BBS: TELESC.NET.BR Assunto: HVYRAIN: Excessive Rainfall Discussion De: COD Weather Processor Data: Sun, 26 Apr 2026 08:02:28 +0000 ----------------------------------------------------------- FOUS30 KWBC 260802 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 402 AM EDT Sun Apr 26 2026 Day 1 Valid 12Z Sun Apr 26 2026 - 12Z Mon Apr 27 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN THE CENTRAL PLAINS... The latest hi-res model guidance has trended substantially toward=20 a corridor of heavy rainfall in the Central Plains this evening and tonight. Therefore, confidence has increased in a heavy rain event, but considerable uncertainty still remains on the location. Some guidance places the heaviest rain almost wholly into Iowa, while other guidance is further south in the vicinity of the I-70 corridor in Kansas and Missouri -- almost 200 miles of variability with approximately 18 hours of lead time. Given the consistent signal for significant rainfall, we have upgraded to a Slight Risk, and drawn it broadly to account for positional uncertainty. The contours were largely based on EAS probabilities from the 00Z HREF; and the major axis of the Slight Risk area intersects the QPF maximum on the AI versions of the GFS and GEFS. Convection is expected to develop this afternoon on the nose of a strengthening low-level jet (LLJ) and plume of instability, likely in northern Kansas or southeast Nebraska initially. The convective evolution in the approx. 6 hours after initiation will be=20 important. In general, all models show a west-to-east progression=20 of thunderstorm clusters, consistent with the bulk shear vectors,=20 and along a focused area of low-level convergence near the nose of=20 the LLJ. Some models show scattered clusters progressing over similar areas, but with intermittent breaks and not precise training; others show a more continuous band of convection training in a specific corridor (sustaining 1-2 inch per hour rain rates for several hours in a given location). Comparing QPFs from those=20 scenarios suggests the latter scenario could double rainfall, with amounts potentially high enough to lead to significant flash=20 flooding. Therefore, this will need to be monitored closely. A Marginal Risk was considered in the Arklatex region as ongoing convection will likely persist in some form beyond 12Z. However, a squall line in southern Arkansas appears to be forward propagating and accelerating, if anything. And other thunderstorm activity is more isolated and generally less intense. Therefore, a non-zero excessive rainfall risk does exist in the region, but no Marginal Risk was outlined at this time. Lamers Day 2 Valid 12Z Mon Apr 27 2026 - 12Z Tue Apr 28 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL PRIMARILY OVER SOUTHEAST IOWA AND NORTHERN ILLINOIS... The training band of convection from Sunday Night is likely to progress eastward into the Midwest on Monday; placement uncertainties grow on Day 2, but there has been a general southward shift in the location of the heaviest rainfall in model guidance over the last couple cycles. Some guidance now shows the corridor of heaviest rainfall on Monday and Monday Night as far south as the I-70 corridor from St. Louis to Indianapolis, while other guidance remains closer to the Illinois-Wisconsin border, where the existing Slight Risk area was concentrated. This is about a 200 mile spread. So while heavy rainfall is expected, confidence remains somewhat low on the location. Given the overall trends, the main change was to shift the axis of the Slight Risk southward, albeit only about=20 70 miles out of deference to continuity. The overall environment will be very supportive of heavy rain rates. A plume of 1.2 to 1.7 inch PWs (above the 95th percentile for late April) and moderate to strong instability will support 1 to 2 inch rain rates in organized convective clusters and lines. Although training convection may continue into Monday morning, convective lines should become oriented more in a north-south fashion later in the day as forcing along an accelerating cold front increases. The best opportunity for training convection, and therefore a longer duration of heavy rain rates, should be in or near the Slight Risk area. Areas further south should not only see steady progression to any convective lines, but have also been much drier lately, so the risk of flash flooding is lower despite some similar QPF from the latest model guidance. Lamers Day 3 Valid 12Z Tue Apr 28 2026 - 12Z Wed Apr 29 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER MUCH OF THE INTERIOR SOUTH... Fairly widespread convection is expected on Tuesday and Tuesday Night over much of the interior South, in a broad plume of anomalously high PWs between 1.5 and 1.8 inches with strong instability. Organized convective clusters and lines should be capable of producing rain rates up to 2 inches per hour, and any training could lead to localized flash flooding. Much of the region has been very dry lately; over the past 60 days most of Kentucky, Tennessee, and eastern Arkansas have seen less than half of their average precipitation. Therefore, the region is generally not primed for impacts from heavy rainfall, even though flash flooding can occur given sufficiently high rain rates sustained for a long enough duration. Given low confidence in mesoscale details, the risk level has been held at Marginal over the entire region for now. It's possible an upgrade to Slight Risk may be needed eventually, and may be more likely in Arkansas, eastern Oklahoma, or northeast Texas where there has been some rainfall in the past couple weeks, including earlier today. Lamers Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4T10gx-N-yGwyIZ0N9RCAPr0UneNxMHf1XKZ1SuqhqQB= 0xKzeOZbejKzCtAMjxg2jSfPTLk-VdZi8GZbIH3-eOcR17k$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4T10gx-N-yGwyIZ0N9RCAPr0UneNxMHf1XKZ1SuqhqQB= 0xKzeOZbejKzCtAMjxg2jSfPTLk-VdZi8GZbIH3-TFOlPOE$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4T10gx-N-yGwyIZ0N9RCAPr0UneNxMHf1XKZ1SuqhqQB= 0xKzeOZbejKzCtAMjxg2jSfPTLk-VdZi8GZbIH3-dPzezcc$=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: Capitol City Online (1:2320/107) ----------------------------------------------------------- [Voltar]