Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jun 28 2023 08:26:18 FOUS30 KWBC 280826 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 425 AM EDT Wed Jun 28 2023 Day 1 Valid 12Z Wed Jun 28 2023 - 12Z Thu Jun 29 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE NORTHEAST, UPPER MIDWEST, MID MISSISSIPPI VALLEY, AND THE NORTHERN ROCKIES... ....Northeast... An upper trough will continue linger over the Northeast, channeling both deep moisture and mid-level energy across portions of the region. PWs are forecast to generally remain near or above 1.5 inches in the deep southerly flow ahead of the associated front. This along with daytime heating will help to generate additional rounds of moderate to heavy rainfall. Supported by a period of south to north training ahead of the slow-moving front, the overnight HREF guidance continued to show the threat for localized amounts of 2-3 inches, maximized along an axis extending from central Massachusetts into New Hampshire, and northeastern Vermont. There are still concerns regarding the need for a targeted upgrade to a Slight Risk, however with the HREF painting its heavier amounts across areas away from those most recently impacted with heavier accumulations, opted to maintain the Marginal Risk for now.=20=20 ....Upper Midwest... Mid-level energy emanating from the trough in the West, along with an amplifying trough approaching from the northwest over central Canada are expected to support an increasing chance for rain across portions of the region on Wednesday into early Thursday.=20 The general consensus of the HREF guidance shows heavier precipitation spreading initially into the Minnesota Arrowhead region in the warm advection pattern and along a ribbon of deeper moisture (PWs around 1.5 inches) nosing through the region. This will likely be followed by the afternoon development of storms in the more unstable air farther south across northwestern Wisconsin. While individual storms are likely to be progressive, some of the guidance does show some potential for west-east training, which may produce locally heavy amounts and an isolated flash flooding threat. ....Northern Rockies... With an upper trough remaining positioned to the west and a relatively moist airmass still in place, isolated to scattered, slow-moving showers and storms are expected to develop once again across the region. These may produce locally heavy amounts and generate isolated flash flooding concerns, especially given the wet antecedent conditions. The 00Z HREF continues to show some appreciable probabilities for rain totals of 1-2" and probabilities of exceeding 2, 5, and 10-year ARI values, maximized near the the track of low-to-mid level center moving across southwestern Montana. ....Central Plains through the Mid Mississippi Valley... Some of the models showed the growing potential for heavy rain and possible flash flooding to occur from Nebraska eastward into the mid Mississippi Valley as mid level energy moving over the top of the ridge interacts with a deepening moisture pool (PWs 1.75-2 inches) coinciding with a low level warm front. Some of the hi-res guidance members are showing upscale growth with one or more of these clusters of developing storms, with redeveloping storms producing heavy amounts. Where these heavy amounts may occur is far from certain, with the models far from agreeing on where and if this development may occur. A Marginal Risk was drawn to highlight the area where HREF probabilities for amounts exceeding 2 inches and 2-year ARI values are relatively higher.=20 However given the uncertainty, this area will likely be adjusted with updates later today.=20=20 Pereira=20 Day 2 Valid 12Z Thu Jun 29 2023 - 12Z Fri Jun 30 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE NORTHEAST AND FROM THE NORTHERN ROCKIES INTO THE CENTRAL PLAINS... ....Northeast... One more day of showers and storms, with locally heavy amounts possible, is expected for portions of northern New England.=20 However the threat will likely be on the downward trend as the upper trough continues to weaken and lift to the northeast, followed by drier air spreading across the region. ....Northern Rockies to the central Plains... Afternoon and evening thunderstorms will remain possible across portions of southwestern Montana and western Wyoming as an upper trough continues to slowly approach the region. Locally heavy rainfall amounts impacting areas already affected by above average rainfall over the past month may result in isolated flash flooding concerns. Meanwhile, mid-level energy ejecting east of out of the trough is expected to support showers and storms moving farther east out into the central Plains. Models continue to present a pretty good signal for training storms and heavy accumulations developing late Thursday into the overnight near a slow-moving boundary and axis of deeper moisture from southeastern Wyoming/northeastern Colorado into central Nebraska. However, they continued to differ on the location of heavier amounts across the Plains, with some painting an axis centered across the less flash flooding prone Sandhills, while other are focused farther to south -- nearer the Kansas border. Pereira=20 Day 3 Valid 12Z Fri Jun 30 2023 - 12Z Sat Jul 01 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE CENTRAL ROCKIES TO THE CENTRAL/SOUTHERN APPALACHIANS AND ACROSS PORTIONS OF THE NORTHEAST... ....Central High Plains to the Appalachians... Mid-level energy will continue to move across the top of the ridge centered over the lower Mississippi Valley and the Southeast, likely to help initiate additional rounds of showers and storms from the Ohio Valley eastward as they interact with an axis of deeper moisture. Meanwhile, a more defined upper trough moving out of the West is likely to generate additional storms back to the west from the foothills of the central Rockies into the Plains. Given the typical uncertainty, a broad Marginal Risk was drawn for now. However, embedded upgrades to a Slight Risk may be forthcoming, especially if the models begin to agree on successive days of heavy rain across the central Plains. ....Northeast... A Marginal Risk was drawn to highlight an increasing threat for heavy rains to spread back into portions of the Northeast that were recently impacted by heavy amounts. Mid-level energy and deeper moisture will be directed northeast into the region ahead of a low centered north of the Great Lakes. Although confidence in the details is limited, there is at least some potential for moderate to heavy amounts to begin to develop across some parts of Pennsylvania and New York that were recently impacted with heavy amounts and where FFGs remain relatively low. Pereira=20 Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4ZZmuE0bv7uFINXVmIeg5GwXGagKpqhosD9rtKz6sTrw= NxEJ4e4jS89mQ4HEQwrDegJGds3ODYBtieAn0Vqud2ReCFU$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4ZZmuE0bv7uFINXVmIeg5GwXGagKpqhosD9rtKz6sTrw= NxEJ4e4jS89mQ4HEQwrDegJGds3ODYBtieAn0VquG8uhZrw$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4ZZmuE0bv7uFINXVmIeg5GwXGagKpqhosD9rtKz6sTrw= NxEJ4e4jS89mQ4HEQwrDegJGds3ODYBtieAn0Vqu1H875X4$=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) .