Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Apr 24 2023 08:17:20 FOUS30 KWBC 240817 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 416 AM EDT Mon Apr 24 2023 Day 1 Valid 12Z Mon Apr 24 2023 - 12Z Tue Apr 25 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF SOUTH FLORIDA AND THE NORTHERN KEYS... A weakening cold front will settle across the southern portion of the FL peninsula today, then become stationary. This feature will serve as a focus for more numerous diurnal thunderstorms across S FL today, aided by the sea/Gulf breezes and a weak upper level shortwave/vort lobe that will pivot across the area between 18-00Z. Sufficient deep-layer QG forcing, along with a moderately favorable thermodynamic profile (PWs increasing to 1.6-1.8 inches, mixed-layer CAPEs at least 1000-1500 J/Kg) will allow for locally intense rainfall rates of 1.5-2+ inches/hr and 3+ inches within 2-3 hours. All high-res CAMs show local QPF maxima between 3-6" within the outlook area, as the 00Z HREF indicates 40km neighborhood probabilities >70% of 12hr QPF exceeding 3", with probs peaking between 25-30% of 12hr QPF exceeding 5". Given the recent heavy rains, evidenced by the lower 1/3/6 hr FFG over S FL, along with top 1 meter soil moisture percentiles >90% of normal per NASA SPoRT, opted to hoist a Marginal Risk in anticipation of at least localized or isolated FF concerns. Hurley Day 2 Valid 12Z Mon Apr 24 2023 - 12Z Tue Apr 25 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PARTS OF SOUTHERN KANSAS INTO MUCH OF OKLAHOMA, THE RED RIVER VALLEY, AND THE ARKANSAS RIVER VALLEY... ....Central-Southern Plains to the Ozarks, Arkansas River Valley, and the ArkLaTex... A vigorous shortwave pivoting across the 4-Corners and southern Rockies on Day 2 will allow for a more difluent upper flow pattern downstream across parts of the Southern Plains east toward the Mid MS Valley. Deep-layer forcing ahead of this shortwave will be enhanced by lingering right-entrance region forcing from a 90-100+ kt upper level jet streak across the Mid MS Valley-OH Valley. The models (including some of the high-res guidance) continue to show a signal for rainfall totals in the 2-3" range with embedded higher totals, however there remains quite a bit of areal spread in terms of where convection will organize and propagate. Areal-average rainfall totals over the Slight Risk area thus may be a bit too high in some locations, while underestimating the potential elsewhere, leading to a continued rather broad risk area. One aspect where forecast confidence has increased is with respect to a western shift in the Slight Risk and Marginal Risk areas compared to yesterday's Day 3 ERO. However, the guidance continues to hint at a bi-modal distribution in the QPF, with one maxima located farther north (northeast OK into south-central-SE KS), likely associated with the best low-level FGEN from the aforementioned upper jet streak to the north, with a secondary maxima closer to the Red River. Regardless, given the noted environment conducive to heavy rainfall and the QPF totals, the potential for heavy rainfall has remained consistent while future hi-res guidance should help to narrow down any more specific adjustments to the location. ....Colorado Front Range into the Rocky Mountain Piedmont... A mid-upper level low will drop southeastward over the region as surface low pressure organizes over the southern Rockies-southern High Plains. This will bring anomalously moist SE-E flow into eastern Colorado. This will lead to a significant ramp up in low-level upslope flow during the day Tuesday along the Front Range, while after 16-18Z the CAMs show the character of the pcpn becoming more convective per simulated reflectivity and hourly QPFs as MUCAPEs climb between 200-600 J/Kg. All CAMs show hourly rainfall rates peaking around 0.75-1.25", with isolated Day 2 QPF totals of 2-4+ inches. Given the isolated nature of these higher amounts, any resultant impacts should be localized and limited to minor street flooding. In addition, as the upper-level low approaches, snow levels will likely quickly lower starting Tuesday evening from around 8000 feet to 6000 feet, bringing a changeover to snow for locations in the foothills and Palmer Divide and limiting the areal coverage of any continued excessive rainfall threat. 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!8oIuNiXYZn4f03W0zTCSMZM2vOzZyn1geVcwWh5GHSIa= v_tSK8akjtcVMWU-KM6yrVh-hHq0n116Npk4FiVmQFkmIp4$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8oIuNiXYZn4f03W0zTCSMZM2vOzZyn1geVcwWh5GHSIa= v_tSK8akjtcVMWU-KM6yrVh-hHq0n116Npk4FiVmSU7NCaM$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8oIuNiXYZn4f03W0zTCSMZM2vOzZyn1geVcwWh5GHSIa= v_tSK8akjtcVMWU-KM6yrVh-hHq0n116Npk4FiVmL-pyRkw$=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) .