Extended Forecast Discussion NWS Weather Prediction Center College Park MD 231 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... Throughout the forecast, an ever 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 into next weekend based on the latest guidance suite. ...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 12Z ECMWF does stand out as being too robust with its mid-level reflection as other solutions are more subtle in nature. Consequently, the 12Z ECMWF becomes slower/deeper while various other pieces of guidance absorb this system into the mean northeastern U.S. trough. One place the solutions do agree is 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 seasonably strong upper cyclone accompanied by 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 still many operational models and ensembles favoring a marked lowering of heights over the Pacific Northwest. More specifically, the 00Z GFS depicts such a solution, albeit with rather poor run-to-run model continuity. Details vary enough to shift more toward an ensemble-based approach into next weekend. The consensus does appear to favor an establishment of an omega block with negative height anomalies anchoring the western/eastern sections of North America. With reasonable model agreement through Day 4/Jun 7, favored a multi-operational model consensus utilizing a combination of the 18Z/12Z GFS with the 12Z ECMWF/UKMET. By the following day, started incorporating the 18Z GEFS/12Z ECMWF ensemble means into the picture with slowly decreasing use of the 18Z/12Z GFS and 12Z ECMWF. Given the anomalous looking nature of the 12Z ECMWF early on, tried to minimize its presence to some degree. ...Weather highlights and hazards... 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 across much of New England while lows drop into the 40s. It should 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, the 00Z GFS shows impressive coverage of QPF for early/mid June. 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 Rubin-Oster