Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1151 AM EDT Thu Jun 27 2019 Valid 12Z Sun Jun 30 2019 - 12Z Thu Jul 04 2019 ...Overview and Weather Highlights/Threats... Upper ridging over and/or just south of Alaska will favor a positively tilted mean trough over the Pacific Northwest, with progressive and low amplitude flow prevailing downstream across the northern U.S. Farther south an eastern Pacific into southern Rockies ridge aloft will weaken a bit after Sun-Mon. At the same time a central Plains/Midwest ridge will merge with another ridge building westward from the Bahamas and settling over Florida/Gulf of Mexico and the the Southeast. Between the western and eastern ridges an upper weakness will drift from near the western Gulf Coast into the southern half of the Plains. This pattern will favor three primary areas of locally moderate-heavy rainfall. Locations from just east of the northern Rockies through the Great Lakes/Ohio Valley will be along/north of a wavy mean frontal boundary which will combine with shortwaves ejecting from the Pacific Northwest upper trough to promote multiple convective episodes. Some convection could also be strong to severe but predictability in specifics is low at this time. Check SPC outlooks as the details come into clearer focus. Rainfall could extend into the Northeast/Mid-Atlantic as a front reaches those regions by Tue. The upper weakness drifting into the southern Plains may bring some areas of enhanced rainfall to locations from the western half of the Gulf Coast northward. The most common theme in the guidance is for best focus to exist near the Gulf Coast with lower confidence pinpointing any enhanced activity farther north. Diurnally enhanced convection will produce pockets of significant rainfall over Florida and portions of the Southeast. Expect the greatest temperature anomalies to be over parts of the northern Plains/Upper Midwest on Sun and perhaps into Mon, ahead of a front approaching the region. Some max/min readings (greater coverage for mins) could exceed 10F above normal. Otherwise anomalies over the lower 48 should be in the single digits during the period. Warmest highs versus normal mid-late period should be over the Mid-Atlantic/Southeast while the West and Plains will likely see near to slightly below normal highs. Min temperatures will tend to be near to above normal over most areas during the period. ...Guidance/Predictability Assessment... Over the past couple days the ECMWF/ECMWF mean, GEFS mean, and to a reasonable degree CMC have settled into a good consistent cluster with respect to holding the Pacific Northwest mean trough in place for most of the period. Very low confidence small scale features within the trough still provide opportunity for meaningful detail changes though. For the second day in a row the 06Z GFS run is significantly more eager to eject the trough than consensus or 00Z GFS and thus could not be used in the forecast blend. The 00Z GFS also becomes somewhat quicker to eject the embedded low that reaches the coast around Mon but the trough that remains through the rest of the period is similar to the majority cluster. Meanwhile consensus shows an upper low tracking from northwestern Canada toward Hudson Bay, with the flow on the southern periphery possibly pushing a cold front into the extreme northern Plains. Again the 06Z GFS becomes the most suspect solution for this upper low late in the period, pulling the track to the west/southwest of other guidance. Other features exhibit lower discrepancies. A 00Z operational model blend early in the period, transitioning to 30-40% GEFS/ECMWF mean input along with the models late, represents consensus well for significant features through the period. 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