Area Forecast Discussion
Issued by NWS Tucson, AZ

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392
FXUS65 KTWC 220908
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
208 AM MST Thu May 22 2025

.SYNOPSIS...A building ridge of high pressure across the region will
result in hot conditions across Southeast Arizona today, with
afternoon high temperatures 7 to 10 degrees above climatological
normal. Otherwise, light winds with occasional afternoon gustiness
due to strong heating can be expected today, with breezy afternoon
winds returning Friday.

&&

.DISCUSSION...The upper pattern this morning is defined by a broad
ridge of high pressure across Northwest Mexico extending into the
Desert Southwest. This should result in hot conditions across the
forecast area today, with 850-700 mb thickness values around
1675m, resulting in an afternoon high temperature at the Tucson
International Airport (KTUS) between 101-104 degrees. In general,
expect afternoon temperatures approximately 100-104 degrees from
Tucson westward (and upper Gila River Valley) and in the 90s
across the eastern valleys. These temperatures will result in a
`Moderate` HeatRisk today...so as I mentioned yesterday, make sure
to check in on those individuals that are sensitive to heat,
making sure they have adequate cooling and are staying hydrated.

A dry trough of low pressure developing along the West Coast
today will begin to amplify the upper pattern as it tracks east
through the Great Basin into this weekend. The southern periphery
of this feature will drag through Southeast Arizona Friday,
resulting in breezy southwest winds 15 to 25 mph with gusts to
30-35 mph. At this time, winds should stay below critical fire
weather thresholds...but it should be noted that brief, near
critical conditions will be possible. The 22/00Z Hot Dry and Windy
Index (HDWI) values indicate that 20-40 percent of the GEFS
members will meet or exceed the 95th percentile Friday. Usually, I
would like to see percentage of GEFS members above 50 percent
(more like 60-80 percent) before considering any fire weather
headlines so I feel comfortable not having one out despite ERC
values for Southeast Arizona above the 90th percentile.

The upper trough slowly moves east across our neck of the woods
Sunday with a shortwave ridge in its wake moving into a position
across the Southern Rockies/New Mexico next week. A ridge in this
location will result in a south to southeast mid-level flow across
the eastern half of the CWA. This mid-level flow will tap into
deeper moisture across SW Texas and NE Mexico resulting in the
western periphery of the 850-700mb Theta-E ridge nudging into
Cochise, Graham and Greenlee counties Tuesday through Thursday.
Both operational runs of the 22/00Z GFS and 22/00Z ECMWF have
maximum Theta-E differences between 0-6km greater than 10K, which
indicates there is enough instability for elevated convection
across the eastern zones, especially Wednesday. Given the dry sub-
cloud layer, any convection will likely be in the form of dry
thunderstorms with the potential for gusty and erratic outflows
near the evaporating downdrafts.

&&

.AVIATION...Valid through 23/12Z. SKC thru the day Thursday,
with SCT-BKN cirrus clouds AOA 20-25k ft AGL moving into the area
from the west during the evening and overnight hours (AFT 23/00Z).
SFC winds generally terrain driven less than 10 kts this morning,
becoming SWLY/WLY 10-15 kts with occasional gusts to 20 kts in
the afternoon due to significant heating. Aviation discussion not
updated for TAF amendments.

&&

.FIRE WEATHER...A building ridge of high pressure across the
region will result in hot conditions today across Southeast
Arizona. Expect afternoon high temperatures 100-104 degrees from
Tucson westward (and upper Gila River Valley) and in the 90s
across the eastern valleys. Although occasionally gusty winds will
be observed due to the significant surface heating the next
several days, the strongest winds will occur Friday as a dry
disturbance tracks across the area. At this time, wind speeds
should stay below critical fire weather thresholds (Southwest
15-20 mph with gusts to 30-35 mph). Single digit min RH values at
all elevations over the next week with poor overnight recoveries.

There is the potential for some mid-level moisture to move into
far eastern areas (east of Tucson) by the middle of next week.
This may lead to some afternoon buildups and/or isolated dry
lightning strikes Tuesday and Wednesday of next week.

&&

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

&&

$$

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