textproduct: NWS Tucson Arizona

SYNOPSIS

Expect scattered storm coverage this afternoon focused on locales generally south and southeast of Tucson. The main hazard from the storms today will be their capability to produce strong gusty outflow winds to 40-45 mph. The threat of heavy rainfall will also be present near Santa Cruz county this afternoon. Otherwise, temperatures will be above normal this week with the potential for extreme heat across Southeast Arizona by the middle of the week.

DISCUSSION

The upper pattern today is defined by an elongated upper high at 500 mb extending across the Southeast Arizona into central New Mexico with the high center at 300 mb a little farther south extending from southern Sonora Mexico into the Big Bend areas of far west Texas. The latest GOES TPW imagery indicted drier values est of Tucson with PWAT values around an inch across Cochise and Graham counties, around 1.30 inches near the Tucson Metro Area with higher values around 1.35-1.45 inches across western Pima county. Surface dewpoints range this afternoon from the mid to upper 40s east of Tucson to the mid to upper 50s across central and western Pima county. The 07/18Z KTWC upper air sounding this morning indicated a PWAT of 1.36 inches. This sounding was a little more unstable than I was thinking it was going to look with a little less warm air aloft and a little deeper, well mixed moisture between the SFC and 700 mb. The steering flow between 700 mb and 500 mb was very weak today. I guess that is what explains why storms are hesitant to move off of the higher terrain early this afternoon.

In general, we are expecting a below normal Monsoon day across the majority of Southeast Arizona today, with higher more typical Monsoon activity across Cochise and Santa Cruz counties. The upper high at 500 mb will be a limiting factor again today as the warm layer will choke off the majority of deep sustained updrafts. With the high center positioned near Nogales this afternoon, we see a slightly diffluent field develop aloft east of Tucson this afternoon. The thing is that this area is drier than other areas, increasing the potential for evaporating downdrafts to accelerate outflows. In fact, the SPC Mesoscale Analysis this morning indicated DCAPE values of 1200-1800 J/kg across Graham, southern Greenlee and Cochise counties this afternoon. The 07/12Z HREF this same area with a 50-70% neighborhood (40-km) probability for wind gusts exceeding 30 kts this afternoon SE of Tucson this afternoon, with even a 10% chance of outflows exceeding 50 kts down in Sonora where all of the CAMS are indicating a large convective system to develop early this evening along the SE periphery of the 500 mb high. As these storms eventually continue to build toward the SW today toward the deeper moisture that is available, the threat of heavy rain increases. The 07/12Z HREF indicated a 30% neighborhood (40 km) probability of exceeding an inch in the 3-hr ensemble probability matched mean for QPF across Santa Cruz county this afternoon. Agree with the previous forecast discussion that mentioned that we will have to watch rainfall totals if storms move thru Nogales Sonora for possible flash flooding of the Nogales Wash.

Otherwise, the main weather story this week will be the expanding strong ridge of high pressure aloft over the state resulting in very hot, near record high temperatures mid-week with a low grade Monsoon pattern. The high centers at 300 mb, 500 mb and 700 mb continue to drift northward, resulting in stacked mid and high level ridge on Wednesday. As was the case yesterday, there is still not much variation in 07/14Z NBM ensemble members Wednesday with only 2 degrees of variation (109-111 degrees) between the 25th-75th percentile at KTUS. The overall probability of exceeding 110 degrees at KTUS is 3% Tuesday, 47% Wednesday and back down to a 17% Thursday. Despite the fact these percentages keep going down with each run, I still am confident in the Extreme Heat Warning for Pima, SE Pinal and Graham counties Wednesday.

We will see the ridge shift the second half of the week into this weekend resulting in a general uptick in thunderstorm coverage, especially across the eastern half of our forecast area. The 500 mb high center is progged to shift into southern California by Friday and even nudge off the southern California Coastline the first half of next week. This location will allow for a stronger diffluent upper flow east of Tucson driving storms that develop in the Whites and along the AZ/NM border in the afternoon SSW into northern Sonora during the evening. I suspect that large day-to-day thunderstorm complexes developing in Sonora will reinforce the surface moisture back into Southeast Arizona behind organized outflows. The first half of next week looks like an active high-grade Monsoon pattern as the flow is not only favorable, but additional deep atmospheric moisture will move its way northward up the Gulf of California thanks to a nearby tropical system progged to move NW up along the Mexican coast.

AVIATION

Valid through 08/00Z. SKC to FEW-SCT 12-15k ft AGL thru 07/18z, then SCT-BKN 7-12k ft AGL with ISOLD-SCT -SHRA/-TSRA mainly S/SE of KTUS thru 08/04Z with CIGS BKN 5-8k ft AGL and gusty outflow winds up to 45 kts. Skies will then become SKC-FEW 12-15k ft AGL overnight, then SCT-BKN 7-12k ft AGL again Tuesday afternoon with ISOLD-SCT -SHRA/-TSRA mainly S/SE of KTUS. SFC winds generally WLY 8-13 kts. Aviation discussion not updated for TAF amendments.

FIRE WEATHER

Although Southeast Arizona will be experiencing a low-grade monsoon pattern the first half of the week, isolated to low-end scattered thunderstorm coverage is expected to the south and southeast of Tucson for the next several days. The main threat for storms will be the potential for strong gusty and erratic outflow winds 40-45 mph. Otherwise, an eventual uptick in monsoon activity is possible the second half of the week into next weekend as the upper high shifts to a more favorable location aloft. Temperatures will be above normal this week with hottest temperatures mid- week. Winds generally light and under 15 mph with the exception of gusty and erratic winds up to 35-45 mph near any thunderstorms.

CLIMATE

RECORD OR NEAR RECORD HIGH TEMPERATURES WEDNESDAY

DATE Jul 09 FCST RCD/YR TUCSON INTL AIRPORT 110 111/2024 AJO 112 116/2024 ORGAN PIPE CACTUS 111 116/1958 PICACHO PEAK 109 113/1994 SAFFORD AG STATION 110 108/2024 SIERRA VISTA FD 101 104/2024 TOMBSTONE 102 106/1979 WILLCOX 105 109/2003 DOUGLAS 103 108/2003

TWC WATCHES/WARNINGS/ADVISORIES

Extreme Heat Warning from 10 AM to 8 PM MST Wednesday for AZZ501- 502-504>506-509.