Area Forecast Discussion
Issued by NWS Flagstaff, AZ

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FXUS65 KFGZ 190436

Area Forecast Discussion
National Weather Service Flagstaff AZ
934 PM MST Fri Aug 18 2017

.SYNOPSIS...Dry conditions will continue across most of northern
Arizona through much of Saturday. There will be a slight chance
of thunderstorms over eastern Arizona on Saturday afternoon.
Higher chances of showers and thunderstorms then move back north
and west and affect much of the area by Sunday and into next week.


.DISCUSSION...The KFGZ 00Z sounding showed an increase of 0.11"
(0.37 to 0.48) since yesterday. Most of that moisture was in the mid
levels (570 mb/16,000 feet MSL). Tucson showed a 0.20" increase.
There is an on going thunderstorm complex over central and southern
Sonora this evening. This trend will continue into next week.

The  only noticeable change in northern Arizona today was more
cumulus clouds. For tonight, no change to the forecast as
temperatures are a few degrees warmer than last night at this time
and the forecast already shows that.


.PREV DISCUSSION /314 PM MST/...Cumulus clouds persist over high
elevation locations in northern Arizona this afternoon, most robust
over areas near the Utah state line. The latest runs of the HRRR
indicate that we may yet see a little rainfall from a few of the
convective clouds over the Kaibab Plateau and Black Mesa late this
afternoon, so we will continue with the minimal precip/thunder
chances up there.

Situated between a ridge over the southern Plains and a trough off
the California coast, we expect moisture to begin to return to
northern Arizona on Saturday, and return in earnest on Sunday. A
A few thunderstorms are forecast over eastern Arizona on Saturday.
With NAEFS mean precipitable water values approaching 1 inch near
the Mogollon Rim by Sunday afternoon, storms on Sunday are
expected to maintain higher rain rates and be capable of producing
flash flooding.

The southerly flow pattern mentioned above is forecast to persist
through at least Wednesday, maintaining moisture and afternoon
showers/thunderstorms. Ensemble models indicate nocturnal
thunderstorm/precipitation activity on Sunday evening, and the
latest GFS forecasts a short wave trough moving northward from
Sonora affecting northern Arizona from late Tuesday night through
Wednesday night. As stated in this morning`s discussion, evening/overnight
thunderstorm activity is a distinct possibility in this pattern
and will have to be watched for.

Southwesterly flow is forecast to develop over Arizona from about
Thursday into next weekend as the trough off the California coast
begins to move eastward. The GFS ensemble mean is more aggressive
with this drying than the ECMWF mean. At any rate, we should
expect a decreasing trend in thunderstorm activity late next week.


.AVIATION...For the 06Z package...VFR conditions will persist at all
TAF sites throughout the next twenty-four hours. A few thunderstorms
are possible over eastern Arizona after 18-19Z Saturday which could
produce isolated MVFR visibility and cloud-to- ground lightning
strikes. Aviation discussion not updated for TAF amendments.


.FIRE WEATHER...Most areas of northern Arizona will remain dry on
Saturday, with a few thunderstorms possible over eastern Arizona.
Moisture returns to all of northern Arizona on Sunday, and with
it chances of mainly afternoon and evening showers and

Monday through Wednesday...Thunderstorm chances persist through
the period. Light southwesterly afternoon breezes are expected.
High temperatures are forecast to be slightly below average.






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