Mesoscale Precipitation Discussion 1032 NWS Weather Prediction Center College Park MD 505 AM EDT Wed Sep 18 2024 Areas affected...Central MT Concerning...Heavy rainfall...Flash flooding possible Valid 180905Z - 181505Z SUMMARY...Heavy rainfall is expected to become more concentrated going through dawn and the early morning hours across portions of central MT. Generally this setup will favor an areal flood threat, but around any burn scar locations, there will be a more enhanced runoff concern with potential for localized flash flooding. DISCUSSION...A deepening upper-level trough and associated area of low pressure lifting up across the northern High Plains will be driving a rather impressive heavy rainfall event beginning early this morning across central MT. Facilitating this will be the evolution of a well-defined TROWAL working in tandem with an increasingly focused area of deep layer frontogenesis along with a strong mid-level deformation zone. This should yield enhanced forcing to help concentrate the heavy rainfall threat in time which will also include an increase in rainfall rates. Gradually the heavy rainfall axis should tend to become oriented in a general south-southwest to north-northeast fashion around the northwest flank of the deepening 500/700 mb mid-level low center and where frontogenetical forcing will be the strongest. However, there is already a fair amount of instability attempting to wrap westward around the north side of the deepening low, and there will likely be a corridor of elevated convective elements that will help drive locally heavier rainfall rates early this morning. The 00Z HREF guidance and recent runs of the HRRR suggest as much as 2 to 4+ inches of rain may fall through the early morning hours (15Z/9AM MDT), with some occasional rainfall rates that may reach upwards of 0.75" to 1"/hour with some of the stronger convective elements that materialize. These rains are expected to gradually drive an areal flood threat, which may also include a threat for localized flash flooding around any burn scars that receive some of these heavier rainfall rates. Orrison ATTN...WFO...BYZ...GGW...TFX... ATTN...RFC...MBRFC...NWC... LAT...LON 49270843 48780760 47520767 46370826 45740926 45751071 46221151 47041177 47821154 48601088 49220976Download in GIS format: Shapefile | KML
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