![National Oceanic and Atmospheric Administration](/build/images/header/noaa.d87e0251.png)
![National Weather Service](/build/images/header/nws.4e6585d8.png)
![United States Department of Commerce](/build/images/header/doc.b38ba91a.png)
Area Forecast Discussion
Issued by NWS Tucson, AZ
Issued by NWS Tucson, AZ
741 FXUS65 KTWC 181618 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 918 AM MST Thu Jul 18 2024 .SYNOPSIS...Temperatures will remain 4 to 7 degrees 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. && .UPDATE...Welp. That low-grade Monsoon day we saw yesterday across Southeast Arizona was short-lived. We can expect to see a ramp up in a activity over the next several days, begining today. In the short term, we are currently seeing scattered light showers with embedded thunderstorms across far western Pima county this morning as a decaying complex from convection along the International Border during the early morning hours continues to push off to the west. Thicker cloud cover extends as far east as Santa Cruz county. Its possible that this feature may delay convective initiation this afternoon across south-central Arizona while it remains in the subsident wake of this departing mid-level feature. In any event, today is shaping up to be a more typical Monsoon day across the entire forecast area. To set the big picture, the 500 mb upper high is centered across eastern Arizona and the 300 mb high center is positioned near the bootheel of New Mexico. Both of these features will drift west to northwest today, becoming stacked over central Arizona by this afternoon. As this happens, we not only cool slightly in the mid-to-upper levels, but we also find ourselves with weak lift due to a stretching deformation aloft. During the Monsoon season, it is sometimes the most subtle features or mechanisms that differentiate a quiet or active day. The NNE flow pattern today isn`t quite the favored NE "rimshot" for us today, that will come overnight and more specifically tomorrow and into the weekend, but it will help force storms off the higher terrain into the lower elevations across Graham and Greenlee counties this afternoon. The latest GOES derived Precipitable Water satellite imagery indicates dry air (between 1.0 and 1.2 inches) situated east of Tucson with the 18/12Z KTWC sounding indicating a value of 1.49 inches over Tucson, and deeper PWAT values to 1.75 inches across the SW corner of Arizona. There is a deeper pocket of dry values near 1.0 inch along the International Border in Cochise county. This is mainly drier air residing between 700-500 mb which should increase the downdraft potential (DCAPE) this afternoon across Santa Cruz as the easterly flow tried to entrain this into storms that develop this afternoon. The 18/12Z SPC HREF indicated an area of 70% probability of 30+kt winds within 25 miles of a given point across Santa Cruz, Eastern Pima and the southern portions of the TON at 00Z this afternoon, with even a 10% chance of wind gusts in excess of 50+kts withing 25 miles of a given point in the Tohono O`odham Nation. The drier air to the east of Tucson will also increase the potential for strong thunderstorm outflows there this afternoon for the stroms that develop over the higher terrain and push off into the lower elevations. Strong thunderstorm outflow winds will be the primary threat from storm this afternoon, with an increasing threat of heavy rainfall as storms push into the deeper moisture across central and western Pima county this afternoon/evening. There is still hints from the high resolution CAMS runs of nocturnal convection, especially with the 18/14Z HRRR, across Southeast Arizona tonight as the lift associated with the shifting upper high center will interact with the elevated CAPE. Nothing strong, but if it does happen it may hinder thunderstorm activity Friday despite the improving NE flow/rimshot potential. As we move into the weekend and next week, the upper high positions itself near southern NV which would suggest the stronger NE flow pattern will continue into next week for our neck of the woods. The strongest days are still looking like Saturday and Sunday as the mid-level flow is the strongest for Southeast Arizona. && .PREV DISCUSSION... /issued 344 AM MST Thu Jul 18 2024/ Residual thunderstorm activity across southern Cochise and Santa Cruz counties continue to linger at the time of this writing forming off outflows from evening convection in Sonora. CAMs have somewhat struggled on resolving this and similar activity over the past few nights, but anticipate it gradually diminishing as it pushes west into south central Pima county this morning. PWATS are currently running around normal for this time of year at around an inch near the NM state line to around 1.3 inches in the Tucson Metro to around 1.5 inches across western Pima county. The overall upper air pattern over the past couple of days has been characterized by a mid/upper level high drifting west over AZ/NM. The flow pattern resulting from the high is currently easterly/southeasterly, but as the high continues to meander northwest over the next few days we will see the flow pattern gradually becoming more easterly/northeasterly heading into the weekend. The northeasterly flow regime favors storms forming off the higher terrain/Mogollon Rim and then propagating into the lower deserts of Southeast Arizona through the late afternoon hours. Right now, Saturday and Sunday appear to be the best chances for convection of that nature. For today, HREF/CAMs are depicting scattered showers and thunderstorms primarily forming over Santa Cruz and southeastern Pima counties this afternoon as well as in the White Mountains and elevated terrain. The main concerns with these storms continues to be gusty outflow winds and locally heavy rainfall leading to the possibility for isolated occurrences of flash flooding. Temperatures will be a degree or two warmer across southeast Arizona today and tomorrow resulting in isolated areas of major HeatRisk. Decided to hold off on heat related products at this time as there is not enough widespread Major HeatRisk to warrant a headline. && .AVIATION...Valid through 19/12Z. SCT-BKN clouds at 8k-12k ft AGL gradually diminishing from east to west after 18/12Z and forming again after 18/19Z associated with SCT TSRA/SHRA development. MVFR conditions in TSRA, with mountain obscurations, vsby reductions, and wind gusts to 40+ kts. Outside of TSRA, SFC winds at most locations will remain under 12 kts favoring SWLY thru NWLY directions during the afternoon/early evening hours and variable in direction at other times. 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 southwest through northwest into the weekend. && .TWC WATCHES/WARNINGS/ADVISORIES...None. && $$ Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson