Extended Forecast Discussion NWS Weather Prediction Center College Park MD 228 AM EDT Mon Oct 03 2022 Valid 12Z Thu Oct 06 2022 - 12Z Mon Oct 10 2022 ...Overview... A stubborn compact upper low/shortwave stuck over the Mid-Atlantic region during the short range period will finally be departing off the Northeast coast by the start of the medium range/Thursday. In it's wake, another shortwave will dive into the Upper Great Lakes from Canada setting up a prolonged period of upper troughing over the Eastern U.S., periodically reinforced by several pieces of energy rounding the top of a building and blocky ridge over the West. Despite the somewhat amplified pattern, relatively quiet weather conditions are expected across the CONUS through next weekend besides some monsoonal moisture and weak energy over the Southwest, and a potent cold front pushing across the central and eastern U.S. leading to rain particularly in the Great Lakes region along with considerably cooler temperatures behind the front. ...Guidance Evaluation/Predictability Assessment... With the pattern becoming dominated by the general ridge in the West and troughing in the East, model guidance remains agreeable with the overall amplified synoptic pattern, but smaller scale details are more uncertain. Guidance shows good enough agreement with the initial shortwave diving into the Great Lakes Thursday-Friday for a purely deterministic model blend. After this, details become increasingly uncertain as multiple pieces of energy round the top of the blocky western ridge into the northern High Plains and eventually acting to reinforce the trough in the East. Models also cannot agree how much the ridge over the West may break down by the end of the period as energy from the Gulf of Alaska moves southward. WPC preferred a blend increasingly towards the ensemble means days 5-7 to help mitigate some of the differences. This also maintains good continuity with the previous forecast. The QPF was based largely on the 01Z National Blend of Models, but with a wider footprint for light amounts added across much of the country as this underforecast of low amounts from the NBM is a known bias. ...Weather/Hazards Highlights... Monsoonal moisture into the Southwest will continue to drive some diurnal showers and thunderstorms, with locally heavy rainfall possible in some spots. Rainfall intensity may wane after Thursday, but showers could linger through the weekend across the Four Corners states. To the north, a cold front shifting across the Midwest and Great Lakes may bring some light rain mainly around Thursday, and lake enhanced showers in the westerly flow behind the front Friday and perhaps Saturday. Temperatures out West will be warm into early next week underneath a blocky upper ridge, with daytime highs over the Northwest 10 to 15 degrees above normal. Despite the anomalies, the resulting temperatures peaking in the 70s and 80s (90s for parts of California) are unlikely to create any heat related hazards. Conversely, Canadian high pressure spilling into the north-central U.S. and expanding eastward behind the cold front will result in much below normal temperatures shifting from the northern Plains into the Midwest and into much of the East Thursday-Monday. Daytime highs in some locations could be 15 to 20 degrees below average while overnight temperatures are forecast to drop into the 30s for many, and even 20s for North Dakota and northern Minnesota particularly Friday morning. 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