Extended Forecast Discussion NWS Weather Prediction Center College Park MD 156 PM EDT Sun Jul 10 2022 Valid 12Z Wed Jul 13 2022 - 12Z Sun Jul 17 2022 ...Excessive rainfall threat for the central Gulf Coast states... ...Guidance Evaluation/Predictability Assessment... One of the biggest areas of uncertainty in the medium range period remains along the central Gulf Coast, where there is good 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. Overnight, some of the guidance (most notably the ECMWF and UKMET) seemed to really want to blossom this into a fairly well defined tropical low, and NHC has recently added this area into their outlook (with a low chance of development). There is a significant uncertainty where though this may (or may not) impact, from generally east TX to the western FL Panhandle. The GFS, CMC, and ensemble means are much less enthusiastic but still suggest the presence of at least a trough or lingering front for some time. Uncertainty remains high, and so the WPC progs/QPF favor something closer to the ensemble means and 13z NBM until confidence increases. 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 trough, but also with a possible closed low towards the Pacific Northwest coast next weekend. With the latter, the ECMWF is weaker/faster to bring energy into southwest Canada, but the CMC and GFS show a much stronger more compact closed low just off Vancouver Island day 7. The WPC blend favored the deterministic models for day 3-5, but quickly transitioned to a 50/50 ensemble mean/deterministic blend by 6 and 7 to help mitigate differences in the West, as well as along the Gulf Coast. Overall, this approach maintains good WPC continuity from the previous shift. ...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, monsoonal moisture flow across the Southwest into the Great Basin/Rockies may offer daily chances for showers with some locally heavier downpours. 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. 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. Interaction with a sub-tropicical disturbance in the Gulf of Mexico may in particular support heavy rain potential near the central Gulf Coast. This could focus slow-moving/repeat cells with very heavy downpours leading to local runoff issues, so a "slight" risk area was maintained on the experimental WPC medium range Excessive Rainfall Outlook for Wednesday. Some of the models hint at the potential for this disturbance to evolve into something more tropical like, although there is significant uncertainty in this, which has implications for how much and where QPF falls. Regardless of development though, there is agreement that heavy rainfall likely impacts the central Gulf coast as moisture interacts with the stalled frontal boundary. Santorelli/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