Extended Forecast Discussion NWS Weather Prediction Center College Park MD 258 PM EDT Tue Jun 28 2022 Valid 12Z Fri Jul 01 2022 - 12Z Tue Jul 05 2022 ...Overview... Guidance agrees fairly well on the large scale pattern, featuring a Rex block configuration centered near 130-135W longitude (ridging over northwest Canada and an upper low anchoring a mean trough off the West Coast), a broad mean trough over eastern Canada and extending into the northeastern U.S., and southern tier U.S. ridging whose northwestward extension drifts from the Rockies into the northern Plains. The eastern North America mean trough will support one or more rainfall-focusing frontal systems to the east of the Rockies while the trough near the West Coast will keep nearby temperatures on the cool side and occasionally bring unsettled weather to the Northwest. The National Hurricane Center is monitoring a broad area of low pressure over the northwestern Gulf of Mexico, with flow around the southern tier upper ridge possibly bringing this feature and its moisture into and beyond the western Gulf Coast region. Expect hot temperatures to expand over the central U.S. during the first half of next week as the Plains ridge aloft becomes more pronounced. ...Guidance Evaluation/Predictability Assessment... Although the models and ensemble means display good consensus on the overall pattern, individual models/sequential runs show significant spread and variability with embedded features that will affect sensible weather over some areas. These include individual shortwaves within the Canadian trough whose influence extends into the northeastern quadrant of the lower 48 (affecting frontal position to the east of the Rockies) and details of the upper trough near the West Coast (with effects on the leading front/s and waves). The small scale of the northwestern Gulf feature leads to low predictability for it by late this week. For the trough near the West Coast, consensus generally shows gradual deepening/sharpening from late this week into the weekend. Then the details become somewhat more uncertain as some of this energy ejects while upstream energy drops into the western side of the mean trough. Within the Canadian into northeastern U.S. trough, there is good initial agreement that a strong system near southern Hudson Bay will anchor a front that should reach the East Coast by Sunday, likely stalling from the Mid-Atlantic into the Plains. With time the models become increasingly diverse and inconsistent with trailing shortwaves, leading to increasing differences for position of the aforementioned leading front and any fronts/waves that may reach the northern tier from Canada. Western trough details also come into play over the central U.S. by late in the period as well. Over the past couple days the ensemble means have been more consistent with the surface pattern to the east of the Rockies late in the period, favoring meaningful incorporation into the forecast by that time. Regarding the northwestern Gulf feature, most guidance suggests the surface reflection may lose definition by the start of the forecast period early Friday. There may still be a reflection aloft but agreement is poor for how long it will persist and exactly where it will track. Based on the latest array of guidance, the updated forecast started with a 00Z/06Z operational model blend of the ECMWF/GFS/CMC/UKMET in order from most to least weight for the first half of the period. Continuity and diverging model details favored incorporating half total weight of the 06Z GEFS/00Z ECMWF means by day 7 Tuesday. ...Sensible Weather and Potential Hazards... A lingering front along the southeastern coast late this week will likely promote the development of scattered to numerous showers and storms. Even with this front departing/dissipating after Friday, the area may still see some activity continue into the weekend depending on specifics of impulses aloft. Meanwhile, check the latest National Hurricane Center products for latest information regarding the feature over the northwestern Gulf of Mexico. Associated moisture may enhance rainfall across portions of Texas and perhaps other areas, depending on persistence and path of a possible upper level reflection. The small scale of this feature and significant guidance differences lead to low confidence in specifics at this time. Farther north, a front initially oriented from the Great Lakes into the central Plains will push gradually southeastward and support organized areas of showers and storms along and ahead of it. Some rainfall may be heavy from the central Plains into the Mid-Atlantic and southern New England, with deceleration of the front later in the weekend helping to maintain the potential for some locally significant totals. Possible interaction with southern tier moisture is yet another factor that will require monitoring. Monsoonal moisture over the Four Corners region may promote scattered areas of heavier rainfall with impulses and moisture lifting northward between upper ridging to the east and trough near the West Coast. This West Coast trough may produce periods of rainfall over parts of the Northwest. There is a signal for increasing rainfall near the Canadian border around early next week as some energy ejects from the trough. Moisture/convection could also extend across the northern Plains/Upper Midwest by next Monday-Tuesday ahead of a High Plains wave and leading warm front. Expect a band of temperatures up to 10-15F above normal ahead of the front crossing the central Great Lakes on Friday, with highest readings versus normal from the eastern Great Lakes into New England. Arrival/persistence of the front near the East Coast thereafter will tend to keep eastern U.S. temperatures near normal for highs and a little above normal for lows. Heat is likely to build again across the central and northern Plains by next Monday-Tuesday in response to the building upper ridge, with north-central areas seeing highs up to 10-15F above normal. Southern Plains locations will see slightly hotter conditions as well but with less extreme anomalies. Finally, below normal highs will spread gradually inland from the West Coast due to nearby upper troughing. There could be a few locations with highs 10-15F below normal around Sunday-Monday. Rausch Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, experimental excessive rainfall outlook, winter weather outlook probabilities and heat indices are at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml