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From | To | Subject | Date/Time | |||
Mike Powell | All | HVYRAIN: Excessive Rainfa |
September 11, 2024 8:34 PM * |
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FOUS30 KWBC 120053 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 853 PM EDT Wed Sep 11 2024 Day 1 Valid 01Z Thu Sep 12 2024 - 12Z Thu Sep 12 2024 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF LOUISIANA AND SOUTHERN MISSISSIPPI... ...Southeast... Francine has come inland over southern Louisiana but continues to show a healthy circulation approaching the greater New Orleans areas. Though some dry air has disrupted part of the core, intense rainfall rates of 2-3.5"/hr are shown per MRMS, with storm totals over 7 inches in south central LA. Rainfall tapers off notably to the southwest of the center. Will maintain the Moderate Risk area near the path of the center overnight given the likelihood of high rainfall rates to continue as additional moisture is drawn in off the Gulf across into southeastern LA and southern MS. The New Orleans metro area will bear the brunt of the rainfall this evening before translating northward, with the inflow band off to the east responsible for the eastward bump in the outline. Francine will continue inland overnight where the threat for excessive rainfall extends northward trough much of Mississippi. Removed much of the rest of Florida that was in a Marginal risk as lingering activity should be diminishing over the next couple of hours. ...Intermountain West... A deep layer cyclone moving across the northern Continental Divide has brought afternoon convection and some flash flooding to parts of Idaho into western Montana. Precipitable water values are sufficient for heavy rain-related issues (0.75", and the Slight Risk area remains for portions of western MT and just into west- central ID overnight. Hourly rainfall rates of 0.50-1.00" have been observed and/or shown via MRMS which have been enough to reach generally low FFG values in areas of complex terrain. With earlier rainfall soaked in, additional rainfall may still exceed FFG values overnight, but did trim off the western side of the risk area as the focus should be mostly over western MT tonight closer to the frontal boundary. Fracasso Day 2 Valid 12Z Thu Sep 12 2024 - 12Z Fri Sep 13 2024 ...A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF THE MID-SOUTH & SOUTHEAST... ...Mid-South/Southeast... 21Z update... The latest guidance favored a general south/southeast trend with the QPF footprint associated with Francine from the previous cycle. As such, this resulted in WPC increasing amounts across eastern Tennessee, northern and central Mississippi, and northern and central Alabama. This uptick increased the threat for excessive rainfall and flooding concerns for both rural and some major metropolitan areas. The Slight Risk area was trimmed a little eastward across eastern Arkansas but also expanded to the south and east to encompass more of central Mississippi, central Tennessee, and west-central and eastern Alabama. The latest guidance also suggested an increase in feeder band convection across the Florida Panhandle thus the Marginal Risk area was extended 1-2 counties to the south. Campbell Francine is expected to be fully extratropical, with a well- developed comma head and trailing front. Guidance suggests that MU CAPE will be modest, 250-500 J/kg. Effective bulk shear should continue to be sufficient for convective organization where enough instability develops/exists. Precipitable water values remain near 2", so hourly rain totals up to 1-2" should be possible, which would be most problematic in urban areas and initially beneficial elsewhere. This region has been quite dry lately. With the volume of rain expected, and the concept of this being on the cusp of a flash flood and longer duration flood event, kept the Slight Risk area which showed minimal change from continuity. Across the Southeast, there is a risk of training convection along Francine's cold front which shows a greater signal for excessive rainfall overnight. Broadened the risk area to encompass the possible training rain band, as enough moisture, instability, and possible stalling to be concerned about hourly rain totals to 3". ...Western MT, Idaho Stovepipe & Vicinity... 21Z update... Multiple impulses within the flow will trigger showers and thunderstorms that will track across the Northern Rockies region. PW values around 0.50-0.75 inches will be pooled over the region throughout this period and will bolster rainfall efficiency wit each passing impulse. Per the CAM guidance any of these storms will be capable of producing periods of moderate to heavy rainfall as they pass over the favored upslope areas and then exit into the adjacent High Plains. There was a trend for increasing QPF coverage and amounts across portions of the Hi- Line. The Slight Risk area was expanded eastward to now include more of north-central and northeast Montana and southwestward to extend into portions western Montana and into Idaho. Campbell One or two surface lows are expected to lift northward this period through MT, drawing in sufficient upslope flow, moisture, and instability from the east to be concerned about the potential for organized convection. The Slight Risk raised by continuity has been maintained across portions of western MT. Hourly rainfall rates may intensify up to 2 inches/hour during this period, with a few isolated locations possibly accumulating up to 4 inches by the end of the day. Roth/Campbell --- SBBSecho 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (618:250/1) |
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