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WPC Medium Range Archive
Medium Range Products Valid On:
11/30/2023
(Day 7 PMDEPD: Valid 11/26/2023 to 11/30/2023)
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD 159 PM EST Thu Nov 23 2023 Valid 12Z Sun Nov 26 2023 - 12Z Thu Nov 30 2023 ...Overview... A broadening and fairly deep upper trough will dominate the pattern over the central and eastern U.S. through much of next week, with some embedded shortwaves and frontal systems. One surface low tracking north through the western Atlantic is likely to brush the Northeast around Monday and enhance precipitation there, behind which westerly flow and chilly conditions will promote lake effect snow through the first half of the week. The pattern in the West is more complex and uncertain, as energy could linger over the Southwest while upper ridging builds in the Northwest early in the week but then model spread increases with when/how these features could interact with an upstream trough coming through the eastern Pacific. This overall pattern should lead to relatively dry and cool conditions across the lower 48. ...Guidance Evaluation/Predictability Assessment... Model guidance is reasonably agreeable early in the forecast period Sunday-Monday as energy digging through south-central Canada causes troughing to expand across the east-central U.S. and ridging comes into the Northwest. At the surface, a nor'easter looks to track quickly north through the Atlantic with a path trending farther west over the past day, potentially over eastern parts of New England, which would increase precipitation potential in the Northeast. The 12Z models maintain this track along with a slightly slower trend in the newer 12Z GFS/ECMWF. After that the details of the trough get more uncertain based partly on the placement of an upper low within it in Canada by Tuesday/day 5. GFS runs have been farthest east toward the St. Lawrence River with the centroid of the low likely combining with other energy, while the CMC runs are west of James Bay. Shortwaves within the trough show a lot of variability and this affects the frontal and surface wave positions Tuesday-Thursday, for more uncertainty than desired. Speaking of uncertainty, model solutions continue to vary over the West first with energy pulled west into the Southwest U.S. and then how upstream Pacific energy (in the form of a closed low that opens up as it progresses east) may interact with it. ECMWF runs have the Southwest energy tracking far enough west that it interacts more with the Pacific feature by around Tuesday compared to other guidance, though the 12Z CMC has started trending in this direction. Overall the ridge that begins over the Northwest should be gradually weakening as it pushes east with a more troughy pattern for the West, but the specifics are yet to be determined. The WPC forecast was based on a blend of the 00Z/06Z GFS and 00Z ECMWF, CMC, and UKMET early in the period. Increased the proportion of the GEFS and EC ensemble means as the period progressed, amid increasing spread. Additionally, increased QPF in the Great Lakes compared to the NBM given the low bias it has with lake effect precipitation. ...Weather/Hazards Highlights... Some moisture may pool near a frontal boundary and wave of low pressure near the Gulf Coast on Sunday for some shower potential over the Gulf Coast states. Meanwhile a separate low developing off the Carolinas and lifting northward through the western Atlantic is trending toward a track closer to or over New England and is likely to spread some precipitation to the Northeast. Snow is possible in the interior regions and especially in the higher elevations. Areas closer to the coast may see a brief bout of heavy rain, and totals have increased from the previous forecast given the low track. However, this rain should be moving quickly so the Days 4-5 Excessive Rainfall Outlooks remain with no risk areas. Behind this system, cold flow will support areas of lake effect snow that may persist through at least midweek. Generally dry conditions are likely elsewhere, with perhaps some light precipitation perhaps coming into the West by midweek after a dry period and some moist return flow into the Gulf Coast around midweek as well. Much of the lower 48 should see near to below normal temperatures especially during the first half of next week. Decent coverage of highs and lows 10-15F below climatology can be expected from the Great Basin into the central/southern Plains early in the week, shifting into the eastern U.S. Tuesday-Wednesday while the west-central U.S. slightly moderates. An exception to the below average temperatures may be across the northern Plains, where by Tuesday and beyond lows in the 20s and highs in the 40s are expected, which are around 5-15F above normal. Lows of a few degrees above average and highs near average in Florida early next week are likely to cool Tuesday and beyond after a frontal passage. Tate 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 forecast, excessive rainfall outlook, winter weather outlook probabilities, heat indices and Key Messages 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 https://www.wpc.ncep.noaa.gov/#page=ovw
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