Extended Forecast Discussion NWS Weather Prediction Center College Park MD 237 PM EDT Thu May 21 2020 Valid 12Z Sun May 24 2020 - 12Z Thu May 28 2020 ...Heavy rainfall possible over the Southern Plains/Texas next week... ...Overview... Upper ridging is forecast to strengthen along the East and West coasts next week which favors troughing over the central/southern Plains. A frontal boundary will very slowly move into Oklahoma/Texas late Sun into Mon and act as a focus for locally heavy rainfall. A Pacific front is expected to move into WA/OR late Mon and push eastward and a bit southward next week. ...Weather/Hazard Highlights... As the upper trough and surface front slowly dip into the Southern Plains, heavy rainfall will be possible in some areas. Sustained moisture feeding out of the Gulf of Mexico will be realized as rainfall and embedded convection near and ahead of the boundary as it sinks southward. Focus on Sun-Mon will be over northern TX into OK and will tend to shift southward and southwestward in time as additional height falls move out of Colorado and through New Mexico Mon-Tue. This could bring several inches of rain to some areas though perhaps over a multi-day period. This area continues to be highlighted on our day 3-7 Hazards Outlook. Building ridging in the West and East will bring rising temperatures to areas west of the Rockies and east of the Mississippi (especially near the Great Lakes). Out West, temperatures should rise to above or much above normal by Tue-Wed with anomalies +10 to +20F possible. Daytime highs will be in the 90s to 100s over much of the interior to inland deserts, and near 110F in the favored warmer locations (Phoenix to Yuma to southern Nevada). Some areas could approach record highs over the Great Basin and central CA Valley where low 100s are also possible. Temperatures in the East will climb into the 70s and 80s after a prolonged cool spell. ...Guidance/Predictability Assessment... Deterministic consensus sufficed to start the period, as the 06Z GFS shifted toward the 00Z ECMWF/Canadian/UKMET (and ensemble) consensus overall. Longwave pattern remains fairly predictable despite the several closed features. Consensus still favors the southern troughing and potential closed low to eventually weaken and lift northeastward around next Thu but this will be sensitive to the steering currents and proximity to the next northern shortwave astride the US/Canadian border. That system has the potential to be a bit stronger than what the ensembles show (per the deterministic runs) but remain in Canada. Attendant cold front may be a bit moisture-starved given the flow out of the Gulf northward then northeastward around the high to the east. Upper high is forecast to develop over the Mid-Atlantic though the surface flow will have an easterly component across the relatively cool Atlantic. By next Wed/Thu, preferred about a 50% weighting of the ensembles as uncertainty in the southern closed low increases as well as with the system to the north. A closed low in the eastern Pacific will likely remain well away from the coast, blocked by the strong ridging over the Southwest. Ensemble trend suggests keeping that system close to 130W. Fracasso Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml