Extended Forecast Discussion NWS Weather Prediction Center College Park MD 152 AM EST Fri Mar 04 2022 Valid 12Z Mon Mar 07 2022 - 12Z Fri Mar 11 2022 ...Heavy rain potential across the Ohio Valley into Monday... ...Overview... The medium range period begins Monday with broad troughing (with embedded shortwaves) across the central U.S. pushing a cold front into the East. This setup brings a threat for heavy to excessive rainfall across the Ohio Valley, with snow to the north. Shortwaves should weaken in the flow as they progress downstream as heights begin to rise over the East Coast. Out West, a strong ridge over the east Pacific should allow for shortwaves to keep reinforced troughing over the Rockies, which eventually should press east into the Plains by late next week. ...Guidance Evaluation/Predictability Assessment... Recent model guidance continues to show good agreement in the large scale pattern through much of the period, with mostly typical timing and detail differences needing to be worked out. Good consensus exists that a surface wave (or two) will develop along the cold front over the Ohio Valley on Monday, progressing into the Mid-Atlantic by Tuesday. There continues to be some subtle timing differences with this low, which stems from differences aloft in the shortwave. The CMC and UKMET are a hair faster than the GFS/ECMWF and ensemble means, but a general blend of the guidance does offer a good starting point on position. Farther west, energy diving south along the West Coast on Monday produces differences that become more notable Tuesday and beyond. Before the new 00z runs this morning, the CMC appeared to be an outlier with a slower/more amplified solution closing off a low over the Southwest on Tuesday and the remainder of the guidance more open/faster (to varying degrees). However, the new 00z guidance arriving this morning from the GFS, the ECMWF, and the UKMET has also trended towards the CMC with a closed low. The WPC forecast for overnight leaned more on the faster side of the envelope given the CMC seemed an outlier, but with the new 00z runs (which were not available at forecast issuance), even the WPC forecast may now be too fast mid week and beyond with the energy as it moves into the central Plains. In other words, this remains a very low confidence forecast. The next shortwave arrives into the Pacific Northwest around Wednesday-Thursday which should help to reinforce broad troughing over the Rockies which eventually pushes into the Central U.S. by the end of the week. There are some timing differences regarding both the trough axis and the associated surface front. The 18z/Mar 3 GFS was faster than the ECMWF with the ensemble means also maybe more in like with the slower ECMWF. The WPC forecast leaned heavily on the ensemble means for this system given the late period/low predictability with some inclusion of the deterministic runs for a little added system definition. ...Weather Highlights/Threats... Rain and thunderstorms will be widespread along and ahead of the cold front moving through the Eastern U.S. early next week. The axis of the heaviest rain by Monday is forecast from the lower Ohio Valley into the central Appalachians and northern Mid-Atlantic. 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 remain in place for day 4. A swath of wintry precipitation could develop on the north side, with light to moderate amounts possible from into the Great Lakes and interior Northeast. Then by the middle of next week, Gulf moisture could return to the Lower Mississippi Valley and Southeast, but uncertainty remains with respect to rainfall totals, all dependent on a stalling boundary and possible waves of low pressure. The West should see a break in the precipitation on Monday, but mountains snows return by Tuesday and beyond for the Pacific Northwest and especially the Rockies. There remains some potential, but low confidence, on snowfall into the northern Plains/upper Midwest late week as low pressure tries to develop over the central states. Temperatures should feel very mild for the south-central to eastern part of the U.S. on Monday ahead of the cold front, with temperatures 10 to 30 degrees above average and dozens of daily record high minimum and maximum temperatures possible. Temperatures should moderate back to near normal after the frontal passage on Tuesday. The West and parts of the central U.S. will generally be cooler than average underneath persistent troughing through much of the period. Although with more substantial troughing into the region mid to late next week, temperatures should trend cooler with anomalies 10 to 30 degrees below normal possible across the northern and central Plains, and as far south as Texas and Oklahoma. 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, 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