Extended Forecast Discussion NWS Weather Prediction Center College Park MD 229 PM EDT Sat Mar 27 2021 Valid 12Z Tue Mar 30 2021 - 12Z Sat Apr 03 2021 ...Overview... A rather amplified mid-upper pattern is expected across the CONUS next week as a sizable longwave trough moves west to east across the country, pushing a potent cold front across the central and eastern U.S. Tuesday through Thursday. Precipitation should spread ahead of those features, with the possibility of some snow in the interior Northeast. Surface high pressure is forecast to move in behind the cold front, drying out much of the country by Friday, though another upper-level trough approaching the Northwest could bring renewed moisture there by late next week. ...Model Guidance and Predictability... 00Z/06Z model guidance clustered well with the synoptic-scale pattern next week--deterministic and ensemble guidance shows good agreement for the aforementioned upper trough with not too many significant differences in position and timing especially early in the period, enhancing forecast confidence. By Friday into Saturday, models have trended in the direction of pivoting the troughing/energy northward into Canada with less influence over the CONUS, but there is still some uncertainty with that, with the GFS suite more aggressive in retreating the energy compared to the ECMWF/CMC suites. This affects the surface frontal position as well, with a front moving faster through the Northeast compared to the previous forecast. The general idea of upper ridging coming in behind this trough also appears well-predicted. With the upper trough tracking through the northeastern Pacific late in the week, there is some variability in its strength and orientation along with its surface low, but a blend of guidance seemed to suffice there. Additionally, a small piece of energy moving eastward across the Pacific midweek making its way into Southern California Friday was agreeable among models, with the exception of the 00Z CMC that had a much weaker, faster feature there. Overall, was able to use a deterministic blend of the 00Z/06Z GFS and 00Z ECMWF/UKMET/CMC for the first half of the period, with the addition of the GEFS and EC ensemble means as the UKMET dropped out and lessening the CMC influence. ...Sensible Weather and Potential Hazards... After some showers and thunderstorms in the Southeast Tuesday with a small southern stream disturbance, the potential for precipitation will increase for the eastern part of the U.S. on Wednesday as Gulf of Mexico moisture streams in ahead of the upper trough and in the vicinity of the cold front. Heavy rainfall is possible, which may be centered near the Southern Appalachians, but model guidance does vary regarding the axis of the heaviest rain. Farther north in the Appalachians and into the interior Northeast, precipitation could start as rain but transition to snow. Snowfall amounts are yet to be determined at this point. Behind the cold front, dry conditions are forecast, and temperatures that are cooler than normal by 10-20 degrees are expected to track across the country from the Rockies and central U.S. Tuesday-Wednesday into the eastern U.S. Thursday-Friday. Additionally, high/gusty winds are possible, particularly in the north-central U.S. on Tuesday given a tight pressure gradient. Then, the upper-level ridge in the central U.S. will help build in warmer than average temperatures for much of the western and central U.S., with temperatures in the 70s reaching as far north as the Dakotas. Elsewhere, precipitation is expected to increase for the Northwest by Friday and Saturday as a front passes through and the next upper trough approaches. 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