Mesoscale Precipitation Discussion 0074 NWS Weather Prediction Center College Park MD 510 PM EST Wed Feb 28 2024 Areas affected...South-Central to Southeast AZ...Southwest NM Concerning...Heavy rainfall...Flash flooding possible Valid 282210Z - 290410Z SUMMARY...Scattered bands of heavy showers and thunderstorms with locally heavy rainfall rates may foster an isolated concern for runoff problems and flash flooding going into the evening hours. DISCUSSION...The latest GOES-W visible satellite imagery in conjunction with dual-pol radar has been showing an uptick in the coverage of convection across areas of south-central to southeast AZ. A relatively strong and compact mid-level low center/trough is seen gradually ejecting east-northeast out of far northwest Mexico, and strong dynamical forcing/divergent flow aloft coupled with the diurnal heating cycle has been favoring the expansion of convection and increase in rainfall rates over the last couple of hours. MLCAPE values across southern AZ have risen to as much as 500 J/kg, and there are pockets of locally stronger moisture convergence in place that are seen helping to facilitate some loosely organized bands of convection around the eastern flank of the mid-level low center. The visible satellite imagery downstream of the current activity involving especially southeast AZ has been reflecting an increasingly agitated CU/TCU field, and this is reflective of the increase in diurnally enhanced boundary layer instability. Despite the dry boundary layer profiles, the 12Z/18Z HREF guidance supports some localized 20 to 30 percent probabilities of seeing 1"+/hour rainfall rates with some of the stronger convective cells going through the 00Z to 03Z timeframe. The heaviest rates should tend gradually shift from south-central AZ into southeast AZ and southwest NM through early this evening. Given some of the uptick in convective organization and banded structures, some spotty storm total amounts of 1.5 to 2.5 inches cannot be ruled out in at little as 2 to 3 hours. These rainfall amounts may cause some isolated concerns for runoff problems and flash flooding, with the normally dry washes/arroyos in this case being the more sensitive areas to closely monitor. Orrison ATTN...WFO...ABQ...EPZ...FGZ...PSR...TWC... ATTN...RFC...CBRFC...WGRFC...NWC... LAT...LON 33760861 33240777 32530764 32010788 31530831 31310899 31190960 31201079 31441192 31771256 32461238 33021150 33690960Download in GIS format: Shapefile | KML
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