Extended Forecast Discussion NWS Weather Prediction Center College Park MD 215 PM EST Thu Mar 03 2022 Valid 12Z Sun Mar 06 2022 - 12Z Thu Mar 10 2022 ...Heavy rain potential across the Mid-Mississippi Valley into Ohio Valley Sunday into Monday... ...Overview... The medium range period will begin Sunday with a shortwave and surface low pressure system over the Great Lakes, bringing lingering snow there, but more significantly a chance for heavy to excessive rainfall along its associated cold front, spreading from the Mid-Mississippi Valley into the Ohio Valley for the early part of the week. Farther west, persistent troughing will be in place in between a ridge in the East Pacific and a subtropical high initially in the Gulf of Mexico. Broad troughing should spread eastward across the lower 48 as the week progresses as the subtropical high gets pushed south into the Caribbean Sea. ...Guidance Evaluation/Predictability Assessment... Recent model guidance begins the medium range period in rather good agreement for the large scale pattern and even with placement of initial shortwaves, including the impactful one in the Great Lakes and a likely closed low in the Four Corners embedded in the West trough. At the surface, good consensus exists that the surface low in the Great Lakes Sunday morning will track quickly northeastward, while a secondary low forms along the trailing cold front by Monday. There have been more model variations with the placement of this latter wave within an elongated area of low pressure, but models seem to be coming to a consensus over the Ohio Valley Monday morning, though GFS runs have been farther southwest, but perhaps is indicating two lows especially in the new 12Z run. There is also some spread with that feature's track northeastward Tuesday, which is dependent on low predictability shortwaves aloft, as the southern stream low that was closed Sunday morning lifts northeastward, opens up, and interacts with northern stream flow. No particular outliers were seen in the 00Z/06Z cycle with this, but confidence is not high either. Farther west, energy diving south into the U.S. Sunday-Monday produces differences that become more notable Tuesday and beyond. The EC and especially the CMC have shown a slower movement of the energy (which it shows as a closed low) eastward out of the Four Corners late Tuesday into Wednesday compared to the GFS suite through the 06Z run. Given typical model biases, leaned a bit more toward the slower solution, and fortunately the 12Z GFS indicates a slower solution much like the 00Z ECMWF with the shortwave in the southern half of the Plains early Wednesday. However, the new 12Z ECMWF trended a bit faster, but hopefully the run to run swings are lessening. Additional energy is likely to come through the Northwest by Wednesday-Thursday, but overall confidence in the details of northern stream flow there and timing and placement of clipper systems in the East is medium to low. The WPC forecast began with a blend of 00Z/06Z deterministic guidance favoring the ECMWF and GFS given good agreement early in the period. Phased in the ensemble means for the middle to later part of the period with the increasing model differences, favoring the ECMWF in terms of the deterministic models. This led to good continuity with the previous forecast. ...Weather Highlights/Threats... Rain and thunderstorms will be widespread along and ahead of the cold front moving through the central/eastern U.S. early next week. Severe weather is possible from southeastern portions of the Plains into the Lower/Middle Mississippi Valley on Sunday into Sunday night per the latest Storm Prediction Center extended outlook. Meanwhile the axis of the heaviest rain is forecast from southeastern Oklahoma into northern Arkansas/Missouri and the Ohio Valley, spreading into the Central Appalachians/northern Mid-Atlantic by Monday. Flooding and flash flooding are possible particularly in areas that see repeat/training convection and in areas where soils are already wet, and newly experimental Slight Risks of excessive rainfall are in place for days 4 and 5. A swath of wintry precipitation could develop on the north side, with light to moderate amounts possible from the central Plains/Mid-Mississippi Valley into the Great Lakes and interior Northeast late Sunday into Tuesday. Then by the middle of next week, Gulf moisture could return to the Lower Mississippi Valley and Southeast, but uncertainty remains with the amounts of rainfall onshore, depending on where a front and low stall. In the West, snow is likely in higher elevations of the Central Rockies in particular on Sunday. Then after a quick break in precipitation, snow chances (with some rain possible in lower elevations) will increase again by Tuesday and beyond for the Pacific Northwest and especially across the Northern Rockies, eventually into the Central Rockies as well. There is more uncertainty for the potential for snow in the Northern Plains with this system at this point. Temperatures will be quite mild for the south-central to eastern part of the U.S. early in the week ahead of the cold front, with temperatures 10 to 30 degrees above average and dozens of daily record high minimum and maximum temperatures could be set. Temperatures should moderate to near normal after the frontal passage. The West and parts of the central U.S. will generally be cooler than average underneath persistent troughing. Particularly cool spots will be the central High Plains Sunday and Monday, with highs 15 to 25 degrees below normal, and across the northern High Plains Wednesday and spreading south and east Thursday. Tate 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, winter weather outlook probabilities and heat indices are at: 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