Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Feb 07 2023 08:30:03 FOUS30 KWBC 070829 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 328 AM EST Tue Feb 07 2023 Day 1 Valid 12Z Tue Feb 07 2023 - 12Z Wed Feb 08 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS NORTHWESTERN ARKANSAS, SOUTHEASTERN OKLAHOMA, AND PORTIONS OF NORTH TEXAS... A positively-tilted trough will eject from the Four Corners region today, interacting with a jet streak over the Ohio Valley that will strengthen to near 130 kts by late Tuesday/early Wednesday. Deep southerly flow ahead of this system will bring in high levels of tropospheric moisture, characterized by precipitable water values of over 1.25 inches (between 2 and 2.5 standard deviations above the climatological mean). This, combined with strong lift and instability (MUCAPE of up to 1000 J/kg), could result in intense rainfall rates of over 2"/hr at times. Deep layer flow being nearly parallel to expected storm motions may also lead to repeated rounds and training of heavy rainfall locally (with the best odds of this occurring in the Slight Risk area, where HREF 40 km neighborhood probabilities for 3" exceedance are has high as 30-40%). It is also worth noting that NASA SPoRT 0-40 cm relative soil moisture values remain above the 80th or even 90th percentile of climatology locally across portions of eastern TX and southern AR, with 7-day precipitation departures as high as 300-600 percent of normal across much of northern and eastern TX (while soils are drier overall across most of OK and northern AR, as low as the 10-20th percentile). Churchill/Bann Day 2 Valid 12Z Wed Feb 08 2023 - 12Z Thu Feb 09 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL MAINLY OVER NORTHERN ARKANSAS AND SOUTHERN MISSOURI... A Slight Risk area has been maintained for the new Day 2 outlook, primarily covering northern Arkansas and southern Missouri (with a small portion in adjoining states). Models continue to show a relatively slow forward speed of the main upper system as it lifts northeastward and takes on a negative-tilt, leading to increased overlap of QPF on Days 1 and 2. The overall setup and forcing remains similar to Day 1, with deep layer southerly flow ahead of the trough increasing tropospheric moisture levels across the MS/OH Valleys, resulting in precipitable water values reaching as high as 1.5-1.8 inches. This increased moisture, along with strong lift and sufficient instability (MUCAPE of 500-1000 J/kg), will result in the potential for heavy rainfall, with areal average rainfall amounts expected to range from 1-3" across the Slight Risk area (and locally up to 3-4 inches in the best overlap areas on Day 1). NASA SPoRT data shows elevated 0-40 cm relative soil moisture values across portions of the Lower MS Valley (as high as the 80-90th percentile across southern AR), while soil moisture values in the Middle MS and OH Valleys are well below normal (as low as the 10th percentile across portions of southern MO/IL/IN and western KY). Churchill/Bann Day 3 Valid 12Z Thu Feb 09 2023 - 12Z Fri Feb 10 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE FLORIDA PANHANDLE AND SURROUNDING PORTIONS OF ALABAMA AND GEORGIA... A Marginal Risk of excessive rainfall has been introduced for the Florida Panhandle and surrounding portions of AL and GA for the new Day 3 outlook, mainly due to a stalling cold front moving into the region. High tropospheric moisture levels are expected ahead of the front, as indicated by GFS progged precipitable water values of 1.5"+. The presence of sufficient instability (MUCAPE of 500-1000 J/kg) will increase the potential for heavy rainfall, with rates possibly exceeding 2"/hr at times. The possibility of repeating rounds of heavy rainfall is also expected, increasing the threat of excessive runoff potential (with ECENS probabilities for 3" exceedance as high as 5% locally). However, antecedent soil conditions in the region are quite dry, with NASA SPoRT 0-40 cm soil moisture values indicated to be as low as the 10-20th percentile. This should significantly limit the areal extent of any flash flooding, with poor drainage/urban areas the most at risk of realized isolated flooding impacts. Churchill Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4kXCp-vsCqg7-ePTtcF8MXOthqwknCaF3f4pEfxt9fFD= 1B7Ut1jwTZ6WzPSe6pVAFg1ey3U02fr7bb-F5-p9tjC6TZQ$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4kXCp-vsCqg7-ePTtcF8MXOthqwknCaF3f4pEfxt9fFD= 1B7Ut1jwTZ6WzPSe6pVAFg1ey3U02fr7bb-F5-p9HNs4ECo$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4kXCp-vsCqg7-ePTtcF8MXOthqwknCaF3f4pEfxt9fFD= 1B7Ut1jwTZ6WzPSe6pVAFg1ey3U02fr7bb-F5-p9k-LTXLU$=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. 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