Extended Forecast Discussion NWS Weather Prediction Center College Park MD 250 AM EDT Tue Jun 30 2020 Valid 12Z Fri Jul 03 2020 - 12Z Tue Jul 07 2020 ...Overview and Guidance Assessment... Guidance continues to agree with the large scale pattern but there are multiple embedded uncertainties. The northern part of an initial Plains/Mississippi Valley into Mexico ridge aloft will gradually flatten while the southwest part will retrograde into the Pacific. This ridge along with Northeast Pacific/Alaska ridging will frame a mean trough over western Canada and the eastern Pacific/U.S. West Coast. Solutions vary considerably over exact details within this trough. Another mean trough will extend from eastern Canada into the Northeast, with this trough likely to trend weaker early next week as the upstream ridge becomes flatter. Over the South the models/ensembles are still signaling an upper weakness but with ongoing differences/trends in the details. As in previous days, individual shortwaves/upper lows within the trough near the West Coast depend upon details of short-range energy progressing across Alaska and the shape/strength of the upper ridge that builds in its wake. While not representative of all solutions, the model/mean average from the 12Z/18Z cycles has generally adjusted a bit northward for the upper trough core/embedded low(s) for a decent portion of the forecast period. Low confidence for compact embedded features also affects the day-to-day details of the wavy mean frontal boundary extending from the northern Rockies across the Northern Plains near the Canadian border and on to the northeast over Canada. Farther east there has been a notable trend toward somewhat later weakening of upper ridging over east-central Canada which in turn has led to greater persistence of the Northeast upper trough and the surface front defining its southern periphery, as well as a delay in southern Canada/northern tier U.S. frontal progression upstream. Recent trends for the upper weakness over the South have been toward a somewhat weaker/suppressed depiction. The small scale and diffuse nature of this feature continue to suggest low predictability at the medium range time frame. Among the 12Z/18Z solutions the 18Z GFS and 12Z ECMWF/UKMET provided the most comparable cluster for use in the first half of the period. The increasing detail uncertainty by the latter half of the forecast as well as 12Z GFS beginning to compare somewhat better to the ECMWF and ensemble means in concept versus the 18Z run led to transitioning the blend to an even model/mean blend incorporating the 12Z ECMWF/GFS and 12Z ECMWF mean/18Z GEFS mean for days 6-7 Mon-Tue. ...Weather/Hazard Highlights... Ongoing trends toward a somewhat more suppressed/elongated upper weakness across the South have led to a higher potential for greatest rainfall being near the Gulf Coast and southeastern coastal areas. Still, such features can be ill-behaved more than a couple days out in time so areas farther inland should monitor the forecast for any reversal in trends. Longer persistence of a wavy front over the extreme northern part of the Plains may lead to higher rainfall totals from Northern Plains showers and thunderstorms with some training/repeat activity possible. Expect diurnal convection over the central/southern Rockies during the period, while the Northeast upper trough and surface front at its southern periphery may promote one or more episodes of showers/thunderstorms. The most prominent temperature anomalies will continue to be of the warm variety centered over/near the Upper Mississippi Valley and Great Lakes. Readings may reach up to 10-15F above normal on one or more days over these areas, and on Fri locally higher anomalies with a few daily records may be possible over northern Minnesota/Wisconsin and vicinity. From late week into the weekend fairly warm anomalies will also extend into the Northern Plains. Elsewhere expect anomalies to be in the single digits. The long term upper trough nearby may keep the Pacific Northwest coast a tad below normal. The rest of the West should be near to modestly below normal late this week and then trend to near/slightly above normal. The central/southern Plains should see pockets of slightly above normal readings. Clouds/precipitation should keep the South near to somewhat below normal though the Florida Peninsula will likely stay a little above normal. 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