Quantitative Precipitation Forecast
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452 FOUS30 KWBC 081959 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 359 PM EDT Sat Jun 8 2024 Day 1 Valid 16Z Sat Jun 08 2024 - 12Z Sun Jun 09 2024 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF SOUTHERN MISSOURI... ...16Z Update... No major changes were needed with this update. Latest CAMs continue to suggest a Moderate Risk event across portions of southern Missouri starting late this afternoon and continuing into tonight. There remains some uncertainty as to where the axis of heaviest rainfall will set up, with the Moderate Risk area remaining a good average of the guidance. Unfortunately given the forcing will be along a nearly stationary boundary set up across the Ozarks of Missouri, until the storms start forming along that boundary later today there`s unlikely to be much change as to where the heaviest rain will set up. There remains considerable concern that once the storms begin forming and training along the boundary/front, there will be multiple hours of training thunderstorms moving along that boundary, as a southwesterly-oriented LLJ pumps moisture and instability into the front, and dry north to northeasterly flow north of the front helps to keep the front in place. Thus, the Moderate risk remains a very good forecast given the potential for significant impacts. Should the storms grow stronger, move slower, or train for longer, it`s possible a narrow area along the boundary may have High risk-level impacts, but certainty as to where that will be is way to low for any further upgrades. It`s probable with the 01Z update that the MDT may need to be adjusted a bit from its current placement, as the event should be underway by then. A secondary maximum in forecast precipitation is expected over western Kansas as well tonight, as storms that form further north and east into eastern Colorado track and merge over western Kansas. The western extent of the supporting LLJ over the TX/OK Panhandles should support potentially backbuilding storms, but it should not as robust totals as further east into Missouri due to faster storm motion. The Slight risk area was expanded a bit north and west to cover the northeastern corner of Colorado with a bit better agreement in the guidance. Wegman ...Previous Discussion... ...Eastern Kansas, Missouri, and Mid Mississippi Valley... A Moderate Risk (Level 3 of 4) was introduced for this forecast cycle for portions of southern Missouri where rounds of thunderstorms through early Sunday are likely to produce several inches of rainfall in a short period. Scattered to numerous instances of flash flooding are likely, with localized significant flooding possible. As of early this morning, a slow-moving MCS is advancing through far eastern Kansas and western Missouri and is expected to weaken some as it moves across Missouri by the beginning of the forecast period at 12Z. It will however likely lay out an outflow boundary west to east across far southeast Kansas through southern Missouri which will become the main focus for additional thunderstorm development later in the period. By late afternoon, the increasing moisture impinging on this boundary (PWs 2"+, 2-3 std above normal) and modest amounts of instability (MUCAPE 2000-3000 J/kg) is likely to ignite another round of deep convection. This activity is likely then to train/repeat west to east as the flow becomes increasingly parallel to the expected storm motions. This will favor some intense rain rates and high totals due to the combination of the favorable ingredients and training flow pattern. Several repeating rounds are possible, particularly over southwest to south-central MO. The HREF probabilities have continued to trend higher this cycle, the 24-hr 5" probabilities are exceeding 50 percent across southwest MO and there are slight signals (10-15 percent) for hourly totals in excess of 3" for several hours later this afternoon/evening. The primary forecast uncertainty is placement, with some north/south differences between the various hi-res models still at this forecast lead time and is likely tied to how this morning`s convection plays out and where the effective boundary ends up settling. The consensus is for somewhere across far southeast KS through Missouri, though some deterministic solutions are a bit to the north. ...Eastern Colorado to Kansas... The combination of robust heating, a modest amount of moisture, and an approaching shortwave trough will ignite a few rounds of intense thunderstorms later today initially over Colorado before evolving into an organized complex over western Kansas. Intense rain rates and some localized/slight threat of training could result in scattered instances of flash flooding. Convection initiation over the Front Range will be driven by the sufficient heating and shortwave trough moving through, and gradually the storms will move into a more moist environment (PWs getting closer to 1-1.25") that will help them grow upscale into an MCS. The latest HREF probabilities are moderate/high for 1" hourly totals (above 60 percent) across northern/northeast CO and even reach 20-25 percent for 2" hourly totals before increasing to above 50 percent across western Kansas when the larger MCS is likely to set up. For 24-hr rainfall totals, the HREF points to western KS for the greatest threat of at least 3 inches (above 40 percent) where the Slight Risk skews toward the higher end of the probability range (25-40%). By evening, the MCS should be rolling through Kansas at a faster clip but still will have enough environmental ingredient support to maintain the Slight for intense rain rates above 2"/hr at times and isolated/scattered instances of flash flooding. Taylor Day 2 Valid 12Z Sun Jun 09 2024 - 12Z Mon Jun 10 