Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 PM EDT Wed Jun 29 2022 Valid 12Z Sat Jul 02 2022 - 12Z Wed Jul 06 2022 ...Overview... Today's models and ensemble means are consistent with the mean pattern. A Rex block configuration should persist through the middle of next week, with ridging over northwest Canada and a mean low anchoring an eastern Pacific trough. Downstream, a broad mean trough over eastern Canada will extend into the northeastern U.S. while southern tier U.S. ridging holds strong and also builds over the Rockies and northern Plains. Within the Pacific trough, consensus shows an initial closed low/surrounding flow ejecting into the western U.S./southwest Canada next week as upstream energy near the Alaska Peninsula early Saturday replaces it. The northern Plains ridge axis may retrograde somewhat by Wednesday once this replacement is complete. 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 still monitoring a broad area of low pressure over the western Gulf of Mexico, with flow around the southern tier upper ridge possibly bringing this feature and its moisture into 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... Guidance continues to show a number of detail uncertainties that may take until the short range time frame to resolve, even though agreement is good for the large scale pattern. Models/ensemble members are still varied and inconsistent from run to run for shortwave details within the eastern Canada/northeastern U.S. mean trough behind a leading system that brings a front into the Northeast/Mid-Atlantic during the weekend. This makes it more difficult to maintain a stable forecast for surface front/wave details to the east of the Rockies but a blend/ensemble mean approach at least mitigates the problem to some degree. Some general clustering is developing for how the initial upper low/trough near the West Coast will eject into the western U.S./southwestern Canada early next week as upstream energy takes its place (but with QPF details still sensitive to specifics), with the resulting axis of the trough as well as ridge to the east likely to retrograde a bit by next Wednesday. However there are still meaningful differences for low-predictability shortwave impulses continuing along the northern tier early-mid week. Compared to prior days the latest model runs have backed off slightly for the depiction of the current western Gulf feature, having the surface reflection dissipate within a couple days and maintaining only a compact mid-level impulse. Currently the 12Z GFS/ECMWF/UKMET share some similarities aloft while the CMC has been consistently ill-defined. Small scale of this feature suggests low predictability for track/strength. The updated forecast started with a blend of 00Z/06Z operational models for about the first half of the period and then steadily worked up to half total weight of the means (06Z GEFS/00Z ECens) by day 7 Wednesday. This maintained the essence of the mean pattern as well as most frontal/wave details over the West. Model adjustments led to some frontal/wave detail changes farther east but late-period ensemble mean input helped to temper continuity differences somewhat. ...Sensible Weather and Potential Hazards... Moisture associated with low pressure currently over the western Gulf may enhance rainfall across parts of the lower Mississippi Valley and into the Deep South. The behavior and rainfall effects of such compact features are notoriously difficult to forecast so confidence in details is below average. Check the latest products from the National Hurricane Center for more information on this feature. Showers and storms may also linger farther east into the Southeast into this weekend with the presence of a weakening boundary and impulses moving through the flow aloft. Farther north, a front initially oriented from the Northeast into the Ohio Valley and central Plains will push gradually eastward during the weekend 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, with stalling of the western end and deceleration of the eastern part of the front assisting in the potential for some locally significant totals. Possible interaction with southern tier moisture is yet another factor that will require monitoring. This front may continue to be a focus for rainfall into next week. 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 the trough near the West Coast. This West Coast trough may produce periods of rainfall over parts of the Northwest and there is a signal for a period of heavier rainfall near the Canadian border around early next week as some energy ejects from the trough. Moisture/convection with some potentially heavy activity could also extend across at least the northern Plains/Upper Midwest, aided by northern tier surface features and shortwaves emerging from the West. The greatest concern for temperatures during the medium range period will be with heat likely to build again across the central and northern Plains by early next week in response to a strengthening upper level ridge. Highs around 10-15F above normal are possible over/near the central Plains, equating to temperatures in the mid 90s to low 100s. Southern Plains locations will see a slightly hotter trend as well but with less extreme anomalies. Out West, below normal highs will spread gradually inland from the West Coast during the weekend into early next week due to nearby upper troughing. A few locations may see highs 10-15F below normal around Sunday-Monday. Expect a moderating trend closer to normal heading into midweek. In the East, a stable upper pattern of westerlies across the Northeast and ridging over the South (with a mean surface frontal boundary between the two) should keep both daytime highs and overnight lows within a few degrees of normal through most of the period. Rausch/Santorelli 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