FXUS65 KTWC 202121

Area Forecast Discussion
National Weather Service Tucson AZ
Issued by National Weather Service PHOENIX AZ
221 PM MST Tue Mar 20 2018

.SYNOPSIS...Strong high pressure aloft will provide much warmer
temperatures into Thursday. Expect record or near record high
temperatures on Thursday. A weather system will then bring a slight
chance of showers mainly north of Tucson Friday. Cooler temperatures
and gusty winds will also occur. Dry conditions with temperatures
closer to seasonal normals this weekend and early next week.



Clear skies are being reported across our CWA this afternoon as a
strong ridge of high pressure is positioned over the desert SW.
To our west, IR satellite imagery shows a large upper level low
located over the Eastern Pacific near 140 W and has remained
nearly stationary over the past 24 hours. Near the surface, the
atmosphere remains bone dry below 500 mb with PWs near 0.19 inches
according to the latest 12Z Tucson sounding. For reference, this
is near the 10th percentile of climatology. Besides this, 850 mb
temperatures are up 5 C over yesterday and has allowed surface
temperatures to warm substantially over yesterday.

Models are in excellent agreement of keeping the upper level low
off the West Coast through at least midweek. During this time,
the downstream flow will become even more amplified strengthening
the ridge over the Desert Southwest. By Thursday, heights could
reach 584 dm which according to the SPC sounding climatology page,
would be near record territory. Consequently, surface
temperatures will be unseasonably warm as temperatures soar to
near 90 in the lower desert. In fact, a few records may fall on
Thursday particularly from Tucson eastward to the New Mexico state
line. One caveat is that thick broken high clouds will move over
the area late Wednesday and Thursday. If clouds are
thicker/thinner than expected, temperatures would most certainly
be cooler/warmer than forecast.

The upper level low in the Eastern Pacific will finally move
inland Thursday as it is picked up by a longer wave trough. This
is expected to bring heavy rains to Southern California but will
weaken dramatically as it moves through the desert SW. Winds will
begin picking up over the Tucson area on Thursday as this trough
approaches our area. However at this point, winds do not look
particularly strong but gusts 20-25 mph Thursday afternoon will
likely be realized across the lower deserts. By early Friday, the
main trough will swing through our area but the best dynamics
will remain well to our north. For us, this will translate into
only a slight chance of showers for our northern zones with most
other areas staying dry. The main impact with this trough will be
the dramatically cooler air that will follow on Friday behind the
cold front.

Saturday through early next week, heights will stay suppressed as
a longer wave trough remains stationary over the Desert SW.
Generally, this will bring seasonably pleasant temperatures along
with relatively dry conditions. A few dry shortwaves will likely
rotate through the area during this period bringing some
afternoon breezes to the area but overall, dry conditions are
expected to prevail.


.AVIATION...Valid through 21/12Z.
No aviation concerns through the TAF period. Skies will be mostly
clear with FEW to SCT clouds mainly aoa 25 kft. Winds will follow
normal diurnal tendencies with speeds mainly less than 10 kts.
Aviation discussion not updated for TAF amendments.


.FIRE WEATHER...Dry conditions with a strong warming trend through
Thursday. High temperatures will be near the upper 70s across lower
desert locations today, increasing into the upper 80s to low 90s on
Thursday! There is a slight chance of showers Friday especially
north of Tucson as a weather system moves north of the area. Dry
conditions will return Saturday into next Monday. 20-foot winds
terrain driven mainly less than 10 mph into Wednesday. Expect some
gusty southwest to west afternoon winds at times Thursday into this




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