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Area Forecast Discussion (AFD)

Issued by NWS Tucson Arizona (TWC)

FXUS65 KTWC 191046

Area Forecast Discussion
National Weather Service Tucson AZ
345 AM MST Wed Jun 19 2019

.SYNOPSIS...Dry conditions will prevail into early next week. Expect 
near normal daytime temperatures through Friday followed by 
moderating temperatures this weekend as a low pressure system moves 
north of the area. Hotter temperatures will return by next Tuesday 
as high pressure aloft builds southeast of the area.


.DISCUSSION...A weak trough aloft prevailed across southeast Arizona 
early this morning. This trough was located between strong high 
pressure aloft centered well west of the northern California coast 
(near 36N/137W), and strong high pressure aloft centered over the 
western Gulf of Mexico. Various 19/00Z numerical weather prediction 
models depict very little change in the upper level pattern through 
Thursday. Thus, continued clear skies across much of southeast 
Arizona (some cirrus at times across far southeast sections) along 
with relatively light winds.

The models depict a deepening upper trough will occur over the 
western U.S. Friday into Saturday as strong high pressure aloft 
remains stationary west of the California coast. A very dry regime 
translating into clear skies is progged to continue across this 
forecast area through this weekend. However, the main impact will be 
a gradual daily cooling trend Friday into Saturday followed by no 
significant change in daytime temps Sunday. Some gusty afternoon 
winds will occur Friday and perhaps more noticeably Saturday in 
response to a tightening mid-level gradient. Somewhat less wind 
should occur Sunday as the mid-level gradient loosens.

Thereafter, the GFS/GEFS and ECMWF/EPS were quite similar with 
depicting a light zonal flow aloft regime across the area Monday. 
The models were very consistent with depicting strengthening high 
pressure aloft southeast of this forecast area next Tuesday (GFS/ 
ECMWF depict 592 dm high centered over western Chihuahua). This 
pattern will likely translate into continued clear skies, but with 
hotter temperatures returning early next week, and especially next 
Tuesday which is day 7 of this forecast package.

Although beyond the scope of this forecast package, have noted the 
19/00Z GFS/GEFS and ECMWF/EPS were fairly similar with moving the 
aforementioned western Chihuahua upper high northward to near the 
New Mexico Bootheel (GFS); or, even further northward toward the 
Four Corners region (ECMWF) during the latter part of the next week.

This pattern suggests an increasingly favorable flow regime for the 
potential development of showers and thunderstorms that may 
primarily encroach upon eastern sections of this forecast area. 
Also, forecast confidence is fairly high based on these solutions 
that even hotter temperatures versus next Tuesday's forecast high 
temperatures will ultimately prevail by late next week. This 
scenario of potentially increased moisture across eastern sections, 
and hotter temperatures especially from Tucson westward, is 
plausible if these solutions ultimately become reality.


.AVIATION...Valid through 20/12Z.
A few clouds above 20k ft MSL across far southeast Arizona or 
especially near KDUG into this afternoon. Otherwise, SKC into 
Thursday morning. Surface wind this afternoon wly/nwly 10-18 kts 
with occasional gusts of 20-25 kts. Strongest speeds expected 
vicinity KSAD. Surface wind variable in direction under 10 kts at 
other times. Aviation discussion not updated for TAF amendments.


.FIRE WEATHER...Dry conditions will continue through next Tuesday. 
Afternoon minimum relative humidity values through Friday will 
generally range from 5-15 percent with fair overnight recoveries. 
Daytime minimum relative humidity values this weekend will mainly 
range 10-20 percent followed by lower daily ranges by next Tuesday. 
20-foot winds mainly terrain driven under 15 mph, although afternoon 
gusts due to daytime heating. However, somewhat stronger southwest 
winds will occur Friday and Saturday as a low pressure system moves 
north of the area. 






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