Extended Forecast Discussion NWS Weather Prediction Center College Park MD 315 AM EDT Sat May 28 2022 Valid 12Z Tue May 31 2022 - 12Z Sat Jun 04 2022 ...Multiple rounds of heavy rainfall are expected across central/southern parts of the Plains and Mississippi Valley next week... ...Overview... The medium range period begins Tuesday with an amplified pattern consisting of troughing over the West and an upper low across the central U.S. while ridging prevails across the Gulf Coast states into the East, with the exception of the Northeast where the ridge is suppressed by an eastern Canada upper low. The upper pattern should flatten across the lower 48 as energy consolidates into a fairly deep upper low across central Canada, but troughing extending from the low will shift a cold front southeastward as next week progresses, providing a focus for rain especially over the central/southern Plains and the Middle/Lower Mississippi Valley where multiple rounds of convection are likely. ...Model Guidance Evaluation/Preferences... On day 3/Tuesday as the period begins, there are already some differences with the details of energy within the western to north-central U.S. trough. The 12Z and newer 00Z ECMWF/UKMET as well as the 12Z EC ensemble mean agree with the existence and position of a closed upper low near the North Dakota/Minnesota border Tuesday morning, and CMC runs are similar though not quite a closed low (depending on the contour interval). However GFS runs seem to be the outliers with more strung out upper energy in the area in the 18Z and 00Z runs, while the 12Z showed a closed low but to the northeast of consensus, and the surface lows showed the same fast/northeast position. So favored the non-NCEP consensus early in the period, but by day 4/Wednesday models including the GFS generally come to better agreement with a consolidated low in central Canada. There are still some questions with additional upstream energy Tuesday-Wednesday around the Great Basin to central Rockies as to whether there could be an additional small closed low and how long the energy will last before getting absorbed into the mean flow. A multi-model blend seemed reasonable though there is variety in the details. Elsewhere, model guidance is agreeable with initial ridging from the south-central to eastern U.S. before an upper high/ridge retrogrades toward the southern Plains/northern Mexico, connecting with the ridge that builds over the Interior West/Rockies. Meanwhile upper energy looks to slowly drift west across the western Atlantic toward Florida Wednesday-Thursday, but with uncertainty in its strength, and then questions as to whether it could merge with troughing across the East. GFS runs show this trough merge more than other guidance, likely because it also combines with energy stemming from what is currently Tropical Depression One-E in the eastern Pacific. There is ample uncertainty with the potential for any redevelopment of the feature and its track and timing, but if any energy or a feature does persist or redevelop, a track as fast as the GFS runs seems unlikely as other guidance is much slower. Then troughing is expected to come into the Northwest late week stemming from an upper low in the eastern Pacific, with about average confidence and a trend toward a farther south upper low in the newer 00Z guidance. Thus the WPC medium range forecast utilized a multi-model deterministic blend early in the period favoring the ECMWF, then phasing in the GEFS and EC ensemble means to half by the end of the period to reduce the influence of individual model runs. ...Sensible Weather/Threat Highlights... The surface low pressure system lifting into central Canada beginning Tuesday will send a cold front across the north-central U.S. and across the northeastern quadrant through the latter part of the workweek. Rain is possible first across North Dakota and the Upper Midwest to Great Lakes along this front Tuesday and then shifting eastward across the Ohio Valley and into the Northeast/Mid-Atlantic by Thursday, after some initial showers in parts of the Northeast Tuesday-Wednesday near a backdoor front. However, the back end of the main front is forecast to move more slowly through central and southern parts of the Plains and Mississippi Valley, and will provide a focus for rain and thunderstorms for multiple days around Tuesday-Thursday. Flash flooding is possible especially where storms repeat over the same area, which at this point appears most likely to occur around Kansas, Oklahoma, and Missouri, but with uncertainty in the details beyond that. Elsewhere, Florida could see a showery pattern next week as weak upper-level energy passes through, with diurnally favored convection. This may increase by late next week as there is potential for moisture and energy associated with what is currently Tropical Depression One-E in the eastern Pacific to lift into the Gulf of Mexico. There is ample uncertainty with the potential for any redevelopment of the feature and its track and timing, but regardless it could enhance moisture and rainfall potential over Florida. The Northwest can expect increasing precipitation (most likely rain) chances later in the week as a front pushes through the region. The eastern U.S./Mississippi Valley upper ridge will promote above average temperatures by 10-20F over the Midwest/Ohio Valley and parts of the Northeast/Mid-Atlantic Tuesday-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/central Plains through midweek 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, though around 10F below normal in rain-cooled Kansas and Oklahoma. The East should see shrinking coverage of warm temperatures on Thursday and especially Friday-Saturday. The West Coast and into the Great Basin could flip back to warmer than normal temperatures by around 5-15F Wednesday and beyond, followed by a modest cooler trend on Friday-Saturday along the immediate West Coast with the arrival of a Pacific front. 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