Quantitative Precipitation Forecast
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189 FOUS30 KWBC 200104 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 904 PM EDT Wed Jun 19 2024 Day 1 Valid 01Z Thu Jun 20 2024 - 12Z Thu Jun 20 2024 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR SOUTH TEXAS... 01Z Update... Across South Texas, maintained but adjusted south the Moderate and Slight Risks. Bands of convection associated with Tropical Storm Alberto will continue to move across the region, producing additional areas of locally heavy rainfall through the evening. HREF and recent runs of the HRRR indicate that additional amounts of 3 inches or more are likely within the Moderate Risk area. Further to the north, maintained a Slight Risk centered over eastern New Mexico where slow-moving storms, producing locally heavy rainfall, fueled by moist, low-level, easterly winds may continue for the next few hours. Additional flash flooding is a concern, especially where heavy rains fall across sensitive burn scar areas. Trimmed away the Slight Risk area from areas further to the northeast into southern Kansas where the signal for any widespread additional heavy rain and flash flooding concerns has waned. However,cannot rule out some isolated concerns for storms to develop and train along a slow-moving front extending northeast into the Great Lakes. Some guidance, including recent runs of the HRRR, show isolated heavy amounts from the lower Missouri Valley northeastward. Pereira Day 2 Valid 12Z Thu Jun 20 2024 - 12Z Fri Jun 21 2024 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PARTS OF EASTERN SOUTH DAKOTA INTO SOUTHEASTERN MINNESOTA... 2030z Update Moderate Risk introduced over parts of South Dakota and Minnesota due to increased QPF trends and over performing antecedent rainfall/storms. The Rockies and Southern High Plains Marginal Risk areas were merged and a Slight Risk area was introduced over parts of the Four Corners/Mesa Verde regions and San Juan Mountains to account for increased QPF trends over elevated terrain. ...Northern/Central Plains and Upper Midwest... Strong diffluence over the North-Central Plains paired with a robust heat dome over the Eastern half of the country will promote active weather over the Central U.S. on Thursday. A stalled out surface front oriented diagonally northeast to southwest across the Plains and Upper Midwest will act as a focus for convection. Impressive instability (1000J/Kg+ MLCAPE) paired with substantial atmospheric moisture content (1.5-2" PWATs) will produce very efficient rain rates within MCS activity that propagates through parts of the Northern/Central Plains and Upper Midwest. The greatest threat of Excessive Rainfall will be over parts of southern South Dakota and southern Minnesota where anywhere between 3-5" of rain could fall by Friday morning. ...Rio Grande Valley and South Texas... Remnant rainfall from what will be rapidly weakening Tropical Storm Alberto Thursday morning will continue to push west with the full force of the open Gulf supporting it. Easterly flow will be well established across the entire Gulf. The rainfall will be moving into increasingly dry areas of west Texas and New Mexico Thursday. Thus...while the heaviest rainfall rates will be diminishing with longitude...what heavy rainfall does occur will be moving over areas less and less used to heavy rain. Thus, the flooding threat will continue into the Rio Grande Valley and south Texas. Further, increasing interaction with the terrain will locally enhance rainfall rates, especially on east-facing slopes. The storm is expected to move a little bit faster than inherited forecasts. This resulted in a bit lower max totals, while spreading the heaviest rains farther west. Most of the increases were in Mexico. For the Texas side of the Rio Grande, this has resulted in a drier forecast for much of central Texas. Thus...the Slight, has been trimmed from the north and east, now almost to the Rio Grande near Del Rio. For South Texas, the aforementioned broad easterly flow over the entirety of the Gulf will keep isolated to widely scattered showers and thunderstorms that develop over the Gulf moving westward across the area...with drier conditions expected to the north where areas to the east are not the abnormally hot Gulf, but rather unusually hot land. Thus...the threat through the day really is focused on areas due west of the Gulf...i.e. south Texas. The combination of upper level ridging and a slow moving trough over the Intermountain West will turn the prevailing flow more southerly, generally following up the Rio Grande Valley...Thus, the rainfall threat will expand northward into west Texas and much of eastern New Mexico through Thursday night. Terrain impacts will locally enhance rainfall rates resulting in isolated flash flooding, as well as any overlap from Day 1 rainfall in northeastern NM. ...4 Corners Region... Moisture from the remnants of Tropical Storm Alberto will track northwestward into the 4 Corners Region Thursday and Thursday night. Upslope flow of anomalous moisture, especially into the San Juans of southwest Colorado, may result in flash flooding. Burn scars in the area are particularly susceptible to flash flooding as well. ...Interior Northeast/Lower Great Lakes... Convection capable of heavy rainfall rates will develop over this region on Thursday. Soils in the area are wetter than normal, so any training or stationary storms that occur, especially over the terrain of the Adirondacks or White/Green Mountains, may lead to isolated but dangerous runoff. Kebede/Wegman Day 3 Valid 12Z Fri Jun 21 2024 - 12Z Sat Jun 22 2024 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FROM SOUTH- CENTRAL MINNESOTA TO WESTERN WISCONSIN... 2030z Update A Moderate Risk of Excessive Rainfall was introduced with this afternoon`s update. This was done, in part, because of the strong signal for heavy rainfall over much of the same areas on Day 2. FFGs are likely to be low and soil moisture high at the start of day 3 (12z Friday) so another round of strong [rainfall efficient] MCSs paired with the aforementioned antecedent conditions support the upgrade. Minor changes were made to the Four Corners/Southern High Plains areas and the Marginals in south Texas and the Northeast. ...Eastern South Dakota through Wisconsin... Multiple sources of forcing will support multiple rounds of heavy rain across the Northern Plains into the Upper Great Lakes on Friday and Friday night. During the day on Friday, the warm front over the Slight Risk area will slow to a stall during the morning as the typical weakening of the LLJ occurs due to diurnal heating. This too should result in diminishing coverage and intensity of rainfall over this area through the morning. Then Friday afternoon and evening, a strengthening low that will develop as a shortwave ejects into the Northern Plains will increase moisture advection ahead of the low and attendant cold front into the Slight Risk area. PWATs will increase with the storms into Friday night perhaps above 2 inches as the bulk of the moisture that was once Tropical Storm Alberto makes its way into the Northern Plains. This tropical moisture and advection, strengthening low, and very favorable antecedent conditions over much of the Moderate Risk area are all ingredients contributing to increasing concern for numerous and more widespread flash flooding in this region. The center of the low will move to central Minnesota by Saturday morning. Expect strong storms with both the warm front to the east of the low and the cold front south of it due to plentiful moisture. Uncertainty remains high as all of the aforementioned ingredients need to all come together at the same time. There have been distinct southward shifts with time in previous days in the placement of heavy rain from convection with all the convection impacting the nation. Thus, the primary point of uncertainty is where the heaviest rain will occur. ...Northern Colorado Plateau... In coordination with SLC/Salt Lake City, UT and GJT/Grand Junction, CO forecast offices, a Slight Risk upgrade was introduced with this update. A potent shortwave moving into the West Coast will interact with some of the remnant moisture from PTC1, which will continue to be advected into the area from the Gulf. Atmospheric moisture will be a much as 4 sigma above normal. Interaction with the terrain, the shortwave increasing forcing, and local burn scars in both CO and UT will all increase the potential for flash flooding in this area, particularly in the south facing slopes of the San Juan Mountains. ...South Texas... Continued easterly flow over the Gulf will push additional convection developing over the Gulf into south Texas Friday and Friday night. The convection is likely to be mostly isolated to widely scattered with little in the way of organization. The potential for local training and the likely very favorable antecedent conditions/low FFGs from the recent passage of PTC1 in the area continues to support a Marginal Risk for this area. ...New England and Hudson Valley... A Marginal Risk area was introduced in this region for the third consecutive day of afternoon convection occurring as waves continue to run the top of the ridge that remains over the Southeast. A small area of high pressure will increase northwesterly flow into northern New England. Meanwhile the plume of moisture originating from the Gulf, moving north up the Plains, then turning west across the Great Lakes and into New England will be ever present. The front pushing south with drier air will provide a source of forcing for more concentrated convection, particularly over southern New England Friday afternoon. The signal remains weak, but isolated flash flooding is possible in flood-prone areas. Kebede/Wegman 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