Extended Forecast Discussion NWS Weather Prediction Center College Park MD 147 PM EDT Mon Oct 16 2023 Valid 12Z Thu Oct 19 2023 - 12Z Mon Oct 23 2023 ...Overview... Guidance continues to support a strong upper ridge over the West persisting through Friday which supports eastern U.S. trough amplification and a likelihood for deepening low pressure over the Northeast this weekend. Behind this system expect the western U.S. ridge to deamplify/shift east into the Plains/Mississippi Valley by the start of next week while a Pacific trough of moderate depth moves into the West and brings precipitation into the Pacific Northwest and northern Rockies by Saturday night. The forecast pattern will favor a broad area of above normal temperatures over the West and into the Plains late this week, followed by a cooler trend over the West as the upper trough arrives. With the exception of above normal readings over New England late this week, most of the East should see near to below average highs for most of the period. ...Guidance Evaluation/Predictability Assessment... Confidence is high on the amplified western ridge with developing eastern trough, but uncertainty still persists on the evolution of the eastern trough. The 00Z ECMWF/06Z GFS (and now 12Z GFS) get to a closed low over the Northeast by 12Z Sunday, but through slightly different routes. The ECMWF digs a deeper eastern tough, well into the Southeast Thursday night, while the GFS/CMC/UKMET are not as meridional. The ECMWF has much more separation between two waves that cross the east and eventually phase into the Northeast low while the GFS is quicker to develop a Midwest closed low that then tracks to the Northeast by Saturday night. However, the CMC and UKMET do not feature a Northeast low by Sunday and are more offshore/progressive. The 00Z ECENS/06Z GEFS ensemble means are in line with the deterministics, lending credence to their solutions. Given the way the ECM/GFS come to a similar solution via different paths, those two deterministic runs dominate the WPC model blend (becoming more reliant on the ECENS/GEFS for Days 6/7) as well as the QPF. With a number of shortwave troughs tracking/interaction at play, there remains uncertainty with the strength/track/timing of East Coast low pressure. For the most part, the upper trough entering the West Saturday night remains better behaved than the eastern system with a favoring of a ECMWF/GFS solution there given strong agreement in timing and amplitude. ...Weather/Hazards Highlights... There are no risk areas depicted in the Days 4-5 Excessive Rainfall Outlooks that cover the Thursday through Friday night time frame. The front extending south/southwest from Great Lakes low pressure late this week will produce areas of rainfall of varying intensity, with some continued uncertainty over precise coverage and amounts. Moisture and instability still do not appear sufficient to yield a meaningful potential for intense rain rates through Thursday. On Friday, moisture/instability could increase enough over the Carolina Coast for heavy rainfall and on Friday night over the northern Mid-Atlantic/southern New England depending on the track of the developing low pressure. However, confidence on magnitude and location is too low at this time to define any risk area yet. Going into Saturday, the most likely forecast scenario would have increasingly heavy rainfall and strengthening winds over the Northeast with brisk to strong winds continuing through at least Sunday. Depending on system evolution/track, highest elevations could see a little snow. Much of the West will be dry into this weekend. The upper trough/leading surface front moving into the region should bring light to perhaps isolated moderate rainfall to the Pacific Northwest Saturday night, with this moisture shifting across the Intermountain West into Monday. Some of the precipitation should fall as snow in the higher northern Rockies. A broad area of temperatures 10 to 20 degrees above normal continues extend across the West into the Plains into this weekend, diminishing/becoming below normal from west to east as the upper trough moves into the Pacific Northwest over the weekend. A handful daily high temperatures are forecast west of the Rockies Friday with many more record high minimum temperatures forecast for Friday and Saturday, mainly over California. Temperatures could challenge record highs over parts of southern Texas Friday into the weekend. The warmth over the central U.S. will also decrease in coverage by the start of next week as the upper ridge loses amplitude. Meanwhile over the East, New England will see 5 to 10 degree above normal temperatures Friday/Saturday with the rest of the eastern U.S. seeing a return of cooler than normal highs Friday onward with the amplified upper trough crossing the region. Jackson 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