Extended Forecast Discussion NWS Weather Prediction Center College Park MD 457 PM EDT Tue Mar 30 2021 Valid 12Z Fri Apr 02 2021 - 12Z Tue Apr 06 2021 ...Overview... Upper ridging/blocking will meander over the northern Atlantic and Pacific with another upper high near Baja California Sur will favor troughing easing toward the west coast and lingering off the Northeast coast. This will leave ridging across much of the middle of the lower 48 amid a rather dry pattern. Some precipitation will move into the West next week with uncertainty in its timing. ...Model Preferences and Predictability Assessment... Through the 00Z/06Z cycle, the models and ensembles were in good agreement to start the forecast with the exiting upper low in the Northeast/southeast Canada that will split into a northern and southern entity. The southern portion will linger just off southeastern New England early next week until ridging from the west nudges it farther out to sea. However, that also depends on how troughing off the West coast evolves through the period. A trough will sink southward out of the Gulf of Alaska late this week into the weekend and split off another trough to its southwest. The northern part will either move east-southeastward through the Pac NW/northern Rockies and atop the central CONUS ridging while the southern part may close off an upper low well west of California (~150W). The difference then lies in the quicker vs slower northern portion (generally GFS vs ECMWF) and how quickly (or not) the southern upper low moves east toward California. The ECMWF has been more consistent in its evolution that brings that southern upper low to the CA coast sometime late Mon into Tue (and mostly absorbing the northern portion into it) which seemed to fit more with its own ensemble mean as well as the GEFS mean. Given such an amplified pattern (which fits climatologically with the time of year) preferred to side with the slower side of the guidance but not as slow as the ECMWF. This fit nicely with the best ECMWF/GEFS ensemble overlap. ...Sensible Weather and Potential Hazards... Broad ridging will maintain a rather dry period for much of the CONUS, with the exception of 1) the West as the upper trough likely approaches CA and southwest flow aloft overspreads the Great Basin and Rockies and 2) the Upper Midwest along a frontal zone. In either case, limited moisture may prevent much more than light to perhaps modest amounts. Off the East Coast, an ocean system may stay just far enough offshore to keep any precipitation associated with it off the coast, but a weakening front and/or a surface trough may touch off a few showers this weekend. Temperatures will be well below normal Friday into Saturday morning in the Southeast 1/4 of the CONUS where some record lows are possible. In addition, freezes are likely for some areas that may have passed their average last freeze date. Temperatures between the Rockies and Great Lakes will be above normal through the period, perhaps by as much as 15-25 degrees (well into the 70s to low 80s for the Plains). This will extend to the Southwest as well where the deserts may approach 100 degrees. This will be the hottest temperature so far this year for many locations and record highs may be broken from the Southwest to the northern Plains this weekend. The West coast will trend cooler with time as troughing inches closer. Fracasso Hazards: - Much below normal temperatures across portions of the Lower Mississippi Valley, the Tennessee Valley, the Middle Mississippi Valley, the Mid-Atlantic, the Southern Appalachians, the Southeast, and the Ohio Valley, Fri, Apr 2. 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