Extended Forecast Discussion NWS Weather Prediction Center College Park MD 242 AM EDT Mon Sep 19 2022 Valid 12Z Thu Sep 22 2022 - 12Z Mon Sep 26 2022 ...Heavy rainfall threat lingers for the Four Corners/Rockies into Thursday... ...Guidance Evaluation/Predictability Assessment... Latest model and ensemble solutions seem pretty well clustered through medium range time scales over the lower 48, bolstering forecast confidence despite some lingering local embedded system timing/strength differences. The WPC medium range product suite was primarily derived from a composite of the 18 UTC GFS and 12 UTC ECMWF/UKMET along with the 01 UTC National Blend of Models (NBM) Thursday-Saturday before switching mainly to the 18 UTC GEFS/12 UTC ECMWF ensemble means and 01 UTC NBM at longer time frames into Sunday/next Monday. Guidance differences seem well mitigated by the blending process consistent with predictability. WPC product continuity is well maintained in this manner and newer 00 UTC model and ensemble guidance generally remains in line. ...Pattern Overview and Weather/Hazards Highlights... The slow ejection of an amplified upper trough/low and frontal system through the north-central Great Basin/Rockies Thursday into Friday favors cooler temperatures that may lead to some snow for high elevations. Maximum daily temperatures are forecast to temporarily dip 10 to 15 degrees F below average. Anomalous moisture lifted across the Four Corners region in advance of the ejecting upper trough will increase chances for moderate to locally heavier rainfall/thunderstorms. There remains a slight risk areas on the Day 4 experimental WPC Excessive Rainfall Outlook across the Four Corners region. Additional activity will work across northern Great Basin/Rockies Thursday to the north-central U.S. and into the East Friday into the weekend given favorable upper system support and well defined cold front. An eroding lead upper ridge over the South will support lingering 10-15F warmer than average temperatures into Thursday. This will be in advance of the aforementioned cold front. Heat will quickly get suppressed with this frontal passage as quite cooled Canadian post-frontal high pressure settles into the central to eastern U.S.. The lingering front may focus some showers across Florida through the weekend. Schichtel 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