Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Oct 15 2025 19:57:32 FOUS30 KWBC 151957 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 357 PM EDT Wed Oct 15 2025 Day 1 Valid 16Z Wed Oct 15 2025 - 12Z Thu Oct 16 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTHERN COLORADO AND NORTHERN NEW MEXICO... ....16Z Update... No significant changes were needed with this update. Some of the northern valleys in Colorado were excluded from the Marginal, given their positioning on the lee side of the San Juans and Sangre de Cristos. Otherwise, the previous discussion remains valid. Wegman ....Previous Discussion... A large mid/upper wave centered across Nevada at 12Z Wednesday will migrate eastward during the forecast period, spreading height falls across the central and southern Rockies. As this occurs, cooling aloft and surface heating will foster development of a few showers and thunderstorms across southern Colorado and northern New Mexico especially during the afternoon and evening hours. Point forecast soundings across the region depict fast storm motions (30-50 knots) with any developing convection, although steep lapse rates aloft and 0.5-0.75 inch PW both suggest potential for brief heavy rainfall especially where any backbuilding can materialize. Wet antecedent conditions and very high streamflows (per the USGS Water Dashboard) are suggestive of ground conditions that are readily supportive of excessive runoff due to poor drainage. Additionally, a few burn scars across the region could support local excessive runoff at times. Areas of 1-2 inch rainfall totals are possible - especially in upslope and terrain-favored areas. Isolated flash flooding is possible in this regime. Cook Day 2 Valid 12Z Thu Oct 16 2025 - 12Z Fri Oct 17 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF EASTERN MONTANA AND WESTERN NORTH DAKOTA... ....2030Z Update... Only a very small westward nudge into more of eastern Montana was made with this update, in keeping with the latest trends in the guidance. Meteorologically the pattern is largely unchanged. This area will be under the comma-head/wraparound region of a developing Plains low that will track north-northeast from western South Dakota through central North Dakota and into Manitoba. The wraparound region will remain largely stationary through the day, as bands of light to moderate rain pivot east to west across the Marginal Risk area. Some convective instability associated with the developing low could result in periods of heavier rainfall rates, especially on the eastern side of the comma-head region. Since soils in northeast Montana are at or a bit above their climatological normal for soil moisture, the prolonged period of light to moderate rain could result in isolated instances of flash flooding, especially in low-lying and flood-prone areas. The Marginal Risk therefore remains in effect. Wegman ....Previous Discussion... Strengthening mid-latitude cyclone will traverse the Northern High Plains by Thursday afternoon and beyond with a developing closed mid-level vorticity center propagating over eastern MT to the MT/ND border. The subsequent evolution will lead to a period of moderate to heavy rainfall across the above areas with a prominent deformation axis anticipated to setup along the MT/ND border. At this juncture, instability will be lacking from a thermodynamic sense, however the dynamical forcing and prolonged period of enhancement with the axis of deformation will likely spur a widespread area of moderate to heavy rainfall capable of low-end flash flood concerns. These concerns will be suited mainly over those urbanized zones and any low-water crossing. Totals area expected to be a widespread 1-2" of rainfall with some localized totals >2", likely over western and northwestern ND as the heaviest rain will hang on there given the proxy of the surface low progression and positioning of the axis of deformation. A MRGL risk was maintained with a small expansion south to account for the latest QPF trends. Kleebauer Day 3 Valid 12Z Fri Oct 17 2025 - 12Z Sat Oct 18 2025 ....2030Z Update... The probability of rainfall exceeding flash flood guidance is less than 5 percent. Wegman Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_EDMx601IvfrJeCAV-B8xxi4DzuiWYut4lsQ_8RQy-Fc= OsC5R2mtvQUhbFhynS4X1A25MRZNvLq8E33Y5VdJ_3myu78$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_EDMx601IvfrJeCAV-B8xxi4DzuiWYut4lsQ_8RQy-Fc= OsC5R2mtvQUhbFhynS4X1A25MRZNvLq8E33Y5VdJtFeH09c$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_EDMx601IvfrJeCAV-B8xxi4DzuiWYut4lsQ_8RQy-Fc= OsC5R2mtvQUhbFhynS4X1A25MRZNvLq8E33Y5VdJkvCmjJU$=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 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .