Weather Service Report

FXUS65 KTWC 151053

Area Forecast Discussion
National Weather Service Tucson AZ
353 AM MST Mon Oct 15 2018

.SYNOPSIS...Scattered showers and thunderstorms developing this 
afternoon followed by widespread showers with embedded thunderstorms 
tonight into Tuesday. Gusty east winds will also prevail tonight 
into Tuesday. Dry conditions across much of the area Wednesday 
through Friday before greater coverage of showers and thunderstorms 
next weekend. Daytime temperatures well below seasonal normals into 
midweek before a warming trend late in the week.


.DISCUSSION...Upper trough axis extended from the central Rockies 
southwestward into southern California early this morning. 
Meanwhile, a cold front was moving westward across southwest New 
Mexico. Various numerical weather model solutions depict a 567 dm 
low to become centered over far southwest Arizona by this evening. 
Several HRRR solutions as well as the 15/00Z NAM12/GFS/ECMWF also 
depict lower level wind convergence to develop this afternoon near 
or just west of the Tucson metro area. This convergence zone is in 
response to strengthening low level easterlies that are progged to 
expand westward across the area by this evening.

The combination of increasing lower level moisture from the east and 
fairly decent synoptic scale ascent associated with the deepening 
low pressure system will enhance rainfall chances across the area 
later today and especially tonight into Tuesday. Several HRRR 
solutions have been quite consistent with the potential development 
of showers and thunderstorms from Tucson westward into the Tohono 
O'odham Nation and northwest into Pinal county this afternoon. The 
threat of severe thunderstorms is quite negligible due to minimal 
CAPE. However, locally heavy rainfall may occur in this area as per 
WPC's Marginal Risk for Excessive Rainfall.

The 15/00Z deterministic GFS/ECMWF were quite similar with depicting 
a 565 dm low to be just southwest of Phoenix early Tuesday morning. 
Expect scattered to numerous showers with embedded thunderstorms 
tonight into Tuesday. The bulk of heaviest rainfall Tuesday should 
occur north of this forecast area. However, some heavier rainfall 
amounts may yet occur within southeast Arizona sufficient for at 
least minor flooding concerns. Gusty east to southeast winds that 
develop across much of the area tonight will continue into Tuesday.

The upper low is progged to move slowly northward toward northern 
Arizona by midday Wednesday. The coverage of showers will decrease 
from southwest to northeast Tuesday night followed by just a slight 
chance of showers and mountain snow showers from Safford 
northeastward by daybreak Wednesday. Except for a slight chance of 
showers mainly across the White Mountains, dry conditions will 
prevail Wednesday through Thursday night.

Thereafter, the GFS/ECMWF were in fairly good agreement with 
depicting the next upper low to develop by midday Friday over 
southern California. Meanwhile, high pressure aloft will become 
established north of the upper low or over the Pacific Northwest. 
This classic Rex Block pattern is progged to continue into Saturday. 
The upper high will move eastward Sunday as the upper low fills 
farther south over southern California. The upshot from this pattern 
is that deeper moisture should once again be pulled westward into 
the area Friday into next week. There is a slight chance of showers 
east of Tucson Friday, then a chance of showers with a slight chance 
of thunderstorms returns Saturday into Sunday.

High temps today will be quite similar to Sunday's temps and 
continue about 10-15 degrees or so below normal. However, daytime 
temps Tuesday will be an additional 2-7 degrees cooler versus today. 
A warming trend is on tap Wednesday through Friday followed by no 
significant change in daytime temps next weekend. Thus, high temps 
Friday into Sunday are expected to be closer to seasonal normals, 
but still remain a few degrees below normal.


.AVIATION...Valid through 16/12Z.
Isolated to scattered -SHRA mainly east of KTUS this morning, then 
scattered -TSRA/-SHRA this afternoon. Scattered to numerous -SHRA 
with embedded -TSRA this evening into Tuesday morning. MVFR 
conditions and local IFR conditions should occur especially this 
evening into Tuesday morning. Otherwise, cloud decks generally 4k-8k 
ft AGL. Surface wind this morning generally less than 10 kts. 
Surface wind this afternoon into Tuesday morning ely/sely 10-20 kts 
with gusts 25-30 kts. Aviation discussion not updated for TAF 


.FIRE WEATHER...Scattered showers and isolated thunderstorms by this 
afternoon followed by scattered to numerous showers tonight into 
Tuesday morning. Scattered showers and thunderstorms Tuesday 
afternoon and evening. Dry conditions Wednesday through Friday 
except for a slight chance of showers across the White Mountains. 
Scattered showers with isolated thunderstorms should return next 
weekend. Gusty east winds developing today east of Tucson, the 
potential strong and gusty east winds at times tonight into 
Wednesday. Somewhat lighter east winds Thursday into Friday, but 
gusty winds should return next weekend. 






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