BBS: TELESC.NET.BR Assunto: HVYRAIN: Excessive Rainfall Discussion De: COD Weather Processor Data: Thu, 28 May 2026 07:21:35 +0000 ----------------------------------------------------------- FOUS30 KWBC 280721 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 321 AM EDT Thu May 28 2026 Day 1 Valid 12Z Thu May 28 2026 - 12Z Fri May 29 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS MUCH OF=20 THE SOUTHEAST TO MIDDLE MISSISSIPPI VALLEY, SOUTHEAST FLORIDA, AND=20 FOR PORTIONS OF THE NORTHWEST... ...Central Plains to Southeast... A bit of an omega block pattern is shaping up across the CONUS=20 with a broad upper trough axis fixated over the Central and=20 Southern Plains with ridging in place over the top. This will cause a rather chaotic flow under the mean trough and several smaller=20 mid- level perturbations basically "stuck" within the overall=20 trough axis. Ample instability with deep moisture presence will=20 certainly continue to support at least a scattered heavy rain=20 footprint across areas underneath influence of the trough.=20 Scattered elevated probabilities between 30-70% exists for=20 localized amounts >3" from KS all the way into the Southeast U.S.=20 with the maxima split between eastern KS to northern AR and the=20 Central Gulf coast. For KS/AR, parked underneath the upper trough,=20 upper forcing and stagnant flow are more favorable for heavier=20 rainfall totals. Maintaining a marginal risk at this time as the=20 heaviest rainfall over the past 12 or so hours was more southwest=20 of where the guidance is showing today and the rest of the region=20 is still somewhat dry and can probably support some heavier totals. Along the Gulf Coast and into the Southeast, instability will be=20 maximized in this area with weak flow supporting slow- moving=20 convection and heavier rainfall over those isolated areas.=20 Antecedent conditions across much of this region are also very wet, so it may not take much to cause issue. Given the still fairly=20 isolated nature, maintaining a broad marginal risk, with any=20 possible upgrades today stemming more from near term radar trends.=20 ...Florida... An active sea breeze pattern with weakening steering flow will=20 lead to periods of heavy rainfall across southeast Florida this=20 afternoon. Greatest concern remains over the South Florida metro=20 corridor from West Palm Beach to Miami. Latest HREF is robust with=20 showing greater than 50% probabilities for 3" in 24-hours, with=20 even some modest, albeit localized, probabilities for 5". This=20 correlates well with CAM guidance, with some indicating bullseyes=20 of greater than 3" within the larger QPF footprint. Locally=20 significant rainfall is likely in this relatively classic pattern=20 with ample moisture and instability present. A marginal risk=20 remains in effect across Southeast Florida.=20 ...Washington/Oregon... A deep upper level low over the West will allow for a broad axis=20 of diffluent flow across the interior Northwest. Precipitable water values 1-1.5" are in the 90-90th percentile, and with sufficient=20 instability, should support convection capable of producing heavy=20 rainfall. Flooding and flash flooding are a concern for mainly the=20 more vulnerable areas - urban, small stream, and low lying areas.=20 HREF 24-hr probabilities for greater than 3" are between 40-70% for especially the Oregon cascades. Given the favorable environment=20 though, a marginal risk extends all the way from far northern=20 California northward to the eastern half of Washington state. A=20 previous marginal risk for parts of the northern Rockies was=20 trimmed out for this update given the lack of QPF signal. Santorelli Day 2 Valid 12Z Fri May 29 2026 - 12Z Sat May 30 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF=20 THE NORTHERN ROCKIES AS WELL AS MUCH OF THE SOUTHEAST TO MIDDLE=20 MISSISSIPPI VALLEY... ...Eastern Washington to Northern Rockies... A marginal risk is in place across far northeast Washington to=20 northwest Montana due to an increase in the heavy rainfall signal=20 for this period as the upper low over the West on Day 1, pivots=20 slightly northeastward, placing this region in an area with better=20 upper forcing and advection of moisture. The presence of anomalous=20 moisture and some instability may present a threat for localized=20 heavy rainfall and flash flooding, especially for burn scar=20 locations within this region.=20 ...Middle Mississippi Valley to the Southeast... Strong Canadian high pressure pressing in from the north will=20 allow for a slow moving cold front to press south over the course=20 of Thursday into Friday with convection likely to spawn along and=20 ahead of the front and dry air advecting behind the front leading=20 to a quick cutoff of activity. The front will arc back into the=20 Tennessee Valley to Middle Mississippi Valley, supported by the=20 persistent troughing over the south-central Plains. A moist and=20 unstable environment near and south of this front will support=20 scattered convection, with some heavier cells likely within the=20 pattern. It is still too hard to pick out any discernible areas of=20 interest, so maintained a very broad marginal risk over this area=20 which is quite wet and will continue to be in the Day 1 period. Santorelli Day 3 Valid 12Z Sat May 30 2026 - 12Z Sun May 31 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE=20 NORTHERN ROCKIES TO HIGH PLAINS AND THE SOUTHEAST... ...Northern Rockies to High Plains... The upper level low over the West during the Day 1 and 2 periods=20 will weaken and shift northeastward, moving over the Northern=20 Rockies to High Plains region on Day 3/Saturday. Moisture anomalies will continue to be in the 90-90th percentile, supporting moderate to heavy rainfall, with widespread QPF greater than 0.5-1" likely=20 across western and central Montana. There may not be a lot of=20 instability to work with, so any flood or flash flood threats=20 should be mainly localized with particular attention to burn scar=20 locations. A fairly broad marginal risk is in place across much of=20 western and central Montana, into parts of northern Wyoming as=20 well. ...Southeast... Same story as Days 1 and 2, with ample moisture and instability=20 present near and south of a cold front that may stall over the=20 region on Saturday supporting convection, across much of the=20 Southeast. Some of this region, especially western parts of South=20 Carolina and into the Appalachians has been very wet as of late and is well primed, so may be more favorable for flooding concerns.=20 The marginal risk though continues towards the coast due to the=20 presence of a weak frontal wave in the region. The Marginal Risk=20 extends from the Southeast coast, westward into northeast Alabama=20 and southeast Tennessee.=20 Santorelli Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-YssY9nv8nNmRWt9Iy4hs-WJzue9EUqyhWBfiUQAj2Mm= jm7shMhPqRSxkaqTtxJPiBQQ4eYOipJmw8XpHK0_TuDwfxo$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-YssY9nv8nNmRWt9Iy4hs-WJzue9EUqyhWBfiUQAj2Mm= jm7shMhPqRSxkaqTtxJPiBQQ4eYOipJmw8XpHK0_JVzP_k8$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-YssY9nv8nNmRWt9Iy4hs-WJzue9EUqyhWBfiUQAj2Mm= jm7shMhPqRSxkaqTtxJPiBQQ4eYOipJmw8XpHK0_548tKWQ$=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. 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