Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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013 FXUS65 KPSR 201817 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 1117 AM MST Mon May 20 2024 .UPDATE...Updated Aviation Discussion... && .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 HREF 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 1815Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: The main aviation weather concern today will be the potential for strong gusty winds mid afternoon as a line of mostly virga showers and some light rain is likely to push through the Phoenix Metro. West winds will start to gust 20-25 kt around 19Z out ahead of the approaching cold front. Confidence is good that virga showers and some light rain showers will form along the cold front that will move through the Metro between 20-22Z. With this cold front winds will gust, out of the west/southwest, up around 35 kt, with some periodic gusts up around 40 kt also possible. After the cold front and virga/light showers exit the Metro ~22Z, westerly winds will start to diminish, but stay elevated (25-35 kt) through sunset. After sunset westerly winds will quickly die off with speeds around 5-10 kt. Winds will then switch back to the east during the overnight hours. SCT-BKN clouds with bases aoa 10-12 kft will quickly clear out this evening behind the cold front. Southeast California/Southwest Arizona including KIPL and KBLH: The main aviation weather concern today will be gusty southwest to west winds. Winds at KIPL will predominately be out of the west and at KBLH will predominately be out of the southwest through the TAF period. At both terminals current gusts of 20-25 kt will pick up around 20-21Z with gusts of 30-35 kt. Winds will then lessen a little bit this evening with gusts going back down to 20-25 kt. Wind speeds will then lessen even more, down to around 5-10 kt for the overnight and early morning hours tomorrow. High clouds currently overhead will clear out this afternoon, with clear skies for the remainder of the TAF period. && .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. && $$ DISCUSSION...Benedict AVIATION...Berislavich FIRE WEATHER...Benedict