Extended Forecast Discussion NWS Weather Prediction Center College Park MD 258 AM 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 the placement of heaviest rain. 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 the potential for interaction and possible phasing of this northern stream trough with southern stream energy starting near Baja California Sunday/day 3. ECMWF runs have remained on the not phased side of the guidance envelope, keeping a separate closed low slowly moving across northern Mexico while the northern stream trough and thus the front track forward a little faster, along with less QPF in the south-central CONUS. Conversely, the CMC and UKMET runs tend to phase the features immediately and move one trough more slowly across the western/central U.S. (for a farther west heavy rainfall axis as well). GFS runs have been waffling over the past couple of days but the 12/18Z runs seemed to be a fair middle ground between these solutions. Thus favored the GFS runs along with a healthy proportion of the GEFS and EC ensemble means for the fronts/pressures forecast. On the positive side, at least these differences of trough timing due to northern/southern stream interaction are not as bad as they had been, but still fairly disagreeable for the forecast lead time. There is also some better agreement for energy moving northward near the East Coast and an associated front/low system at the surface spreading some rainfall onshore early next week. For both this area and QPF across the central U.S., the WPC forecast trended wetter from continuity but not as high as the 01Z NBM, for a smoother transition of an increasing forecast. Then while there is general agreement for the trough to track eastward through the middle part of next week, there are differences in the details with the amplitude, while there are also model differences upstream with additional troughing coming into the West with possible ridging in between. Utilized more than half ensemble means for the fronts/pressures forecast blend by days 6-7 given the remaining differences. ...Sensible Weather and Potential Hazards... Precipitation is forecast to continue across the Rockies early next week in the form of snow 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 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. More enhanced rainfall totals are actually forecast in the East earlier in the week, when upper energy and a low pressure system just offshore into the Atlantic will provide support for rain. 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. Coastal/southeastern New England appears to have the greatest chance of receiving rain from this system due to its geographic protrusion into the Atlantic, but the interior Northeast and coastal Mid-Atlantic could see some rain as well. 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 10-254F 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. 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