Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Apr 26 2023 08:14:32 FOUS30 KWBC 260814 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 413 AM EDT Wed Apr 26 2023 Day 1 Valid 12Z Wed Apr 26 2023 - 12Z Thu Apr 27 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE SOUTHERN PLAINS INTO THE ARKLATEX, ARKANSAS RIVER VALLEY, AND SOUTHERN OZARKS... ....Central-Southern Plains to the Ozarks, Arkansas River Valley, ArkLaTex, and Lower Mississippi Valley... The closed mid/upper level low is expected to push out into the southern Rockies and High Plains this morning, then across central-eastern OK Thursday morning. With a stationary boundary draped across the region, southerly flow surging northward anomalous moisture will overrun this boundary and is expected to produce rounds of convection that track eastward across portions of southern Oklahoma and northern Texas early in the period before additional convection forms along the dryline across portions of Texas later in the day into the evening/overnight hours. The 00Z guidance, including the HREF, continues to show a bi-modal distribution of heavier QPF: one area across central-eastern OK, owing to stronger deep-layer forcing (upper divergence and low-level FGEN within the right-entrance region of the upper jet streak across the Midwest), with another area north of Austin Metro into North TX, the Piney Woods, and ArkLaTex closer to the track of the surface warm front/triple point where more robust deep-layer instability can be tapped. In addition, the strong low-mid layer shear (both speed and directional) would favor forward propagating convection and thus limit the risk of cell training, at least for a prolonged period of time. Given the progressive shortwave track, degree of deep-layer shear, and bi-modal distribution with the QPF maxima, per collaboration with the WFOs we felt that an upgrade to Moderate Risk within the broad Slight Risk was not warranted at this time, and that any potential upgrade to a Moderate with subsequent updates to the Day 1 ERO will be highly dependent on the heavy rainfall evolution this morning associated with the elevated convection, as FFGs may lower considerably in some areas before possibly getting clipped by the next round(s) of stronger convection later today. Within the Slight Risk area, the CAMs show max QPFs of 3-5+ inches, with 00Z HREF probabilities of 40-50% in central-eastern OK and 50-70% across northeast TX for >3" totals over the 24-hr period. Hurley/Taylor Day 2 Valid 12Z Wed Apr 26 2023 - 12Z Thu Apr 27 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PARTS OF EASTERN LOUISIANA INTO SOUTHERN MISSISSIPPI-ALABAMA AND THE FLORIDA PANHANDLE... The closed low ejecting out of the Colorado Rockies begins to open up as it tracks through the Southern-Central Plains and Mid-MS Valley Thursday-Thursday night, with multiple embedded vort lobes helping to provide large scale forcing for ascent across the outlook area. Deep layer southwesterly flow will bring up anomalous moisture, with 850-700 mb moisture flux anomalies between 2-2.5 standard deviations above normal per the GEFS and SREF. As the primary surface low lifts through the Ohio Valley, another area of low pressure is expected to form off the North Carolina coast. Overall, the convection that is expected to develop should be more on the progressive side, helping to limit the intense rain rates and overall duration. For this reason, the risk area remains capped at Marginal over much of the outlook area, where broadly he system will become increasingly progressive with generally lower duration potential for heavy rainfall. However, the exception will be along the Gulf Coast from the New Orleans area east to near Tallahassee, where higher available PW (1.7 to 1.8") along with greater deep-layer instability (MUCAPEs 1000-2000 J/Kg) will allow for more intense short-term rainfall rates on Thursday, i.e. 2-3"/hr, with multiple rounds of convection along/south of the surface warm front and ahead of the approaching cold front. Within the Slight Risk area, the 00Z HREF indicates a broad area of 60-90+ percent probabilities that 24hr QPF will exceed 3", with a smaller area of 40-70% probabilities of exceeding 5". Hurley 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!5dF3U5YCWdiX70ATTSRzQyicrMXk6Cp-AH0GvffGvKiO= T_trolFvWIoM06edrTlAhJIgTQkNM61X7tXj9FgxFrCHGE0$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5dF3U5YCWdiX70ATTSRzQyicrMXk6Cp-AH0GvffGvKiO= T_trolFvWIoM06edrTlAhJIgTQkNM61X7tXj9FgxwEzMvYg$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5dF3U5YCWdiX70ATTSRzQyicrMXk6Cp-AH0GvffGvKiO= T_trolFvWIoM06edrTlAhJIgTQkNM61X7tXj9Fgx6SOr9NI$=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) .