Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Feb 02 2023 20:26:28 FOUS30 KWBC 022026 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 325 PM EST Thu Feb 02 2023 Day 1 Valid 16Z Thu Feb 02 2023 - 12Z Fri Feb 03 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY INTO CENTRAL GEORGIA... 16Z Excessive Rainfall Outlook Discussion... Made a few adjustments to the boundary of the on-going Marginal risk to better fit the 1 inch and 2 inch rainfall contours of rainfall in the GEFS and SREF spaghetti plot. That lines up with the mid-morning trends in radar. With the front still so far south of the area...very little instability should limit coverage of the best rainfall rates. However...some frontogenesis associated with the mid level forcing appears could result in isolated areas with somewhat higher rainfall rates and appears to be behind a stripe of locally higher amounts ending at 15Z. Still feel that a Marginal is sufficient given the antecedent conditions. Additional updates may be made later this afternoon to clear areas once the upper trough passes and cold advection commences. Bann ....0830Z Excessive Rainfall Outlook Discussion... Antecedent saturated soil conditions due to consistent parade of storms over the last few weeks have been highlighting the concern for the potential for showers and thunderstorms to present an elevated risk for excessive rainfall and flash flooding has highlighted within prior day's Excessive Rainfall Outlook discussions. Soil conditions (per NASA SPoRT-LIS products) are not much improved with soil moisture values running above normal particularly across much of LA into MS as well as increased streamflows noted in USGS gauges, warranting a one category bump in risk. However, the prior Slight Risk was predicated on stronger cells and available instability and moisture flux convergence to drive stronger cells and higher rainfall totals across this region.=20=20=20=20 00z model cycles along with satellite and observational trends has seen the shortwave trof over the Southwest continue to shear into the confluence zone across Texas into the Tennessee Valley with reduced amplification. This, in turn, has further reduced the strength of the return Western Gulf low level jet. While there is a narrow window just crossing the 02.12z time barrier into early morning for enhanced isentropic ascent and moisture convergence to develop some broken area of showers and weak thunderstorms, the reduced upslope flow has tempered moisture flux convergence and advection of unstable air northward as in prior guidance cycles.=20 While some guidance suggests thunderstorms capable of 1"/hr, most have trended away with 00z HREF probability of 1"/3hr falling below 40% throughout the time period with max values across S LA into SW MS. Given this is concurrent with the most saturated ground conditions, there was some weak potential for maintaining a small Slight Risk across this area. However, in coordination with local forecast offices, the limited coverage and forward progression of cells that would develop would be scattered enough to be better suited for a Marginal Risk. Additionally, the Marginal Risk from prior cycles was trimmed southward and narrowed across MS/AL into central GA. There is increased convergence in model guidance toward the axis of prolonged light to moderate over-running precipitation throughout the day with areal averages of 1-1.5" possible. Consideration for saturated ground conditions across NW LA to broaden the Marginal ever so slightly relative to downstream locations across E GA into SC, where the Marginal Risk was removed given better soil conditions and lower rainfall rates. Gallina Day 2 Valid 12Z Fri Feb 03 2023 - 12Z Sat Feb 04 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Bann Day 3 Valid 12Z Sat Feb 04 2023 - 12Z Sun Feb 05 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9At8NdVZ_F7yo15J0fJAuIwjN0GoYqoOC8wRuNOwdf93= 2066CHWOLsPdNTFE0p_TTKSAYYYOXMoKnQaGjn6gbCkWxXI$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9At8NdVZ_F7yo15J0fJAuIwjN0GoYqoOC8wRuNOwdf93= 2066CHWOLsPdNTFE0p_TTKSAYYYOXMoKnQaGjn6gpiPcv8g$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9At8NdVZ_F7yo15J0fJAuIwjN0GoYqoOC8wRuNOwdf93= 2066CHWOLsPdNTFE0p_TTKSAYYYOXMoKnQaGjn6gscmYsrY$=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) .