Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jun 28 2023 00:11:42 FOUS30 KWBC 280011 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 810 PM EDT Tue Jun 27 2023 Day 1 Valid 01Z Wed Jun 28 2023 - 12Z Wed Jun 28 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE NORTHEAST, NORTHERN & SOUTHERN PLAINS, NORTHWEST, & NORTHERN ROCKIES... ....Northeast/Northern Mid-Atlantic... The upper low is forecast to transition to an open wave and begin to drift slowly eastward into the Northeast. Ongoing convection over the Northeast and Mid-Atlantic is expected to wane over the next several hours. As convection had mostly left the Slight Risk area, dropped the threat level down to Marginal Risk. ....Northern Rockies and Plains... A slow-moving trough in the West and sufficient moisture have supported another day of showers and storms developing over the northern Rockies and northern Plains. Guidance indicates that this activity should have another four or so hours before fading.=20 Based on radar reflectivity trends in the northern Plains, shifted the risk area a little more southward into South Dakota. Although widespread heavy amounts are not expected, locally heavy amounts may produce an isolated flash flooding threat, especially given the wet antecedent conditions across portions of the area. ....Near the Kansas/Oklahoma border... Storms have recently formed and moved east as mid-level energy emanating from the trough in the West moves over the downstream ridge and interacts with moisture deepening along a low level warm front. As the low level inflow into the front increases, guidance shows PWs increasing to at over above 1.75 inches near the Kansas-Oklahoma border. Merging cells, with some potential for backbuilding, may produce some locally heavy amounts and isolated flash flooding concerns before these developing storms are expected to consolidate and track progressively to the east overnight. Radar reflectivity indicates that mesoscale guidance is a tad too far to the north with this activity, so broadened it somewhat to the south from continuity. ....Northern Cascades... Ample moisture (PWs near an inch) and instability, along with weak flow aloft will once again support slow-moving storms, capable of producing locally heavy amounts for a few more hours. Heavy amounts that do occur may produce isolated flash flooding, especially across areas recently impacted by wildfires. Roth/Putnam/Pereira Day 2 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, AND THE NORTHERN ROCKIES... ....2030Z Update... No areal adjustments were made to the current MRGL risk for the Northeast, although consideration was given to upgrading to a SLGT risk for portions of central New England. Incoming 12Z hires guidance indicates the potential for some rain totals of 2-3" which would exceed FFGs on a more regional areal basis. However, the expectation is for storms along an eastward moving cold front to remain progressive enough to limit the coverage of these amounts to a few locally heavy totals. Some additional storms may form ahead of the front aided by strong, moist southerly 850 mb flow, particularly for portions of southern New Hampshire along the Monadnocks and southern White Mountains southeastward towards the coast, but this looks to also remain a relatively localized concern for now. Additional rainfall today may also lead to wetter antecedent conditions and higher streamflows. The MRGL risk in the Northern Rockies was expanded northwestward to cover portions of western Montana to the Idaho border. Another day of scattered, slow moving thunderstorms rotating around under the base of an upper-level low is expected. Similar to today, some locally heavy downpours with rain rates upwards of 1" per hour look possible given precipitable water values around or above 0.75 inches. The available 12Z hires guidance indicates some appreciable probabilities for rain totals of 1-2" and probabilities of exceeding 2, 5, and 10-year ARI values, respectively, as well. Similarly, the MRGL risk in the Upper Midwest was expanded further into northwest Wisconsin based on 12Z hires guidance.=20 Putnam ....Previous Discussion... ....Northeast... An upper trough will continue linger over the Northeast, channeling both deep moisture and mid-level energy across portions of the region. Daytime heating is likely to help support additional showers and thunderstorms, with locally heavy amounts possible, especially across portions of eastern Upstate New York into New England. ....Upper Midwest... Mid-level energy emanating from the trough in the West, along with an amplifying trough approaching from the northwest over central Canada is expected to support an increasing chance for rain across portions of the region on Wednesday into early Thursday.=20 Deepening moisture (PWs increasing to around 1.5 inches), along with some potential for west-east training, may produce at least some locally heavy amounts from northern Minnesota to the western U.P. of Michigan. ....Northern Rockies... With an upper trough remaining positioned to the west and a relatively moist airmass still in place, isolated to scattered 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. Pereira=20 Day 3 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 NORTHERN ROCKIES INTO CENTRAL PLAINS... ....2030Z Update... The previous forecast remains on-track with very minimal areal adjustments based on the updated 12Z guidance. As noted, rainfall amounts look to be trending downwards over the Northeast compared to previous days. Any isolated threat for flooding may largely be reliant on what areas have already received higher totals Monday/Tuesday. Some differences also remain in the location of heavier rain totals in the 12Z guidance for portions of the Central Plains, with the potential that areal coverage may focus a bit northward into north-central Nebraska where a regionally lower risk for flash flooding exists due to the Sandhills. However, enough of the guidance still indicates that the higher potential for storm coverage/training will be to the south from northeastern Colorado into southern Nebraska. Putnam ....Previous Discussion... ....Northeast... One more day of showers and storms, with locally heavy amounts possible, is expected for portions of northern New York and New England. The threat is expected to become more localized as the associated upper trough continues to weaken and finally begins to lift out ahead of a developing upper low moving across central Canada. ....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. With differences in the details, models are presenting 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. Pereira=20 Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!73Chg2jWogF1A7V2q_QNN6PQ6rsKqvRvM2ngXlsLwrC6= LdSK_aE9-LY52Msj5_AWqHfZMPbAeZji4TGUiozTWlTsUeQ$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!73Chg2jWogF1A7V2q_QNN6PQ6rsKqvRvM2ngXlsLwrC6= LdSK_aE9-LY52Msj5_AWqHfZMPbAeZji4TGUiozTtj1yxL0$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!73Chg2jWogF1A7V2q_QNN6PQ6rsKqvRvM2ngXlsLwrC6= LdSK_aE9-LY52Msj5_AWqHfZMPbAeZji4TGUiozTOcxy8iU$=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) .