Sunrise 5:45 AM   Sunset 7:07 PM Moonrise 8:10 PM   Moonset 5:59 AM

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FXUS65 KPSR 241155 AFDPSR

Area Forecast Discussion National Weather Service Phoenix AZ 455 AM MST Wed Apr 24 2024

UPDATE
Updated 12z Aviation Discussion...

SYNOPSIS
Noticeable cooling will take place over the next few days as an area of weak low pressure traverses the Desert Southwest. This system will help generate breezy to locally windy conditions over the next few days while potentially sparking a few light showers over southwestern Arizona Thursday morning. Another more potent low will then affect the region through the end of the week and into the start of the weekend, ushering in the return of rain chances Friday night into Saturday morning and helping to keep cooler and breezy conditions in the forecast.

DISCUSSION
The ridging pattern that resulted in several days of well- above normal temperatures has started to push of to the east as a weak area of low pressure advances towards the southern California/northern Baja Coast. As these two features continue their easterly progressions', a noticeable cooldown occur over the next few days once the aforementioned low moves to a close enough proximity to the southwestern CONUS. Temperatures this afternoon will be around 10 degrees cooler than what was observed Monday, with daytime highs in the upper 80s and lower 90s across the lower deserts. Highs by Thursday will then fall another 5-10 degrees, with only low to middle 80s in the forecast for lower elevation communities, a good 15-20 degrees cooler compared to where we started the week.

The other noticeable impact of this approaching system will be the generation of breezy to locally windy conditions across the region. Today, the strongest winds will focus over parts of southeast California, where gusts in over 40 mph will be common.
Due to the high likelihood of gusts exceeding that threshold, a Wind Advisory was posted for much of Imperial County and the area around Joshua Tree NP that goes into effect this afternoon/evening.
Another Wind Advisory may be posted Thursday afternoon and evening for areas in and around the Imperial Valley and Salton Sea, as advisory level gusts will once again be possible (60-70%). Elsewhere, winds over the next 1-2 days should remain below advisory criteria, gusting primarily between 20-30 mph across the lower deserts, with higher gusts of 25-35 mph expected over the Arizona high terrain.

Moisture with this system will be lacking, yielding very low rain chances across the Desert Southwest. However, recent model runs have this shortwave trending slightly deeper as it pushes east, resulting in a slight increase in PoPs over parts of southwestern and south-central Arizona for early Thursday morning. Though chances remain only around 10-15%, a stronger trough could conceivably help spark some virga and very light showers due to the greater degree of forcing and cooler air aloft. This shower potential is now being highlighted in the CAMs, with members showing activity over parts of La Paz and far northern Yuma Counties, as well as western Maricopa County during the above- mentioned window. Any totals observed with this activity will be minimal, amounting to only a few hundredths of an inch at most.

Another more potent trough will dive south from the Pacific Northwest toward our forecast area on Friday, yielding a continuation of cooler-than-normal temperatures through at least Saturday and persistent breezy to locally windy conditions. Model trends now have the base of the cold core moving over the Desert Southwest earlier than previous runs, and as a result, forecasted wind speeds have trended upwards for Friday afternoon and evening. Widespread gusts of 30-35 mph now look likely across much of the region, with advisory-level gusts possible for the high terrain areas of south-central Arizona, and once again for parts of southeast California. However, any subtle shifts in the forecast back to a slower progression of this system may result in a very different wind forecast for Friday as the strongest winds aloft associated with this trough would arrive outside of the window of peak mixing, making it harder to get those higher momentum winds down to the surface.

Dynamically, this trailing system will be much more impressive than the proceeding shortwave. The better kinematics combined with greater regional moisture flux compared to its predecessor has resulted in increasing rain chances for parts of the region, specifically for Saturday morning, when the area of greatest forcing and coldest air aloft will move over the region. PoPs during that timeframe have risen to around 30% over northern Maricopa and southern Gila Counties, while other areas across Maricopa, Pinal, and La Paz Counties have seen PoPs rise to 15-25%. Initial QPF totals are light, ranging from 0.01-0.20", with the higher totals focused over higher terrain areas.

Global ensembles show this disturbance quickly ejecting out of the region by Sunday, allowing for ridging to build in its wake, resulting in a quick warm-up back towards above-normal temperatures by the start of next week. A fair amount of temperature spread remains as long-range guidance currently does not agree on how amplified the ridging may be and where the axis will be located. Nonetheless, the return of middle to upper 90s across the lower deserts appears likely by as early as Monday.

AVIATION
Updated at 1145Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Winds today will continue to exhibit diurnal tendencies, with another prolonged period of southerly crosswinds near 10-12 kts likely beginning 16-17z before eventually switching out of the west to southwest after 21-22z. Speeds later this afternoon through early this evening are expected to increase with gusts near 20 kts. Skies will generally remain mostly clear with FEW high clouds passing to the southeast later this morning through this afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH: Winds at KIPL will remain out of the west and out of the south to to southwest at KBLH throughout the period. Wind speeds will pick up by this afternoon with gusts up to 20-25 kts at KBLH and up to 25-30 kts at KIPL. At KIPL, winds early this evening could occasionally gust upwards of 35-40 kts, potentially causing blowing dust and reduced visibilities. Winds late this evening through the overnight hours will diminish aob 10 kts at KBLH but remain elevated upwards to 20-25 kt at KIPL. Skies will remain clear throughout the period.

FIRE WEATHER
Multiple systems will impact the region through the start of this weekend helping to cool temperatures and generating daily occurrences of breezy to locally windy conditions. Elevated fire weather conditons will exist this afternoon across the western districts due to gusts approaching 40 mph and RH values hovering around 10-15%. Elsewhere, similar RH values will be observed but winds will not be as gusty, though isolated instances of elevated fire weather conditons cannot be ruled out. Though widespread gusty winds are likely to continue through this at least the start of this weekend, any further fire risk should be limited by increasing RH levels, which will rise to about 20-25% by Thursday. Decent to good overnight recoveries will be common across the region over the next few days, with MaxRHs ranging between 45-75% before those values increase further by the start of the weekend.

PSR WATCHES/WARNINGS/ADVISORIES
AZ...None.
CA...Wind Advisory from 5 PM this afternoon to 3 AM PDT Thursday for CAZ560-563-565>567.

Wind Advisory from 5 PM this afternoon to midnight PDT Friday night for CAZ562.

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