Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Thu Mar 30 2023 Valid 12Z Sun Apr 02 2023 - 12Z Thu Apr 06 2023 ...Strong Plains through Upper Midwest storm early-mid week to bring strong winds, northern Plains snow, heavy rainfall and severe thunderstorms from the South into the Ohio Valley... ...Synoptic Overview... The strong storm system over the eastern U.S. in the short range period should be over eastern Canada by Sunday morning with improving weather for the East Coast to conclude the weekend as a surface high moves in from the west. A progressive surface low tracking eastward along the U.S./Canada border through Monday will bring a colder airmass behind it across the northern Plains for the beginning of the week. The main weather story next week will be the development of another strong low pressure system tracking from the central High Plains northeastward as a potent upper trough ejects from the western U.S. By Wednesday-Thursday this low may follow a path a little northwest of the one expected this Friday/Saturday. This storm should bring a broad area of significant/hazardous weather to areas from the Rockies eastward and a large area of well below normal temperatures in its wake, from the West through the northern Plains. In contrast, upper ridging over the Gulf Coast should build northward over the eastern U.S. and support anomalous warmth ahead of the storm's associated cold front. ...Model Guidance/Predictability Assessment... The 00Z/06Z guidance generally showed additional consolidation from the prior cycles with respect to trends for handling upstream North Pacific/Alaska flow and resulting effects on the amplifying western U.S. upper trough along with subsequent ejection and central U.S. storm evolution. Latest consensus has the upstream energy dropping into the back side of the larger scale trough in sheared fashion, delaying ejection a bit compared to some guidance in previous days. New 12Z runs have nudged a bit stronger again with this incoming energy but not nearly to the extent of what had been a stronger/closed cluster. The end result is gradually improving clustering for the timing and track of the overall system lifting northeastward across the northern tier by midweek. The new 12Z CMC is still a tad on the slower side but not to the degree seen in the 00Z run. Based on other guidance through 06Z, an average among the slower or westward GFS/GEFS and faster ECMWF/ECMWF mean seemed reasonable given recent guidance spread/variability and typical errors by 5-7 days out in time. Behind this system there is a general consensus on some lingering troughing over the West but with uncertainty in the details. By mid-late week a lot of model and ensemble member spread develops for flow details over the eastern Pacific/West Coast. Operational GFS/CMC runs have been showing more pronounced shortwave energy nearing the West Coast, with other models/means suggesting this energy will be somewhat weaker and/or slower. The new 12Z GFS has trended to a less amplified shortwave while the 12Z GEFS mean/CMC hold onto more ridging into Thursday. A operational model blend (with ECMWF input split between the 00Z and 12Z/29 runs) provided a reasonable depiction of significant features for about the first half of the period. The forecast then transitioned toward a blend of ECMWF runs/06Z GFS along with the 06Z GEFS/00Z ECMWF means to depict an intermediate track/timing for the northern tier into eastern Canada storm while accounting for the guidance spread near the West Coast late in the period. ...Weather/Hazards Highlights... Reloading of upper level troughing over the northwestern U.S. by the weekend and continuing into early next week will support multiple days of rain/mountain snow with terrain enhancement from the Pacific Northwest and northern California/Sierra Nevada into the northern and central Rockies, with the moisture shield pushing gradually farther southeast with time. Heavy snow is likely for the Cascades and the Olympic Mountains and significant snow may reach central and northern portions of the Sierra Nevada by early next week. Also expect a period of heavy snow to extend across favored terrain from the Great Basin eastward into the Rockies during Sunday-Monday. Well ahead of this system, a southern stream shortwave interacting with a Gulf Coast warm front along with sufficient moisture/instability may produce some locally heavy rainfall from eastern Texas into the Lower Mississippi Valley with the Day 4 Excessive Rainfall Outlook (12Z Sunday-12Z Monday) depicting a Marginal Risk area across this region. Some of this activity could extend eastward into daytime Monday but with too much uncertainty in details for a risk area at this time. There are also some signals that a stalling front over the Midwest/Lower Great Lakes could begin to focus increasing rainfall but again with enough ambiguity on the threat to preclude any risk area in the Day 5 (12Z Monday-12Z Tuesday) outlook. The big headline will be the deepening Plains low that develops along a strong frontal boundary early next week. Numerous showers and thunderstorms are likely to make a return to locations from the central Gulf Coast to the Ohio Valley Tuesday night and especially into Wednesday as this storm system gets better organized across the central Plains and advects copious Gulf moisture northward. Also the threat of strong to severe storms is increasing in the expansive warm sector, with the Storm Prediction Center already monitoring that possibility on Tuesday. At the same time recent model runs maintain/add confidence for the idea of a significant cold sector snow event northwest of the low track, with probabilities for at least three inches of snow steadily increasing along an axis from eastern Wyoming across much of South Dakota/portions of North Dakota and then northern Minnesota Monday night into Wednesday. Heavy snow will be possible within portions of this band. This storm will also produce strong winds, with best potential for the highest wind speeds extending from the Southwest through southern High Plains and northward through the northern Plains. Other areas farther east may see brisk to strong winds even if to a less extreme degree. A pronounced temperature contrast will develop across the nation early-mid week with well below average readings spreading across much of the western U.S. and central/northern Plains, and well above average temperatures expanding from the southern Plains/Gulf Coast through much of the eastern U.S. Tuesday-Wednesday look to be the coldest days versus normal over the West/Plains with some areas seeing highs 20-30F below normal. The reverse will hold true over the southern Plains early in the week and farther eastward thereafter, with highs generally 10-20F above normal and lows 15-25F above normal. Daily records mainly for cold highs will be possible over the West during the first half of the week. Farther east in the warm sector, Tuesday-Thursday will offer the best potential for some daily records, with warm lows tending to be more numerous than record highs. Rausch/Hamrick 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, experimental excessive rainfall outlook, 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/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml