Sunrise 5:39 AM   Sunset 7:32 PM Moonrise 5:08 PM   Moonset 3:46 AM

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FXUS65 KPSR 201013 AFDPSR

Area Forecast Discussion National Weather Service Phoenix AZ 313 AM MST Mon May 20 2024

SYNOPSIS
A passing disturbance today will lead to widespread breezy to locally windy conditions, and even a band of light showers in South-Central Arizona. The showers will be capable of producing brief wind gusts in excess of 40 miles per hour, while also producing very little if anything in the way of rainfall at the surface. Spring-like conditions, with dry breezy afternoons and seasonally hot temperatures then prevail through the rest of the week.

DISCUSSION
A low circulation off to the west over the eastern Pacific will open up into a shortwave trough and quickly slide through the region today just ahead of another trough moving down the CA coast. The shortwave will bring breezy to locally windy conditions today along with a band of elevated showers/virga and "cooler" temperatures. The wind will be the greatest impact today with potential for peak wind gusts over 40 mph. The overall surface gradient winds may peak around 25-35 mph, but a band of elevated showers in South-Central AZ this afternoon will be capable of mixing down stronger wind gusts. The last several runs of hi-res modeling have been supporting the potential for localized wind gusts up to 40-50 mph associated with the showers. The 00Z HRRR probability of 40+ mph gusts is upwards of 40-50% in Maricopa, Pinal, and Gila counties. The time period for these showers and stronger wind potential will likely be brief, with modeling only showing the higher gusts for up to 2-3 hours. For the greater Phoenix area this time period looks to be between 1-5 PM. With the magnitude of wind gusts possible this afternoon, yard decorations, furniture, etc., disposal bins, and unsecured temporary structures may be blown around and/or toppled. There is even the risk shallow-rooted or compromised trees could be knocked down.
There may also be some localized blowing dust this afternoon depending on land use and open desert areas. While there is no guarantee winds will get as strong as advertised (momentum transfer not as strong as modeled), it is still not a bad idea to take precautions.

As for the western deserts, west of where the band of showers are expected, peak wind gusts may still reach upwards of 35-40 mph, especially in favored areas like the Imperial Valley with downsloping enhancements. The winds out west will also be capable of kicking up dust and may make for difficult vehicle handling on roads with crosswinds. Winds across the region should subside this evening and tonight.

For the band of elevated rain showers this afternoon, the environmental setup supports most of the rain falling as virga or a very light shower, with a very dry sub-cloud layer. The evaporative cooling in this dry layer is what will help with the generation of the stronger wind gust. So, do not count on seeing much if any in the way of accumulating rainfall. With that said however, there will be a very good fetch of moisture into the region today. Global ensembles even show IVT values as high as 400-500, which would classify as a weak to nearly moderate AR event. Compared to climatology these IVT magnitude will be near record levels, granted this the driest time of the year. Still, it is not out of the question that there could be a little bit more rain than currently advertised, but rainfall amounts are forecast to remain under 0.10". The chance for a few lightning strike or two is not zero with little to no instability in the hail growth zone, but a little bit of mid-level cooling on the back side of the band later in the afternoon could present a low chance.

Conditions dry out, with clearing skies, pretty quickly following the band of showers and conditions are forecast to remain dry for the next several days. Temperatures will mostly remain seasonal, which is lower desert highs mostly in the middle 90s, through this weekend as a general broad troughing pattern persists across the west. There are indications of at least a couple more embedded shortwaves, Wednesday and Saturday, within the flow that may lead to some breezier conditions as well. Overall, typical Spring-like conditions are expected through the week with dry, low-humidity, conditions with afternoon breeziness.

AVIATION
Updated at 0545Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Wind directions will follow their typical diurnal tendencies through at least early tomorrow morning. The typical SE switch is expected to take hold by 08-10Z at KPHX, KIWA, and KDVT.
Overnight, mid and high level clouds will begin to fill in over the region, with bases reaching their lowest midday tomorrow at around 12 kft. Late tomorrow morning, winds will switch out of the SW sooner than usual before increasing and developing gusts into the mid 20s by the afternoon. Confidence is good in virga showers passing over the terminals during the early afternoon (coinciding with the lowest cloud bases) ahead of a front. Anticipate the front to sweep over the terminals sometime between 20-23Z and temporarily bring gusts upwards of 30-35 kt. Skies will clear rather rapidly late afternoon following frontal passage.

Southeast California/Southwest Arizona including KIPL and KBLH: The primary aviation weather concern through the next 24 hours will be gusty SW to W winds. Directions will favor W at KIPL and S to SW at KBLH through the period, with lower speeds overnight and gusts picking up again tomorrow morning. Gusts will peak tomorrow afternoon between 30-35 kt at both terminals, and with the stronger winds, reductions in visibility from lofted dust will be possible. Expect FEW-SCT and at times BKN clouds mostly aoa 20 kft overnight into tomorrow morning.

FIRE WEATHER
A short-wave trough moving through the region today will generate widespread breezy to locally windy conditions. Strongest wind gusts may be generated by a band of high-based showers in South- Central AZ this afternoon, with 40-50% chance for gusts in excess of 40 mph, primarily between 1300-1700MST. There may be a brief period, up to 2-3 hours in eastern districts during the early to mid afternoon, with critical fire weather conditions. Outside of shower-generated gusts, widespread wind gusts, across all districts, up to 25-35 mph are anticipated with some localized areas like the Imperial Valley seeing up to 35-40 mph. This will result in widespread elevated fire weather, borderline red flag, conditions today as minimum RHs fall to 10-15%. Land managers should be cautious for rapid, uncontrolled spread of any ongoing fires or new starts Monday.

Following today, typical Spring-like conditions are expected, with daily afternoon breezes up to 15-25 mph, min RHs between 5-15%, and afternoon high temperatures in the 90s across the lower deserts. Winds may elevate a little higher than seasonal levels, and elevated the fire weather conditions, with a couple more passing waves Wednesday and Saturday.

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

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