Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Mar 03 2023 08:30:14 FOUS30 KWBC 030830 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 329 AM EST Fri Mar 03 2023 Day 1 Valid 12Z Fri Mar 03 2023 - 12Z Sat Mar 04 2023 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FROM NORTHEASTERN ARKANSAS NORTHEAST INTO SOUTHEASTERN MISSOURI, SOUTHERN ILLINOIS, AND CENTRAL INDIANA... A complex synoptic and mesoscale pattern will continue to evolve overnight and throughout the day Friday into early Saturday morning as a potent, negatively tilted mid to upper-level shortwave moves northeastward from the Southern Plains towards the Midwest and eventually the Northeast. At the surface, an area of low pressure will better organize/consolidate over the ArkLaTex early Friday morning and deepen rapidly as the system occludes, moving northeastward through the Middle Mississippi and Ohio Valleys and eventually to the Lower Great Lakes by Saturday morning. A cold front will sweep eastward across the South and Tennessee/Ohio Valleys as the warm sector expands northward behind a warm front pushing across the Ohio Valley, Appalachians, and Mid-Atlantic. Deep moisture transport northward from the Gulf will be quite robust with a strong 65-75 knot low-level jet leading to anomalously high PW values upwards of 2-3 standard deviations above the mean, particularly where convergence is maximized along the track of the surface low/occluding front through the Middle Mississippi and Ohio Valleys. Multiple areas of heavy rainfall are expected as storms progress to the northeastward throughout the day, with the focus on the Mississippi and Ohio Valleys. In coordination with MEG/PAH/ILX/IND/LMK, a Moderate Risk has been introduced for portions of the Lower/Middle Mississippi and Ohio Valleys from northeastern Arkansas to central Indiana. While CAPE values will be relatively low ( ~ 500 J/KG ) for the expectation of heavy rainfall rates, the combination of strong mid to upper-level dynamic forcing, the rapidly deepening cyclone, convergence along the occluding surface fronts, and significantly anomalous surface moisture will compensate to produce a period of intense rainfall following the surface low track. Multiple Hi-Res guidance members including the HRRR, FV3-LAM, and HRW-ARW2 have a strong signal for areal average rainfall totals of 3-5 inches, with the bulk of this rainfall occurring over a relatively short frame given the system's rapid movement to the northeast. HRRR max hourly rainfall totals confirm the expectation of rainfall rates of 1-2" per hour. In addition, clusters of storms forming along and ahead of the surface fronts will have the tendency to train over the same regions as they track to the northeast. The expectatioin is these rainfall totals will easily exceed FFG values given already wet antecedent conditions and additional rainfall that will likely already have occurred overnight with convection extending north-northeastward along and to the north of the warm front moving into the Ohio Valley. While intense downpours and heavier areal average rainfall totals of 1-3" will continue further eastward into the Upper Ohio Valley later Friday afternoon, the decreasing coverage of advance rainfall along with the continued rapid system movement will lessen the areal coverage of impactful heavy rainfall in the Slight Risk area compared to further west. A couple rounds of rainfall are likely for the Mid-Atlantic both with a band of rain lifting northward ahead of the warm front and later along and to the east of the Appalachians as the cold front pushes through late Friday afternoon and into the early overnight hours Saturday. Some locally heavy rainfall totals of 1-2" will be possible as storms tend to track northeastward along the front, particularly for upslope favored areas along the Appalachians. There is less confidence in the coverage of impactful rainfall further south into the Tennessee Valley given the progressive nature of convection developing along the surface cold front. However, the Hi-Res guidance still does hint at the potential for some localized heavier downpours and with wet antecedent conditions in place, the Marginal Risk was maintained. Putnam Day 2 The Day 2 outlook will be updated by 0830Z. Day 3 The Day 3 outlook will be updated by 0830Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-fqa2akN87n04rtw06jcHgkAeHWnGVxlflYQW-erTVgW= zeyJTzK237mcdNifkL5Ftt5ufS2zbdTcp4uRLd5MI69qhkE$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-fqa2akN87n04rtw06jcHgkAeHWnGVxlflYQW-erTVgW= zeyJTzK237mcdNifkL5Ftt5ufS2zbdTcp4uRLd5MWV0rBps$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-fqa2akN87n04rtw06jcHgkAeHWnGVxlflYQW-erTVgW= zeyJTzK237mcdNifkL5Ftt5ufS2zbdTcp4uRLd5MqJfVl30$=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) .