Weather Service Report

FXUS65 KTWC 212301

Area Forecast Discussion
National Weather Service Tucson AZ
400 PM MST FRI OCT 21 2016

.SYNOPSIS...Dry conditions will prevail into Sunday morning. A
trough of low pressure moving into the western states will then
bring a slight chance of showers Sunday afternoon and Sunday night.
A better chance of showers and thunderstorms exists Monday into
Monday night, then dry conditions return late Tuesday into next
Friday. Above normal daytime temperatures will continue this weekend
and into the upcoming week.


.DISCUSSION...Clear skies prevail across southeast Arizona at this
time except for a narrow band of high-based and fairly flat
cumuloform clouds extending from west of Nogales nwwd into the
eastern Tohono O'odham Nation. These clouds should dissipate this
evening with the loss of daytime heating leaving clear skies later

The forecast confidence regarding precip potential, timing and
amounts for this weekend and early next week has decreased versus 24
hours or longer ago given the 21/12Z NWP model suite. High pressure
aloft will become centered over south Texas Saturday as a trough
aloft deepens near the Pacific Northwest coast. Mainly mid and high
level moisture will be drawn northward across the area Saturday due
to the upper pattern flow regime.

The increased uncertainty stems from generally drier model solutions
starting Saturday afternoon and continuing into Monday. Based on the
various NWP solutions, have removed the previous mention/depiction
of showers for Saturday afternoon into Sunday morning. Thus, dry
conditions are now expected to prevail thru Sunday morning. A slight
chance of showers now exists Sunday afternoon and Sunday night. The
previous official forecast mention/depiction of thunderstorms was
also eliminated due to a very stable progged regime (e.g. zero CAPE
as per the 21/12Z GFS).

The bulk of deeper moisture remains to be progged well west-to-north
of this forecast area Monday as an impulse embedded within the
longwave trough moves northeastward into the southwestern CONUS. If
the Univ of AZ WRF-NAM and the deterministic GFS is reality, then no
measurable precip will occur in southeast AZ Monday. However, based
on continuity as well as neighboring WFO gridded data PoP fields,
have maintained chance-category PoPs most sections Monday. 

The GFS depicted about 100-200 J/kg CAPE to be across the area
Monday, although values near 700 J/kg are progged to be just west of
the area. Thus, some argument can be made to justify the mention/
depiction of thunderstorms, and have continued with this scenario
for Monday only. At any rate, the best chance for any measurable
precip of significance may actually occur Monday night, assuming
the GFS and to some extent the drier ECMWF to be reality. 

Given a very stable progged environment, a chance of showers exists
Monday night from Tucson east to the New Mexico border. There
appears to be enough lingering moisture for a slight chance of
showers across the White Mountains Tuesday. Dry conditions will then
prevail Tue night into next Friday as high pressure aloft initially
builds over the area, then eventually moves east into the
central/southern CONUS.

Expect above normal daytime temperatures to continue this forecast
period, despite some modest cooling to occur Monday and Tuesday.


.AVIATION...Valid through 23/00Z.
A FEW clouds around 10k-15k ft AGL early this evening then SKC after
around 22/04Z and continuing into Saturday morning. Expect a FEW to
SCT clouds mostly 10k-15k ft AGL Saturday afternoon. Surface wind
variable in direction less than 12 kts thru the valid period.
Aviation discussion not updated for TAF amendments.


.FIRE WEATHER...Dry conditions through Sunday morning followed
by a slight chance of showers Sunday afternoon and Sunday night. A
chance of showers and thunderstorms exists Monday and Monday night,
and a few lingering showers may occur early Tuesday across the White
Mountains. Dry conditions will then prevail late Tuesday into next
Friday. Otherwise, expect above normal daytime temperatures and
terrain driven winds generally under 15 mph this weekend and into
the upcoming week.


.CLIMATE...Today is the 15th consecutive day of at least 90 degrees
recorded at Tucson International Airport for October 2016. This is
the seventh longest period of 90 degrees or warmer for any October
on record (dating to 1894). The current official forecast indicates
that 90 degrees or warmer should also occur Saturday and Sunday. If
this happens, there will be 17 consecutive days this month of at
least 90 degrees recorded at Tucson International Airport. This 17
consecutive day period would be the sixth longest on record.





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