Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Feb 02 2024 15:48:06 FOUS30 KWBC 021548 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1046 AM EST Fri Feb 02 2024 Day 1 Valid 16Z Fri Feb 02 2024 - 12Z Sat Feb 03 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS EASTERN PORTIONS OF THE SOUTHERN PLAINS TO THE MIDDLE AND UPPER TEXAS COAST... 16Z Update... The 12Z HREF guidance and recent runs of the HRRR remain generally in good agreement with the overnight guidance concerning the expectation for at least some broken bands of convection to develop across portions of the southern Plains as shortwave energy/height falls advance east out of the Southwest. Some localized swaths of 1 to 2+ inch rainfall totals seem likely given the level of dynamical forcing that will be in place along with at least some modest elevated instability. The strongest instability will most likely be focused down across area of south-central to southeast TX and this is where generally the heaviest rainfall rates should be focused. Based on all of this, the previous Marginal Risk area was maintained with just some subtle tweaks made to account for the new HREF guidance. Orrison Previous discussion... The latest model guidance remains consistent with the increasing shower/thunderstorm activity across the Southern Plains Friday afternoon/evening as strong height falls push through the Southwest and into the Southern High Plains. PW values expected to continue to increase day 1 ahead of these height falls as low level southerly flow strengthens off the western Gulf and spreads northward into the Southern Plains. The well defined upper difluence ahead of these height falls and the axis of increasing PW values will support potential for areas of heavy rains. There continues to be a lot of spread with where the heaviest totals will occur. This is illustrated well with the HREF neighborhood probabilities showing a large area of high probabilities for 1"+ totals across central to eastern Texas, northward into portions of southeast to western Oklahoma and south central Kansas. However, the EAS probabilities for 1"+ amounts day 1 are much lower indicating poor overlap in the latest hi res models. The previous marginal risk area still fits the geographical spread in the latest guidance, leading to no changes at the moment in the marginal risk area. No changes also to the risk level given the current spread in qpf details and consensus that any precip will be generally to the northwest of where the heaviest amounts have occurred over the past few weeks. Oravec Day 2 Valid 12Z Sat Feb 03 2024 - 12Z Sun Feb 04 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM EAST TEXAS INTO PORTIONS OF THE LOWER MISSISSIPPI VALLEY/CENTRAL GULF COAST... ....Central Gulf Coast into the Lower Mississippi Valley... The expanding convection across eastern Texas at the end of day 1, will continue to push eastward day 2 across the Central Gulf coast and toward the Lower Mississippi Valley. Overall favorable conditions continue for heavy rains day 2 with well defined upper difluence spreading east in an axis of strong southerly onshore flow off the Gulf and PW values of 1 to 1.5". There is better model agreement, however, that the heaviest qpf axis will be closer to the Gulf coast, where instability will be better.=20 Subsequently, we have trimmed the northern end of the previous slight risk area by about 150-175 miles. In the area where the slight risk was removed, rainfall has been less over the past week compared to previous weeks. This is evident in many of the USGS sites that show river gauge heights lowering over the past week.=20=20 Closer to the Gulf coast where the heaviest qpf is expected, the convection will still be fairly progressive. There still is the potential for the convection to be offshore of the central Gulf coast, but with still enough models showing heavy precip across southern LA into far southern Mississippi, did not want to remove the slight risk entirely. The marginal risk area extending northwestward into Arkansas, eastern Oklahoma, eastern Kansas and far southwest Missouri, was narrowed from the previous issuance to better match the narrow axis of moderate to locally heavy precip totals. ....Central California Coast... The previous marginal risk area was expanded to the north by approximately 80 miles to cover the spread of qpf that falls by the end of day 2 associated with the next atmospheric river event. All models are in agreement that the heaviest rainfall amounts will be during the day 3 period. However, with recent heavy rains across this area and potential for additional heavy rains to start by the end of the day 2 period, a marginal risk of runoff issues is warranted. Oravec Day 3 Valid 12Z Sun Feb 04 2024 - 12Z Mon Feb 05 2024 ....THERE IS A SLIGHT MODERATE RISK OF EXCESSIVE RAINFALL ALONG COASTAL SECTIONS OF CENTRAL TO SOUTHERN CALIFORNIA... ....Central to Southern California... While there are still some detail differences with deepening low pressure off the Central California coast Saturday night into Sunday, all models agree the next Atmospheric River event will commence as strengthening southerly low level flow impacts the Central to Southern California coastal region during day 3. IVT values are expected to be stronger than the first AR event Wednesday-Thursday, reaching 600-800 kg/m/s along the Central to Southern CA coastal region. Widespread 2-4" totals likely along the Central to Southern CA coast, with the heaviest amounts in the western portions of the Transverse range where the strong southerly low level flow will have the strongest upslope component, with totals of 5-8"+ possible. Overall, not a lot of changes made to the previous outlook. The moderate risk area was extended farther to the north to cover the northwest portion of WFO LOX and the far southwest portion of WFO MTR. ....Southeast, eastern Gulf Coast and Florida... The broad closed upper low over the Southern Plains at the end of the day 2 period will be pushing east southeastward into the north central to northeastern Gulf day 3. Strong southerly to southeasterly low level flow will press across the eastern Gulf coast/FL and the Southeast. This will support a broad region of moderate to heavy precip totals across the Southeast, eastern Gulf Coast and Florida. Heaviest totals likely where this precip area pivots and low level east southeast to easterly flow persists over the same region the longest. Model consensus is for this to be from the Lower coast of South Carolina, across south Georgia , North Florida into southern Alabama. Observed precip amounts have been below average over the past few weeks across this region, warranting just a marginal risk at the moment. The best area of instability and potential for organized convection is across Southwest to South Florida late Sunday afternoon/evening. Any associated precip moving off the eastern Gulf and across Southwest to South Florida likely will be very progressive, which will keep precip totals from being very heavy. This potential convection, however, will be moving over the more urbanized regions of Southwest to Southeast Florida, which will keep some threat of urban runoff issues, although precip totals are expected to be less than areas farther to the north. Oravec Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-0uUTx8NItUNMyKK4dV6YrGcDGo244-R1UQTSV1hEi7g= Rhyzpbcf8R1I2eRLMuUDx4QzzI3fxE65JA-o1fQqTnJnHHw$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-0uUTx8NItUNMyKK4dV6YrGcDGo244-R1UQTSV1hEi7g= Rhyzpbcf8R1I2eRLMuUDx4QzzI3fxE65JA-o1fQqNy4pnZU$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-0uUTx8NItUNMyKK4dV6YrGcDGo244-R1UQTSV1hEi7g= Rhyzpbcf8R1I2eRLMuUDx4QzzI3fxE65JA-o1fQqt_zxdQc$=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 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .