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Area Forecast Discussion
Issued by NWS Tucson, AZ
Issued by NWS Tucson, AZ
432 FXUS65 KTWC 182110 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 210 PM 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. && .DISCUSSION...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. 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+ kts 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 storms 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. && .AVIATION...Valid through 20/00Z. SCT-BKN clouds at 8k-12k ft AGL thru 19/05Z and again aft 19/18Z, with diminishing cloud cover between 19/05Z and 19/18Z. SCT TSRA/SHRA thru 19/05Z. SCT TSRA/SHRA developing again aft 19/19Z. 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/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 July moisture levels expected into at least early next week. 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 hours will primarily be west to northwest through the weekend, especially from Tucson westward and in the upper Gila River valley. && .TWC WATCHES/WARNINGS/ADVISORIES...None. && $$ Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson