textproduct: NWS Tucson Arizona

SYNOPSIS

Expect isolated to scattered storm coverage today 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. Otherwise, temperatures will be above normal this week with the potential for extreme heat to return to Southeast Arizona by the middle of the week.

DISCUSSION

A slow start to storm development today across Southeast Arizona as the latest satellite imagery indicated mostly sunny skies across the forecast area with a few buildups over the higher terrain. The upper pattern is defined by an upper high extending across Sonora Mexico into southern New Mexico. The 500 mb high center shifts ever-so-sligtly into western Sonora this afternoon, resulting in a very weak diffluent flow across Santa Cruz and Cochise counties this afternoon. This very subtle shift this time of year is one of the factors that help initiate and assist convection. The deeper moisture that was in place yesterday has shifted west, with the latest GOES TPW imagery indicating 1.25-1.40 inches across western Pima county, around 1.00-1.25 inches near the Tucson Metro Area, and lower values of 0.95-1.05 inch across Cochise/Graham and Greenlee counties. This matches up with the 06/18Z KTWC upper air sounding that indicated a PWAT of 1.24 inches.

Given the lower atmospheric moisture, the 06/12Z HREF members are suggesting the majority of the storms today will be across Santa Cruz into Cochise county with a 10-30% chance for 3-hr ensemble probability matched mean values (40-km neighborhood probability) exceeding an inch confined to Santa Cruz/SW half of Cochise counties. The drier air does bring back the potential for evaporating downdrafts resulting in strong outflow winds with around a 50 percent chance that outflows will exceed 30kts this afternoon across the same area. The 06/18Z sounding was not very excited about strong storms today with a very pronounced warm layer AOA 550 mb choking off the tops of the storms. I have backed off of the high-scattered pops given with the NBM this afternoon, pairing them back to isolated with low-end scattered along the International Border.

As mentioned in the previous forecast discussion...the main theme this week will be an expanding strong ridge of high pressure aloft over the state resulting in very hot, near record high temperatures mid-week and a low grade monsoon pattern. The high centers continue to drift north the next few days, resulting in stacked mid and high level highs Wednesday. Not much variation in 06/19Z NBM ensemble members Wednesday with only a 1 degree variation (110-111 degrees) between the 25th-75th percentile at KTUS. The overall probability of exceeding 110 degrees at KTUS is 6% Tuesday, 77% Wednesday and back down to a 19% Thursday. Solid confidence in the Extreme Heat Watch in effect for Pima, SE Pinal and Graham counties Wednesday so we decided to upgrade it to an Extreme Heat Warning.

We will see the upper high shift the second half of the week into the weekend resulting in a general uptick in thunderstorm coverage, especially across the eastern half of our forecast area. The 500 mb high center is now progged to shift into southern California by Saturday and sit there for a while. This location will allow for a more diffluent upper flow across the eastern zones driving storms that develop in the Whites and along the AZ/NM border SSW into northern Sonora. Its not a favored location for the more active rim-shot pattern for storms to drive SW into Tucson, but I suspect that large day-to-day thunderstorm complexes will develop in Sonora, reinforcing the surface moisture back into Southeast Arizona with their outflows and eventually having a hand in nudging the upper high centers back toward northern Arizona.

Until then, expect a low-grade Monsoon pattern to persist with afternoon high-temperatures moving into the very hot/record high temperature range Wednesday.

AVIATION

Valid through 08/00Z. SKC to FEW 10-12k ft AGL thru 06/19Z then SCT-BKN 7-12k ft AGL with ISOLD-SCT -SHRA/-TSRA mainly S/SE of KTUS thru 07/04Z 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 Monday afternoon. Surface winds generally WLY 8-13 kts, becoming SLY less than 10 kts overnight. 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. 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.

TWC WATCHES/WARNINGS/ADVISORIES

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