Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 190430

Area Forecast Discussion
National Weather Service Tucson AZ
929 PM MST Sat Mar 18 2017

.SYNOPSIS...Dry conditions with unseasonably warm daytime
temperatures will continue into the middle of the upcoming week. A
storm system will then bring a chance of showers Wednesday night
followed by cooler temperatures with lingering showers Thursday.
Expect dry conditions with a warming trend next Friday and Saturday.


.DISCUSSION...Another warm day across southeast Arizona as high
pressure aloft continued to influence the weather pattern. Expect
similar conditions again tomorrow before the pattern starts to
change by Tuesday. Current forecast looked on track. Please refer to
the additional sections for more details.


.AVIATION...Valid through 20/06Z.
Patches of cirrus clouds at times into Sunday morning with a few
cumulus clouds this evening around 10-12k ft over the southern
mountains. Then expect scattered cumulus clouds again Sunday
afternoon mainly southeast of Tucson. There is a slight chance of
-TSRA just southeast of KDUG. Winds will continue to be light with a
few gusts to 20 kts this evening and becoming northwest to 12 kts
after 19/19Z. Aviation discussion not updated for TAF amendments.


.FIRE WEATHER...Very warm and dry conditions will continue into
early next week with low RH levels in the afternoon and marginal
overnight recoveries. Winds Sunday afternoon will be westerly but
remaining below 15 mph with a few higher gusts. One or two dry
lightning strikes are not out of the question in the Chiricahua
Mountains of far southeast Cochise county Sunday afternoon with a
modest mid level moisture increase from Mexico.

A Pacific storm system is expected to move across the area the
middle part of next week with gusty SW winds Monday through
Thursday. Moisture is not expected to ramp up until at least late
Wednesday so dry and breezy conditions expected for a few
afternoons. Borderline critical conditions possible Wednesday and
Thursday mainly zone 152 then there is a fair chance of showers
Wednesday night into Thursday. There is a decent chance for another
storm system late next weekend.


.PREV DISCUSSION...The 18/12Z NAM/GFS/ECMWF/CMC were similar with
maintaining or even enhancing the mid-level moisture across eastern
sections Sunday afternoon. The 12Z NAM and 18Z NAM were the most
aggressive with the potential of measurable rainfall within this
forecast area Sunday afternoon, with the depiction of a few
hundredths of an inch of rainfall mainly near the Chiricahua/Dragoon
Mountains in eastern/ southern Cochise County.

Although the official forecast continues with dry conditions Sunday
afternoon (chance of measurable precip less than 10 percent), there
is the potential for a few lightning strikes to occur across far
southeast sections. However, forecast confidence was too low to have
dry thunderstorms in this issuance. The models were then similar
with depicting mid-level drying to move into the area from the
southwest Monday. Dry conditions will continue Monday night through
Wednesday, although southwesterly flow aloft will strengthen ahead
of an approaching vigorous shortwave trough from the west.

There were differences between the deterministic GFS/ECMWF regarding
the progression of this system across the southwestern CONUS
Wednesday night and Thursday. The GFS was faster with the
progression of this system versus the ECMWF, and the ECMWF briefly
attempts for a closed upper low centered over northwest Arizona
midday Thursday. Both of these solutions trended PoPs higher for
most of this forecast area Wednesday night and Thursday. Meanwhile,
the CMC seemed to represent a good compromise between the GFS/ECMWF.

Thus, PoPs were subsequently raised for the official forecast
package, and now depict a chance of showers Wednesday night
generally northwest of a Kitt Peak-Tucson-Hannagan Meadow line with
lesser precip chances southeast of this line. There is a slight
chance of showers most sections Thursday, with chance-category PoPs
northeast of Safford. Dry conditions should return Thursday night
under northwesterly flow aloft, then continued precip-free
conditions Friday into next Saturday as a progressive shortwave
ridge moves east of the area.

Expect no significant change in daytime temps Sunday and Monday,
with forecast highs to range about 15-20 degrees above normal. Some
minor daily cooling will occur Tuesday and Wednesday, then more
significant cooling is on tap Thursday. In fact, high temps Thursday
are forecast at this time to be quite close to normal values, but
nevertheless will be quite a change versus about the past 10 days.
However, daytime temperatures next Friday and Saturday are forecast
to warm above seasonal normals once again.






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