Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jul 21 2025 18:11:35 AWUS01 KWNH 211811 FFGMPD NMZ000-AZZ000-220000- Mesoscale Precipitation Discussion 0773 NWS Weather Prediction Center College Park MD 210 PM EDT Mon Jul 21 2025 Areas affected...Southeast Arizona, far Southwest New Mexico Concerning...Heavy rainfall...Flash flooding possible Valid 211810Z - 220000Z Summary...Showers and thunderstorms will expand across southern Arizona trough the afternoon,with rain rates increasing to as much as 1"/hr. These storms will move slowly, and may repeat in some areas, leading to 1-2" of rainfall with isolated higher amounts. This could produce instances of flash flooding. Discussion...The GOES-E visible satellite imagery late this morning shows billowing Cu expanding across southeast Arizona, which when combined with the GOES-E day cloud phase RGB indicates rapidly expanding and intensifying updrafts from northern Mexico into Arizona. This activity is building in response to ascent driven by a shortwave lifting northwest across Chihuahua, Mexico, and increasing diffluence in the RRQ of a jet streak pivoting into the Four Corners region. The combined lift of these features is working upon robust thermodynamics characterized by PWs which were recently measured via GPS to be 1.5 inches, well above the 90th percentile for the date, overlapping SBCAPE of 500-1000 J/kg. The region is pinched between a broad ridge centered over the Gulf Coast and a trough emerging from the Pacific Northwest, leaving deep southerly flow across the Southwest. It is this southerly flow that will allow thermodynamics to become even more impressive by the afternoon. As forcing for ascent and thermodynamics maximize atop the area in the next few hours, convection should rapidly increase in coverage and intensity. This is supported by simulated reflectivity from the HRRR, RRFS, and 3kmNAM, as well as the recent HRRR-UA WRF output. Rainfall rates within this convection may exceed 1"/hr at times (40% chance from the HREF), with locally even more intense rain rates producing 15-min rainfall as much as 0.5". With mean cloud-layer winds remaining southerly at around 10 kts, storms should move slowly northward, but redevelopment into the higher thermodynamics is expected resulting in repeating rounds of heavy rainfall across southern Arizona. Where multiple cells repeat, total rainfall of 1-2" of rainfall is likely, with isolated higher amounts possible as reflected by the HRRR-UA WRF and HREF 6-hr PMM. 1-hr FFG across this area is only 0.75 to 1.00 inches, and the HREF neighborhood exceedance probabilities reach as high as 40%, with 3-hr FFG exceedance peaking above 60% (due to repeating rounds). These probabilities suggest that flash flooding is possible anywhere due to these intense rain rates. However, the most vulnerable locations will be atop sensitive terrain, recent burn scars, or urban areas, where any training or slower motion of these intense rain rates would quickly become runoff leading to flash flooding. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_sCwZbSKYWwnn7E6bdUjj_kaXZSog4TtJLOnO77XbeumxD1mkznMZonD2x-Z87-wB2Xc= nYTsq_oE0YiU2rMytDf_vZQ$ for graphic product... ATTN...WFO...EPZ...PSR...TWC... ATTN...RFC...FWR...STR...NWC... LAT...LON 33121030 32970960 32800891 32540842 32120817=20 31410809 31090849 31091024 31281134 31501179=20 31811209 32331219 32811185 33091112=20 =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .