Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jul 13 2025 15:59:35 FOUS30 KWBC 131559 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1159 AM EDT Sun Jul 13 2025 Day 1 Valid 16Z Sun Jul 13 2025 - 12Z Mon Jul 14 2025 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE TEXAS HILL COUNTRY... 16Z Update... ....Southern Plains into Eastern Arkansas... The ongoing convective complex over Central Texas continues to=20 show weakening trends overall from a very active overnight/morning. A large MCV is noted between San Angelo and Killeen which should=20 continue to allow some development/expansion southeast toward San=20 Antonio and on the west side north of Del Rio through the early=20 afternoon. However, the reduction of the LLJ through this morning=20 should maintain lower rain rates than were experienced this=20 morning.=20 The question is what happens tonight with convection. 12Z CAMs are overall not very concerning, but the RAP presence of 2.25" PW=20 pooling south of the current MCV which becomes the inflow for the=20 LLJ tonight means anything that does develop in central TX should=20 have healthy inflow for additional heavy rains. Therefore, will=20 maintain a Moderate Risk, but with a bit more of an east-west=20 orientation and a little south than current. This is mainly along=20 the SJT/EWX boundary including a fair portion of the Texas Hill=20 Country including Kerr Co. Farther northeast/downstream of the existing MCV and east of a stationary front, elevated moisture and instability will continue to allow some organization over northeast TX, eastern OK, western AR where a Slight Risk remains in effect. ....New Mexico... The westward periphery of the PW plume emerging from the Gulf is spreading into New Mexico, spreading PWs above 1" (+1 sigma) into=20 the High Plains and into the terrain of the central part of the=20 state. This PW will overlap with a ribbon of MUCAPE around 2000=20 J/kg to support scattered to numerous thunderstorms developing=20 during peak heating over the higher terrain. These storms will=20 initially move slowly on 0-6km mean winds of just 5 kts, but the=20 presence of 20-25 kts of bulk shear will help drive modest=20 organization as storms come off the terrain and drift southward on=20 Corfidi vectors around 10 kts. With rain rates above 1"/hr likely,=20 this could result in instances of flash flooding, especially over=20 sensitive terrain features, urban areas, or burn scars. A Slight Risk is maintained over the Sacramento into north-central NM terrain. The Marginal Risk is expanded to southeast AZ, more of south-central CO, and more of eastern NM. ....Missouri and Illinois... Minor expansion of the Slight Risk over northeast MO and south- central IL. Ongoing activity is present along a stationary front. MPD 0669 is forthcoming with further information. ....Mid-Atlantic into the Northeast... 16Z Update...Minor expansion east with Slight Risk over/toward the I-95 corridor per 12Z CAM consensus. Mid-level ridge gradually pulsing northward from the Gulf Coast will interact with a broad and slow moving trough advecting across the Great Lakes to produce pinched SWly flow across much of the eastern CONUS. This will manifest as impressive thermodynamics being drawn northward from the Mid-Atlantic into interior portions of the Northeast. These thermodynamics will be characterized by PWs of 1.75 to 2.0 inches (90th - 99th percentile according to NAEFS) and collocated MUCAPE of 1000-2000 J/kg to produce an environment favorable for heavy rain. Into this environment, a cold front, pushed slowly eastward by the mid-level trough to the west, will combine with slow height falls to drive pronounced ascent, creating scattered to numerous thunderstorms from the eastern Ohio Valley into Northern New England. These storms will contain heavy rain rates that have a 30-50% chance of exceeding 1"/hr with brief 2+"/hr rates also possible. Although bulk shear is progged to be minimal such that convection will generally remain of the pulse variety, brief training as 0-6 km mean winds aligns to the front will allow for some longer duration of this heavy rainfall in a few areas, leading to HREF and REFS 24-hr probabilities that peak above 70% for 3". While it is difficult even at this time range to identify the areas most at-risk to flash flooding due to uncertainty in exact convective placement, 0-10cm soil moisture is above the 90th percentile according to NASA SPoRT from central VA through Upstate NY, which is also collocated with the locally higher ensemble probabilities. This suggests that the inherited SLGT risk is warranted, and only adjusted cosmetically for new guidance, although there is a signal in the guidance for some locally heavier rainfall across the Finger Lakes region of NY due to repeating/backbuilding cells which could result in some locally more substantial impacts. ....Florida... 16Z Update... Expansion west of Marginal Risk per 12Z CAM consensus. Slow moving 500mb trough east of Florida will strengthen gradually as it drifts W/SW today. The accompanying vorticity maxima will=20 provide some locally enhanced forcing to the eastern side of FL,=20 while the entire peninsula remains sandwiched between this and a=20 ridge to the west, producing northerly flow across the area. As the vort swings westward, some locally enhanced diffluence will=20 develop aloft as well, and as this occurs in the presence of PWs=20 above 2 inches collocated with MUCAPE of 2000-3000 J/kg, widespread convection with heavy rain will result. CAMs suggest storms will=20 fire on the E/NE side of the peninsula and then drift SW, with some locally enhanced organization possible into clusters thanks to=20 20-30 kts of bulk shear. With rain rates progged by the HREF to=20 have a 30-50% chance of exceeding 2"/hr, this could result in total rainfall of 3-4", locally higher, as suggested by 24- HREF/REFS=20 probabilities and PMM. Where this rain occurs over more urban=20 areas, local flash flooding could result. ....Louisiana... Added a Marginal Risk for central LA as outer bands from a tropical wave over the central Gulf continues to produce development in a moist/unstable environment. This includes Baton Rouge and Lafayette. Jackson Day 2 Valid 12Z Mon Jul 14 2025 - 12Z Tue Jul 15 2025 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE FLORIDA PENINSULA AND PORTIONS OF THE MID-ATLANTIC STATES... ....Florida... The westward-advancing and deepening mid-level wave will reach the FL peninsula on Tuesday, providing widespread increasing ascent across the state. In addition to the height falls/PVA accompanying this trough, modest upper diffluence will develop as northerly flow continues, enhancing deep layer lift. This impressive and amplifying ascent will impinge into intensifying thermodynamics with PWs surging above 2.25 inches, or above the 90th percentile according to NAEFS. There continues to be some evolutionary discrepancies among the various models, but in general the setup will be favorable for widespread thunderstorms with heavy rainfall, especially during peak heating when MUCAPE climbs above 2000 J/kg. The heaviest rainfall will again likely develop across the NE portion of the peninsula, similar to Sunday, and then track SW along outflows and any weak low-level convergent boundaries. With rainfall rates likely eclipsing 2"/hr, some bulk shear 20-30 kts to help organized convection into clusters, and chaotic/weak storm motions, total rainfall could exceed 3" in places again on Monday. The inherited SLGT risk was adjusted slightly, but in general remains as inherited and over the greatest ensemble probabilities from the HREF, SREF, and ECMWF EFI. ....Mid-Atlantic States... A cold front will gradually traverse southeast across the Mid- Atlantic and Northeast on Monday, with thunderstorms likely developing along it during the afternoon and evening. This front will be pushed eastward downstream of an advancing, but weakening, mid-level trough axis, with the resultant and lingering strung out vorticity helping to provide additional ascent along the boundary. This ascent will work into thermodynamics that will be extremely supportive to heavy rain within thunderstorms, as broad return flow ahead of the front (SW at 10-15 kts) draws a ribbon of PWs above 2 inches (above the 90th percentile according to NAEFS) and collocated MUCAPE over 1000 J/kg into New England. This will also be an area where warm cloud depths are progged to reach extreme values above 15,000 ft, supporting efficient warm-rain processes which have a 40% chance of exceeding 2"/hr according to the HREF, especially in the Mid-Atlantic. While heavy rain rates are expected within any convection along this advancing front, in general, storms should be more progressive with greater latitude. However, there is a signal in the available guidance for some convection to develop ahead of the front and then backbuild into the greater thermodynamics across the Mid-Atlantic region leading to some locally higher ensemble probabilities for 3"/24hrs and a modest but notable ECMWF EFI signal. This area has also been wet the past 7 days, and soil infiltration capacity is limited (FFG as low as 1-1.5"/3hrs). For these reasons, a SLGT risk has been added for Monday, with urban areas and most sensitive soil regions of VA/MD/PA favored for the greatest potential for excessive rainfall. ....Desert Southwest through the Ozarks... The same cold front moving into the Mid-Atlantic Monday will sag southward but weaken and dissipate across the Southern Plains as it interacts with slow height rises as a ridge slowly builds from the south. Despite the weakening front, ascent will remain as a shortwave and accompanying strung-out vorticity drift over the area, especially near the Ozarks as it gets trapped within a col between neighboring high pressures. There will also likely be other modest vorticity impulses rotating through the flow into the Southwest to additionally provide locally targeted ascent. This lift will work into a still very favorable environment to support heavy rainfall as PWs remain nearly 2 inches into the Ozarks and above 1" as far as southern Arizona thanks to persistent moist advection out of the Gulf leading to PW anomalies reaching above the 90th percentile locally from West TX into NM and near the Ozarks. These are the locations that may have slightly higher potential for excessive rainfall on Monday, with slow moving storms over West Texas/New Mexico (0-6km mean winds 5 kts or less) and organized convection on 20-30 kts of bulk shear from OK into MO/AR. However, at this time, despite some modest signals for a locally enhanced flash flood risk, the MRGL risk remains as confidence is not higher enough for an upgrade at this time. ....Northern Plains... Potent but positively tilted shortwave will dig out of British Columbia and emerge into a belt of pinched westerlies aligned to the Canada/United States border. This will help elongate a cold front as it drops southward into the Northern Rockies and Northern High Plains, producing locally enhanced ascent across the area. A piece of this vorticity lobe will swing rapidly eastward and interact with the low-level baroclinic zone, which will intensify due to warm advection on an 850mb LLJ surging to 30 kts Monday evening up the Plains, drawing thermodynamics characterized by PWs of 1-1.25 inches and MUCAPE of 1000 J/kg northward. This will support scattered thunderstorms Monday night, and although cells should remain progressive on 0-6km mean winds of 20-25 kts, aligned Corfidi vectors to the mean wind and the front suggests training which could produce 1-2" of rainfall and local FFG exceedance. Weiss Day 3 Valid 12Z Tue Jul 15 2025 - 12Z Wed Jul 16 2025 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE SOUTHERN FLORIDA PENINSULA AS WELL AS THE UPPER MIDWEST... ....Florida... The same mid-level wave traversing the Florida Peninsula on D2 will continue its westward advance D3, reaching the eastern Gulf Coast by Wednesday morning. Once again, the ascent accompanying this feature will act upon impressive thermodynamics, with PWs reaching 2-2.25 inches collocated with MUCAPE above 1000 J/kg. The guidance suggests that this may manifest as a surface low by D3, (and NHC is monitoring this area with a low probability of development in the TWO), which could additionally enhance ascent. As winds behind the wave turn back to the S/SE across the peninsula, it will likely result in weakly convergent boundaries upon which thunderstorms will blossom and track NW with 2+"/hr rates. Where these cells exhibit even short-term training, especially atop urban areas or across soils moistened from rainfall on D1 and D2, instances of flash flooding could result from 2-3" of rain with locally higher amounts. ....Northern Rockies through the Upper Midwest... A broad mid-level trough with pinched flow will translate gradually southeast through D3, within which waves of vorticity will advect. This will push a cold front, initially aligned generally west-to- east, to become more SW to NE as it approaches the Upper Midwest the latter half of the period. Although there remains considerable placement uncertainty in the axis of heaviest QPF due to differences in frontal position, the accompanying ascent (driven by low-level convergence, PVA, and jet-level diffluence) will produce widespread convection on Tuesday. As the front shifts east, waves of low pressure may additionally develop along this front, providing locally enhanced ascent into PWs above the 90th percentile according to NAEFS. This will support rainfall rates of 1-2"/hr, with training of echoes likely due to boundary parallel mean flow. The greatest potential for heavy rainfall appears to be focused in northern MN and eastern ND where training along the boundary may be most efficient, and where ECMWF EFI is highest. However, there is a secondary max in consensus QPF across eastern SD and northeast NE where backbuilding/regenerating cells may be more likely. After coordination with the affected WFOs, despite uncertainty in the exact placement, a SLGT risk was added for this region. ....Mid-Atlantic and Southeast... A generally moist and unstable environment will remain across much of the eastern CONUS Tuesday as broad ridging expands from the Atlantic. 850mb flow around the offshore ridge will become increasingly S/SE, surging a ribbon of PWs above 2" from the Gulf Coast through southern Virginia. Although forcing for ascent will be modest, widespread showers and thunderstorms are expected, many of which will have 1-2"/hr rain rates despite their pulse nature. This has resulted in some minor adjustments to the MRGL risk to capture the highest GEFS/ECENS probabilities for 1-3" of rainfall due to the slow moving storms. There is a potential that a SLGT risk may be needed with future iterations for the Appalachians where upslope flow may enhance rainfall in western NC and VA, but confidence at this time is not high enough for an upgrade. Weiss Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8EkPMoDFV6SgeEzcq1BjqosG67lgFSQEbpTSjpUkpglQ= sJqaWNFrJ-JpijbDRjPvtpOhZd_LGgK628PKvDPr1uWpC9M$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8EkPMoDFV6SgeEzcq1BjqosG67lgFSQEbpTSjpUkpglQ= sJqaWNFrJ-JpijbDRjPvtpOhZd_LGgK628PKvDPrPcs1fzc$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8EkPMoDFV6SgeEzcq1BjqosG67lgFSQEbpTSjpUkpglQ= sJqaWNFrJ-JpijbDRjPvtpOhZd_LGgK628PKvDPrntf-NDc$=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) .