textproduct: NWS Tucson Arizona

SYNOPSIS

Chances for thunderstorms will develop each afternoon and evening this week with day to day variability. Thunderstorms may produce severe outflow winds with areas of blowing dust, as well as locally heavy rainfall with a flash flooding risk. High temperatures will remain a few degrees above normal through the weekend.

DISCUSSION

The atmosphere is primed for another day of scattered strong to severe thunderstorms this afternoon and evening. An elongated ridge is in place with modest mid-level flow of 20-30 kts at 500 mb. This will lead to 0-6 km shear of 25-35 kts with CAPE values 1000-1800 J/kg and seasonal PWAT values. Hi-res guidance shows initial development over the White Mountains and Sky Islands east of Tucson by mid-afternoon. Current satellite shows cumulus development over northern Greenlee County. Storms then progress westward into the lower elevations of Santa Cruz, Cochise, and eastern Pima Counties late afternoon into the evening. Tucson will likely be the northern extent of storm coverage. Heavy rainfall will be a threat in Cochise and Santa Cruz Counties with HREF one inch in one hour probabilities within 25 km of a point 20-50 percent between 4PM - 10PM. Areas that received heavy rain yesterday will also be more likely to see runoff and flash flooding. Because of this a Flood Watch is in effect for these areas from 3 PM - 11 PM. With the aforementioned shear some storms could be rotating, which could lead to an isolated hail threat and a more widespread severe wind threat. Model soundings also show a nose of dry air around 400 mb which would act to enhance downdrafts through entrainment. Because of all of these factors some storms may be capable of wind gusts 70-80 mph. There is also a small tornado threat as well with 0-3 km helicity values 150-250 m^2/s^2. The best environment for a tornado looks to be along the international border and over Sonora, but confidence is low in any tornado developing.

Overnight activity looks limited with just some showers over Graham and Pinal Counties after midnight. This should allow the atmosphere to reset and be ready for another round of scattered thunderstorms Wednesday afternoon and evening. Mid-level winds decreases slightly compared to today with 500 mb winds 15-20 kts leading to 0-6 km shear generally 20-30 kts. Plenty of instability will be in place along with seasonable PWAT values. This will lead to a threat of strong to severe winds gusts from Tucson south and eastward. Locally heavy rainfall leading to flash flooding will also be a threat with HREF 1 inch in 1 hr probabilities 30-60 percent south and east of Tucson and 30 percent between Sells and Three Points. Past rainfall from today and Monday will lead to easier runoff in Cochise and Santa Cruz Counties with area washes and rivers seeing faster responses from rainfall.

Looking ahead through the weekend expect daily afternoon and evening thunderstorms from central Pima County eastward with typical monsoon threats of isolated severe winds and heavy rainfall leading to flash flooding. Areas that receive repeat heavy rainfall each day will be especially susceptible to flash flooding. The most likely areas where this will happen will be Santa Cruz and Cochise Counties. There will likely be some day to day variability. Right now Saturday stands out as a day that could see enhanced storm coverage and strength due to 500 mb winds increasing to 25-30 kts. Medium confidence in winds being this strong even though its a few days out with ensemble probabilities for winds greater than 20 kts at 500 mb 40-60 percent Saturday.

High temperatures will be 2-7 degrees above normal through the weekend.

AVIATION

Valid through 06/00Z. Scattered thunderstorms expected to develop this afternoon mainly between 04/22Z to 05/05Z with lingering isolated activity through 05/07Z. Coverage around KTUS more likely 05/03Z-05/05Z and KOLS/KDUG 05/00Z-05/06Z. Gusty erratic winds of 35-50 kts possible with any thunderstorm. Cigs will be BKN 8k-12k ft AGL this afternoon and evening, slowly dissipating overnight. Expect another round of TSRA Wednesday afternoon and evening. Outside of storms SFC winds WLY/NWLY at 8-12 kts with occasional afternoon gusts to 20 kts. SFC winds light and terrain driven after 05/05Z. Aviation discussion not updated for TAF amendments.

FIRE WEATHER

An active monsoon period looks favorable this week with daily chances for showers and thunderstorms each afternoon and evening, with day to day variability. Minimum relative humidity values will likely remain above 25-40 percent through the week with temperatures 2-4 degrees above normal. Outside of thunderstorms, winds terrain driven to around 10 mph with occasional afternoon gusts to 25 mph.

TWC WATCHES/WARNINGS/ADVISORIES

Flood Watch until 11 PM MST this evening for AZZ503-504-507- 508-511>513. Blowing Dust Advisory until 8 PM MST this evening for AZZ507>509-511>513.