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Flash Flood Guidance
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Issued by NWS
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920 AWUS01 KWNH 021810 FFGMPD NMZ000-AZZ000-030000- Mesoscale Precipitation Discussion 0540 NWS Weather Prediction Center College Park MD 209 PM EDT Tue Jul 02 2024 Areas affected...Eastern Arizona...Western New Mexico... Concerning...Heavy rainfall...Flash flooding likely Valid 021810Z - 030000Z SUMMARY...Slow moving monsoon thunderstorms. Spots of 1-2" over areas with well above normal rainfall over last few weeks, will pose scattered but localized flash flooding incidents. DISCUSSION...A broad longwave trough continues to slide through the central Rockies of WY/CO resulting in gap in return flow across NW Mexico into the Southwest, generally centered along the AZ/NM border before angling northeast across north-central NM. The leaves much of NE AZ, N NM within favorable right entrance divergence outflow channel. CIRA LPW also notes a wave of 700-500 over the Sun Valley lifting northeast highlighted by enhanced moisture along downstream confluence streamlines with eastern deformation zone across the SE San Francisco Plateau, while deeper 850-500 moisture lifts north out of central Sonora into SE AZ and across the Mogollon, Black, Gallo and Gallina Mtns. While deep layer moisture totals generally overlap through this axis the range is a tad lower than the last few days with 1-1.25" total PWats, still more will filter through the terrain with some 1.5" values expected across Cochise county coming out of the Sea of Cortez. Full sun has allowed for solid instability to build with localized pockets of SBCAPEs start to reach 2000-2500 J/kg where valley Tds are in the low 60s in SE AZ/SW NM, though average values of 1500 J/kg even up into the Plateau should feed stronger thunderstorms later into the afternoon. Initial convection appears to be developing along favored upslope ridge lines across the deep moisture axis. Initial thunderstorms are likely to support .25-.5"/hr rates as the mid-levels fully saturate. However, deep layer steering is very weak at the periphery of that outflow channel to the north; this supports effective bulk shear of 20-25kts across the central border of AZ/NM, so there may be slightly better organization to support multiple up/down draft cycles. Deep layer steering is weak at 5-10kts with south-southeast propagation at 0-5kts, so slow motions should allow for increased duration. As the afternoon goes, the stronger heating and therefore updrafts that are spurred on by outflow boundary collisions by the first few rounds may support rates of 1-1.5"/hr and spots of 1-2" totals. Coverage should be scattered to numerous in nature today, though equal areas are likely to miss out given the expected small to middle size updraft widths. NASA SPoRT 0-40cm soil saturation ratios are in the 90th percentile plus across the area of concern. However, areas of Catron, W Sacorro, central Cibola and S Apache county have seen well above average moisture as soil saturation values are well above that percentile with ratios over 55% and spots of 75-80% suggesting limited further infiltration in areas of deeper soil, but also rain should fall on barren rock areas as well, so give this, there will likely be multiple incidents of flash flooding though highly localized in nature through 00z. Gallina ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...ABQ...EPZ...FGZ...PSR...TWC... ATTN...RFC...CBRFC...WGRFC...NWC... LAT...LON 36670690 36110600 35160640 34130671 33100711 32010782 31240815 31200955 31261131 31851174 33551160 34901213 35571074