Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jul 31 2024 00:59:16 FOUS30 KWBC 310059 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 859 PM EDT Tue Jul 30 2024 Day 1 Valid 01Z Wed Jul 31 2024 - 12Z Wed Jul 31 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF THE MID MISSISSIPPI VALLEY, LOWER OHIO VALLEY, UPPER TENNESSEE VALLEY INTO THE SOUTHERN APPALACHIANS... ....Midwest/Mid Mississippi Valley to the Southeast Coast... ....0100 UTC Update... Minor changes were made to the ongoing Day 1 ERO over these regions, based on the current activity/observational data along with most recent HREF/RRFS/HRRR guidance and trends. Starting to see renewed convection across the eastern Dakotas and northeast NE, with the southern clusters expected to grow upscale upon reaching IA after 05-06Z. Given the lower across IA, the highest=20 probabilities of 3 hourly QPF exceeding the FFGs per the 18Z HREF are across central to southeast IA (30-40% between 09-12Z).=20 Hurley Day 2 Valid 12Z Wed Jul 31 2024 - 12Z Thu Aug 01 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE UPPER MISSISSIPPI VALLEY INTO THE MID WEST, OVER PORTIONS OF NORTHERN NEW ENGLAND, AND SOUTHERN ARIZONA... 20z Update: Main change with this update was to introduce a Slight risk across portions of southern AZ. Models show an uptick in both moisture and instability compared to today, with indications of a weak wave moving in from the southeast. This combination of increased forcing and better thermodynamic environment should support greater convective coverage with locally heavy rainfall rates. HREF probabilities are elevated as well...with 2"+ neighborhood probabilities of 40-60% and 1" EAS probabilities of 5-15" indicating at least some ensemble agreement on location/coverage of convection. Also worth noting that the GFS has consistently been indicating a heavier QPF event over southern AZ this period. Today also look less active than recent days, which in theory should allow for a more primed environment tomorrow. Given all these factors will go ahead and upgrade to a small Slight risk over southern AZ. Mainly just minor changes to the Slight risk over the Plains and MS Valley. An MCS should be ongoing at 12z Wed somewhere over IA ad/or IL...and some flash flood risk may exist with this activity as it pushes southeastward. Stronger forcing moves into the Plains Wed afternoon, which will result in organized convective development over SD/NE, which should then grow upscale into portions of MN/IA overnight. At least some flash flood risk should exist with this activity. The Slight risk over portions of VT/NH looks in good shape. In fact given the recent flooding and wet antecedent conditions over this area, do consider this a higher end Slight risk. Locally significant flash flooding is a possibility...although the expected coverage remains below MDT risk levels at this time. Chenard ....Previous Discussion Below... ....Upper Mississippi Valley into the Midwest... The progressive northern stream flow will continue into day 2 with the next strong area of height falls expected to push eastward across the Northern Plains and into the Upper Mississippi Valley. There is potential for additional organized convection/heavy rainfall to push eastward with these height falls across eastern portions of the Northern Plains and into the Upper Mississippi Valley as low level southerly flow strengthens into the west to east oriented frontal boundary expected to stretch from the NE/SD border, east across northern IA into northern IL. 850-700 mb moisture flux anomalies into this front expected to rise to 2 to 3 standard deviations above the mean in the 0000 to 1200 UTC Thursday period. There are still a lot of model qpf spread with some typical latitude differences with the max qpf axis. The day 2 slight risk area was drawn to favor the more southern solutions of the NAM, NAMNEST and CMC. ....Eastern New York State into western New England... The strong height falls moving out of the Central Appalachians into the Northern Mid-Atlantic day 1, will progress across eastern NY State into New England day 2. There is a typical amount of qpf spread for the day 2 period, but general consensus for potential of moderate to locally heavy rainfall amounts in a region of much above average PW values ahead of these height falls. A small slight risk area was added along the VT/NH border where very heavy rainfall amounts have occurred early Tuesday morning and where several models show potential for additional heavy rains during day 2. Otherwise,a broad marginal risk area was maintained from the previous issuance to capture the heavy rainfall spread in the models across this area day 2. ....Southwest... Similar to the day 1 period, the mid to upper level ridge will remain centered over the Southern Plains. Scattered convection again likely over portions of the Southwest as shortwave energy again rotates northward on the western side of this ridge and into the Southwest. Localized heavy rains and isolated runoff issues again possible for southeast Arizona into southwest to central New Mexico. Oravec Day 3 Valid 12Z Thu Aug 01 2024 - 12Z Fri Aug 02 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE OHIO VALLEY... 20z Update: Main change was to add in a Slight risk across portions of the OH Valley. From an ingredients based perspective things appear favorable for a swath of excessive rainfall Thursday into Thursday night. Pretty impressive forcing will move into the region, with a well defined closed mid level low and associated upper jet. Should also end up with plentiful low level moisture transport and convergence near a stationary front. Plenty of instability is expected near and south of this front, and PWs will increase at least 1-2 SD above early August averages. Thus confidence in heavy rainfall appears above average. However plenty of uncertainty still exists with regards to the placement of the greatest risk. Given the ingredients in place...think upgrading the risk now is warranted...although certainly a good chance the exact location will shift some as the event nears. The Slight risk follows pretty close to the CSU UFVS machine learning ERO...which is a bit south of the global QPF consensus and better aligns with the expected axis of favorable ingredients and stationary front position. Chenard ....Previous Discussion Below... ....Upper Mississippi Valley, Lower Lakes, Ohio Valley... The strong height falls pushing through the Northern Plains into the Upper Mississippi Valley day 2 will sink more to the southeast into the Mid Mississippi Valley/Mid West region day 3. Additional heavy rains likely ahead of these height falls and the associated surface low in a region of above average PW values and anomalous 850-700 mb moisture flux. There are some large model qpf difference's with respect to the axis of the heaviest rains. The marginal risk was drawn to encompass this range form the northern solutions of the UKMET/GEM from southern WI into the southern L.P. of MI, to the southern solution of the NAM and EC from southern IL, southern IN, southern OH, into northern KY. Given the spread and low confidence at the moment with which qpf axes is the best, the risk level was kept at marginal. ....Southwest into southern California... The upper ridge over the Southern Plains is forecast to build to the west and northwest across the Rockies, Great Basin and Southwest during day 3. This will help to push the axis of above average PW values farther west into southern to central California and southern Nevada. This will support an expanding area of scattered diurnal convection into portions of central and southern CA/southern NV from days 1 and 2. The marginal risk area was also expanded westward from the previous issuance to include western AZ, southern NV into southern to south central CA. Oravec Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6KN1_ZS-i88A8sd3bFu1EqKj5I6pn9wCaQS8q-3EKT-4= 1tyA2_ho_BBst1K1t_SS7m71VRxWyym4UIOz1n52mwy-BLQ$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6KN1_ZS-i88A8sd3bFu1EqKj5I6pn9wCaQS8q-3EKT-4= 1tyA2_ho_BBst1K1t_SS7m71VRxWyym4UIOz1n52XCmJC-k$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6KN1_ZS-i88A8sd3bFu1EqKj5I6pn9wCaQS8q-3EKT-4= 1tyA2_ho_BBst1K1t_SS7m71VRxWyym4UIOz1n52jDS5Zx4$=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .