Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Feb 08 2023 20:10:04 FOUS30 KWBC 082010 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 309 PM EST Wed Feb 08 2023 Day 1 Valid 16Z Wed Feb 08 2023 - 12Z Thu Feb 09 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF ARKANSAS AND SOUTHEASTERN MISSOURI... A Slight Risk area has been maintained for the Day 1 ERO update, primarily encompassing much of Arkansas from the southwest to northeast corners of the state as well as into southeastern Missouri (along with some small portions of adjoining states). Showers and thunderstorms are ongoing this morning in the ArkLaTex region, and the relatively slow forward speed of the main upper trough as it lifts northeastward (and gradually takes on a negative-tilt) is expected to lead towards a distinct QPF maxima (per WPC) of 2-4 inches (centered over northern AR). Deep layer southerly flow ahead of the trough will facilitate these precipitation totals, as tropospheric moisture levels are in the process of broadly increasing across the MS/OH Valleys, which should result in precipitable water values peaking as high as 1.3-1.7 inches (from 1.0-1.4 inches early this morning) across the outlook area. For many of the impacted locations, these PW values are just under the maximum daily moving average according to SPC's sounding climatology page. This increased tropospheric moisture, along with strong lift and sufficient instability (MUCAPE of 500-1500 J/kg), will result in multiple rounds of heavy rainfall across the Slight Risk area (with only one distinct round of more progressive convection farther south in LA/MS). Soils throughout the much of central/southern AR and northeast TX are already primed this morning from ongoing rainfall, meaning any rainfall rates to exceed 1"/hr could create localized flash flooding concerns. Meanwhile, 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). These drier soils (along with a lack of instability) will likely preclude meaningful coverage of any flash flooding well north of the AR/MO border, but strong frontogenetic forcing may still allow for an isolated occurrence or two of meaningful runoff into portions of southeast/central MO and southern IL. Farther south across LA/MS, any instances of flash flooding should remain rather isolated given the progressive nature of the convection (with 0-6 km shear on the order of 40-60 kts). The 12z suite of CAM guidance reinforces the above information and forecast QPF. Rainfall rates locally exceeding 2"/hr are most likely throughout LA and MS this afternoon and evening as convection develops ahead of an advancing cold front and within an area of surface-based CAPE greater than 1500 J/kg (according to the 12z HREF). However, the quick-moving nature of these storms while limit the flash flood potential after a very brief period of potential training between 21z and 00z over northeast LA. Rainfall rates should remain rather tame across AR into the Mid-Mississippi Valley and lower Ohio Valley within the mostly stratiform rain to the north of the warm front, although widespread rainfall totals by Thursday morning will likely add up to over an inch from northeast Texas to southern Illinois. The better potential for rainfall rates to exceed 1"/hr will be along a lifting warm front that is forecast to mainly stretch from north-central AR to southeast MO, which is included in the Slight Risk. Churchill/Snell Day 2 Valid 12Z Thu Feb 09 2023 - 12Z Fri Feb 10 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE WESTERN FLORIDA PANHANDLE, SOUTHERN ALABAMA, AND WESTERN GEORGIA... A Marginal Risk of excessive rainfall has been maintained for the western FL Panhandle, southern AL, and portions of western GA for the Day 2 ERO update, mainly due to a stalling cold front moving into the region. High tropospheric moisture levels are expected ahead of the front, as indicated by HREF mean precipitable water values of 1.3-1.6 inches (well above the 90th percentile per TLH sounding climatology). The presence of sufficient instability (MUCAPE of 250-750 J/kg, per the HREF) will increase the potential for heavy rainfall, with rainfall rates locally approaching 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 2" exceedance as high as 15-25%). 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 realizing any isolated flooding impacts. A more impressive surge of moisture is expected by the very end of the period near 12z on Friday as an approaching upper-level low diving into the Lower Mississippi Valley funnels moisture along a strengthening mid-level convergence axis extending into the Southeast. This potential will be monitored for any potential upgrade (most likely needed for the Day 3 time frame), but could bleed into the Day 2 period. Churchill/Snell Day 3 The Day 3 outlook will be updated by 2030Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_A0trTrvYWN-ITARGLj9fM-CXAh_qYZWydiN84jytSoT= db-6LxfVcc6shIjmhNoZSTfnbOM51cOMz_0xP7dQm9ZbdnI$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_A0trTrvYWN-ITARGLj9fM-CXAh_qYZWydiN84jytSoT= db-6LxfVcc6shIjmhNoZSTfnbOM51cOMz_0xP7dQQnTKVkc$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_A0trTrvYWN-ITARGLj9fM-CXAh_qYZWydiN84jytSoT= db-6LxfVcc6shIjmhNoZSTfnbOM51cOMz_0xP7dQq2yhLwk$=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. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .