Extended Forecast Discussion NWS Weather Prediction Center College Park MD 219 PM EDT Sat May 02 2020 Valid 12Z Tue May 05 2020 - 12Z Sat May 09 2020 ...Record heat for the Southwest midweek... ...Guidance/Predictability Assessment... Quasi-zonal flow at the start of the medium range period (D3 Tues May 5) is expected to evolve into an amplified western US ridge and central/eastern US trough by the end of the period. Model guidance shows relatively good agreement in the overall pattern and transition through 7 days, however the biggest differences actually lie early in the period. Shortwave energy tracking from the Pacific NW through the Northern Rockies and southern Canadian Rockies is bottled up before increasing troughing associated with a deeper closed Hudson Bay low eventually carves out the longwave trough over the eastern CONUS. How this energy ejects into the northern Plains and is absorbed into the troughing is different between the various deterministic guidance. Overall the GFS solutions (00Z/06Z) were considered an outlier and the better consistency was seen in the latest ECMWF/CMC/UKMET. By day 5, shortwave energy attempts to break into the western US ridge, and the GFS advertises a much faster progression compared to the slower ECMWF/UKMET, and the slower solutions were generally favored. For these reasons, the GFS was largely discounted from the entire medium range blend, and instead heavily leaned on the 00Z ECMWF early on and then transitioned to higher weights of the 00Z ECENS mean. As the flow becomes more amplified and a strong front pushes way south through Florida, the resulting surface pattern across the CONUS largely features sprawling high pressure, which has good agreement with the many of the latest deterministic and ensemble guidance. ...Weather/Hazard Highlights... Record heat will continue to be the main impact into next week. Temperatures 10-20F above normal over the Southern Rockies/Plains will migrate westward into the Southwest and California next week as the upper ridge builds along the West Coast/120W. By contrast, much of the east, and especially around the Great Lakes/Northeast, will see cooler than normal temperatures more typical of early April (about 5-10F below normal) through much of the week. An even colder shot of air could accompany the upper trough axis passage into next weekend. Temperatures could be 20 or so degrees colder than normal which may approach record cold levels for some areas. Farther south, a cold front will likely push all the way into and past southern Florida by the end of the week though in a very modified state. Precipitation will accompany and precede the system out of the Corn Belt Tuesday across the Ohio Valley to the Mid-Atlantic/Southeast overnight. Next frontal system out of the Pac NW Tue will slide eastward into the Plains by Thu with generally light rain and some embedded heavier elements. As this system passes the Mississippi River Valley and enters the base of the eastern trough, rainfall may expand to its east ahead of the cold front before it clear the coast early Saturday. Airmass could be cold enough for some snow at the highest elevations in New England late next Friday into Saturday. Fracasso/Taylor 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