Extended Forecast Discussion NWS Weather Prediction Center College Park MD 256 AM 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 and embedded low in the West and ridging over much of the East (though suppressed in the Northeast by an eastern Canada upper low). This 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 pattern is forecast to flatten quickly as the western trough lifts into south-central Canada and consolidates with an upper low. The highest precipitation chances should shift into the central/southern Plains and across the East along and ahead of a cold front. ...Model Guidance Evaluation/Preferences... While 12/18Z and the newer 00Z model guidance cycles show general agreement for the initial trough/ridge pattern flattening for the latter half of the week as an upper low consolidates in south-central Canada, uncertainties in the details remain. Models display various ways of handling energy within the upper trough/low, as well as upstream energy that could spill into the West Monday-Tuesday and affect the timing of the trough's movement east and its lift northward and merging with energy across Canada. There has been a general trend for the western energy to eject faster, leading to a faster trend for a cold front just ahead of the trough as well as the QPF, and this trend continued in the 12/18Z models and again in the 00Z cycle. Even considering the faster trend, the 12Z UKMET remained on the fast side of guidance with the trough's movement eastward as it lifts north, but the 00Z may be more in line with consensus. Though the amplitude of the trough flattens, there is decent agreement for troughing to trek across the Midwest/Great Lakes Thursday into Friday and push a cold front eastward. Elsewhere, there is good agreement for ridging across much of the East on Monday and flattening through the week as upper highs (with less certain placement) could build across the southern tier. An eastern Canada upper low producing low amplitude troughing in the Northeast for the first half of the week could send a backdoor front across the area, which could potentially stall for a time but shows uncertain placement in general. Despite some individual model intricacies, a blend of the deterministic guidance led by the ECMWF and GFS runs worked for the early part of the WPC forecast, and added and gradually increased the proportion of the GEFS and EC ensemble means to almost half by the end of the period to minimize the specifics of any particular model. ...Sensible Weather/Threat Highlights... Early next week, the upper low moving over parts of 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 anomalous trough/low creates 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. Severe weather and heavy rainfall are both possibilities with this convection. As the upper pattern flattens, lower amplitude troughing is forecast to 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 with low confidence in 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, which may become more widespread by late week. Light rainfall is also possible in the Northeast 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. The central to eastern U.S. upper ridge will promote above average temperatures by 10-20F from the Plains to the Midwest/Ohio Valley and the Northeast/Mid-Atlantic early in the workweek, with some daily record high maximum and minimum temperatures possible. Meanwhile the Intermountain West should be quite cool underneath the upper trough as highs in particular are forecast to be 10-20F below normal. The cold front pressing eastward while the upper pattern flattens will lead to cooling temperatures in the Plains by midweek while the anomalous warmth gradually is shunted eastward, though anomalies will weaken all around. The West Coast and into the Great Basin could flip back to warmer than normal temperatures by around 5-10F Wednesday and beyond. 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