Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM EST Thu Nov 14 2024 Valid 12Z Sun Nov 17 2024 - 12Z Thu Nov 21 2024 ...Heavy Rainfall threat for the Central U.S early next week... ...Tropical Storm Sara to bring uncertain heavy rainfall/runoff threats from the central Gulf Coast to Florida Tuesday/Wednesday... ...Overview... Upper troughing over the West by this coming weekend will split sending northern stream energy through the northern Plains/Upper Midwest, while a southern stream cutoff low shifts across the Four Corners region and into the Central U.S. next week. This is now slated to be ejected by a dynamic upper trough work digging from the Northwest Monday to around the south-central U.S. next midweek. At this surface, this will translate to early week cyclogenesis in the lee of the Rockies with a deepening storm system tracking from the southern Plains through the MIdwest Monday- next Thursday. This pattern would support heavy rainfall potential from the south- central Plains into the Mississippi Valley by late this weekend into early next week, with some snow possible on the backside of the low across the Upper Midwest, but dependent on the quality of cold air filtering in behind this system. Meanwhile, NHC guidance shows Tropical Storm Sara emerging out of the Caribbean/Yucatan and into the east-central Gulf of Mexico next week, with potential but still uncertain heavy rainfall/runoff threats possible from the central Gulf Coast to Florida, with lead activity enhanced by deep moisture feed into an approaching mid-latitude front that may merge with increasingly extratropical Sara over/off the Southeast. ...Guidance/Predictability Assessment... The WPC med-range product suite was primarily derived from a composite blend of reasonably well clustered guidance from the GFS/ECMWF/UMKET/Canadian, the National Blend of Models and WPC continuity valid for Sunday/Monday. This solution has good ensemble support as well. Cycle to cycle guidance continuity is not stellar for later next week however in a pattern with increasing forecast spread and uncertainty, lending an ensemble forecast approach. Opted to lean on ECMWF/Canadian ensembles that are more in line with latest model trends and latest guidance from the NHC on Sara. ...Weather/Hazards Highlights... The coverage and intensity of precipitation across portions of the Four Corner to the Southern/Central Plains/Mid-Mississippi Valley will increase over the weekend; which will boost the threat for heavy rain for the south-central Plains/Mid-Mississippi Valley for the start of the week. Given the degree of spread amongst the guidance, specifics for amounts, location and degree of impacts remain very uncertain; however there continues to be a signal focusing in the vicinity of northern Texas into Oklahoma and back towards the southern High Plains where a marginal risk is in place on the Day 4/Sunday Excessive Rainfall Outlook. The heavy rain threat lifts northeastward on Monday, but with uncertainty on exactly where the greatest threat lies. For now, the Day 5/Monday ERO highlights a broad marginal risk spanning across much of the central Plains into parts of the mid to upper Mississippi Valley. Depending on cold air filtering in behind the deepening storm system, some accumulating snow may be possible across the Rockies into the northern Plains early-mid next week in a pattern with potential for high winds. Generally wet conditions is expected to accompany the cold front late period as it pushes to the east- central states and to the East. Out West, an atmospheric river is expected to support moderately heavy rain and mountain snows across the Pacific Northwest through Sunday, with modest precipitation extending inland across the West with system/pattern translation. WPC is maintaining the Marginal risk for the Day 4 ERO across western Washington and Oregon. This system also offers an opportunity for more dynamically enhanced mountain snows over favored terrain near the track over the West. Deep moisture from newly formed T.S. Sara as it emerges into the Gulf of Mexico may begin impacting parts of Florida or the Gulf Coast by early-mid next week, but there is a lot of uncertainty in exact impacts and amounnts. This system needs to be monitored, but can still focus a heavy rainfall threat despite not being forecast to strengthen to hurricane strength. Above seasonal normal temperatures will spread from the central U.S. to the East by Sunday into Monday leading to daily maximum temperatures to climb 10 to 15 degrees warmer in a some locations. For the western U.S., it will be trending cooler as upper troughing amplifies over the region. Well below normal temperatures will provide a cold snap spread to the Central U.S. next week. Santorelli/Schichtel Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation forecast (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml https://www.wpc.ncep.noaa.gov/#page=ovw