Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Aug 25 2023 08:29:58 FOUS30 KWBC 250829 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 429 AM EDT Fri Aug 25 2023 Day 1 Valid 12Z Fri Aug 25 2023 - 12Z Sat Aug 26 2023 ....A SLIGHT RISK OF EXCESSIVE RAINFALL IS IN EFFECT FOR PORTIONS THE CENTRAL ROCKIES AND ADJACENT HIGH PLAINS... ....Southwest to the central Rockies and Adjacent High Plains... Energy that had once been Harold will continue to make its way around the periphery of building mid-level heights over the Plains states...with a surface reflection being a low center to the east of the Central Rockies and the presence of anomalously deep moisture setting the stage for a potentially impactful event.=20 Precipitable water values of 1.75 inches over eastern and central Kansas/Nebraska gets pulled westward by low level easterly flow feeding into the area of low pressure by this evening...which helps push precipitable water values over northeast Colorado and nearby southeast Wyoming to 3 standardized anomalies greater than climatology. The 25/00Z HREF's highest probabilities of the 24hr QPF exceeding 2 inches in 24 hrs peaks over 50 pct where flow over a northwest-southeast front aids lift as well as an second area farther south given proximity to better instability (1000-1500 J/Kg surface-based CAPE per the HREF). By later in the period...the surface low begins to move east and a line of precipitation to slowly press southward. Local precip maxima from deterministic models and signals from the 25/00Z HREF EAS probabilities show a potential for locally heavy rainfall with enhanced rates of up to 1"/hr and totals near 1-2". This area was already covered in Thursday's Day 2 ERO and needed little change. Afternoon and early evening convection is expected in and near the higher terrain around the 4-corners region which poses a low-end risk of excessive rainfall given favorable moisture profiles from the area soundings. ....Northeast and Mid Atlantic and into parts of the Ohio Valley/Southern Lakes.., Area low pressure will track to the northeast from the Great Lakes area on Friday with increased mid-level difluence out ahead of a stronger shortwave trough digging eastward out of Ontario. First round of rainfall will be on-going at the start of the Day 1 period at 12Z today...which eventually exitd off Southern New England. A second round of convection will develop near a warm front pushing northward along the coast with a trailing cold front pressing east along the base of the surface low. General instability axis will preside within the warm sector from the Mid Atlantic up into New England with PW anomalies a solid 1-2 standard deviations above normal, especially across New England where the heavy precipitation signature is most prominent. Any thunderstorm will be capable of producing locally heavy rainfall with rates up to 1"/hr. A secondary area of focus back into eastern KY extending back into parts of Indiana with diurnally driven convective initiation in a region of moist confluent flow. Precipitable water values will climb during the afternoon to values between 1.75 and 2 inches along this corridor which should support local downpours...especially where terrain can help provide focus for the flow.=20 Bann Day 2 The Day 2 outlook will be updated by 0830Z. 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!_rL_FjRVSOYfnJMhtpb5EeItam-06sbJQdAKVn_pkDDg= C86TuQbIlss-bQNm-JpK6GrSeEQb2aEGsqSFuYaWDCs0F7k$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_rL_FjRVSOYfnJMhtpb5EeItam-06sbJQdAKVn_pkDDg= C86TuQbIlss-bQNm-JpK6GrSeEQb2aEGsqSFuYaWaJT9zfs$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_rL_FjRVSOYfnJMhtpb5EeItam-06sbJQdAKVn_pkDDg= C86TuQbIlss-bQNm-JpK6GrSeEQb2aEGsqSFuYaW5Ed6YJ8$=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) .