Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Apr 25 2023 15:52:19 FOUS30 KWBC 251552 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1151 AM EDT Tue Apr 25 2023 Day 1 Valid 16Z Tue Apr 25 2023 - 12Z Wed Apr 26 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PARTS OF THE COLORADO FRONT RANGE INTO SOUTHERN KANSAS, MUCH OF OKLAHOMA, THE RED RIVER VALLEY, AND THE ARKANSAS RIVER VALLEY... 16Z Update: No significant changes were made to the risk areas from portions of the Colorado Front Range into the Central-Southern Plains and Ozarks with the meteorological reasoning below remaining valid for the risk areas. The 12Z HREF neighborhood probabilities continue to suggest potential for hourly totals approaching 1" later this afternoon/evening across CO Front Range and southeast CO and then convection is expected to develop and linger through the evening/overnight for portions of the OK/TX Panhandle into central Oklahoma with the potential for hourly totals of 1-1.5". Through early Wednesday, the greatest signal for totals exceeding 3" is across southern Oklahoma (30-40% probability) leading to scattered instances of flash flooding. ....Southeast Florida... A moist environment characterized by PWs approaching the 90th percentile combined with the afternoon/evening sea breeze and a lingering surface trough in the vicinity will likely lead to another round of vigorous deep convection across portions of the central/southern Florida Peninsula later this afternoon/evening. The 12Z HREF neighborhood probabilities do show the potential for localized 1-1.5" hourly totals with a slight signal for totals through the overnight approaching 3-5"in localized/isolated spots. While the risk and confidence of flash flooding isn't great enough to introduce a Marginal Risk, there is a non-zero chance for flash flooding if convection were to develop over the urbanized corridor across southeast Florida due to the intensity of the rain rates possible. Taylor ---previous discussion--- ....Central-Southern Plains to the Ozarks, Arkansas River Valley, and the ArkLaTex... A vigorous shortwave pivoting across the 4-Corners and southern Rockies today will 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 (both low and high-res guidance) continue to show a signal for scattered 24hr rainfall totals in the 2-3" range with embedded higher amounts (3-5"). Again though, there continues to be 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. This as the guidance continues to hint at a multi-modal distribution of the heavier QPF, with one maxima located farther north (southern KS into central-eastern OK), likely associated with the best low-level FGEN from the aforementioned upper jet streak to the north, with a secondary maxima along and south of the Red River where stronger deep-layer instability will reside closer to the surface warm front. Regardless, given the noted environment conducive to heavy rainfall and the QPF totals, the potential for heavy rainfall has remained consistent. ....Colorado Front Range into the Rocky Mountain Piedmont... Most notable change from yesterday's Day 2 ERO was an upgrade to a Slight Risk across the CO Front Range into SE CO. 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, leading to a significant ramp up in low-level upslope flow during the day along the Front Range. Meanwhile, after 18Z the CAMs continue to show the character of the pivoting pcpn bands becoming more convective per simulated reflectivity and hourly QPFs, as MUCAPEs climb between 200-600 J/Kg. All CAMs show hourly rainfall rates peaking between 0.50-1.00", with isolated Day 1 QPF totals of 2-4+ inches. Moreover, both the HREF and WPC guidance show elevated probabilities of 24hr QPF exceeding the 2-year ARI (40-80%) and 5-year ARI (20-60%) within the Slight Risk area. The 00Z HREF even shows a small area of 30-40% that the 24hr QPF will exceed the 10 year ARI. Therefore heavy rain impacts are likely to be felt not far east from where heavy snow is expected, aided by the slow movement and cyclonic rotation of the heavier pcpn cores (which will foster some training).=20 Hurley Day 2 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... Maintained fairly broad Slight and Marginal Risk areas per yesterday's Day 3 ERO, casting a fairly wide net given the continued model spread with the heaviest rainfall. The aforementioned shortwave on Day 1 will track slowly along or north of the Red River Valley Wed-Wed night. The 00Z guidance continued the trend of somewhat better clustering with the heavier QPF compared to prior runs, however there remains a decent amount of spread, with again hints of a multi-modal distribution of the maxima per the global guidance (especially the GFS, ECMWF, and CMC. Once again it appears the models are attempting to resolve the likelihood that areas with the best deep-layer forcing (associated with the aforementioned right-entrance region upper jet forcing) will likely not coincide with the best deep-layer instability (farther south, i.e. south of the Red River Valley). For now, will maintain rather broad Slight and Marginal Risk areas, hoping to gain more clarity over the next few forecast cycles as the event gets within the high-res CAM windows. Hurley Day 3 Valid 12Z Thu Apr 27 2023 - 12Z Fri Apr 28 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM PARTS OF THE LOWER-MID MISSISSIPPI VALLEY AND CENTRAL GULF COAST REGION THROUGH THE TENNESSEE AND LOWER OHIO VALLEYS, SOUTHERN APPALACHIANS, AND PARTS OF THE SOUTHEAST... Shortwave trough will push east of the Lower-Mid MS Valley by 12Z Fri, with multiple embedded vort lobes along and east of the main trough axis. Broad scale forcing ahead of this system is fairly robust, with 850-700 mb moisture flux anomalies per the SREF and GEFS climbing to around 2 standard deviations above normal toward the end of the period (12Z Fri). This as the primary surface low lifts through western TN-KY, while another low begins to develop off the NC Coast later Fri. However, at least at this point, nothing from a dynamical or thermodynamical standpoint appears remarkable (PWs around 1 standard deviation above normal), while progressive nature of the trough (and strong pre-frontal low-mid level shear) should limit the duration of stronger convective cells and more intense short-term rainfall rates. Therefore, at least for now, will maintain a broad Marginal Risk area, which is supported by the relatively large spread in the models with the heavier QPF axes and thus a continuation of multi-modal distribution of maxima. Hurley Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8vcOjAuqddYW8PURRldki6ogXBgffN94h50x15k8qFRR= F-OihmbfONMxlcZcvQgPxse6xxYfiSvePIHgQidHvEnc2Ac$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8vcOjAuqddYW8PURRldki6ogXBgffN94h50x15k8qFRR= F-OihmbfONMxlcZcvQgPxse6xxYfiSvePIHgQidHKx_M_eM$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8vcOjAuqddYW8PURRldki6ogXBgffN94h50x15k8qFRR= F-OihmbfONMxlcZcvQgPxse6xxYfiSvePIHgQidHLKFgcmA$=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) .