Extended Forecast Discussion NWS Weather Prediction Center College Park MD 256 AM EDT Mon Jul 11 2022 Valid 12Z Thu Jul 14 2022 - 12Z Mon Jul 18 2022 ...Multi-day Excessive rainfall threat for the central Gulf Coast states... ...Guidance Evaluation/Predictability Assessment... A significant area of uncertainty in the medium range period remains along the central Gulf Coast, where there has been increasinging agreement that some sort of upper level energy will get left behind by an upper trough shifting east at the end of the short range, but the evolution of that is in question towards next weekend. Some guidance (most notably recent runs of the ECMWF and UKMET) really want to blossom this into a fairly well defined tropical low, and NHC has recently added this area into their outlook. There is significant uncertainty where this may impact from Louisiana to the western FL Panhandle. The GFS and CMC remain less enthusiastic, but still suggest the presence of at least a trough or lingering front for some time and overall guidance QPF is trending upward. Accordingly, WPC QPF has increased inland across the central Gulf coast. Please refer to the latest tropical weather outlooks from NHC for the latest information on this feature. Otherwise, there is continued good agreement for some sort of amplified troughing across the East, as a weak shortwave slides into the Pacific Northwest on Wednesday and rides overtop a strong central U.S. ridge Thursday-Friday. Eventually, this energy should drop back towards the Great Lakes serving to reinforce troughing over the East by late period. Typical late period uncertainties with timing and details begins to arise by days 6-7 both in the Eastern U.S. trough, but also with a possible closed low towards the Pacific Northwest coast in about a week. Given noteable model smaller scale differences at medium range time scales that affect headline threat messaging, the WPC medium range product suite was mainly derived from the 18 UTC GEFS mean, 12 UTC ECMWF ensemble mean, 01 UTC National Blend of Models and WPC continuity to smooth out these less predictable features and interactions while reasonably trending continuity consistent with gradually growing guidance signals. The latest 00 UTC guidance suite generally maintains the line with prior respective runs, but falls short of providing much threat clarity. ...Overview and Weather/Hazards Highlights... A main upper high/ridge will settle westward into the Four Corners this week to support above normal temperatures across much of the West, but the most anomalous heat is forecast to spread downstream across the north-central U.S. as ridging/heights build over the region. In this pattern, modest monsoonal moisture flow across the Southwest into the Great Basin/Rockies under the upper ridge may offer daily chances for showers with some locally heavier downpours with slowed cell motions. Meanwhile, a series of uncertain impulses will round the top of the ridge to periodically focus strong convection locally over the north-central Plains/Upper Midwest, but rains may prove more progressive in nature. Upper trough positions will sandwich the upper ridge both off the Pacific Northwest where rainfall chances are limited and also the East where fronts will focus rain and thunderstorms. Moisture will pool from the eastern Mid-Atlantic to the Southeast and Gulf Coast states near a wavy stalled lead front. Possible sub-tropical/Tropical interaction over the northern the Gulf of Mexico may support heavy rain potential into the central Gulf Coast and vicinity as slow-moving and repeat cells with very heavy downpours lead to local runoff issues. A "slight" risk area was issued on the experimental WPC medium range Excessive Rainfall Outlook through mid-late week. Models offer potential for a disturbance or tropical low, although there is significant uncertainty in this as per NHC. Regardless, there is a growing guidance signal that heavy rainfall likely impacts the central Gulf coast as fueled by pooling deep moisture and instability near the lingering boundary. 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