####018004472#### FXUS02 KWBC 170700 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Wed Apr 17 2024 Valid 12Z Sat Apr 20 2024 - 12Z Wed Apr 24 2024 ...Overview... The pattern during the medium range period will continue to transition to more progressive flow by this weekend as an Omega block over the northeast Pacific into western North America and the northern U.S. tier begins to break down. Energy from the west side of a deep upper low initially over southeast Canada on Saturday will interact with another shortwave into the Southern Plains, increasing the heavy rain threat across much of Texas on Saturday, continuing into Sunday across the Southeast as the frontal boundary is slow to move through the region. Secondary energy ejecting from an upper low/trough over the Northeast Pacific will skirt the northern tier and move through the Great Lakes into the Northeast early next week. Troughing generally will get reestablished over the West Coast by next Tuesday-Wednesday. ...Guidance/Predictability Assessment... The latest guidance shows very good agreement across the CONUS through much of the period (Saturday-Wednesday). There are some timing differences with shortwave troughing through the Southeast Sunday-Monday and again with the next shortwave through the Great Lakes/Northeast Tuesday-Wednesday. These details create some uncertainty in the eventually (generally light) precipitation pattern across the Southeast and Northeast early next week. Lots of uncertainty late period as well with the evolution of a deep closed low over the Gulf of Alaska which looks to send some energy/troughing towards the West Coast. The WPC forecast for tonight used an equal blend of the latest GFS, ECMWF, and CMC for Days 3-5 (Saturday-Monday). For Days 6 and 7, replaced the CMC with the GEFS mean given greater CMC differences off the West Coast. The UKMET and ECENS data continue to be unavailable due to ongoing IT issues at WPC/College Park, MD. ...Weather/Hazards Highlights... Shortwave energy into the Southern Plains interacting with a slow moving frontal boundary and anomalous moisture and instability will increase the threat for heavy to excessive rainfall across much of the Southern Plains into the Lower Mississippi Valley on Saturday. A slight risk continues on tonights Day 4 Excessive Rainfall Outlook (Sat-Sun morning) across central to northeast Texas. Rainfall will continue into the Southeast/Carolinas on Sunday as the front slowly sinks through that region, and this is covered by a marginal risk on the Day 5 ERO. The next shortwave through the Northern Plains-Great Lakes-Northeast will be accompanied by some generally light precipitation as well early next week. The upper trough over the northern tier states and eventually into the East will support below normal temperatures (with greater anomalies for highs than lows) for most east of the Rockies but Florida by next weekend. Above normal temperatures across the Southwest should gradually expand northward underneath a building Western U.S. ridge and progress eastward into the Rockies early next week. Northern parts of the West may stay near normal due to the upper shortwave/cold front crossing the region next week. 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 forecast (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: 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 $$