Heat in Arizona, May 27 to 31, 2025

Area Forecast Discussion
National Weather Service Tucson AZ
252 AM MST Tue May 27 2025

.SYNOPSIS...Temperatures will gradually warm this week, peaking on
Friday about 3 to 7 degrees above normal. A weather system this
weekend will draw some moisture into the region. This will result in
the potential for scattered showers and thunderstorms, especially on
Sunday and perhaps continuing into Monday.

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.DISCUSSION...Clear skies at this time across southeast Arizona,
though IR satellite imagery does show some high level clouds
approaching from the west. These clouds are associated with a weak
upper low over southern California that won't really have an
influence on our weather today outside of some high level clouds.
Temperatures will warm about 2 or 3 degrees today compared to
yesterday.

As the week progresses, we're going to watch a more well defined
upper low approach the southern California coast Wednesday, becoming
completely cutoff from the mean flow while becoming situated
Thursday through Saturday off the north central Baja peninsula. The
system will eventually get kicked eastward across Arizona Sunday
into Monday. Ensembles have become in better agreement this model
cycle on placement, especially through Saturday with still some
minor differences in timing and placement Sunday into Monday.

Initially, Wednesday through Friday a ridge axis will be located
near the AZ/NM border and with gradually increasing
heights/thicknesses for our forecast area this week, temperatures
will be gradually warming as the week progresses. Highs should peak
on Friday about 3 to 7 degrees above normal. The current forecast
for Tucson on Friday is 103 but the latest NBM does have about a
~20% chance of 105. We are monitoring some mainly mid level moisture
in New Mexico that will attempt to push west across the AZ/NM border
but now doesn't really look like it will do so until Friday. At this
time, expect some build-ups near the NM and a slight chance of dry
thunderstorms for the White Mountains on Friday.

The aforementioned quasi-stationary upper low will help to funnel
moisture northward up the Gulf of California, aided by moisture
partially attributed to what is likely to become a tropical cyclone
off the coast of Mexico to the southeast of the southern tip of
Baja. The NHC has a 90% chance of development in this area over the
next 48 hours. Moisture levels are expected to peak Sunday into
early Monday in our area at 200-300% of normal PWAT. Now keep in
mind this is a climatologically dry time of year so these anomalies
translate to about 1 inch of PWAT, which is certainly enough for
some shower and potential thunderstorm activity, especially when
aided by dynamics which is most likely to occur on Sunday as the
upper low/trough approach. While moisture will be on the increase on
Saturday, that day will tend to have a bit more in the way of dry
thunderstorm potential with any build-ups that occur. Precipitation
chances will diminish by late Monday as the trough pulls away and
drier air filters back in from the west. With the increased
moisture, temperatures will drop back down to seasonable levels
Sunday and Monday.

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.AVIATION...Valid through 28/12Z.
SCT to ocnl BKN clouds AOA 20k ft AGL will move in from from W to E
thru 28/17Z and remaining that way thru end of valid period. SFC
winds light and terrain driven at less than 10 kts thru 27/17Z,
becoming NWLY/WLY 8-14 kts with gusts to around 20 kts thereafter
til 28/03Z. Light and terrain driven winds at 10 kts or less return
again thereafter thru the end of the valid period.  Aviation
discussion not updated for TAF amendments.

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.FIRE WEATHER...Dry conditions continue for most of the upcoming
week with single digit min RH values at all elevations, with poor
overnight recoveries. Expect seasonally typical afternoon
breezes/gusts each day through the week due to strong daytime
heating.

The weather pattern will be more changeable late in the week and
through the weekend as a weather system to our west and southwest
will draw some moisture into the area. The moisture increase will
initially mainly occur in the mid levels in far eastern areas (along
the Arizona and New Mexico state line) by Friday, where build-ups
may result in a dry lightning strike or two. As the weekend
progresses, additional moisture will move in from the south, most
notably on Sunday and perhaps lingering into early Monday. Given the
still marginal moisture on Saturday, there will be the potential for
some dry lightning with build-ups. By Sunday and Monday, moisture
will increase enough to result in a greater potential for some of
the stronger build-ups to produce wetting rain. Gusty and erratic
winds would occur with any thunderstorm activity. Dry weather
returns by next Tuesday.

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

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