Extended Forecast Discussion NWS Weather Prediction Center College Park MD 433 PM EDT Mon Mar 14 2022 Valid 12Z Thu Mar 17 2022 - 12Z Mon Mar 21 2022 1830 UTC Update... No major changes to the forecast thinking from the overnight shift following the 00z/06z model runs. The last few runs of the GFS (including the most recent 12z run from today) continues to be stronger with southern stream energy through the Plains/Midwest late this week, resulting in a more wrapped, deeper, and farther north surface low placement. Again, todays update to the WPC forecast leaned more towards the better clustered ECMWF, CMC, and UKMET solutions for this system. Elsewhere, an ECMWF/GFS blend with the ensemble means seems to continue to serve well with the next trough/closed low in the Southwest early next week amidst good large scale agreement but plenty of detail uncertainties still to be worked out. See previous discussion below for additional information concerning the medium range period forecast and associated weather/hazard threats. Santorelli ...Previous Discussion issued at 0628 UTC... ...Overview... A fast, progressive flow pattern with increasing amplitude is expected to evolve over the CONUS throughout the forecast period. The initial system over the Southeast Thursday will quickly depart to the northeast offshore while another storm system brews over the southern Plains Thursday/Friday before lifting into the Great Lakes by next weekend. By late in the weekend to early next week, a much stronger and amplified trough will progress through the western U.S., reaching the Plains by early next week. This could bring widespread, beneficial rains to the western U.S. and evolve into a strong storm system just beyond the forecast period. No significant cold air outbreaks are anticipated and temperatures will generally oscillate between near normal and much above normal ahead of the various waves of low pressure. ...Guidance Evaluation/Predictability Assessment... While large scale features in the latest deterministic and ensemble guidance show average to above average predictability and agreement, there are some notable surface differences that have impacts on timing and sensible weather. Initially, the first area of model differences lies with the neutrally titled shortwave trough coming through the Plains late in the week. The associated surface low has significant latitudinal differences with the GFS being a fast, progressive and northern outlier compared to the slower ECMWF/UKMET/CMC. This is largely driven by its deeper, stronger 500 mb trough that takes on a slight negative tilt as it swings through the Midwest. For now, the WPC blend favored the slower, non-GFS solution but did include some of it to maintain continuity. Beyond that system, the flow pattern takes on more amplitude with the western U.S. likely to see a digging trough that eventually closes off around the Four Corners region by the end of the period. While there are some timing difference, both the ECMWF/GFS and ECENS/GEFS means show fairly good agreement in this setup. As the energy reaches the Plains, strong cyclogenesis is possible. Overall, the WPC blend incorporated the 12Z ECMWF/CMC and 18Z GFS for days 3-5 then included more of the ECENS/GEFS for days 6-7 given the typical model spread. ...Weather Highlights/Threats... The slow-moving Gulf to Southeast coastal system will bring widespread light to moderate rainfall to the coastal regions Thursday before the system moves well offshore into Friday. The next system moving through the Plains could bring some moderate to locally heavy rainfall as well as potential winter weather on the northwest/cold side, though the aforementioned model differences and marginally supportive thermal profiles for winter weather will keep the latest Winter Weather Outlook for Day 5 generally very low. Finally, the active/unsettled weather greeting the western U.S. toward the end of the period will be mostly beneficial and welcomed precipitation. Temperatures look to be mostly near to above normal, ahead of the various waves of low pressure. Some dips to below normal readings are possible across the West and interior West as the next large scale weather system moves through thanks to clouds and precipitation. Taylor 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 Hazards: - Heavy precipitation across portions of the Central Great Basin, the Great Lakes, the Northeast, California, and the Southwest, Sat, Mar 19. - Heavy rain across portions of the Central Plains, the Middle Mississippi Valley, the Lower Mississippi Valley, and the Southern Plains, Mon, Mar 21. - Flooding likely across portions of the Northern Rockies and the Northern Great Basin. 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