Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon May 22 2023 08:16:23 FOUS30 KWBC 220816 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 415 AM EDT Mon May 22 2023 Day 1 Valid 12Z Mon May 22 2023 - 12Z Tue May 23 2023 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF THE CENTRAL/SOUTHERN PLAINS AND FOR PORTIONS OF THE SOUTHEAST... ....Southern to Central Plains... Scattered dry-line induced showers and thunderstorms are expected later today across portions of the Texas Panhandle into south-central Kansas, aided by a weak mid/upper level shortwave tracking through the region and a modest low-level jet. The 00Z HREF shows scattered signals for 1-2" hourly totals, particularly the TX/OK Panhandle region where the various hi-res models show potential for 2-4" totals through the 24-hr period. This additional rainfall today is expected to fall on increasingly wet soils due to the recent rainfall over the last several days (7-day departures are as high as 400-600 percent of normal in places). As a result, isolated to scattered instances of flash flooding will be possible. ....Southeast... Widespread to numerous showers and thunderstorms are expected to develop along a residual stationary boundary draped across the region. Meanwhile, the mid/upper levels feature weak shortwave energy that is expected to slide eastward from the ArkLaTex region to southern Georgia today. Moist easterly flow has allowed anomalous moisture to pool along the surface boundary and precipitable water values are forecast to remain at or above 1.5" across the risk area, approaching 1.75" locally. These values are near 1.5 to 2.0 standard deviations above normal. With maximum daytime heating producing ample instability, deep convection firing up along the frontal boundary and other residual boundaries should lead to loosely organized convective clusters capable of producing intense rainfall rates. The 00Z HREF neighborhood probabilities indicate potential for 1-2" hourly totals with localized 2"+ hourly totals, most likely across southern Georgia southward into the Florida peninsula. This is where the HREF probabilities also suggest around 30-40% chances for 24-hr totals ending 12Z Tuesday of 4-5". These types of rain rates and totals may lead to isolated to scattered instances of flash flooding, particularly over the more urban and susceptible locations. Taylor Day 2 Valid 12Z Tue May 23 2023 - 12Z Wed May 24 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHEAST... ....Southeast... Heavy rainfall will be possible again across portions of the Southeast Tuesday into Tuesday with the stationary boundary remaining draped across the region. Moisture will continue to be above normal with the favorable easterly flow bringing in PWs 1.75"+ around the stationary boundary. Meanwhile, a weak mid/upper level shortwave will slide eastward across the Southeast, reaching the eastern Gulf and Florida Peninsula late in the period. This will bring another cold front southeast and this combination of lift, moisture, and peak daytime heating instability will be sufficient for widespread showers and thunderstorms. The ingredients will support intense rain rates, upwards of 2-3" in an hour at times, particularly across northern/northeast Florida into southern/southeast Georgia. Slow storm motions and colliding boundary interactions may also play a factor into the rain totals, which could top 2-4" in places for the period. Soils are likely to become increasingly more saturated by Tuesday thanks to a few days of heavier rainfall expected and this may lead to more scattered instances of flash flooding, particularly for the more susceptible locations and urban areas. ....Southwest OK through North Central TX... Another round of dry-line induced showers and thunderstorms is expected Tuesday into Tuesday night, a bit displaced to the east compared to today's expected convection. The latest guidance shows a better/strong low level jet upwards of 30-35 kts at 850 mb along with a large pool of higher moisture across the region. The 00Z guidance remains on track for showing potential of 1-2" areal average totals in the risk area with some signal for higher amounts possible and the Marginal Risk was only minimally changed for this update. ....Intermountain West... A very slow moving longwave trough over the West Coast will direct a large stream of moisture northeastward in advance of the trough. Embedded within the trough is an upper level low that will be over the BC/AT border north of WA/ID. A shortwave disturbance pinwheeling south of the low will approach the intermountain west Tuesday. This will locally increase the forcing over the Marginal Risk area over northeast NV, northern UT and southeastern ID. Anomalous moisture will still be in place, with PWATs up to 0.75 inches are over 3 sigma above normal. This will support training storms tracking northeast from NV through UT and into ID. The storms that are forced by the local mountains may stay more stationary, which will locally increase the flash flooding potential. ....Northern Plains... Scattered to numerous showers and thunderstorms are likely to develop across portions of North Dakota into northern Minnesota Tuesday evening as a cold front approaches from Canada and intercepts a low level southeasterly jet of 25-30 knots that will be advecting deeper moisture into the region. Localized 1-2" totals are expected based on the latest forecast guidance and although the areal coverage of heavy rainfall isn't expected to be high, the storms that do form will be capable of producing intense rain rates that could be great enough to cause isolated instances of flash flooding.=20 Taylor Day 3 Valid 12Z Wed May 24 2023 - 12Z Thu May 25 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF NORTHERN MAINE AND EASTERN COLORADO INTO WESTERN KANSAS... ....Colorado into Kansas... Southwesterly flow across the Rockies is expected as the central U.S. ridges builds further and a closed low moves onshore the West Coast. Embedded shortwave energy will pass through the southwesterly flow with one wave likely to reach the Central Rockies Wednesday into Thursday. Meanwhile, low level southerly flow across the Plains ahead of the approaching trough will bring higher moisture northward into eastern Colorado and western Kansas. Convection is likely to initiate off the higher terrain then move eastward into the Plains, interacting with any residual surface boundaries. The sufficient instability and moisture combined with the signal for a few repeating rounds suggests an isolated risk of heavy rainfall (1-2" hourly totals) that will be capable of producing flash flooding and a Marginal Risk was introduced this cycle. ....Maine... A deepening trough crossing the Hudson Bay region is expected to become negatively tilted and close over eastern Ontario by late Wednesday into early Thursday. A sharp cold front will slip southeastward into the region with an area of low pressure developing along the front. The strong frontogenesis and mid/upper level diffluence is likely to lead to an axis of heavier precipitation from the northern portions of New Hampshire into northern Maine along the Canadian border. Moisture return isn't overly impressive and there's likely to be limited instability (perhaps up to 500 J/kg), nonetheless guidance shows fairly strong signals for 1-2" totals over the period which could be in a narrow axis over a relatively short period of time leading to isolated instances of flash flooding. Taylor Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!5JeVUCd9KRvYRrO1kDvlEi9dKrEF8p-R1ZLyL2psbShP= HoP0hDPlhWzx1amiPEqB03wXkuaf4OFf7TT7LGr1scSzu4g$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5JeVUCd9KRvYRrO1kDvlEi9dKrEF8p-R1ZLyL2psbShP= HoP0hDPlhWzx1amiPEqB03wXkuaf4OFf7TT7LGr1Rd-A_bg$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5JeVUCd9KRvYRrO1kDvlEi9dKrEF8p-R1ZLyL2psbShP= HoP0hDPlhWzx1amiPEqB03wXkuaf4OFf7TT7LGr1M0w4D3E$=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) .