Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Fri May 27 2022 Valid 12Z Mon May 30 2022 - 12Z Fri Jun 03 2022 ...Potential for heavy precipitation next week from the northern Rockies to Upper Midwest and then southward through the Plains... ...Weather Pattern Overview... The medium range period begins Monday with a rather amplified upper level pattern for late May, consisting of an anomalously deep trough with embedded low in the West and ridging over much of the East (though suppressed in the Northeast by an eastern Canada upper low). This configuration will allow for potentially heavy precipitation to spread from the northern Rockies into the northern Plains and Upper Midwest. Higher elevation snow is possible in the Rockies while heavy rain and severe weather are threats in the Plains to Midwest along with warmer than normal temperatures. As next week progresses, the mean flow aloft should flatten quickly as the main western upper low lifts into south-central Canada and consolidates with separate central Canada energy to yield a fairly deep upper low. The highest precipitation chances should shift into the central/southern Plains and across the East along and ahead of the cold front that pushes eastward from the Plains. Toward the end of next week an upper trough may bring a front and some associated moisture into the Northwest. ...Model Guidance Evaluation/Preferences... Latest guidance through the 00Z/06Z cycles has generally followed through on recent trends toward faster ejection of the main western U.S. upper low through the northern tier and then stronger interaction with central Canada energy to yield a rather deep upper low and vigorous surface system just southwest of Hudson Bay by midweek. The deeper evolution ultimately leads to somewhat faster progression of the front that begins to push eastward from the Plains. Even with the faster trend, other 12Z models suggest the new GFS may be too fast with the northern U.S./southern Canada system by early Tuesday. Details of a separate weaker northwestern U.S. upper low shearing out as the mean pattern rapidly flattens continue to be somewhat ambiguous, and will affect frontal wave/rainfall specifics to the east of the Rockies. Outside of the UKMET, new 12Z models have trended stronger with this feature through Tuesday-Wednesday. Meanwhile there is decent agreement in principle that energy underneath the eastern U.S. upper ridge may try to consolidate into a closed low somewhere near the Southeast coast/Florida/northern Bahamas by midweek. However by day 7 Friday recent GFS/GEFS mean runs have developed a deeper and more expansive trough covering the Southeast U.S. and eastern Gulf relative to most other guidance. The 12Z GEFS mean trended a bit weaker with its day 7 upper trough though. On the northern side of the eastern ridge, guidance is gradually consolidating toward an episode of fairly strong cyclonic flow around a far eastern Canada upper low. This leads to increasing potential for the associated cold front reaching New England early in the week to push as far south as the northern Mid-Atlantic as a backdoor front before eventually returning north as a warm front. Consensus is reasonable for upper ridging to retrograde from the East/Mississippi Valley and then settle over the southern Plains/northern Mexico, connecting with the ridge that builds over the Interior West/Rockies. For the upper trough approaching the West Coast late in the week, GFS runs show a little more southeastward amplitude versus the majority at times but ultimately model/mean differences are within typical error ranges for forecasts that far out in time. Guidance comparisons led to using a 00Z/06Z model blend early in the period followed by transitioning to a model/mean mix, with slightly more weight to the 00Z ECMWF/ECMWF mean versus the 06Z GFS/GEFS mean (with lingering 00Z CMC input) due to aforementioned issues over/near the Southeast. ...Sensible Weather/Threat Highlights... Early next week, the upper low emerging from the West along with areas of low level upslope flow should combine to generate moderate to heavy precipitation over the northern Rockies and High Plains. Higher elevations of the northern Rockies particularly in southern Montana to northern Wyoming could see significant late season snow as the anomalously deep system leads to colder than average conditions. Farther east, rain and thunderstorms are threats across the northern Plains into the Midwest along a wavy front that should initially be slow to move. Along this front, a fairly strong surface system developing over the northern tier into southern Canada during the first half of the week may help to focus rainfall as well. Severe weather and heavy rain are both possibilities with this convection. As the upper pattern flattens, lower amplitude troughing will likely move slowly eastward across northern parts of the central and eastern U.S. and push a cold front ahead of it into the East back into the central/southern Plains. This front will serve as a focus for convection as it presses east across the Ohio Valley to the Eastern Seaboard and south across the Plains and Mississippi Valley for the latter half of the workweek. Some moderate to heavy rainfall is possible especially across parts of the central U.S. but still with lower than average confidence for the areal details and amounts. Elsewhere, Florida can expect some scattered diurnally favored convection, aided by energy aloft to the south of the eastern U.S. upper ridge. This convection may become more widespread by late week. Also the Northeast may see mostly light rainfall along a backdoor front for the first half of the workweek before the better focus for rainfall around Thursday just ahead of the main cold front. A front expected to push into the Northwest late in the week may bring areas of light rainfall. The eastern U.S./Mississippi Valley upper ridge will promote above average temperatures by 10-20F from the Plains to the Midwest/Ohio Valley and the Northeast/Mid-Atlantic Monday-Wednesday, with some daily record high maximum and minimum temperatures possible. The backdoor front reaching New England and possibly as far south as the northern Mid-Atlantic would bring a cooler trend to these areas though. Meanwhile upper troughing will bring very cool temperatures to areas from the Intermountain West through northern Plains early in the week with highs forecast to be 10-20F or below normal. The flattening pattern aloft will push the initial Plains cold front eastward while leading to a moderating trend for below normal temperatures over the central U.S., with mostly single-digit negative anomalies by Thursday-Friday. The East will see shrinking coverage of warm temperatures after Wednesday. The West Coast and into the Great Basin could flip back to warmer than normal temperatures by around 5-10F Wednesday and beyond, followed by modest cooler trend on Friday along the immediate West Coast with the arrival of a Pacific front. Rausch/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, 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