Extended Forecast Discussion NWS Weather Prediction Center College Park MD 202 AM EST Thu Nov 14 2024 Valid 12Z Sun Nov 17 2024 - 12Z Thu Nov 21 2024 ...Heavy Rainfall threats for parts of the Central U.S... ...Potential Tropical Cyclone Nineteen to bring uncertain tropical threats to Florida or the Gulf Coast next week... ...Overview... 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. The next shortwave into the Northwest on Monday will interact/combine with the upper low as it lifts northward eventually resulting in a deep and very amplified upper low/trough spanning the central into eastern U.S. late period. 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 to the Great Lakes Monday- 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, guidance shows Potential Tropical Cyclone Nineteen emerging out of the Caribbean and into the southern Gulf of Mexico next week, with some potential but still very uncertain heavy rainfall threats possible for parts of Florida or the Gulf Coast. ...Guidance/Predictability Assessment... Considering the increasingly active and amplified pattern to evolve in the medium range period, the guidance is in generally good agreement on the large scale, but still with plenty of uncertainty in the details which would have large implications on sensible weather. There are some minor timing differences still with the upper low as it lifts through the Central U.S., but the greater uncertainty comes early to mid week with regards to energy dropping into the mean trough and how this interacts with the downstream upper low. Regardless of the evolution details, by mid to late next week, there is good agreement that a very amplified and active pattern should be in place across the CONUS with deep troughing over the Central to Eastern U.S. and strong ridging over the West. Especially by the medium range period, there is a ton of uncertainty still with the track and intensity of currently Potential Tropical Cyclone Nineteen. The latest forecast from the NHC has this system moving northward through the Yucatan Peninsula into the Gulf as a tropical storm. Good agreement in the guidance that the upper trough through the central U.S. should help steer this system but a lot of uncertainty how quickly it may get pulled into the approaching cold front. Some of the latest 00z guidance is suggesting an earlier interaction and more northward track towards the Central Gulf Coast as a weaker system as it becomes absorbed into the larger scale flow. But also plenty of support for a more easterly track across the Florida Peninsula. Monitor products from the NHC for the latest information on PTC Nineteen. The WPC progs for tonight used a general blend of the GFS, ECMWF, and UKMET early period, and leaning increasingly more on the ensemble means late period to help mitigate the detail differences. ...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 Plains and 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 northward on Monday but with a lot of 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. Generally wet conditions is expected to accompany the cold front late period as it pushes into the east- central states and Great Lakes. Out West, another atmospheric river is expected to support heavy rain and mountain snows across the Pacific Northwest through Sunday, with lighter precipitation extending inland across the northern Rockies and Great Plains. WPC is maintaining the Marginal risk for the new Day 4 ERO today across western Washington and Oregon. Moisture from PTC Nineteen as it emerges into the Gulf of Mexico may begin impacting parts of Florida or the Gulf Coast by mid next week, but there is a lot of uncertainty in exact impacts and amounts. There is a cluster of guidance that takes this across Florida as a possible tropical storm, but some of the newest guidance tonight pulls it more northward towards the Gulf Coast. This system will need to be monitored. 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 and the first cold snap of the season will shift into the Central U.S. next week. Santorelli 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