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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS65 KPSR 262137
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
237 PM MST Fri Apr 26 2024

.SYNOPSIS...
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Breezy to windy conditions are expected through this evening, with
the highest wind gusts, up to 40 to 50 miles per hour, expected in
southeast California, as a weather system moves through the region.
There will also be a slight chance for rain showers and a few
thunderstorms this evening in south-central Arizona, mainly north
and east of the Phoenix metro area. The weather system will depart
through Saturday, but still with some lingering breezy conditions
before high pressure sets in late this weekend and temperatures warm
back into the nineties next week.
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&&

.DISCUSSION...
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Very breezy and windy conditions are already occurring across the
region. The elevated wind speeds and gusts will continue and
strengthen in some areas through this afternoon and evening as an
upper level jet max passes over southern CA and AZ and as afternoon
mixing increases. The dynamic synoptic pattern driving today`s
weather is detailed well in the air mass satellite product from GOES-
West, with the strong upper level jet evident extending northwest
through CA and out into the Pacific. Also evident is a vort max
southwest of Vegas. This vort max is expected to track eastward
through this evening through Central AZ and help generate convection
across the region, with slight chances (20-30%) in the AZ lower
deserts.

First off, winds in portions of SoCal started gusting over 40 mph
(base advisory criteria) this morning, including in the Imperial
Valley. This was a little earlier than anticipated on the magnitude
of wind gusts for the Imperial Valley. At least based on modeling,
but visible satellite shows widespread mountain wave activity in
SoCal. So, the early strong wind gusts may be attributed to the
mountain wave, and possibly rotors and/or downsloping enhancements.
So far there has not been much in the way of observable blowing dust
on satellite or webcams, just a little hazy, but this will likely
change as gradient winds strengthen this afternoon and evening.
Winds regionally are forecast to reach their peak by 5 PM MST/PDT as
the jet max passes over the area. Westerly wind gusts in SoCal, and
even into the Yuma area, will be capable of reaching upwards of 45-
55 mph. The latest NBM even has a 20% chance of a peak gust reaching
60 mph in the Imperial Valley. Gusts in South-Central AZ are not
expected to be quite as strong as out west, with peak magnitudes
mostly in the 30-40 mph range, but there may still be some localized
brief gusts over 40 mph. The Wind Advisory in parts of SE CA will
continue until midnight tonight, with the exception of the far
southwest corner of Imperial County which has been extended until 5
AM PDT Saturday.

As previously mentioned, a vorticity maximum at the base of the
shortwave trough is expected to track pretty much due eastward
across central AZ later this afternoon through this evening,
triggering elevated convection in the region. The exact track looks
to be along the northern county borders of of La Paz and Maricopa
counties. This track will keep most of the convection over the
northern half of AZ. However, the dynamic forcing will still be
close enough to bring slight chances for rain and thunderstorms (10-
30%) to portions of the lower deserts, including Phoenix. There is
some uncertainty how far south the convection will extend, but it is
conceivable for the convection to extend south through all of
Phoenix. The convection will be fast moving, moving westward upwards
of 35-45 mph, given the strong winds above the surface. So, do not
expect much more than a brief (10 min or less) downpour. As
mentioned, the environment will be suitable for isolated
thunderstorms, which will pose a lightning threat and strong gusty
wind threat. Any storm in South-Central AZ this evening could
produce localized wind gusts over 40 mph. HREF conditional
probability of wind gusts over 35 mph in the vicinity of convection
this evening is upwards of 50-70%. Main timing of convection in
South-Central AZ will be between 6 PM - 12 AM MST.

On Saturday, the trough will quickly move northeastward towards the
central Rockies. There will still be some residual breeziness, but
noticeably lighter compared to today as peak gusts area wide are
expected to remain under 30 mph. There will also be some additional
afternoon convection Saturday, but the activity is expected to
remain just to the north and east in the AZ higher terrain. Once the
trough has fully cleared the Desert Southwest, the ensemble model
guidance is in good agreement of low amplitude ridging developing
overhead through next week with dry and tranquil conditions
prevailing.

Under the influence of the troughing feature, high temperatures
today and Saturday will remain below normal with highs across the
lower deserts topping out in the low to mid 80s. Beginning on Sunday
and continuing through early next week, as high pressure builds over
the region, temperatures will be on a strong warming trend. High
temperatures on Sunday will rise back up to near normal levels with
readings in the mid to upper 80s before rising further into the low
90s on Monday and then into the mid to upper 90s by Tuesday. Not
much change in temperatures is expected during the middle to latter
half of the week with readings remaining steady state, in the mid to
upper 90s, with a low chance (10-20%) that some areas, including
Phoenix, reach 100 degrees.
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&&

.AVIATION...Updated at 1844Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Gusty winds will continue to increase through the afternoon as
breezy southerly winds continue to veer toward a westerly
component. Going through the afternoon, gusts will increase to
upwards of 25-30 kts. Could see a few gusts reach or exceed 35 kts
late this afternoon into the evening hours. A few isolated
(20-30%) showers and perhaps a thunderstorm or two will be
possible across northern portions of Maricopa County this evening.
For now, have added VCSH to the KDVT and KSDL TAFs. Winds will
gradually weaken tonight into the overnight hours, while a diurnal
easterly switch is not expected. FEW-SCT clouds down to around 8
kft will develop this afternoon and continue throughout the
period.

Southeast California/Southwest Arizona including KIPL and KBLH:
Strong winds will be the primary aviation weather concern through
the TAF period. Westerly winds will continue to increase at the
terminals through the afternoon/evening with the strongest gusts
residing at KIPL. Gusts at KIPL are expected to peak late this
afternoon and evening upwards of 35-45 kts before weakening later
tonight. These strong gusts could lead to some blowing dust being
generated that could cause some visibility reductions. At KBLH,
gusts will not be as strong with peak gusts upwards of 25-30 kts.
Mostly clear skies will persist with a few passing mid/high clouds
at KBLH.

&&

.FIRE WEATHER...
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A weather system will produce a period of strong winds, especially
for the remainder of this afternoon and evening. The strongest winds
are expected across portions of the western districts, where gusts
in excess of 40 mph are likely at times. Elsewhere, winds will be
lighter but still gusty, peaking up to 30-40 mph. MinRHs will be
high enough, between 20-30%, to prevent any critical fire weather
conditions from materializing. There will be a chance for showers
and thunderstorms this evening into early Saturday morning, mainly
across the higher terrain areas north and east of Phoenix. However,
the chances for wetting rains will be low at around 10-20%. On
Saturday, winds will trend downward with peak gusts of only 20-30
mph. Rapid drying will result in lower MinRHs Saturday, down to 10-
20% most areas. Temperatures today and tomorrow will remain below
normal with highs only topping out in the low to middle 80s across
the lower deserts. Thereafter, a significant warming trend takes
place Sunday through early next week with little change in
temperatures expected by the middle and latter half of the week.
With the warming trend, RH values will trend downward with MinRHs
bottoming out at around 10-15% starting on Monday. Winds through
most of next week will be lighter with the typical afternoon upslope
breeziness expected.
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&&

.PSR WATCHES/WARNINGS/ADVISORIES...
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AZ...Wind Advisory until midnight MST tonight for AZZ532.

CA...Wind Advisory until midnight PDT tonight for CAZ560-563-565>567.

     Wind Advisory until 5 AM PDT Saturday for CAZ562.
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&&

$$

DISCUSSION...Benedict/Lojero
AVIATION...Smith
FIRE WEATHER...Benedict/Lojero