Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1155 AM EDT Sun Jun 03 2018 Valid 12Z Wed Jun 06 2018 - 12Z Sun Jun 10 2018 ...Heat wave from the Desert Southwest to the south-central U.S... ...Pattern overview... A persistent mid/upper-level ridge will maintain control of the pattern with a general position over the south-central U.S. With an area of lower heights remaining over the West Coast, many such impulses are forecast to act as "ridge rollers" as they track downstream toward the Great Lakes and into the Ohio Valley. These features should eventually adjoin the mean upper trough across the northeastern U.S. The overall set up will likely change very little this week. ...Model guidance/predictability evaluation/preferences... An initial closed low over southern New England will be accompanied by a modest area of low pressure off the Delmarva coast. This well clustered system is forecast to eject east of Nova Scotia by Thursday morning. Meanwhile the focus shifts back toward a notable perturbation in the flow straddling the southern border of Manitoba mid-week. The solutions do agree better with the poleward expansion of the sprawling upper ridge across the south-central states. Where they disagree is with mesoscale details of evolving impulses off the upstream higher terrain. At this forecast juncture, it is too early to resolve such spatial scales at this time. It is safe to say multiple convective episodes will be likely north and east of this ridge with activity congregating from the Northern Plains downstream into the Great Lakes/Ohio Valley regions. Across the eastern Pacific, a unseasonably strong upper cyclone with 500-mb height departures on the order of 2 standard deviations below climatology will be a key player in the forecast. While the strongest forcing/height falls should swing through British Columbia and Alberta, there are some operational models and ensembles favoring a marked lowering of heights over the Pacific Northwest. Recent GFS runs in particular depict such a solution, albeit with poor run-to-run model continuity and outlier status without almost any ensemble support. Overall, good model agreement into Day 5/Fri allowed for a WPC multi-operational model consensus utilizing the 06 UTC GFS and the 00 UTC ECMWF/UKMET/Canadian. Quickly transitioned to a reasonably clustered 06 UTC GEFS mean and 00 UTC NAEFS/ECMWF ensemble means blend days 6/7 amid growing forecast spread/uncertainty. ...Weather highlights and hazards... It remains the case that the major weather story will be the abundant heat filling out the Desert Southwest eastward into the Southern Plains. This is in response to the persistent upper ridge holding strong over the region. Forecast highs will be in the triple digits over many of these regions, particularly the California, Arizona, and Nevada deserts as well as the state of Texas. Temperature anomalies should maximize over the Southern Plains with departures around 10 to 15 degrees above climatology. On the contrary, an upper trough departing the northeastern U.S. will keep temperatures on the cooler side for Wednesday/Thursday as readings hold into the 60s over much of New England as lows drop into the 40s. It should meanwhile prove to be an unsettled start to the period with cool cyclonic flow maintaining showers over the northeastern U.S. on Wednesday while thunderstorms are likely across the southeastern U.S. along the advancing cold front. Farther upstream, a series of convective complexes will evolve north of the upper ridge with hefty rainfall amounts likely from the Northern High Plains eastward into the Middle Mississippi Valley and eventually toward the Ohio Valley. While excessive rainfall concerns are somewhat unknown, some convectively driven hazards are likely with any such complex. Across the Pacific Northwest, it could prove to be quite wet if the trough amplifies as much as suggested. While extreme, recent outlier GFS runs show impressive coverage of QPF for early/mid June, but such potent height falls looks way overdone. WPC medium range forecasts of 500 mb heights, surface systems, weather grids, quantitative precipitation, and winter weather outlook probabilities can be 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 Schichtel