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Area Forecast Discussion
Issued by NWS Tucson, AZ
Issued by NWS Tucson, AZ
148 FXUS65 KTWC 162155 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 255 PM MST Tue Jul 16 2024 .SYNOPSIS...Temperatures slightly above normal through the rest of this week, with typical mid July moisture levels across the region. This will result in the daily chances for showers and thunderstorms. The main threats will continue to be strong gusty outflow winds and heavy rainfall leading to localized flash flooding. && .DISCUSSION...We started this morning with some weak showers/ thunderstorms across Southeast Arizona, and we will likely finish the day with more established stronger storms. The storm activity we saw this morning was associated with a mid-level MCV that tracked across southern Pima county and eventually moved into NW Sonora Mexico. Typically in the wake of these types of features, we see a subsidence field that hinders storm development. In this case though, it is far enough away where it shouldn`t have too much impact on Southeast Arizona this afternoon. There are three things that are around to help thunderstorm activity/development today. The overall pattern is defined by a mid-upper high centered over central New Mexico with the flow around this feature resulting in a weak diffluent area across Southeast Arizona. A trough moving into the Pacific Northwest will force this high to align more into a NW-SE orientation, resulting in an area of weak stretching deformation assisting with the overall lift. The third thing of note today is a weak vort max in northern Chihuahua Mexico that will continue to rotate around the base of the upper high and push into the far SE corner of the state this evening. So, with this in mind...our thinking is that we will see thunderstorms develop NE of Tucson this afternoon (which we are already watching develop via radar). The latest 16/20Z HRRR has these storms moving off the higher terrain into the Upper Gila River valley between 4-6 pm. I would expect these storms to produce a strong outflow as it moves off the terrain, potentially impacting Safford. Otherwise, thunderstorms east and southeast of Tucson will be pulse-type and/or delayed until the late afternoon and evening as we start to see the impact of the approaching vort max. I have confidence in the University of Arizona 16/12Z WRF-RR run since it has been resolving the timing/location of convection very well the past few days. This run delays the majority of the activity well into the evening hours. Tucson will likely stay on the northern periphery of the majority of storm activity, just clipping the Tucson Metro Area late (between 8-10 pm MST) this evening. Drier air in the mid-levels of the storm residing in NM and will push west and entrain into the thunderstorms along the Arizona/New Mexico border. The 16/12Z HREF is suggesting a 50-70 percent likelihood of wind gusts in excess of 30+ kts from storms east of Tucson today. It should be noted that 16/00Z HREF run had a 10 percent chance of wind gusts in excess of 50 kts but has backed off on this run. The 16/12Z HREF is also pinpointing the heaviest rainfall to occur S and SE of Tucson in Cochise and Santa Cruz counties this afternoon/evening with a 10-30 percent chance of 3-hr rainfall amounts in excess of 1 inch, and even a 10 percent chance of rainfall in excess of 3 inches along the International Border. In general, the main threat from storms today will be strong and gusty thunderstorm outflows, but heavy rainfall is also in the mix...especially S and SE of Tucson in Cochise and Santa Cruz county where there is a better mix of moisture and will be impacted by the weak vort max later this evening. Otherwise, we will see a continued chance of mainly afternoon and evening thunderstorms persist into early next week. The upper high center will slowly drift into NW Arizona by late this week, then near southern Nevada by the weekend. This puts us in into a more favorable pattern for strong storms as the flow will move off the Mogollon Rim/higher terrain into SE AZ. However, resolving which day that will be more active at this juncture is difficult. && .AVIATION...Valid through 18/00Z. SCT-BKN clouds at 8k-12k ft AGL thru 17/05Z and again aft 17/18Z, with diminishing cloud cover between 17/05Z and 17/18Z. SCT TSRA/SHRA thru 17/05Z, mainly east through south of KTUS and in the White Mountains. SCT TSRA/SHRA developing again aft 17/19Z. MVFR conditions in TSRA, with mountain obscurations, vsby reductions and wind gusts to 40+ knots. Outside of TSRA, SFC wind at most locations 12 knots or less favoring a WLY/NWLY direction during the afternoon and early evening hours and variable in direction at other times. The exception will be in the upper Gila River valley near KSAD where WLY/NWLY SFC wind will be 16-22 kts with gusts to 32 kts thru 17/04Z. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Deeper moisture remains across southeast Arizona, with typical mid July moisture levels expected through at least the upcoming weekend. This will result in the daily cycle of mainly afternoon and evening showers and thunderstorms. The main threats will be strong, gusty and erratic outflow winds and heavy rainfall leading to localized flash flooding. Minimum relative humidity values will be 20-30 percent in most lower elevation locations and 25-40 percent in mountain areas. Away from thunderstorms, 20-foot winds will generally be 15 mph or less, with afternoon/early evening gusts to 20-25 mph and light winds overnight. Wind direction during the afternoon will primarily be west to northwest into the weekend. The exception will be in the upper Gila River valley around Safford, where afternoon/early evening winds will be west-northwest around 20 mph and gusts to 30-35 mph through this evening. && .TWC WATCHES/WARNINGS/ADVISORIES...None. && $$ Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson