Extended Forecast Discussion NWS Weather Prediction Center College Park MD 253 AM EDT Mon Mar 21 2022 Valid 12Z Thu Mar 24 2022 - 12Z Mon Mar 28 2022 ...Overview... An amplified upper level pattern will be present during the medium range period as an elongated upper low over the Mid-Mississippi Valley to Upper Great Lakes Thursday lifts out but additional energy comes in to maintain troughing across the East through early next week. Meanwhile farther west, mean ridging (though initially disrupted on the northern side by a shortwave) will be present over the West and cause potentially record warmth late week, then gradually move eastward ahead of an incoming trough from the Pacific to the West Coast. This pattern should promote generally dry conditions across the country aside from some East Coast precipitation exiting Thursday-Friday, some clipper systems in the Great Lakes region, and increasing precipitation chances in the West by the beginning of next week with the trough's approach. ...Guidance Evaluation/Predictability Assessment... Model agreement for the 12/18Z yesterday cycle is fairly good through the latter part of the week, with good consensus for a closed upper low lingering into Thursday in the east-central U.S. and a surface low in the Great Lakes region. Guidance has continued a trend toward slightly faster movement of the low's associated cold front across the Southeast/Florida but perhaps slower farther north with the occluded part of the cyclone, leading to a slight increase in precipitation in the Northeast with this cycle. There was good consensus in the 12/18Z guidance for another surface low to develop near the New England coast by Friday morning perhaps as a combination of the triple point low from the original cyclone and a weak low tracking north along the coast, but newer 00Z guidance is not so agreeable, though the 00Z EC in particular still indicates a similar surface low. This indicates the spread still remaining in the timing and orientation of the trough as it lifts out Friday. But this as well as additional energy incoming by Saturday show at least a similar pattern with typical medium range differences in the details. Thus the early part of the WPC forecast was based on a blend of the 12Z ECMWF, CMC, and UKMET and 18Z GFS, with the blend tending to smooth out the smaller model variations. Meanwhile in the West, guidance agrees that a ridge in the Southwest will be initially suppressed in the Northwest Thursday as a shortwave tracks through. After that, ridging should continue to amplify over the weekend across the Intermountain West and Rockies, with GEFS members generally on the more amplified side, with the operational CMC one of the less amplified models. This is also related to greater differences with the upstream trough coming in from the East Pacific. Timing differences abound with the trough, along with differences with a possible southern stream low developing as flow splits, with some guidance more phased than others at times. For the WPC forecast, tended toward the trough axis of the ECMWF mean and EC operational run. This appeared to be a middle ground between the slower GFS/GEFS (though the 18Z and 00Z GFS runs were faster than the 12Z) and the faster CMC mean. However, varying ensemble members and run to run model differences indicate that further changes are likely to the forecast in this area. ...Weather Highlights/Threats... An occluded low pressure system will be in place over the Upper Great Lakes early Thursday, with lingering light precipitation there but with heavier amounts possible along its associated cold front near the East Coast. Mainly rain is expected, but snow is forecast for northern New England, which could linger on Friday in Maine near a developing coastal low. Shortwave energy and weak low pressure/frontal systems could lead to light precipitation spreading from the northern Rockies/Plains Thursday into the Great Lakes region to the central/northern Appalachians and Northeast late week into the weekend. Light precipitation in the Pacific Northwest is possible through the latter part of the week, but precipitation chances should increase and spread inland across the West by around Sunday, but with some differences in timing and magnitudes at this point. Warm temperatures will build and expand underneath upper ridging from the western U.S. into the Plains. Highs are forecast to be around 10-20F above normal for California and the Central Great Basin/Southwest Thursday and Friday, with 20+ anomalies building in the Great Basin Saturday and shifting to the northern/central High Plains early next week as the ridge axis shifts. Daily record temperatures could be tied or set across California and eastward. Meanwhile, cooler air underneath the upper trough/low in the central U.S. should moderate as it moves eastward, with temperatures generally 10F or less below normal. However, additional cold fronts and upper energy will bring below normal temperatures to parts of the eastern third of the U.S. by Sunday, with the Great Lakes seeing 10-15F below normal highs. 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 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