BBS: TELESC.NET.BR Assunto: HVYRAIN: Excessive Rainfall Discussion De: COD Weather Processor Data: Sun, 19 Apr 2026 00:26:17 +0000 ----------------------------------------------------------- FOUS30 KWBC 190026 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 826 PM EDT Sat Apr 18 2026 Day 1 Valid 01Z Sun Apr 19 2026 - 12Z Sun Apr 19 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTHEAST TEXAS INTO SOUTHWEST LOUISIANA... 01Z Update: Lingering instability and deep layer moisture along I-10 between Houston and Lake Charles will maintain an isolated heavy rain threat through the next 2-3 hours before dwindling. Drier theta_E advection regime is already ongoing just to the north with the last bit of low-level convergence centered right along the I-10 corridor where the front is aligned. Expect a slow filtering of more stable air between 850-700mb to help alleviate the threat over the course of the evening with the threat completely diminished after 06z. The front tilts northeast towards KLCH, so the threat may linger longer over southwest LA, but still a low-end threat relegated to the urban zones. The MRGL risk remains over a small area extending between Houston and Lake Charles with the risk greatest over the I-10 corridor and the cities themselves, including Beaumont, TX.=20 Kleebauer Day 2 Valid 12Z Sun Apr 19 2026 - 12Z Mon Apr 20 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTH TEXAS... ...1900Z Update... No major changes were needed to the Day 2 South Texas Marginal. Lack of instability will certainly be a limiting factor across the region, and HREF probabilities of exceeding 3h and 6h FFG are nil. But a low-end flash flooding risk could emerge due to the moist environment with stalling/slow-moving convection discussed below, so will give the Marginal another cycle in the outlook. It looks like convergence along coastal areas may produce locally higher rain totals during the day, while northwestern areas of the Marginal could see renewed convection overnight as the shortwave approaches. Tate ...Previous Discussion... The cold front from Saturday night should be just off the coast and into the Gulf Sunday morning, although a residual inverted trough extending from the tail of this front is expected to linger across South Texas much of the period. As the day progresses, weak shortwave energy embedded within a shallow southern stream trough will emerge from Mexico to produce modest ascent through divergence and PVA, combining with convergence along the aforementioned trough to create scattered showers and thunderstorms across the region. Downstream of this feature, subtle ridging will halt the progression of the surface trough, while additionally keeping PWs pooled across South Texas, which is reflected by NAEFS ensemble tables indicating that PWs will remain above the 90th percentile of the CFSR climatology. The overlap of this ascent into the moist column will manifest as heavy rain producing convection, with both HREF and REFS indicating a low end potential for 1"/hr rainfall rates. While the high-res simulated reflectivity still features wide variation in coverage, making confidence in the excessive rainfall potential a bit lower than usual, storm motions within any of this convection will likely be slow (0-6km mean winds of just 5-10 kts), so any of these heavy rates could be sufficient to overcome the FFG. The greatest potential may be along the immediate coast due to the overlap of slower storms (pinned) and lower FFG, but anywhere these slow storms develop, isolated instances of flash flooding could result. Weiss Day 3 Valid 12Z Mon Apr 20 2026 - 12Z Tue Apr 21 2026 ...THERE IS A MARGINAL CHANCE OF EXCESSIVE RAINFALL ACROSS PARTS OF NORTHERN CALIFORNIA AND ACROSS THE LOWER-MIDDLE TEXAS COAST TO THE HILL COUNTRY... ...1900Z Update... Both the northern California and Texas Marginal Risks for Day 3 still look on track. Little to no changes were needed based on new guidance, and the previous discussion's reasoning remains valid. Tate ...Previous Discussion... ...Northern California... Deepening upper level low eventually closes off late in the weekend off the northern CA coast. Afterwards, the guidance shows this broad, deep low pinwheeling slowly eastward on day 3, thereby allowing for a prolonged period of favorable forcing, i.e. upper diffluence/deep layer ascent and anomalous low-mid layer moisture transport. The latest GEFS in fact indicates 850-700 mb moisture flux peaking between 2-3 standard deviations above normal from the Bay area into the northern CA coastal ranges and Sacramento Valley. Due to the nature of the upper system (closed mid-upper low), this will not be a typical AR event, per the 'weak' AR classification from CW3E. However, Integrated water vapor transport (IVT) values do peak around 500 Kg/m/s, while the guidance (GFS-ECMWF-NAM) does indicate elevated CAPEs of 100-250 J/Kg. Areal average QPFs per the guidance on Day 3 (12Z Mon-12Z Tue) support widespread 1-2" rainfall totals, though higher-res members (including the RRFS) do show isolated higher totals closer to 3". Given the potential for at least 0.50"/hr rainfall rates on Day 3, the Marginal Risk area was maintained (and expanded) to account for the possibility of some excess runoff over burn scars. ...Lower-Middle Texas Coast to the Hill Country... Guidance continues to show subtle/flat southern stream shortwave traversing this area Mon-Mon night, which will likely become convectively-aided from any MCV(s) emanating out of northeast Mexico. Uptick in deep-layer forcing along with moisture pooling from the western Gulf (PWs increasing to 1.7-1.8") and some, albeit weak instability (MUCAPEs ~500 J/Kg) will lead to a more favorable environment for widespread rainfall with embedded heavier cores. We maintained the Marginal Risk area inherited from yesterday's Day 4 ERO, while expanding a little farther north to include parts of the Hill Country based on the latest guidance trends (deterministic and probabilistic QPF). In addition, the latest ECMWF Extreme Forecast Index (EFI) for QPF peaks between 0.6-0.7 during this event, with a shift-of-tails close to 1 along the coast. Hurley Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_tpcB94G50aWaIuC0TXYjs_5aZgm15kzlUe2QgMMEi5m= Mf5ckqJc2Bh96YlNOQKxm-aj8T3-LyCm0FeD_Fh3iF0u-3A$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_tpcB94G50aWaIuC0TXYjs_5aZgm15kzlUe2QgMMEi5m= Mf5ckqJc2Bh96YlNOQKxm-aj8T3-LyCm0FeD_Fh3SqC2hLs$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_tpcB94G50aWaIuC0TXYjs_5aZgm15kzlUe2QgMMEi5m= Mf5ckqJc2Bh96YlNOQKxm-aj8T3-LyCm0FeD_Fh3RunA7E4$=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]