Heat in Arizona, May 5 to 6, 2018

Area Forecast Discussion
National Weather Service Tucson AZ
905 AM MST Sat May 5 2018

.SYNOPSIS...The hottest temperatures so far this year will occur
this weekend, with highs from 100 to 107 from Tucson westward.
Temperatures will remain well above normal during the upcoming week.
Expect gusty east winds today and continued dry conditions through
the week. One exception; we may see just enough moisture for a few
buildups near the mountains Monday afternoon.

&&

.DISCUSSION...Skies were clear across southeast Arizona this
morning. This will continue throughout the day as high pressure
builds over the desert southwest. The surface pressure gradient was
already increasing with east to southeast winds picking up across
much of the area. This process can occasionally push us a degree or
two higher with regard to afternoon temperatures, so we'll have an
outside chance of the first 100 degree day at KTUS this afternoon.
Otherwise, forecast thicknesses and MOS guidance suggest that a
triple digit day tomorrow is pretty much a slam dunk. This would be
13 days earlier than the current climatological average (1981-2010).
Our first 100-degree day in 2017 was May 4. The near-term forecast
looks good and no updates are needed this morning. Please see the
remaining sections for additional details.

&&

.AVIATION...Valid through 06/18Z.
SKC through the forecast period. SFC wind ELY/SELY at 10-20 kts with
gusts to 25 or 30 kts possible through about midday today. ELY wind
then diminishes to mainly less than 12 kts this afternoon through
Sunday morning. Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Besides from a few towering cumulus possible near
the International Border Sunday and Monday afternoon, expect dry
conditions to prevail through next Friday. High temperatures will be
the warmest we've seen so far this year through the forecast period.
Gusty east to southeast winds will occur this morning into early
Sunday. Otherwise, 20-foot winds will be southwesterly to westerly
at generally less than 15 mph, though occasional afternoon gusts
should be anticipated due to strong daytime heating. At this time,
all wind speeds should remain below critical fire weather criteria.

&&

.CLIMATE...Here is a table of forecast high temperatures and record
highs this weekend. It appears that record or near record highs
will occur for much of southeast Arizona on Sunday.

                             May 5           May 6
                          FCST RCD/YR      FCST RCD/YR
TUCSON INTL AIRPORT        98 104/2017     102 104/1989
BISBEE-DOUGLAS AIRPORT     91  97/1997      94  97/1997
AJO                       102 105/2017     105 104/1947
KITT PEAK                  83  81/2017      85  83/2017
ORGAN PIPE CACTUS         101 104/1997     103 103/1989
PICACHO PEAK               99 105/2017     103 102/1997
SAFFORD AG STATION         94  99/2000      98  98/2000
SIERRA VISTA FD            88  95/1989      92  98/2017
TOMBSTONE                  90  99/1989      93 100/1989
WILLCOX                    91 101/1947      95 100/1947

&&

.PREV DISCUSSION...High pressure will dominate our weather for most
of the coming week. Thicknesses support near record temperatures
Sunday and Monday, with the first 100 at KTUS by tomorrow. We'll get
close today, but probably not quite, even with some downslope flow
in many valley locations. That downslope flow is due to a surface
high building down the front range and a resulting breezy easterly
flow today and tonight.

Meanwhile, as our flow weakens and opens up and a trough digs into
Texas, the moisture axis through eastern and central Mexico is
shifting back into Chihuahua and western Mexico. We'll see a modest
lower level moisture increase, but even more so in the 700-500mb
range (emphasis on H5). With our area on the northern periphery of a
strong H7 theta-e ridge by Monday afternoon, we should have enough
moisture and surface heating for a few afternoon thunderstorms near
the mountains. This will be dampened somewhat by mid levels that
will be a little too warm with the ridge, and likely some flavor of
subsidence inversion. Still, a few buildups are likely.

Beyond that, we'll maintain a ridge of varying strength, but enough
to keep temperatures well above average through the week.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...None.

&&

Carpenter/Meyer/Pegram

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