Extended Forecast Discussion...Amended NWS Weather Prediction Center College Park MD 147 AM EDT Mon May 28 2018 Valid 12Z Thu May 31 2018 - 12Z Mon Jun 04 2018 ...Record heat expected across the southern Plains & western Gulf Coast... ...Post-Tropical Cyclone Alberto crosses the Great Lakes & New England... Synoptic Overview ~~~~~~~~~~~~~~~~~ A strengthening Rex Block near the 165th meridian West should lead to downstream ridging across the eastern Pacific and troughing across the Northwest. Farther east, relatively strong mid-level height anomalies persist across the North Atlantic and Southeast Canada through the period, keeping the flow pattern blocked across the region and the polar jet stream suppressed, with a pseudo Rex Block forming across southeast Canada and the East. Guidance Assessment/Choices ~~~~~~~~~~~~~~~~~~~~~~~~~~~ There is relatively good agreement through Saturday before the 27/12z ECMWF becomes a decided outlier in showing greater progression with systems across the Lower 48. As the operational ECMWF appears out of tolerance with its own ensemble mean in southwest Canada, it is likely too progressive with the eastern trough downstream. For pressures, winds, and 500 hPa heights, a compromise of 12z Canadian, 12z UKMET, 18z GFS, and 12z ECMWF was useful into Saturday. Thereafter, used declining percentages of the 12z ECMWF and bulked up the percentages of the 12z NAEFS mean & 12z ECMWF ensemble mean. This led to greater progression of a front moving into the West from Friday onward but otherwise maintained good continuity with day shift. The weather, dew point, temperature, cloud, and precipitation chance grids were more evenly distributed between the above deterministic and ensemble mean guidance. An early draft of the precipitation forecast is composed of a blend of the 12z Canadian, 12z ECMWF, 18z/00z GFS, and the 00z National Blend of Models for days 4-5, with days 6-7 an even blend of the 12z Canadian, 18z/00z GFS, and the 00z National Blend of Models. Weather highlights & Threats ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Post-Tropical Cyclone Alberto's circulation aloft, merged with an incoming mid-level disturbance from the Westerlies, is expected to drop southeast into the Mid-Atlantic States, setting the stage for heavy rains in the northern Mid-Atlantic states. Abundant tropical moisture spilling into the southern and eastern states will keep rainfall chances above climatology through much of the week; heavy rains are possible near the central Gulf Coast this weekend near/ahead of an approaching cold front. Farther upstream, highly divergent flow aloft in advance of the western U.S. trough will foster the development of late season rainfall for the Northwest and the northern Rockies, with the heaviest precipitation expected near North Dakota. Heat will dominate the forecast throughout much of the week, outside the influence of upper troughs such as the Northwest and Northeast. The hot spot should be the Southern Plains where numbers approach 110 degrees along the lower Rio Grande while century degree readings also encompass much the region surrounding the Red River. A heat wave with forecast record high temperatures and record high minima in the southern Plains and western Gulf Coast is expected through the Medium Range period. Surrounding locations get in on the action as widespread 90s are expected across the central Plains as well as the lower Mississippi Valley. Roth/Ryan/Rubin-Oster 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