Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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663 FXUS65 KPSR 130600 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 1100 PM MST Wed Jun 12 2024 .UPDATE...Updated 06Z Aviation Discussion. && .SYNOPSIS... Very hot and dry conditions will persist over the next few days with an Excessive Heat Warning in effect through Thursday for the lower deserts of south-central Arizona. A weak area of low pressure will move over the region Thursday into early Friday, leading to increasing cloud cover, breezy conditions, and perhaps a few showers, primarily east of the Colorado River. Temperatures will continue to run well-above normal through this weekend as high pressure builds in once again. && .DISCUSSION... Atmospheric analysis reveals our forecast area flanked by an area of building high-pressure to our east, while a cut-off low continues to spin just off the coast of the Baja Peninsula. This setup will remain relatively unchanged over the next 24 hours or so and will help to keep very hot conditions over the region for today and Thursday, with lower desert highs ranging between 108-112 degrees. Phoenix will continue to flirt with record high temperatures during this timeframe, with 113 (2022) and 114 (1936) being the records for today and Thursday respectively. Widespread Moderate, to areas of Major HeatRisk will result from these unseasonably hot conditions. Extra caution should be exercised if you work outdoors or have plans to be outside during the hottest period of the day. Take frequent breaks and be sure to hydrate accordingly. In response to this elevated HeatRisk, and Excessive Heat Warning remains in effect for Maricopa and parts of Pinal Counties through Thursday evening. Model guidance shows the cut-off low starting to progress eastward by late Thursday morning, reaching southern California by Thursday evening. Southerly flow will increase as this disturbance advances toward our forecast area, resulting in enhanced moisture flux, with PWATs forecasted to increase to the tune of 0.8-1.0 in. The associated dynamic ascent with the cyclonic circulation, combined with increase in moisture may lead to some shower activity across the region Thursday afternoon through early Friday, with the best chances (20-30%) focused over the high terrain areas of Maricopa and Gila Counties. Chances across the lower elevations of south-central and SW Arizona are only around 10-20%, which is likely due to the dry sub-cloud layer that will be in place, limiting the likelihood of seeing measurable rainfall over the lower deserts. Most of the shower activity over these areas is likely to be virga, but a few sprinkles or light showers reaching the ground cannot be completely ruled out. Hi-res guidance keeps the majority of rainfall east of the Colorado River, but it would not be surprising to see a stray shower or two over parts of SE California. Locally gusty winds associated with these virga showers will also be possible (10-30% chance of gusts exceeding 35 mph), primarily over southwestern Arizona. This low will also tighten up the regional pressure gradient resulting in afternoon and evening breeziness across the region regardless of precipitation activity. Models have been trending toward a weaker and more progressive low over the past several runs, with the most recent runs now indicating the center of circulation over the Arizona-Utah border by mid-day on Friday. Heights aloft over south-central Arizona will fall slightly with the passage of this system, promoting a slight cool down in day-to-day temperatures, but MaxT forecasts have been trending upwards over the past few days as a result of the weaker system projections. Daytime highs for Friday are now forecasted between 106-109 for the Phoenix metro, with hotter temperatures expected further west as ridging quickly develops in the wake of the low, with daytime highs there expected to be around, and for some areas in excess of 110 degrees. Positive height anomalies then spread over the remainder of the region by Saturday, with widespread highs above 110 degrees expected across the lower deserts. These temperatures will once again lead to Major HeatRisk for some areas heading into the weekend. In turn, an Excessive Heat Watch has been posted for the Imperial Valley and eastern Riverside County for Friday and Saturday. Clusters remain in great agreement regarding a deep trough moving over much of the western CONUS during the start of next week, with the southern fringes extending as far south as the Desert Southwest. The main uncertainty that remains is how deep this trough becomes, though most of the models favor the greatest height falls/coolest air remaining well off to our north. Nonetheless, some cooling is expected next week, with NBM MaxT forecasts showing a gradual decrease in temperatures starting Sunday, with daytime highs by Tuesday falling toward near and slightly above normal levels. && .AVIATION...Updated at 0555Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Winds will tend to follow their typical diurnal pattern, with speeds generally aob 10 kt outside of tomorrow afternoon and early evening. A slightly later switch back to the east is expected in the morning, with the easterly component not expected to develop until 11-12Z. Another extended period of variable wind directions (140v250) should be common again tomorrow during the transition to westerly winds during the late morning and early afternoon hours. Winds will gust 15-20 kt tomorrow afternoon through sunset. Clear skies will continue overnight with SCT-BKN mid-level clouds moving into the region around sunrise. Some virga showers are possible late tomorrow morning through the evening. Best time for any activity/sprinkles to reach the ground would be tomorrow evening. Any virga showers could cause some erratic wind directions with some occasional gusts up around 30 kt. Southeast California/Southwest Arizona including KIPL and KBLH: At KIPL, current NW`rly winds will become light and variable around sunrise and then become SE`rly tomorrow afternoon. Then, around 00Z sundowner winds will cause winds to gust 25-30 kt tomorrow evening. At KBLH, current westerly winds will go S/SW`rly around 08Z. Wind speeds tomorrow afternoon will gust 20-25 kt through sunset. At both terminals, FEW mid-level clouds will move into the region tomorrow afternoon, but quickly clear out in the evening. Any rain or storms that develop tomorrow afternoon are expected to stay east of the Colorado River. && .FIRE WEATHER... Well above normal temperatures along with dry conditions will prevail over the next couple days. Lower desert high temperatures will top out between 107-112 degrees through Thursday. Winds will continue to favor diurnal tendencies with occasional afternoon gusts up to 20 mph today and to around 25 mph on Thursday when some high based virga shower activity could bring a brief enhancement of the winds. MinRH values will range between 5-10%, while poor overnight recoveries can be expected with MaxRHs only reaching towards 15-35%. Above normal temperatures will continue through the upcoming weekend, while winds increase further with afternoon gusts of 20-30 mph likely. The combination of the increased winds and continued low RHs will create even higher fire danger across the area this weekend. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Warning until 8 PM MST Thursday for AZZ534- 537>555-559-560-562. CA...Excessive Heat Watch from Friday morning through Saturday evening for CAZ562-563-566-567-570. && $$ DISCUSSION...Kuhlman AVIATION...Berislavich FIRE WEATHER...Kuhlman