Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Jun 23 2023 08:17:43 FOUS30 KWBC 230817 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 416 AM EDT Fri Jun 23 2023 Day 1 Valid 12Z Fri Jun 23 2023 - 12Z Sat Jun 24 2023 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF THE HIGH PLAINS AND THE FLORIDA PANHANDLE INTO SOUTHERN GEORGIA... ....Montana into the Plains... Shortwave energy currently moving into Nevada early this morning will quickly lift northeast toward Montana by tonight. Strong/favorable setup for upper diffluence will be provided by dual left exit and right entrance region of the upper jets positioned over the Four Corners and southern Canada. Higher moisture seeping into Montana will reach upwards of 0.75", fairly modest at around 1.5 standard deviations above normal, but sufficient enough when combined with the greatest forcing and available instability expected. Based on the 00Z guidance and HREF probabilities, the best setup for widespread 1-2" totals and hourly totals as high as 1-1.5" will be across south-central Montana into southeast Montana. Localized 3"+ will be possible as indicated by the localized 20-25 percent neighborhood probabilities in the 00Z HREF, especially over southern Montana. A secondary area of heavier rainfall is expected across portions of the Plains, particularly southern South Dakota into far northern Nebraska, later this evening into early Saturday morning with a surging low level nocturnal jet expected as the aforementioned shortwave energy reaches the western Dakotas. Convection early this morning should lift northward into North Dakota followed by a relative lull this afternoon, before additional clusters of strong thunderstorms track through SD/NE. Training thunderstorms will be possible along with repeating rounds with the latest HREF probabilities suggesting isolated 2-4" possible across southern South Dakota between 00-12Z Saturday. Both of these areas have the setup, ingredients, and wetter antecedent conditions toward the higher-end of the Slight Risk range (15-40%) and if guidance continues to come together, a targeted upgrade to a Moderate could be possible across southern MT and/or southern SD. For the southern Plains, the typical afternoon showers and thunderstorms will redevelop again Friday afternoon, but since they will be a bit more isolated and less organized as the upper level flow diminishes, the flash flooding risk is expected to be more isolated as compared with previous days. ....Florida... Heavy rainfall continues early this morning across portions of the Florida Big Bend region as a steady fetch of deep Gulf moisture directs into the region. The environment will remain very conducive for heavy rainfall as PWs are near/above 2" and warm cloud depths very high. Little forward movement in the stalled frontal boundary is expected today/this evening, so additional showers and thunderstorms are likely to develop across portions of the FL Panhandle this afternoon then move eastward into the Big Bend and northern Florida region this evening. The Slight Risk area looks on track, highlighting the greatest risk area for additional heavy rainfall over areas that are increasingly very saturated due to recent heavy rainfall events over the past couple of days. ....Mid-Atlantic... The upper trough positioned across the Ohio Valley and Central Appalachians today into tonight will allow for nearly stationary boundary across the coastal areas to lift northward as a warm front through the Mid-Atlantic today. Expect the axis of deepest moisture to remain along/east of I-95 across the Mid-Atlantic, upwards of 2.0" per the latest guidance, while sounding profiles suggest a very favorable environment for efficient rainfall producing showers and thunderstorms characterized by tall/skinny CAPE profiles and higher warm cloud depths. Storms should continue lifting out of the Carolinas early this morning, reaching the Mid-Atlantic by mid-morning with additional development possible later this afternoon. Rainfall rates of 1-2"/hr will be possible in the strongest cores, which based off the latest hi-res guidance, could track through the urbanized I-95 corridor across VA into MD. Some of this rainfall could be intense, resulting in flooding of urban and other poor drainage areas. Further west toward the center of the upper trough across portions of the Appalachians, slower storms will pivot around the low and these slower storm motions also in the favorable environment for heavy rain could result in localized/isolated flash flooding. Taylor Day 2 Valid 12Z Fri Jun 23 2023 - 12Z Sat Jun 24 2023 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR MUCH OF MINNESOTA AND THE EASTERN DAKOTAS... ....ND/MN area... A deepening shortwave trough is expected to track from portions of Montana and Wyoming early Saturday morning toward central Minnesota by Sunday morning. Ahead of that feature, southerly flow in the low levels will bring northward anomalously high moisture to the region, characterized by precipitable water values to near 1.5" or +2 standard deviations above normal. A stationary boundary is expected to remain draped across the region ahead of the main low pressure system, helping to focus the convection over a couple of days in the Northern Plains and portions of northern Minnesota. Rainfall amounts of 1-2" appear possible across the Day 2 Slight Risk area with upwards of another 1" or so in the preceding day which would help to saturate the soils some. As a result, isolated to widely scattered instances of flash flooding appear possible, particularly across the eastern Dakotas into much of western and northern Minnesota.=20 ....Northeast... The slow moving, stubborn upper level trough will inch forward during the day on Saturday, beginning in the Ohio Valley and reaching New England by Sunday morning. The combination of anomalous moisture (PWs up to 1.5"+), warm cloud depths, and skinny CAPE profiles, efficient rainfall producing showers and thunderstorms will be capable of producing localized heavy rainfall. With the mean flow remaining somewhat parallel to the overall storm motions, some repeating rounds will be possible, supporting isolated/localized instances of flash flooding. ....Southeast Florida... A deep axis of higher than normal moisture will position itself across South Florida this weekend and with weak flow and modest shear, higher coverage of afternoon/evening thunderstorms are expected to develop. The environment will support intense rain rates given the tall/skinny CAPE profiles and warm cloud depths. The latest guidance suggests the greatest convection may end up developing just inland away from the highly urbanized corridor, but there's enough ingredients and support in the various models to maintain the Marginal Risk in the ERO. Taylor Day 3 The Day 3 outlook will be updated by 0830Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8gSHnd_ISxi8ZO3HaSe2-iGGhtkHBmjfRI_37Pq4php4= EiDnlQCDhmvXHMg7MmlVWQD3guiHtSE7SVvH4Gf12d8gnxo$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8gSHnd_ISxi8ZO3HaSe2-iGGhtkHBmjfRI_37Pq4php4= EiDnlQCDhmvXHMg7MmlVWQD3guiHtSE7SVvH4Gf1U-WA71w$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8gSHnd_ISxi8ZO3HaSe2-iGGhtkHBmjfRI_37Pq4php4= EiDnlQCDhmvXHMg7MmlVWQD3guiHtSE7SVvH4Gf1NjWUipc$=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) .