows.

Isolated thunderstorms are expected to expand in coverage across
southern Coconino and eastern Yavapai counties late this
afternoon. Look for a gradual decrease in the coverage of showers
and thunderstorms through the early overnight hours. The last
three operational runs of the GFS have shown overnight
thunderstorms up to the Mogollon Rim. The current forecast covers
this with a slight chances of precipitation, but any developments
towards this trend will continue to be monitored through this

An analysis of upper air forecast soundings shows a notable
increase in mid-level moisture by Thursday afternoon across much
of the southern two-thirds of northern Arizona. These conditions,
combined with daytime heating, will expand the coverage of
showers and thunderstorms on Thursday afternoon. Chances begin to
decrease again though by Friday as a strong area of high pressure
will build over the Southwest.

The strong high pressure system will quickly increase daytime
temperatures beginning Friday afternoon and into the weekend. The
hottest temperatures this weekend are expected Sunday, but Monday
also remains very warm. Due to these temperatures, an Excessive
Heat Warning is in effect from 11 AM MST Friday until 8 PM MST
Monday for the lower elevations of Yavpai County and in the Grand
Canyon. There is a chance this product will have to even be
extended beyond the current time period, but confidence was not
high enough in the long-range pattern to issue it beyond Monday.


.AVIATION...For the 00Z package...Expect mainly VFR conditions
over the next 24 hours. Until 02z Scattered showers and thunderstorm
possible around the White Mountains, with a slight chance or no
chance elsewhere. Outflow wind gusts to 35 kts from storms / virga
shafts. Precipitation chances ending btwn 02z-06z. Surface winds SW-
W to 15 kts through the period. After 18z Thursday, similar shower
and storm coverage. Aviation discussion not updated for amendments.


.FIRE WEATHER...Scattered thunderstorms to persist each
afternoon and evening through Friday around the White Mountains.
Elsewhere expect a slight chance at best. Gusty outflow winds will
be possible. Very hot temperatures to return Friday.

Saturday through Monday...Dry and hot weather for most of the
northern Arizona through at least Monday. Daily high temperature
records may fall. Afternoon haines indices at 5 or 6. Only a slight
chance of afternoon storms around the White Mountains.


.FGZ WATCHES/WARNINGS/ADVISORIES...Excessive Heat Warning from 11 AM
Friday to 8 PM MST Monday FOR AZZ006-037-038.




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