Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Jul 18 2023 07:31:48 FOUS30 KWBC 180731 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 331 AM EDT Tue Jul 18 2023 Day 1 Valid 12Z Tue Jul 18 2023 - 12Z Wed Jul 19 2023 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE MID MISSISSIPPI VALLEY, LOWER OHIO VALLEY AND LOWER TENNESSEE VALLEY... ....Lower Missouri Valley, Mid Mississippi Valley into the Lower Ohio and Lower Tennessee Valleys... Models continue to show the potential for a narrow axis of very heavy rainfall amounts, especially in the 0000-1200 UTC Wednesday period from the Lower Missouri Valley/Mid Mississippi Valley/Lower Ohio Valley and Lower Tennessee Valley region along and to the north of the expected west to east oriented frontal boundary across these areas. There is model consensus on two rounds of precip to affect areas from the Lower Missouri Valley/Mid Mississippi Valley/Lower Ohio Valley into the Lower Tennessee Valley region during the upcoming day 1 period. An initial round of convection firing early day 1 ahead of a vort moving east southeast from the Central Plains into Missouri. Model consensus is that this initial organized area of convection will be fairly progressive to the southeast across the risk area during the day time hours of Tuesday. This would then be followed by a second round of greater training potential convection sometime in the 0300 to 1200 UTC Wednesday period when the low level inflow into the front attains a more westerly component, increasing the potential for back building and downstream training of convection=20 While there is general agreement in this scenario, there are some fairly significant differences in where the training episode will set up. The FV3LAM is the farthest north across southern IL/far southwest IN into west central KY and east central TN. In contrast the NAM NEST has the training axis from southeast MO, across far southern IL, western KY into north central TN. The ARW2 and HRRR from 0000 UTC are closer to the farther southern solutions. Given the spread in the locations of the training convection portion of the day 1 precip event, the slight and moderate risk areas were broadened and expanded to the south into central to western TN, while the northern portions of the risk areas were trimmed across northeast MO into south central IL. The new moderate risk area axis fits well with the latest max HREF neighborhood probabilities for 2 and 3"+ amounts and the Ensemble Agreement Scale (EAS) max axes for 1 and 2"+ amounts. Max precip amounts in the latest guidance continues to show 5-8"+ amounts.=20 These totals seem reasonable given the potential for two rounds of convection and the potential for the training episode in the early hours of Wednesday. This scenario is one where a high risk may be warranted, but given the spread in the area of best training early Wednesday morning, we will hold off for the time being and re-access with the 1200 UTC Tuesday hi res runs. ....Northeast... No significant changes made to the marginal and slight risk areas from the previous outlook across the Northeast. The slow moving front currently over the eastern Great Lakes region will begin to push more quickly eastward day 1 across the Northeast. A narrow axis of above average PW values in the 1.5-1.75"+ range expected along and ahead of this front. These values will be lower than PW values with the heavy rainfall event on Sunday as that anomalous PW axis has moved well off the northeast coast. Additional convection likely to stretch along this front on Tuesday, supporting locally heavy rainfall totals from in the vicinity of northern NJ/eastern NY State, northeast through western and northwestern New England. The slight risk area fits well with the HREF neighborhood probabilities for 1 and 2" amounts. The 1"+ probabilities are high 60-90% in the slight risk area, with probabilities for 2"+ amounts in the 30-80% range but in a more narrow axis. There will be some overlap with heavy rains on Sunday and day 1 expected heavy axis from southeast NY State into northwest CT and western MA and east central NH. Much of the remainder of the heavy rains on Sunday farther to the southeast over southeast New England will remain to the southeast of the day 1 expected qpf axis. ....Southwest into the Southern Great Basin... Widespread monsoonal convection possible day 1 across portions of the Southwest, northward into the southern Great Basin. An axis of more anomalous PW values expected to rotate eastward on the north side of the persistent southwest upper ridge across portions of NV into western CO, supporting scattered slow moving convection across these areas. HREF probabilities do show 40-60% probabilities of .50"+ amounts here and over portions of southeast AZ. This could produce some isolated runoff issues, especially across any burn scar regions or slot canyons. Oravec 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!5PFLKNG84p8o2cXDyeJcOB3DYcF2fevmwqlf_66Xrz11= _xD3g8exGHl64mdl1OzV_UVZr6GKgkxNa_2mC6HW3-F5vas$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5PFLKNG84p8o2cXDyeJcOB3DYcF2fevmwqlf_66Xrz11= _xD3g8exGHl64mdl1OzV_UVZr6GKgkxNa_2mC6HWID4JwVA$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5PFLKNG84p8o2cXDyeJcOB3DYcF2fevmwqlf_66Xrz11= _xD3g8exGHl64mdl1OzV_UVZr6GKgkxNa_2mC6HWaPjuVKU$=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) .