Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Tue Mar 22 2022 Valid 12Z Fri Mar 25 2022 - 12Z Tue Mar 29 2022 ...Overview... An amplified upper level pattern is expected during the medium range period, beginning Friday with troughing across the East and ridging in the West. Additional impulses coming into the trough will reinforce it at least for the northeastern U.S. through early next week, with cool temperatures and periodic light precipitation. Meanwhile the ridge should be gradually pushed toward the central U.S., spreading warmer temperatures there after potentially record-setting warmth in the West, as troughing approaches from the East Pacific. There is uncertainty in the trough's timing and amplitude, but it should cause increased precipitation chances and cooler temperatures in the West when it comes in, with potential for a surface low pressure system to strengthen in the Plains but the end of the period next Tuesday. ...Guidance Evaluation/Predictability Assessment... Model guidance from the 12/18Z yesterday cycle begins with generally good agreement for the large scale pattern, with typical differences with shortwaves embedded within the trough over the eastern third of the country. An initial coastal low just off New England early Friday clusters well among guidance. Models show stronger energy with the possibility of a small closed upper low early Saturday likely over the Great Lakes/Ohio Valley, but with some latitudinal variations in how far south the trough/low reaches--ECMWF runs have generally been among the farthest south. But the bigger outlier with this feature was likely the 12Z UKMET, which separated streams by Sunday to create a southern stream low in the Southeast, so leaned away from that solution. There is generally good agreement in principle that troughing will lift gradually early in the workweek for the Southeast, but with some semblance remaining in the Northeast. However, farther west, more significant differences in the pattern arise. While early agreement for ridging shifting eastward is reasonably good, there are notable timing issues with individual models as well as ensemble means with the incoming troughing, as well as differences in potential stream separation and its timing. The 12Z and newer 00Z ECMWF show a much slower closed low compared to most of the recent guidance and its ensemble mean, after its previous runs were among the faster solutions. In contrast, GFS runs are now faster with an inland track and more phased, after runs about a day ago showed an upper low hovering in the Pacific longer. This flip-flop as well as individual ensemble member spread becoming very broad late in the period leads to fairly low confidence in the trough's timing. The CMC and its mean are faster and more clustered with the GFS/GEFS, but did think the 12Z CMC ensemble mean may be slightly fast with the trough axis by next Tuesday. Thus the WPC medium range forecast favored an operational model blend at the beginning of the period. Lessened the proportion especially of the ECMWF by the end of the period as better clustering seemed to be with the ECMWF mean, GFS runs, GEFS means, and CMC. Given the uncertainty, shifts in the forecast are possible if not likely particularly with the timing of the trough and the associated fronts ahead of it. ...Weather Highlights/Threats... Snow may linger in Maine on Friday as a coastal low forms. Then shortwave energy and weak low pressure/frontal systems could lead to light precipitation spreading across the northeastern quadrant of the country through early next week, from the Great Lakes region to the central/northern Appalachians and Northeast late week into the weekend. Some of this precipitation will be in the form of snow in higher elevations and northern latitudes, and gusty winds are also possible. Precipitation ahead of the approaching eastern Pacific upper trough is likely to reach the Pacific Northwest around Friday and then spread across more of the West thereafter. Most of this activity should be in the light to moderate range but some locally heavier totals could be possible depending on exact system details. Coverage and intensity of this precipitation becomes increasingly uncertain by late weekend into early next week. Unseasonably warm temperatures will build and expand underneath upper ridging from the western U.S. into the Plains. Highs that are 10-20F above normal will be common over California and the Great Basin/Southwest Friday, with some plus 20-25F anomalies appearing in the Great Basin Saturday and moving to the northern/central High Plains early next week as the upper ridge axis shifts. Daily record temperatures could be tied or set across California and eastward. Temperatures in the West are likely to cool closer to normal by around Monday but the exact timing will depend on the trough's movement inland. Meanwhile the East should see near to slightly below average temperatures given mean upper troughing, with coolest temperatures of 10-15F below normal in the central Appalachians for the weekend and in the Great Lakes 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