Extended Forecast Discussion NWS Weather Prediction Center College Park MD 250 PM EDT Thu Oct 20 2022 Valid 12Z Sun Oct 23 2022 - 12Z Thu Oct 27 2022 ...Overview... Upper level troughing will be established across the West as the medium range period begins Sunday and should shift into the central U.S. as the week progresses, though uncertainty remains with the details due to model variations with handling a southern stream upper low and its potential phasing with the northern stream trough. But there is general agreement that precipitation will spread from the western U.S. Sunday into the central U.S. through Monday-Tuesday along a strong cold front, with snow likely in the Rockies and perhaps even into the northern High Plains on the backside of a surface low as cooler temperatures spread behind the front. There is also potential for moderate to heavy rain farther south, but with considerable differences in placement. Meanwhile rain is becoming more likely for portions of the Mid-Atlantic to Northeast early next week with a smaller scale upper low and a slow-moving frontal system just offshore. Lighter rain could then shift into the East midweek just ahead of the cold front and upper trough, while another round or two of precipitation is possible across the Northwest. ...Model and Predictability Assessment... While model guidance starts out with decent agreement for troughing across the West, there are still considerable differences for the days 3-5 forecast period with potential interaction and possible phasing of the northern stream trough with southern stream energy/closed low starting near Baja California Sunday/day 3. The ECMWF has remained consistent in showing less/little phasing between these two systems resulting in a much faster track of the northern stream trough and slower progression of the Baja California energy inland. Conversely, the CMC have tended to phase the features immediately and have a distinct closed low tracking from the Southwest into the south-central Plains and Midwest Mon-Wed. Prefer a preference at this point in the middle of these two solutions, closer to the GFS and UKMET both which show some degree of phasing but not as quickly or vigorously as the CMC, with an amplified trough shifting across the central U.S.. This solution also seems to be the best proxy for the more middle ground (though weaker) ensemble means and also is close to WPC continuity. Elsewhere, better agreement on energy off the East Coast, though with plenty of lingering uncertainty in the details and resulting QPF. The next trough into the West around Wednesday shows some timing/amplitude differences most likely stemming from the considerable uncertainty downstream in the Central states. A blend towards the ensemble means late period, seems to work well right now. ...Sensible Weather and Potential Hazards... Precipitation is forecast to continue across the Rockies early next week in the form of snow, potentially heavy, at higher elevations. As a surface low pressure system strengthens and tracks across the Plains, the northern High Plains even in lower elevations may also see notable early season snow to the northwest of the low. Gusty winds and blowing snow could also be a threat with this reasonably strong low. Farther south along and ahead of the cold front, moisture streaming in from the Gulf will lead to rain chances increasing across the central part of the country. Enhanced to possibly heavy rainfall is likely in the south-central U.S., but the placement of heaviest rain varies in the model guidance across the southern half of the Plains into the Mississippi Valley. As the cold front and upper trough track eastward, rain chances are expected to shift toward the East but with likely lighter rainfall amounts. Earlier in the week, upper energy and a low pressure system just offshore into the Atlantic should provide support for rain across especially southern New England, but also maybe parts of the interior Northeast and mid-Atlantic. There is better agreement for rain to fall onshore now than there had been the past few days, but still with some uncertainty in exact placement. Additionally, a parade of fronts coming into the Northwest will support additional precipitation continuing/reforming there through much of next week. Temperatures are likely to be warmer than average across the mid-section of the country up into the Great Lakes continuing into Sunday with southerly flow strengthening ahead of the western upper trough. Highs and lows of 10-25F above normal will be widespread across parts of the Plains and Midwest. Meanwhile, an area of below normal temperatures will expand from the West on Sunday toward the north-central U.S. Monday-Tuesday as the upper trough and cold front(s) move through, with lows around 5-15F below average and highs 10-20F below average. This will push warmer than average temperatures into the northeastern U.S. by Monday-Wednesday, with the east-central U.S. returning to around normal temperatures behind the cold frontal passage. Santorelli/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, 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