Extended Forecast Discussion NWS Weather Prediction Center College Park MD 250 AM EDT Wed May 06 2020 Valid 12Z Sat May 09 2020 - 12Z Wed May 13 2020 ...Record cold over the East especially this weekend... ...Heavy rain possible over southern Florida Sunday... ...Overview... Amplified upper pattern more reminiscent of winter than late spring will start to break down next week as a Pacific system finally comes ashore. Deep troughing in the east will be responsible for widespread record and near record lows this weekend with only a slow moderation early next week. Areas west of the Rockies will see decreasing temperatures from their recent run of record warmth. In the Gulf, a wave along a frontal boundary could bring some heavy rain to the southern half of Florida on Sunday. ...Guidance/Predictability Assessment... The models continue to mostly align with the ensemble means on the pattern evolution but differ on timing/track of the embedded features in an otherwise highly predictable longwave pattern. The 12Z ECMWF continued to be the model best representing the most reasonable solution, followed by the 12Z GFS and then some aspects of the 12Z UKMET/Canadian. The 18Z GFS was not preferred in most areas but the 18Z GEFS mean was clustered near the ECMWF/ECMWF ensemble mean for most features. Main question may be how quickly the pattern in the west breaks down and allows Pacific energy inland. Blended solution seemed prudent given how the northern stream may play a role out of Canada and the fact that the upstream Pacific becomes quite uncertain by next week. Flattening of the pattern tends to favor the GFS, which usually runs too quick, but it was mostly aligned with the ECMWF as the Canadian kept the upper low off the coast and even retrograded it back to the northwest. Reality may be a partial ejection of height falls eastward, and this was reflected at the surface by a progressing cold front toward the Plains next Wed. Over the Gulf, most solutions bring a modestly organized area of low pressure along the stationary front toward southern Florida Sunday afternoon. Though this has been hinted at for a few cycles, specifics remain unclear at this time range. Trend is toward more rainfall in each cycle per the consensus, and overall pattern/setup suggests maintaining watch on this feature. ...Weather/Hazard Highlights... Parts of the West will still see well above normal temperatures (by 10-20F centered north of Lake Tahoe. As the upper/sfc low/front approach the area, temperatures will cool back to near then below normal by the end of the period. The central Rockies may be the only area in the CONUS by next Wed to see above normal temperatures. To the east of the Rockies the pattern will seem more like late winter, especially over the Great Lakes and Northeast. The most extreme temperature anomalies should be on Sat when locations from the eastern Great Lakes through the central Appalachians may see highs 20-25F below normal. Temperatures on Sat and/or Sun may approach or break daily records for lows/cold highs within the broader area of minus 10F or greater anomalies covering much of the eastern half of the lower 48. Also over some areas this cold surge would lead to a late frost/freeze where the growing season has already started. By next Mon-Tue parts of the South may still see lows reaching 5-10F or so below normal but highs may recover to near-normal levels. However min/max temperatures will tend to remain 10-20F below normal from the northern half of the Plains into the Mid-Atlantic/Northeast with incremental moderation by the end of the period. Exiting system over Maine on Sat will bring some rain and elevation snow to northern areas as it departs. Behind the system, lake-effect/enhanced rain/snow is also possible and a period of brisk to strong winds will add to the late-winter feel of the chilly air over the Northeast. Western/southern Gulf of Mexico waviness that may develop along the tail end of the late-week/weekend system's front may bring a period of heavy rainfall to extreme southern Texas and then to parts of the Florida Peninsula between Fri night and early next week. Confidence is low in specifics, but a local heavy rainfall threat exists for areas south of I-4. By next Mon-Wed the Central Plains and vicinity may see some rainfall as moisture and shortwave energy interact with the stationary front draped over central High Plains/Southern Plains. As the warm front begins to move eastward from the Front Range, moisture return may be sufficient to spark at least some modest rainfall. Fracasso/Rausch 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