Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 311636
AFDTWC

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

.SYNOPSIS...A weak low pressure system will bring isolated to
scattered showers and thunderstorms especially near the mountains
into this evening and again Wednesday. A slight chance of showers
and thunderstorms exists near the New Mexico border Thursday.
Otherwise, much hotter daytime temperatures will prevail Thursday
into early next week. Highs will be around 110 degrees near and west
of Tucson this weekend.

&&

.DISCUSSION...A few cumuloform clouds were across the White
Mountains and mainly across the Chiricahua Mountains in eastern
Cochise County at this time.  A few lightning strikes were detected
just southeast of this forecast area across far northwest Chihuahua
Mexico. Otherwise, clear skies prevailed across southeast Arizona.
Dewpoints at lower elevations valid 16Z generally west of a Safford-
Sierra Vista line were mainly in the mid teens to 20s. These temps
were about 15-35 degs lower versus 24 hours ago. However, KDUG
dewpoint was 48 degs valid 16Z.

31/12Z KTWC sounding total precip water value of 0.34 inch was 0.21
inch lower versus 24 hours ago. The profile exhibited the bulk of
drying in the surface-675 mb layer. 31/12Z upper air plots depicted a
573 dm low centered adjacent the international border southwest of
Tucson. High pressure aloft was centered just west of the northern
California coast with a ridge axis extending north into British
Columbia. Light sly to wly flow aloft prevailed across southeast
Arizona.

Based on several HRRR solutions as well as the 31/12Z NAM/GFS and
the Univ of AZ WRF-NAM, opted to make a few adjustments to the
inherited PoPs for this afternoon/evening. The first adjustment was
to remove isolated thunderstorms and patchy blowing dust for locales
west of Tucson. The second adjustment was to increase PoPs slightly
for locales south of Tucson late this afternoon and evening. The Hi-
Res models were quite similar with depicting the best chance of
measurable precip to occur mainly near the mountains northeast of
Tucson into this evening. However, they have also been similar with
depicting the potential for showers/tstms to occur from just of
Tucson southward toward Nogales.

Given the aforementioned very dry surface regime across much of the
area, the main concern associated with any showers/tstms will be the
potential of gusty outflows producing blowing dust capable of
reducing visibilities substantially. The bulk of any showers/tstms
should end by around midnight tonight. However, the Univ of AZ WRF-
NAM suggest the potential for some showers to linger across eastern
sections late tonight. Am leaning toward at least increasing cloud
values late tonight across eastern sections. The best chance for
showers/tstms Wednesday appears to be east of Tucson as per the
inherited forecast.

&&

.AVIATION...VALID THRU 01/18Z.
Isolated to scattered -TSRA/-SHRA will occur mainly near the
mountains east of KTUS to the New Mexico border this afternoon and
evening. A few -TSRA/-SHRA may develop this afternoon and evening
south of KTUS, and perhaps in the vicinity of KOLS. The main threat
from any -TSRA/-SHRA given the very dry surface environment will be
the potential for wind gusts to near 40-45 kts or so. Otherwise, a
few clouds around 12k ft msl this morning will become sct-bkn clouds
this afternoon and continue into Wednesday morning. Surface wind
this afternoon and evening will be swly/wly at 10-20 kts with gusts
to near 25 kts. Surface wind will be less than 10 kts at other times.
Aviation discussion not updated for TAF ammendments.

&&

.FIRE WEATHER...Isolated to scattered showers and thunderstorms are
forecast to occur this afternoon and evening mainly near the
mountains east of Tucson to the New Mexico border. Isolated showers
and thunderstorms also exists late this afternoon and evening south
of Tucson. Scattered showers and thunderstorms will then occur east
of Tucson Wednesday, and a slight chance of showers and
thunderstorms continues Thursday mainly near the New Mexico border.
Expect strong, gusty and erratic winds with these showers and
thunderstorms. Thereafter, dry conditions with very hot daytime
temperatures and generally light winds will prevail Friday into early
next week.

&&

.PREV DISCUSSION /227 AM MST/...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.

&&

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

&&

$$

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Francis
PREVIOUS DISCUSSION...Mollere



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