Extended Forecast Discussion NWS Weather Prediction Center College Park MD 245 AM EDT Mon Jun 04 2018 Valid 12Z Thu Jun 07 2018 - 12Z Mon Jun 11 2018 ...Heat wave from the Desert Southwest to the south-central U.S... ...Pattern overview... Two primary synoptic-scale features will be focal points during the period spanning June 7-11, each of which will be rather anomalous relative to climatology. A sprawling upper ridge across the south-central U.S. as well as a deep-layered cyclone off the British Columbia coast are forecast to feature anomalies on the order of 2 sigma. This particular regime is expected to change very little during the period of interest, generally sustaining an omega block setup as lower heights across eastern North America fill out this signature. The largest changes are expected during the Day 5-7, June 9-11, timeframe as an impressive longwave trough accelerates through the Pacific Northwest. Ultimately, this should help erode the northern extent of the upper anticyclone over the south-central states. Across the southeastern U.S., a persistent mid/upper-level weakness will linger in the vicinity of Florida for much of the period. This area should be juxtaposed by a rather healthy moisture plume as evidenced by the 1.50 inch and above precipitable water values. ...Model guidance/predictability evaluation/preferences... Starting across eastern North America, a conveyor belt of low-amplitude shortwaves should migrate across Quebec while potentially grazing northern New England. A more amplified system will likely take shape by late in the weekend into the following week which ultimately shifts a wavy frontal zone south/east toward the Carolinas by 11/1200Z. Overall differences are not terribly significant here with the global guidance suite all in favor of this evolution. Likewise, there is solid agreement regarding the position of the weakness across the southeastern U.S. into the eastern Gulf of Mexico. Eventually the signal shears out over the weekend although multiple embedded vorticity centers are likely to still spin about the region in its wake. Moving to the center of the nation, a stout upper ridge will be a fixture for the foreseeable future with the 588-dm height contour of the mid-level heights extending up toward the Northern Plains at times. Like yesterday, the 12Z CMC seemed to be more suppressed with this ridge which is directly in response to the creation of sizable perturbations rounding the ridge axis. Otherwise, solutions appear to be within tolerance into the weekend as eventual upstream Pacific height falls begin to dent the northern extent of the anticyclone center. Much of this of course is based on the level of Pacific amplification which remains somewhat nebulous at this time. Over the West Coast, a semi-permanent upper low remains fixed off the British Columbia coast. Eventually a notable shortwave rounds the base of this trough with potent height falls accelerating across the Pacific Northwest by Saturday. Ensemble spaghetti plots vary with the depth of this trough as well as the temporal evolution. It appears the GFS/ECMWF have taken turns with being more anomalous than the consensus solution as the trough moves across the Pacific Northwest potentially down to northern California. More specifically, it was the 00Z GFS yesterday and the 12Z ECMWF. Such solutions have gained some company with the 00Z CMC joining it, albeit in a much slower fashion. While many uncertainties exist in the pattern, most are on the mesoscale revolving around the "ridge rollers" which cannot be adequately forecasted at this time. As such, felt a multi-operational model blend would suffice through Day 4/Friday utilizing a combination of the 18Z/12Z GFS with the 12Z ECMWF/UKMET solutions. Thereafter, removed the 12Z UKMET in favor of a consensus of the operational GFS/ECMWF models in conjunction with their respective ensemble means. The blend became fairly heavy in ensemble use by the end of the forecast with slightly more weighting toward the 18Z GEFS mean. ...Weather highlights and hazards... The heat wave will be the main story with readings 100 degrees plus anywhere from the Desert Southwest eastward along the Mexican border into the state of Texas. Departures from climatology should be around 10 degrees although slightly higher numbers can be found farther north into the remaining Great Plains states and into the Intermountain West/Rocky Mountain chain. Widespread 80s and 90s are likely over these locations accompanied by temperature anomalies in the 10 to 15 degree range. Regarding cool spots, Thursday should prove to be near or slightly below climatology across the East Coast with such conditions persisting into the weekend across Florida given immense cloud cover and rainfall. Elsewhere, deep upper troughing over the Pacific Northwest will hold temperatures around 5 to 10 degrees below average from Saturday onward. It should remain intermittently wet over the southeastern U.S., particularly Florida, given a stagnant upper trough/weakness in conjunction with an anomalous moisture feed. Back toward the middle of the country, multiple convective complexes are likely to erupt north of the ridge with propagation downstream likely toward the Middle Mississippi Valley and into the Great Lakes/Ohio Valley. Details would be fuzzy at best this far into the forecast but expect bouts of heavy rainfall accompanied by discernible severe weather threats. Elsewhere, it should prove to be quite wet over the Pacific Northwest given the deep cyclonic flow overhead. Strong forcing with the trough and eventual frontal passage could spread considerable early/mid June precipitation to the region. 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