Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1200 PM EDT Thu Jun 28 2018 Valid 12Z Sun Jul 01 2018 - 12Z Thu Jul 05 2018 ...Overview and guidance evaluation/preferences... Model guidance this morning continues to indicate the likelihood of a heat wave expanding into the East Coast this weekend and continue well into next week as a strong subtropical high becomes a dominant feature. In contrast, an upper-level vortex dropping down from the Gulf of Alaska will keep a trough in place across the western U.S. into the middle of next week. There are differences in the way the smaller scale shortwaves are handled in the models but the general consensus is for a positively tilted trough to maintain itself near or just off the coast of the Pacific Northwest as a closed upper-level center attempts to form. Toward the middle of next week, models are unanimous on building the subtropical high westward across the central U.S. into the Rockies, and begins to push the trough slightly off the West Coast. It is also worth-mentioning that underneath the strong subtropical high over the U.S., models are indicating some sort of weak upper-level disturbance (notably the ECMWF) moving generally westward across the southeast U.S. during the weekend and then along the Gulf Coast early next week, reaching the Texas coast by next Thursday. It appears that convection interacting with a weak coastal boundary will keep a threat of locally heavy rain along the Gulf Coast into the middle of next week. It remains to be seen whether a surface circulation will be spawned near the boundary. In addition, models are showing the possibility of a cyclonic circulation forming in the vicinity of Bermuda during the weekend as a result of wave-breaking underneath the strong subtropical high. This circulation is then carried generally westward toward the southeast U.S. by Day 7 next Thursday. With the above considerations, the WPC morning grid package is a consensus of the 00Z ECMWF/EC mean and the 06Z GFS/GEFS (with a small percentage from the 00Z Canadian model), trending toward 70 percent of their ensemble means for days 6 and 7. Kong ...Weather threats/highlights... The upper Great Lakes to Plains front as of early Sun will bring areas of showers and thunderstorms into the East. Most heavy activity should be fairly localized as upper dynamics lift into Canada. The trailing part of the front over the Plains will lift back north as a warm front during the period and help to focus periods of convection, with best potential for heavier activity over the northern Plains/upper Midwest regions. Locations along and/or inland from the Gulf Coast may also see one or more days of significant rainfall enhanced by upper level energy and a weak surface reflection. Confidence is low in the specifics of these features but the overall pattern is favorable for rainfall. Between this activity and the eastern front, expect some periodic convection of varying intensity in response to daytime heating. Portions of the Northwest may see scattered and mostly light-moderate rainfall in response to the upper trough developing near the West Coast. Parts of the southern half of the Rockies and vicinity may see a little scattered rainfall as well. Guidance changes over the past day suggest potential for greater persistence of hot/humid weather over the Northeast, though expect this weekend and Mon to be the focus for the most extreme heat index values. Record warm lows are possible within a fairly large area over the East. Record highs are likely to be less numerous and tend to be between the eastern Great Lakes and northern Mid Atlantic/Northeast. In that time frame some readings could locally reach 15-20F above normal. Anomalies may still reach or exceed plus 10F over some areas in the Great Lakes/Northeast into midweek. Meanwhile the strengthening central U.S. ridge aloft later in the period will bring a return of well above normal temperatures (up to plus 10-15F anomalies) to the northern Plains/Midwest by Wed-Thu. The most persistently cool temperatures in association with the West Coast upper trough will be over the Pacific Northwest/northern Rockies with Mon-Tue likely to have the coolest highs, approaching 10F below normal. California should trend cooler after the weekend as the upper trough amplifies. Rausch WPC medium range forecasts of 500 mb heights, surface systems, weather grids, quantitative precipitation, and winter weather outlook probabilities are found at: http://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif http://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif http://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html http://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml http://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4