Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 310927

Area Forecast Discussion
National Weather Service Tucson AZ
227 AM MST TUE MAY 31 2016

.SYNOPSIS...A weak and slow moving low pressure system will keep
temperatures around average through Wednesday, with enough moisture
for isolated thunderstorms. Strong high pressure will then build
over the region late in the week into next weekend, resulting in
much hotter daytime temperatures with highs in the triple digits for
most of the lower elevations of southeast Arizona. Highs around 110
degrees possible near and west of Tucson this weekend.


.DISCUSSION...Water vapor imagery shows the weak upper low spinning
in the general vicinity of western Maricopa county. There is a
fairly distinct demarcation between dry and moist air aloft
associated with this system, with the moist air generally east of a
line from Globe to Silverbell to Sells. IR satellite imagery shows
mostly clear skies across southeast Arizona at this time, with
plenty of cloudiness over central and southern New Mexico and into
Chihuahua, Mexico and west Texas. The latest CIRA Layered PW Total
shows the highest values of PW well to our south over southern
Sonora, with values exceeding 1 inch, but values of around 0.70-1.0
inches still reside to our immediate east over southern New Mexico
and Chihuahua, Mexico. In addition to the higher moisture seen in WV
imagery over the eastern half of my forecast area, there is a moist
swath of mid level air on the back side of the low over southern
California and western Arizona.

As the low makes its way south and east through late tonight/early
Wednesday we could see isolated showers and thunderstorms develop
this afternoon, especially along the dry/moist air interface. In
addition, models are indicating lapse rates ranging from 8.5-9.5
Degs C/km in the 850-500MB layer as the low moves nearly overhead
this afternoon. That said, the best threat for showers and storms
today should be over the White mountains of east central Arizona,
but also over the mountains of Santa Cruz, Cochise and Graham
counties, with a small threat for the western deserts near the
center of the circulation associated with the upper low. Any of the
showers and storms that develop today could have the potential to
produce brief strong and gusty winds with little to no
precipitation, since low to mid levels of the atmosphere are quite

We will hang on to mostly mountain showers/thunderstorms again on
Wednesday, mainly between Tucson and the New Mexico border. Once the
system exits the region late Wednesday, ridging will begin to build
in from the west during the latter part of the week and remain in
place through early next week. Enough lingering moisture to our east
to justify slight chances for the White mountains nearly each day
through the remainder of the forecast period.

As a result of the building high pressure, expect considerable
warming of temperatures late this week and weekend. The first 100
degree day for Tucson may occur on Thursday. However, if we miss
that elusive 100 degree mark again on that day, we will easily
surpass that threshold each day Friday through early next week, when
highs will range from 105 to near 110 for the far western deserts. A
bit early for headlines at this point, but day shift may want to
consider an Excessive Heat Watch for mainly central and western
parts of the forecast area for this weekend, if guidance temps
remain high.

For Tucson, high temps will generally range from 2 to 4 degs below
normal today and Wednesday, then around 2 to 4 degs above normal for
Thursday. Thereafter, highs will range from 7 to 10 degs above
normal, although the hottest days will occur this weekend. Low temps
will be near normal Wednesday morning, then 4 to 5 degs above normal
Thursday and Friday and 7 to 9 degs above normal this weekend into
early next week.


Mostly clear skies will prevail thru mid-morning, with few-sct
clouds aoa 10k ft agl thereafter. There is a slight chance of -SHRA/-
TSRA for areas mainly near the NM and international borders
including the KDUG/KOLS terminals this afternoon and evening. Expect
mainly light and terrain driven winds thru late morning, becoming
swly to nwly at 8-12 kts after 31/18Z. Speeds will diminish to
mainly less than 10 kts after sunset. Aviation discussion not
updated for TAF ammendments.


.FIRE WEATHER...There is a slight chance of a shower or
thunderstorm today for areas near the international and NM border,
and across western Pima County. The focus Wednesday/Thursday will
shift toward eastern areas. The main threat will be dry lightning.
20-ft winds will be around 15 mph, except for some higher gusts near
any convection which develops.

Late this week into this weekend, a potent upper ridge will build
over the region resulting in very hot temperatures, low relative
humidities and generally light winds through next Monday. As a
result of the hot and dry air mass, unstable Haines 6 conditions
will develop across much of southern Arizona from Friday onward
through Monday.


.TWC Watches/Warnings/Advisories...None.




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