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634
FXUS65 KPSR 232337
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
437 PM MST Sun Jun 23 2024

.UPDATE...
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Updated Aviation section.
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&&

.SYNOPSIS...
Elevated moisture will continue to result in daily
thunderstorm chances through at least the middle of this week, with
the highest chances confined over the higher terrain areas.
Temperatures today will be near to slightly above normal but then
warm up somewhat heading through the middle of the week as high
pressure strengthens over the Desert Southwest.

&&

.DISCUSSION...
An expansive subtropical ridge centered over Texas is continuing to
provide a southerly wind flow across the region, providing moisture
advection into the region with well-above normal in PWATs in place.
Latest SPC Mesoanalysis depicts PWAT values ranging between 1.7-2.0"
across most of central and southern AZ and between 1.5-1.9" across
southeast CA. These PWAT values are currently near 250% of normal
for this time of the year. The highly anomalous moisture content,
similar to yesterday, has resulted a stream of mid to high-level
clouds to encompass most of south-central AZ from Phoenix and
points eastward through southern Gila County with radar showing a
few light showers/virga in association. Once again the cloud cover
is adding a layer of complexity when it comes to convective
potential later this afternoon/evening as it will likely limit
the overall instability across south-central AZ. This is reflected
in the latest hi-res model guidance, which shows very limited
activity across south-central AZ the rest of today with most of
the activity confined across the High Country and southeast AZ
where better insolation and orographic lifting will aid in
storm development. There is a slight chance, however, that
portions of southwest AZ in the vicinity of the Kofa Mountains as
well as the higher terrain areas in northeast La Paz County as
well as Joshua Tree National Park in southeast CA could see
storms pop up this afternoon as these areas are seeing better
insolation and thus higher instability. Even though south-central
AZ may not see much in the way of storms, any outflows from
distant storms could still impact the area with a 10-30% chance of
winds exceeding 35+ mph. Given the high moisture content as well
as the very weak steering motion in place, heavy rainfall leading
to flash flooding will be the biggest threat with gusty winds
being a secondary threat given the more limited DCAPE.

The subtropical ridge will continue to migrate westward and be
centered near the AZ/NM border heading into the first half of the
week while also strengthening slightly in the process as 500 mb
height fields increase from 592-593dm currently to 594-596dm by
mid-week, increasing the subsidence aloft. Still, with abundant
moisture remaining in place with PWATs projected to remain at
1.5+", daily thunderstorm activity is still expected, mainly
across the higher terrain areas. There continues to be excellent
agreement amongst the ensembles of a large-scale trough moving
through the Pacific Northwest and Intermountain West Region by the
latter half of the week. This troughing feature will weaken the
subtropical ridge over the Desert Southwest but at the same time
will cause the mean flow to become westerly, which is likely to
advect drier air into the region. Thus, heading through the end of
the week and at least into the start of next weekend, the overall
thunderstorm activity is likely to trend downward across the
majority of the region. This drying trend, however, looks to be
short-lived as once the troughing feature lifts away into Canada
by late next weekend, the subtropical ridge is likely to re-
strengthen to our east with a more southerly flow returning. This
would increase the monsoonal moisture once again heading into the
first week of July, increasing thunderstorm activity.

With the abundant cloud cover and high moisture content in place,
temperatures today across the lower deserts will continue to
average near normal with highs in the mid to upper 100s. As the
upper-level ridge builds over the area through midweek, temperatures
are expected to heat up some with highs likely topping out
between 109-112 degrees across the lower deserts. Even though
these temperatures will keep the overall HeatRisk in the moderate
category, it will still be sufficiently hot and humid that the
necessary heat precautions should still be taken if engaging in
outdoor activities. Temperatures are likely to cool off slightly
as the ridge weakens towards the end of the week.

&&

.AVIATION...
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Updated at 2337Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:

Cloud cover has been thinning this afternoon but instability is
expected to be insufficient for storm development over the Valley
floor this evening. However, storm activity over southeast AZ and
Yavapai County will lead to the potential for outflows to affect
the TAF sites this evening roughly between 02Z-04Z but not
necessarily with strong winds. Anticipate southeasterly outflow to
be more likely to reach KIWA and KPHX and northerly outflow to
reach KDVT and KSDL. Of course, that is subject to change.
Otherwise, expect generally light winds with a lot of directional
variability tonight and Monday morning followed by light west by
early afternoon. As for sky cover, anticipate ceilings to remain
AOA FL200.


Southeast California/Southwest Arizona including KIPL and KBLH:

At KIPL, S/SEly winds will be most common through the forecast
period. One caveat is storm activity over the northern Baja MX
mountains which may produce outflow that could lead to a SWly wind
shift. At KBLH, expect SWly/Sly directions to prevail for much of
the forecast period. However, storm activity currently over
southwest Yavapai County is anticipated to expand into southern
Mohave County and produce some southwestward moving outflow later
this afternoon and evening. The end result at KBLH is anticipated
to be a change from southerly to variable directions later this
evening but with speeds below 10kts. Southerly breeziness (gusts
to 20kts) resumes during the day Monday. As for sky cover
anticipate SCT-BKN cirrus with FEW high based cumulus during the
afternoon.
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&&

.FIRE WEATHER...
Monsoonal moisture will continue to result in daily chances for
shower and thunderstorm activity, with the best chances for
activity across the higher terrain areas. With the elevated
moisture in place, MinRH values through early this week will
range between 35-45% across the far eastern districts to between
15-25% across the western districts before slowly drying into the
middle to latter half of next week. Winds will follow their
typical daily tendencies, with gusty outflows from any
thunderstorm activity anticipated over the next several days.
Temperatures through today will average near to slightly above
normal before increasing some heading into the middle of next
week. Chances for wetting rains will generally remain around
15-25% for the higher terrain areas and 5-10% for the lower
deserts of south-central Arizona through the first half of the
week.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

DISCUSSION...Lojero
AVIATION...AJ
FIRE WEATHER...Young/Lojero