Extended Forecast Discussion NWS Weather Prediction Center College Park MD 142 AM EDT Sat Apr 11 2020 Valid 12Z Tue Apr 14 2020 - 12Z Sat Apr 18 2020 ...Heavy rain threat Tuesday into Wednesday for parts of the Southeast... ...Overview and Guidance/Predictability Assessment... The synoptic pattern remains fairly consistent through the extended period, with an expansive ridge over the eastern Pacific and broad longwave trough over much of the central and eastern CONUS. The main feature, a rapidly deepening low pressure system will be lifting into eastern Canada on day 3, as a series of shortwaves/impulses follow behind days 4-7 crossing the Great Lakes into the Northeast. Despite the normal timing/intensity differences, models are in fairly good agreement on the large scale, and a general model compromise should work well for the WPC medium range fronts and pressures for these features. Main question in the medium range remains with shortwave energy undercutting the eastern Pacific ridge, potentially bringing a closed low to along or just off the West Coast by about day 5. While most of the deterministic models show the existence of such a feature, timing and intensity continue to vary widely between the individual models. Run to run continuity is quite poor within any particular model and so after day 5, confidence regarding the evolution of this is low at best. Given the spread, as expected, ensemble means are more washed out with this feature, though at least show an open wave present near California which eventually drifts into the Four Corners region by day 7. After day 5, preferred a blend of the ensemble means (ECENS/GEFS), though continued a fair percentage of deterministic models for system definition. The 12z/April 10 ECMWF and the 12z/April 10 CMC were preferred because they seemed to be the closest in position to the ensemble means, while the 18z/April 10 GFS remains slow and much farther north than the better consensus. ...Weather/Hazard Highlights... The impressively deep surface low over the Great Lakes at the end of the short range period, should be lifting towards Hudson Bay by the beginning of the medium range period. Most weather hazards associated with the system should be gone by day 3, with the exception of some lingering gusty winds across portions of the Great Lakes and New England. Farther south however, a weak surface wave may develop along the associated frontal boundary near the Gulf Coast/Southeast. This will increase the chance for showers and thunderstorms continuing through Tuesday into Wednesday, with heavy rainfall possible. Elsewhere, the weather should be fairly quiet in terms of precipitation hazards, though a weak frontal boundary dropping into the Central U.S. may bring some snow to the favored terrain of the Northern/Central Rockies. Broad troughing across the Central and Eastern U.S. will maintain a colder than average airmass for mid-April standards. The greatest temperature anomalies are expected across the Plains to the Midwest early next week where daytime highs could be 20+ degrees below normal. Cold anomalies east of the Rockies should moderate back closer to normal during the middle to latter parts of next week, while temperatures should trend warmer across parts of the West as upper ridging builds aloft. Santorelli 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