Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Sat Mar 19 2022 Valid 12Z Tue Mar 22 2022 - 12Z Sat Mar 26 2022 ...Heavy rain will likely impact the Deep South to the Tennessee Valley Tuesday-Wednesday ahead of a strong low pressure system as severe storms move across the Gulf Coast states and some wintry weather across the northern tier... ...Overview... The most active weather during the medium-range will likely be from Tuesday to Wednesday as a strong low pressure system intensifies over the central/southern Plains and tracks toward the Great Lakes. The heaviest rainfall is expected farther inland from the Deep South to the Tennessee and lower Ohio Valley while severe storms are forecast to track across the Gulf Coast states. Rain intensity should be trending downward as the system is forecast to move through the eastern U.S. mid to late next week. On the cold side of the system, heavy snow/wintry weather should be ending by early Tuesday morning over the central Rockies into the High Plains, but some precipitation should progress through the northern tier and into the interior Northeast. Behind this system a strong upper ridge will build into the West, bringing potentially record high temperatures to parts of California midweek. ...Guidance Evaluation/Predictability Assessment... Model guidance this morning continues to indicate the likelihood of an intensifying low pressure system to track across the central/southern Plains Tuesday as it interacts with a surge of colder air intruding from the northwestern quadrant of the system. The trend has been for the cold air intrusion to be stronger than earlier forecasts, with the cyclone evolving toward a more classical occlusion configuration by Wednesday as it tracks toward the Great Lakes. This has led to a better-defined precipitation shield across the Great Lakes, and with a tendency for the western edge of the precipitation to extend further back into the upper Midwest. The Canadian model (CMC) was most aggressive with this occlusion process, leading to a much slower exit of the system across the eastern U.S. late next week, especially the 00Z run. The GFS has also slowed down the exit of this system later next week to better agree with the ECMWF solutions, which is not quite as slow as the 00Z CMC. The 12Z CMC was much more agreeable with the ECMWF-GFS consensus. Off the Pacific Northwest, some model differences were noted regarding the timing of shortwave energies moving toward the coast. The CMC was much too fast in bringing the next shortwave onshore by Day 4. The ECMWF and the GFS reasonably agree with each other in this regard. Therefore, the WPC medium-range package was based mainly on the consensus of the 00Z ECMWF/EC mean and the 06Z GFS/GEFS mean, with increasing usage of the ensemble means toward the end of next week. A small contribution of the 00Z CMC was included for Days 3-4 followed by a small amount from the CMC mean Days 5-7. The results are reasonably compatible with WPC continuity. ...Weather Highlights/Threats... Ample Gulf of Mexico moisture flowing into the surface/upper-level lows tracking northeastward over the central U.S. will lead to widespread rain and thunderstorms for the Mississippi Valley to the East Coast particularly on Tuesday and Wednesday ahead of the cold fronts. Storms could be severe across the Deep South down to the Gulf Coast Tue/Wed per the Storm Prediction Center. Furthermore, heavy rain will increase the threat of flash flooding across portions of the lower Mississippi, Tennessee, and lower Ohio Valleys, where high rain rates are forecast to be highest and most sustained. Therefore, a Slight Risk is indicated Tuesday in the experimental WPC medium range Excessive Rainfall Outlook. Some isolated flash flooding is also possible Wednesday for the southern/central Appalachians and interior Southeast. Some areas of heavy rain are also possible along the Eastern Seaboard ahead of the cold front. Additionally, some precipitation appears likely from the northern parts of the Plains through the Northeast, which could be in the form of snow. Currently the highest probabilities for notable snow are in the Upper Great Lakes region. Some wintry precipitation should also be possible across the interior Northeast Thursday morning ahead of a warm front, followed by lighter wintry mix/snow lingering into next weekend. In the West, mainly dry weather is expected, except northwestern Washington with the passage of a wave of moisture midweek followed by possibly the arrival of a more widespread moisture surge by next weekend. The strong upper ridge building into the West will lead to a broad area of highs 10-20F above normal Tuesday-Saturday with slightly higher localized anomalies possible. The best potential to reach daily record highs will be over California during Tuesday-Thursday. Leading upper level troughing should support temperatures 10-20F below average across the central/southern High Plains Tuesday and Wednesday. The cooler air should moderate closer to normal by the latter part of next week as it progresses eastward. Ahead of the trough and cold fronts, generally warmer than normal conditions are likely across much of the eastern third of the U.S. for much of the week, transitioning to near normal temperatures by Friday and Saturday. Isolated record highs are possible over parts of Florida Tuesday-Wednesday. Kong 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 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml