Area Forecast Discussion
Issued by NWS Flagstaff, AZ

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FXUS65 KFGZ 191124

Area Forecast Discussion
National Weather Service Flagstaff AZ
424 AM MST MON SEP 19 2016

.SYNOPSIS...A low pressure center off the Baja coast and a high
pressure center over Texas will bring moisture over Arizona early
this week. Clouds will increase today with showers and storms across
northern Arizona late Monday night through Wednesday. A strong low
is expected to move across the Great Basin later in the week for
breezy conditions, cooling temperatures and a chance of


Quiet conditions over northern Arizona this morning, though a fair
amount of lightning is currently being observed off the coast near
San Diego. Thunderstorms are occurring ahead of a closed low which
has been sitting off the coast of northern Baja, even retrograding
a little, for quite some time. More or less all operational
guidance, including the 00Z and 06Z GFS, shows this low beginning
to fill by late this morning. With northern Arizona in southerly
flow between the low off the coast and a high centered over west
Texas, moisture will begin to be pulled northward from now-
Hurricane Paine.

Expect increasing clouds throughout the day today, but with very
little precipitation likely over northern Arizona before late
tonight. Individual members from the GEFS/NAEFS, NCAR ensemble,
etc. vary on exactly where the heaviest rainfall will ultimately
fall during the day on Tuesday. A few members keep the rain
relatively far to the west, with not much at all making it into
even Coconino/Yavapai counties. Several more members show the
main swath of rain far enough east that from Yavapai County up
onto the Coconino Plateau/Mogollon Rim should see some
precipitation. Regarding precip intensity, Tuesday`s airmass
should be moist but fairly stable. NAMBufr soundings for the
Prescott area on Tuesday morning show a moist and stable layer
between about 700 and 500 mb, with a fairly dry layer to overcome
below that. It`s worth noting that the probability matched mean
QPF from the NCAR ensemble shows 0.10"-0.25" or less across
western/northern portions of the forecast area through Tuesday. A
few ensemble members show isolated rain of over an inch, but on
the whole the heavy rain/flood threat from this event appears low.

Wednesday, expect enough moisture to remain for the development of
scattered afternoon thunderstorms. Attention then turns to
Thursday as a strong trough moves toward the Great Basin.
Noticeable timing differences exist between ensemble members with
this feature, but despite these differences expect a strong cold
front with the possibility of precipitation/thunderstorms along it
sometime in the Thursday/early Friday time frame. Even in the last
few hours, the 06Z GFS appears to have slowed the timing of the
front somewhat relative to the 00Z GFS. With such strong winds
aloft and some available moisture, we checked on the CIPS analog
tool to see if we had any severe event analogs to the
Thursday/Friday trough. At this point it appears that with similar
events any severe reports tend to be either minimal or farther
north toward the low center, but the possibility bears watching.

Expect some fairly crisp fall temperatures behind the cold front,
with max temps Friday and Saturday from 5 to 10 degrees below
average. Temperatures are forecast to return to near average by
early next week.


.AVIATION...For the 12Z package...VFR conditions will continue
through at least 06z Tues. Expect increasing cloud cover from south
to north today, with bases lowering to aoa 18kft by 00z Tues, and
aoa 12 kft msl by 12z Tues. There is a slight chance of showers
and thunderstorms south of the Mogollon Rim aft 00z Tues, this
chance expands through Coconino county by 12z Tues. Sfc winds
variable to 10 kts. Aviation discussion not updated for TAF






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