Extended Forecast Discussion NWS Weather Prediction Center College Park MD 258 AM EDT Wed Mar 23 2022 Valid 12Z Sat Mar 26 2022 - 12Z Wed Mar 30 2022 ...Overview... Over the weekend, troughing will be present across the eastern U.S. while periodic shortwaves and fronts cause light precipitation and cool temperatures from the Great Lakes to Northeast. Meanwhile a ridge causing potentially record warmth will shift from the Intermountain West slowly eastward into the High Plains ahead of another trough/upper low entering the West from the eastern Pacific. While there remain some timing differences with the trough/low, when it enters the country it should cool down the West and increase precipitation chances. By Tuesday/Wednesday, there is decent agreement for a surface low pressure system to develop in the central Plains, leading to wetter conditions across the central U.S. and potentially some springtime snow for the Midwest/Great Lakes. ...Guidance Evaluation/Predictability Assessment... Recent model guidance shows fairly good agreement for the early part of the medium range period over the weekend with the initial western ridge/eastern trough pattern. Shortwave energy embedded within the trough shows minor variations among models, but with the general idea that the shortwave/clipper will track from the Great Lakes Saturday to the east Sunday and possibly induce modest cyclogenesis just off the New England Coast. Though deterministic models vary with the exact positioning of the low, ensemble members and means indicate this potential, and the differences are within typical spread for a medium range forecast. Greater model differences arise with the eastern Pacific upper trough. Recent model guidance has at least converged on indicating a closed low on the southern end of the trough just west of California early next week, whereas models were more mixed on a closed/open solution over the past couple of days. This has led to a slower trend with the incoming trough/low overall, though the past 3 or 4 ECMWF deterministic runs have been the exceptionally slow solutions compared to other guidance. By late Monday into Tuesday, guidance varies with the handling of the upper low potentially phasing back with the northern stream as additional shortwave energy in the northern stream may interact with it. In the 12/18Z yesterday model cycle, the ECMWF showed no phasing between the features as the southern stream low was farther west and the shortwave farther east, missing each other. The 12Z GFS was phased by Tuesday with the 18Z GFS phased by Wednesday, while the CMC showed some separation. Thus there are ample timing differences with the feature and ensemble members show considerable variability as well. Regardless of these differences, most models/ensembles show a developing surface low in the Plains by Tuesday/Wednesday. Thus the WPC medium range forecast utilized a multi-model deterministic blend for the early part of the period, but with increasing proportions of the somewhat better clustered GEFS and EC ensemble means by the latter part of the period given the operational model differences. Overall the track of the western low/trough was a bit slower than continuity but not nearly as slow as the deterministic ECMWF runs. ...Weather Highlights/Threats... Shortwave energy and weak low pressure/frontal systems are expected to produce light precipitation as they move across the Great Lakes region to the central/northern Appalachians and Northeast over the weekend. Some of the precipitation will be in the form of snow in higher elevations (West Virginia in particular) and near the Canadian border, followed by strong and gusty winds with falling temperatures. Precipitation ahead of the approaching eastern Pacific upper trough could affect the Pacific Northwest Saturday with light amounts, but spread farther south to California and east into the Rockies and Intermountain West early next week. Most of this activity should be in the light to moderate range but some locally heavier totals are possible, particularly in higher elevations where upslope flow could enhance amounts. Rain chances could increase in the south-central U.S. by Tuesday ahead of low pressure forming. Meanwhile farther north, precipitation including some snow/wintry weather could affect the Midwest and Great Lakes region, but with considerable uncertainty in the details. Unseasonably warm temperatures will build and expand underneath upper ridging from the western U.S. into the Plains. Highs that are 10-25F above normal will be common over the weekend from the West Coast across the Great Basin and Southwest to the Plains, and several daily record high temperatures could be set or tied. As the ridge axis shifts eastward, warm anomalies of 15-25F are likely for the High Plains Monday while the West Coast moderates closer to normal. Warmer than normal temperatures remain forecast in the south-central U.S. on Tuesday but may moderate Wednesday while pushing into the Southeast. Meanwhile the East should see near to below average temperatures given mean upper troughing, with coolest temperatures of 10-20F below normal in the Great Lakes and central Appalachians for the weekend and spreading into the Northeast early next week. 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