Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jul 31 2023 08:20:35 FOUS30 KWBC 310820 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 419 AM EDT Mon Jul 31 2023 Day 1 Valid 12Z Mon Jul 31 2023 - 12Z Tue Aug 01 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE SOUTHWEST TO CENTRAL HIGH PLAINS, THE MID MISSOURI TO MID MISSISSIPPI VALLEYS, AND OVER PORTIONS OF THE FLORIDA PENINSULA... ....Southwest to the central High Plains... Above normal moisture will continue to be present across portions of the Southwest, particularly portions of Arizona today but also extending northward toward portions of the Central High Plains/Central Rockies. First, moisture anomalies peak near 2-3 standard deviations above normal today across portions of Arizona which combined with expected daytime heating/instability should produce higher coverage of storms and intensity compared to recent days. This is supported by the various CAMs and the 00Z HREF which shows peak 0.5" hourly total probabilities this afternoon at 60-80 percent from northern AZ into far southern UT. This raises the concern for isolated flash flooding for both urbanized areas and complex terrain. Across portions of Colorado and Wyoming, shower/thunderstorm activity is expected to be enhanced with approaching shortwave energy timing during the peak of the afternoon. Localized hourly totals up to 1-1.5" will be possible, especially by early evening as storms move east off the terrain into the foothills and Plains. ....Mid Missouri to the Mid Mississippi valley... Current convection across portions of the Plains early this morning will continue to move southeast in the northwest flow regime, rounding the periphery of the strong upper ridge axis centered over Texas. This activity will move along/northeast of a stalled frontal boundary in the region and act on the southwesterly low-level jet with upwards of 30-35 kts of inflow at 850 mb. As the main complex of storms moves southeast, additional convection is likely to develop ahead of it across portions of far eastern KS and much of Missouri. Hourly totals exceeding 1" will be possible with the strongest cores this morning, resulting in a localized flash flood threat. Additional convection is expected to develop late this evening into tonight (early Tuesday morning) across portions of the region, as the low-level jet increases, and some of this rainfall may overlap, particularly across portions of northern MO as supported by the 24-hr HREF probabilities of 3"+ which reach 30-40 percent. The environment will be certainly conducive for training, highly efficient rain producing thunderstorms that could produce localized but higher totals. If the trends toward a higher end heavy rainfall threat continue to grow for tonight across central Missouri, an upgrade to Slight Risk could be needed. ....Eastern Florida Peninsula... Continued deep moisture present across Florida, characterized by precipitable water values exceeding 2" (near 1.5-2 standard deviations above normal) will interact with a stalled frontal boundary to the north to enhance the daily afternoon/evening thunderstorm coverage and intensity today. Hourly totals between 1-2" will be possible during the peak heating this afternoon/evening, supported by the 00Z HREF neighborhood probabilities for 2" in 1-hr peaking at 40-70 percent across the eastern Florida Peninsula. This supports the potential for localized flash flooding for mainly the urban locations. Taylor Day 2 Valid 12Z Mon Jul 31 2023 - 12Z Tue Aug 01 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF MISSOURI AND THE CENTRAL ROCKIES... ....Southwest to the northern High Plains... The anomalous deep monsoonal moisture begins to move out of the Southwest during the period, reaching further north into northern Utah, Wyoming, and northern Colorado. This will begin to limit the threat of flash flooding for portions of Arizona and Utah. However, shortwave energy lifting through the flow will bring another day of unsettled/active weather and the threat of intense rain rates and heavy rainfall, particularly for portions of Colorado and southern Wyoming where rain rates of 1-2"/hr may fall over recent burn scars and areas of relatively low flash flood guidance. ....Northern Plains... Localized heavy rainfall will be possible during the period as an axis of higher moisture surges ahead of an approaching front combined with favorable forcing and enough instability to produce localized intense thunderstorms that may lead to a few instances of training thunderstorms that could produce flash flooding. ....Mid Missouri to the lower Ohio Valley... Repeating shortwave energy rounding the periphery of the strong upper ridge axis centered over Texas will keep an active pattern in place from portions of the Plains through the Mid Missouri to Mid Mississippi Valley. In the northwest flow regime, there is greater than normal uncertainty with how convection will develop and evolve but the guidance continues to suggest activity will be ongoing at the start of the period (Tuesday morning) across portions of southern Iowa into Missouri. Depending on how that plays out, additional convection may develop later in the period, followed by another round of overnight convection into early Wednesday morning. Each round could produce locally heavy rainfall and intense rain rates, and the nighttime convection has the synoptic setup that bears watching for localized intense rain rates and training convection that could produce localized higher rainfall totals. As a result, with growing support from the 00Z deterministic and ensemble guidance, a Slight Risk was introduced this cycle. Taylor Day 3 Valid 12Z Tue Aug 01 2023 - 12Z Wed Aug 02 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE MID MISSISSIPPI VALLEY, GREAT BASIN, AND CENTRAL ROCKIES... ....Mid Mississippi Valley... Another complex of thunderstorms is likely to be ongoing at the start of the period (Wednesday morning) across the outlook area, associated with shortwave energy moving within the northwest flow regime, generally along/east of a quasi-stationary frontal boundary draped in the region, and interacting on the nose of the nighttime southwesterly low level jet that is expected to reach 30-40 kts at 850 mb. Precipitable water values are likely anomalous, 2 standard deviations above normal, helping to fuel the intense rain rates. Then another round of thunderstorms will be possible late in the period (early Thursday morning) developing on the nose on the increasing low level jet again over portions of eastern MO, southern IL, and southwest KY. The synoptic setup will remain conducive for training/backbuilding convection and this would likely be the third consecutive day of potentially overlapping rainfall events, so the cumulative totals may begin to saturate some soils and heighten the flash flood risk. The 00Z deterministic and ensemble guidance shows potential for higher rainfall this period compared to today and Tuesday, and as the mesoscale details become clearer in the next couple of days, some localized higher rainfall totals may materialize somewhere in the region. ....Great Basin to North/Central Rockies and High Plains... Widespread showers and thunderstorms are expected Wednesday into Wednesday night aided by shortwave energy and right entrance dynamics with a strengthening jet streak over the northern Rockies. Moisture will very anomalous, upwards of 1-1.25" of precipitable water and nearly 3 standard deviations above normal, based on the latest model guidance and with the daytime heating and terrain influences, localized intense rain rates exceeding 0.5"/hr will be possible. The 00Z guidance continues to highlight portions of eastern Idaho, western Wyoming, and northern Utah with the grater probabilities of seeing the higher rainfall totals as well as portions of Colorado and southeast Wyoming where Slight Risks were maintained from the previous forecast cycle. Taylor Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_wVbodR2IxurfyjVmujQfZ-PFpJPcbP_xxOUlCh6pAW1= yWyTBnZFAb3Fx8huRhqwui0tebpZORL1Q0BQWFEgqZYr4ww$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_wVbodR2IxurfyjVmujQfZ-PFpJPcbP_xxOUlCh6pAW1= yWyTBnZFAb3Fx8huRhqwui0tebpZORL1Q0BQWFEgzZtL16M$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_wVbodR2IxurfyjVmujQfZ-PFpJPcbP_xxOUlCh6pAW1= yWyTBnZFAb3Fx8huRhqwui0tebpZORL1Q0BQWFEg7h-flSQ$=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) .