Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Apr 25 2023 20:15:22 FOUS30 KWBC 252015 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 414 PM 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... The closed mid/upper level low is expected to push out of the Four Corners region early in the period, opening up as it approaches the Southern-Central Plains by early 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 12Z guidance including the HREF continues to show clustering of the greatest QPF signal for southern Oklahoma into northern Texas where the overlap of best forcing/low level convergence, moisture transport, and instability axis lies. HREF neighborhood probabilities reach 50-60% across parts of the Slight Risk area for 3-4" totals over the 24-hr period with some signal for 1-2" hourly totals at times, especially late in the afternoon into the evening hours. The Slight Risk was maintained with minimal adjustments based on the latest guidance and QPF trends. Hurley/Taylor 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... 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, roughly around 1-1.5 standard deviations above normal. 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 where broadly he system will become increasingly progressive with generally lower duration potential for heavy rainfall. Rainfall totals up to 1" (locally higher between 2-3" along the central Gulf Coast from New Orleans to FL Panhandle) will be possible. Hurley/Taylor Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6sok62VzayZtpK3TemagfX-TKcN1MzOhts6zs8sUEGr9= GYBoColIYakJE5gK949nzNe77XytVKXwZhHWh2WPlybNZmg$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6sok62VzayZtpK3TemagfX-TKcN1MzOhts6zs8sUEGr9= GYBoColIYakJE5gK949nzNe77XytVKXwZhHWh2WPUNq0cvc$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6sok62VzayZtpK3TemagfX-TKcN1MzOhts6zs8sUEGr9= GYBoColIYakJE5gK949nzNe77XytVKXwZhHWh2WPtCHuikY$=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) .