Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed May 31 2023 07:22:27 FOUS30 KWBC 310722 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 321 AM EDT Wed May 31 2023 Day 1 Valid 01Z Wed May 31 2023 - 12Z Wed May 31 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE SOUTHERN AND CENTRAL PLAINS... ....Central and Southern High Plains... The notable change from yesterday's Day 2 ERO was the considerable expansion of the Slight Risk area east-northeast across southeast CO, southern to eastern KS, and parts of western MO. This is due in part to the recent heavy rains (including Tuesday night), but also given the next batch of more widespread convection later Wed afternoon and overnight. Compact mid/upper low migrating across AZ-southern UT will lead to a fairly substantial increase in upper level difluence and divergence over the southern High Plains by afternoon. Convection is expected to fire along/ahead of the dry line in eastern NM this afternoon, then become better organized/grow upscale this evening and overnight upon lifting east-northeast. This as the mid/upper low continue to track eastward, which will shift the most favorable region of difluence aloft (north of ~100 kt subtropical jet) into the TX/OK Panhandles into southern KS. Meanwhile, expect the upper divergence to become significantly enhanced locally ahead of the developing mesoscale-convective vort lobe. Above normal PWs (around the 90-95th percentile) along with robust deep-layer instability later this afternoon (mixed-layer CAPEs 1500-2500 J/kg will foster hourly or sub-hourly rainfall rates between 1.5-2.5" into the evening hours. This will support a more enhanced flash flood threat within the Slight Risk area, especially across eastern NM into the TX/OK Panhandles where it has been quite wet during past week (QPE 500-600%+ of normal). This generally aligns with the SPC Slight Risk for sever, as well as the CSU machine-learning first guess fields. Farther north-northeast, across the eastern half of the Slight Risk area, FFG values are currently higher, but expect them to drop during this morning with any lingering convection late Tue night. ....West into the Northern Rockies and Plains... The localized risk for excessive rainfall looks to continue across portions of northern CA into northwest NV today, also extending farther northeastward across ID/MT and into ND as well. This is primarily due to the aforementioned mid-upper low over SoCal beginning to lift northeastward through the Four Corners region (with another shortwave trough in the northern stream digging on its approach into the PacNW). Axis of sufficient instability, above normal PWs (as high as ~0.9" and around the 90th percentile per the NAEFS) and generally weak flow aloft will combine with afternoon heating to support another day of isolated to scattered showers and storms. 00Z models continue to show considerable spread with regard to the QPF, though there are a couple areas where there is better clustering with the heavier totals. One is over southwest MT, while the other over southwest ID. These will be areas to watch with subsequent updates to the Day 1 ERO; at this point however, given the spread in the guidance and lack of run-to-run continuity with the heavier QPF, will maintain the Marginal Risk inherited from yesterday's Day 2 ERO. ....Southern half of the Florida Peninsula... Weak mid/upper trough will remain nearly stationary over the eastern GOMEX during day 1 (Wed-Wed night), with 500 mb heights within the trough averaging ~2 standard deviations below normal. This synoptic setup will favor persistent broad-scale, weak deep-layer QG forcing east over the FL Peninsula through the period, which combined with the high (above normal) PWs for late May (1.75-2.00") and sufficient deep-layer instability (mixed-layer CAPEs 1000-2000 J/Kg), will favor intense hourly to sub-hourly rainfall rates of 2 to 2.5" underneath the strongest convective cores. The pattern is supportive of a Marginal Risk for th Day 1 ERO, as the CAMs show numerous areas of QPF between 1-3+ inches this afternoon and evening as the upper level forcing coincides with peak diurnal heating. In fact, the 00Z HREF indicated widespread probabilities of 50-70+ percent of 24hr QPF exceeding 3" within the Marginal Risk area, while probs for >5" averaged between 20-40 percent. Hurley 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!7MN1MzFT9h-q60K2VQ0wF5ZqZqI1vadKYf3pDgEp6fQG= 7uEMeHIYZW6zzob9QlEOWX-my-MqVsE4fNhG11Y3n0lhDPc$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7MN1MzFT9h-q60K2VQ0wF5ZqZqI1vadKYf3pDgEp6fQG= 7uEMeHIYZW6zzob9QlEOWX-my-MqVsE4fNhG11Y3Tp__hY4$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7MN1MzFT9h-q60K2VQ0wF5ZqZqI1vadKYf3pDgEp6fQG= 7uEMeHIYZW6zzob9QlEOWX-my-MqVsE4fNhG11Y3m17G8q4$=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) .