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588
FXUS65 KPSR 270953
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
253 AM MST Thu Jun 27 2024

.SYNOPSIS...
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A period of drying conditions will carry through the end of the week
with rain chances decreasing to near zero across south-central
Arizona by Friday. Moisture and subsequent rain chances begin to
increase again by Sunday, likely lasting through the middle of
next week. Above normal temperatures will persist through at
least early next week with lower desert highs approaching or
exceeding 110 degrees, especially in some of the typically hotter
locales.
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&&

.DISCUSSION...
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The impacts of drier air filtering in from the west were very
apparent yesterday with the overall lack of convection across
most of Arizona. The center of the ridge has shifted westward over
the past 24 hours, now positioned over northern Sonora and this
is helping to increase subsidence into southern Arizona. For the
rest of today and through Friday, the ridge will begin to weaken
while also gradually recentering itself again to our east. At the
same time, a trough passing across the northern tier states will
bring some slight influences into our region by reinforcing the
westerly flow aloft. Additional drying is forecast through Friday,
especially in the mid-levels with boundary layer moisture only
drying very slightly. Due to the continued drying and subsidence
aloft, only minimal shower and thunderstorm chances are expected
over the higher terrain in far eastern Arizona. Temperatures will
remain a few degrees above normal for the rest of the week, but
still below excessive heat levels as heights aloft are kept in
check with the passing trough.

The pattern will begin to shift beginning Saturday as the ridge
becomes fully centered over the Southern Plains and quickly
restrengthens. The strengthening of the ridge is expected to
modestly impact our region as our heights aloft are forecast to
temporarily rise, adding a degree of warming on Saturday and
another on Sunday. This should push daytime highs into a 108-113
degree range on Saturday right before we see a strong moisture
push out of the southeast Saturday night into Sunday. Models are
in fairly good agreement showing an easterly wave tracking across
Mexico Friday into Saturday reaching northern Sonora Saturday
evening. This should bring enhanced convection to our southeast on
Saturday with subsequent outflows and mid-level gravity waves
spreading northwestward into south-central Arizona by Sunday
morning. As of now, NBM PoPs are fairly low (5-10%) Saturday
night/Sunday morning into south-central Arizona, but it would not
be surprising to see some nocturnal elevated convection due to
the advancing higher moisture and increasingly unstable air mass.

Moisture advection is likely to persist through much of Sunday
as PWATs likely increase to 1.5-1.75" over much of southern
Arizona, allowing for building instability. NBM forecast
temperatures are also quite hot for Sunday due to the increased
heights aloft, despite the increased dew points with highs mostly
between 109-114 degrees. Sunday is likely to be the worst day for
heat across the area, especially when taking into account the
humidity, but only a few small localized areas reach into the
Major HeatRisk category at the moment. There are indications
Sunday evening could see some good chances for convection
(potentially strong) working into south-central Arizona from the
southeast, or at the very least strong outflow winds and blowing
dust. A southeasterly steering flow will be present to help push
any convection near Tucson toward the Phoenix area, but it will
likely still have to contend with some weak CIN over the lower
deserts. This will definitely be something to watch over the next
few days.

For the first half of next week, guidance all point toward keeping
good monsoon moisture in place across much of southern Arizona.
As the ridge center stays well to our east and another center
develops well off the coast of California, we may end up seeing
some influence from an extension of an upper level trough that
sets up over the Northern Rockies into the Great Basin. The lack
of any strong subsidence aloft in this scenario would likely
result in at least one other busy monsoon convective day at some
point early next week. Temperatures should also cool off slightly
during the first half of next week, but NBM forecast temperatures
are still on average a few degrees above normal most days. Looking
at the latter half of next week, ensemble guidance generally
agrees bringing in a strong ridge off the California coast into
the Great Basin area. As of now, this would likely lead to a
period of northerly drying flow into our region around next
Thursday/Friday and hotter temperatures.
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&&

.AVIATION...
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Updated at 0505Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No significant weather concerns will exist through Thursday evening
under occasional passing mid/high cloud decks. West winds should
prevail well into the overnight, and confidence is good that the
typical widespread overnight easterly component will not
materialize. In fact, winds at KPHX may only become light and
variable for a few hours after sunrise before reverting back to a
westerly component. Otherwise, similar to today, a few gusts 15-20kt
will be common late Thursday afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH:
No major weather issues will exist through Thursday night under only
a FEW occasional mid/high clouds. Winds will vary between SE during
the morning and early afternoon to SW during the evening and
overnight period. Wind gusts 20-30kt should become more common for
both aerodromes late Thursday afternoon and evening.
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&&

.FIRE WEATHER...
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Drier conditions will continue to spread across the region from
the west through Friday, lowering humidities and essentially
ending rain chances across all areas except for far eastern
Arizona. MinRHs will lower into the teens across the majority of
the lower deserts starting today to 25-30% over higher terrain
areas. Afternoon breeziness will be common today and Friday with
gusts reaching to or just over 20 mph in many locations. The dry
conditions with virtually no chances for rain should persist
through Saturday before moisture returns Sunday, increasing
humidities and potentially bringing back chances for thunderstorms
across south-central and eastern Arizona. Temperatures through
the period are expected to average several degrees above normal.
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&&

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

$$

DISCUSSION...Kuhlman
AVIATION...18
FIRE WEATHER...Kuhlman