Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 160405

Area Forecast Discussion
National Weather Service Tucson AZ
905 PM MST Sun Oct 15 2017

.SYNOPSIS...Dry conditions with above normal daytime temperatures
will continue this week. Gusty east to southeast winds will also
occur at times into early Tuesday. Some minor cooling is expected
next weekend, along with a few showers Saturday mainly near the
White Mountains.


.DISCUSSION...Patches of cumulus clouds formed across Santa Cruz
County once again this afternoon. The loss of daytime heating at
sunset resulted in their dissipation, however, there are still high
cirrus clouds propagating eastward mainly over Pima County and areas
south. These clouds will remain overhead through the overnight

Gusty winds were prevalent in our corner of the state today. The
strongest winds occurred across eastern locations as they saw gusts
in the 25-30 mph range earlier this afternoon. These breezy
conditions will continue for Monday, with several locales such as
Tucson experiencing their highest winds later tonight and into early
Monday morning before gradually tapering off during the evening
hours. Otherwise, dry conditions with temperatures well above
average will prevail through at least mid-week. No updates to the
forecast are needed at this time, so please see the previous
discussion for more details.


.AVIATION...Valid thru 17/06Z.
Expect FEW to SCT cirrus 20-25k ft AGL at all terminals through the
period. Winds will be easterly/southeasterly at 8-18 kts with gusts
of 30 kts possible. The strongest gusts will likely occur at KTUS
starting 16/09z. Winds area wide begin to weaken by Monday
afternoon. Aviation discussion not updated for TAF amendments.


.FIRE WEATHER...Dry conditions will persist through Friday followed
by a slight chance of showers in the White Mountains Saturday. 20-
foot winds will be out of the east/southeast through Tuesday
morning. Gusts between 20-25 mph will be possible starting tonight
through early Monday afternoon then gradually taper off into Tuesday
morning. Winds will then return to their normal diurnal pattern for
the remainder of the week with some afternoon gusts possible Friday
and Saturday.


.PREV DISCUSSION...High pressure aloft is progged to amplify over
the Desert Southwest into Monday. The 15/12Z NAM/GFS/ECMWF suggest
that clouds will gradually thin and yield clear skies by daybreak
Monday as a result of the building high pressure system. Meanwhile,
a fairly tight surface pressure gradient will also prevail as
surface high pressure strengthens over west Texas. This pattern will
translate into gusty east to southeast winds at times into Monday,
and for some locales into Tuesday morning. The strongest speeds for
the Tucson metro area and especially Tucson International Airport
appear to be tonight into Monday morning. Would not be surprised to
see some haze Monday due to the gusty ely/sely winds. The gusty
ely/sely winds will abate by Tuesday afternoon as the surface
pressure gradient loosens.

A flat ridge aloft will maintain dry conditions Tuesday into
Wednesday. Have noted that the 15/12Z GFS and to a much lesser
extent the 15/12Z ECMWF depicted a shortwave trough to move eastward
across Arizona on Thursday. The GFS depicted to measurable rainfall
to occur with this system, mainly across central and northern
Arizona. However, the ECMWF kept the entire state precip-free and
have followed the ECMWF solution in this regard. Dry conditions will
continue Friday under strengthening westerly flow aloft.

Thereafter, there continued to be differences between the GFS/ECMWF
and their respective ensembles regarding the synoptic scale pattern
over the central/western CONUS next weekend. The 15/12Z GFS was
fairly similar to ECMWF solutions of 24 hours and longer ago with
the depiction of a closed upper low to be over northeast Arizona by
Sunday morning. The GFS then moved this upper to near El Paso Texas
by Sunday evening.

However, the 15/12Z ECMWF remained consistent versus the 15/00Z
ECMWF by depicting a low amplitude upper trough to move rapidly
eastward into the central Rockies on Saturday, then depicting a
strengthening upper high over southern California/western Arizona
next Sunday. The ECMWF eventually closes an upper low over central
Texas by next Sunday evening, or considerably further east versus
the GFS. At any rate, have opted to maintain a slight chance of
showers but remove the mention of thunderstorms across the White
Mountains Saturday. Dry conditions should then prevail area-wide
next Sunday.

Daytime temperatures through at least Friday will likely remain well
above normal for much of the area. Have opted for only some minor
cooling next weekend with the official forecast temps trending
closer to the ECMWF versus the much cooler GFS. However, if the
ECMWF is reality, the forecast high temps especially for next Sunday
are likely at least a few degrees too cool.






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