Extended Forecast Discussion NWS Weather Prediction Center College Park MD 251 AM EDT Fri Jul 06 2018 Valid 12Z Mon Jul 09 2018 - 12Z Fri Jul 13 2018 ...Overview/Guidance Evaluation/Preferences ... A broad mid/upper-level ridge will remain fixed over a good chunk of the nation with general 2 to 2.5 standard deviations above climatology observed in 500-mb height fields. This 594-dm anticyclone should periodically be disturbed by incoming Pacific features as well as amplification within the northern stream which generally straddles the international border with Canada. While solutions agree on timing of the Pacific shortwave crossing into the Pacific Northwest and southern British Columbia on Tuesday morning, they continue to struggle across other areas of downstream amplification. Models seem to take turns showing local invigoration of the flow with various models exhibiting such behaviors. Most recently, the 00Z GFS shifted back toward a stronger upper trough sweeping through southern Ontario down into the upper Great Lakes on Monday which was seen in the 12Z cycle. Additionally, the 00Z GFS has struggled with a remnant upper low spinning off the Carolinas showing slow, but general strengthening while lifting up along the Gulf Stream. The 00Z/12Z UKMET has depicted a similar scenario but with more eastward displacement. Overall, the effects of these disturbances on the synoptic-scale pattern will be to reduce the strength of the persistent 594-dm ridge across the nation. The guidance occasionally show re-establishment at this strength but vary in details. To support the above assessment, a multi-model approach was utilized with reduced influences of operational solutions beyond Day 5/Wednesday. While ensemble means sufficiently dampened forecast details, many aspects of the pattern remain unresolvable as such time ranges. Weather threats/Highlights... The upper ridge should keep numbers above average across a vast majority of the country. In terms of forecast departures, the Pacific Northwest and upper Intermountain West can expect temperatures to diverge around 10 to 15 degrees from early/mid July climatology by the middle to end of next week. This would allow for upper 90s to thrive over much of this region with 70s and 80s more commonplace closer to the coast and into Seattle, WA. Meanwhile, slightly below average readings are in the forecast from the Four Corners eastward across the Southern Plains and into the Gulf Coast. This will be in response to enhanced cloud cover and daily precipitation threats, particularly within the active southwestern U.S. monsoon. Besides these locations, showers and thunderstorms are expected across the north-central U.S. depending on how amplified the flow becomes. Some residual downstream precipitation threats would be likely as the frontal zone advances and occasionally meanders. Overall, difficult to say where the heaviest rainfall will occur during the period although model numbers are fairly conservative in a 24-hour sense. Rubin-Oster WPC medium range 500 mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indexes 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 http://www.wpc.ncep.noaa.gov/heat_index.shtml