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF SOUTHEAST COLORADO, NORTHEAST NEW MEXICO, AND THE TEXAS PANHANDLE AS WELL AS MUCH OF THE OZARKS OF MISSOURI AND ARKANSAS... ...20Z Update... ...Southern High Plains... In coordination with ABQ/Albuquerque, NM and PUB/Pueblo, CO forecast offices, the Slight risk inherited for some of the Plains area east of the Front Range and Sangre De Cristos was expanded north and west to include those ranges, adjacent valleys, and associated burn scars. The meteorology remains little changed, but CAMs guidance covering the entire period suggests that while most storms will form immediately downrange of those aforementioned mountains, moisture will get into the mountains and valleys to the west, resulting in some convection in and west of the mountains. Thus, the Slight was expanded. There is particular concern around the Hermits Peak fire burn scar northwest of Las Vegas, New Mexico. The forecast of 1-3 inches of rain from convection may cause significant flooding in the area. This area is in a higher end Slight and continued increases of both coverage and intensity of convection in the area in and around the southern Sangre de Cristo range may require a future Moderate Risk. For now the convection appears to be a bit too scattered so impacts as of now appear too limited for a MDT. We will continue to monitor the trends in the CAMs in the area. ...Ozarks... The heavy rainfall event ongoing from Day 1 tonight is expected to continue into the morning hours of Sunday. Rainfall amounts of up to 1.5 inches are possible after 12Z/7am CDT, which would continue any ongoing flooding across the area. There`s good agreement that the rainfall will quickly weaken with the diminishing of the LLJ, so this Slight Risk upgrade is expected to only be for the morning, and should be removed with the midday update. ...Southeast Florida... A small Marginal Risk area was introduced with this update for expected moisture-laden sea breeze convection Sunday afternoon occurring over the urban I-95 corridor. An isolated instance or 2 of flash flooding can`t be ruled out should the convection form and persist over an urban area. Wegman ...Previous Discussion... ...Southern Plains to Central High Plains... Scattered to numerous thunderstorms are expected to develop across the region during the period, with a Slight Risk (Level 2 of 4) of excessive rainfall and flash flooding. A frontal boundary is forecast to be draped across the region, from eastern New Mexico through the Texas Panhandle. With that, a very anomalous pool of moisture will bank up against the terrain with PWs forecast to be above 1.5", which is 2-3 std above normal. A shortwave trough coming out of northwest Mexico is forecast to reach the region by the period, and this will help drive the more widespread convection, particularly over eastern NM. The latest model guidance continues to highlight potential for several inches (1-3") over eastern NM into parts of the TX Panhandle and with that and the environmental ingredients for more intense rain rates, the Slight Risk was only adjusted minimally from the previous forecast. ...Mid Mississippi Valley... The frontal boundary draped across the region along with favorable amounts of moisture will support isolated to scattered thunderstorms, with storms likely ongoing at the start of the period across Missouri that move eastward and weaken through the day. By later in the period, loosely organized convection is likely but without any strong focus, the Marginal Risk was maintained for potential of localized 1-1.5" totals. Taylor Day 3 Valid 12Z Mon Jun 10 2024 - 12Z Tue Jun 11 2024 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF NORTHERN PLAINS, SOUTHERN PLAINS, AS WELL AS SOUTH FLORIDA... ...20Z Update... No major changes were made with this update. All Marginal Risk areas are expected for the CONUS for Monday. The Marginal for the northern Plains was extended north to the Canadian border with the potential for a few training storms in generally flood-resistant North Dakota and northwest Minnesota. The southern Plains Marginal remains in place with little in the way of signal for persistent heavy rain...rather it looks like typical dry line convection will develop in the region Monday afternoon. A Marginal Risk area was introduced for southern Florida. Despite most of the state remaining well below average for precipitation, this will start a multi-day rainfall event as deep tropical moisture moves across the state along a stalled frontal boundary. While the coverage of rain will be more extensive Monday than Sunday...no significant forcing mechanisms will be around to organize the convection into anything likely to produce any more than isolated flash flooding. Wegman ...Previous Discussion... ...Northern Plains... A shortwave trough and a cold front will move through the region. Ahead of this feature, a ribbon of higher moisture will be advancing northward and will be characterized by PWs between 1-1.5". Along with MLCAPE values above 1000 J/kg, there is good overlap of the moisture, lift, and instability to support rounds of thunderstorms by afternoon/evening. With cell mergers and boundary interactions, an isolated flash flood threat can`t be ruled out with potential for isolated 1-2"/hr rain rates that could cause flash flooding, so a Marginal Risk was introduced. ...Southern High Plains to Southern Plains... A forming closed low straddling NM/TX border will slowly settle east/southeast through the period and across the entire region there should be fairly high moisture remaining in place (PWs 1.25-1.75") that will support scattered thunderstorms. The focus will be on the Texas Panhandle southward into west-central Texas where totals may approach 1-3". Taylor Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt