Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Mon May 16 2022 Valid 12Z Thu May 19 2022 - 12Z Mon May 23 2022 ...Persistent record-breaking heat is likely in the south-central U.S. through this week with anomalous heat expanding into the East by the weekend... ...Overview... A digging trough over the West and rising heights across the East late this week will result in a more amplified pattern across the lower 48 yielding cooler temperatures and lowering snow levels in the West and a continued hot regime for the South and East. A closed low across the northern tier Thursday-Friday and a strong cold front shifting East will chances for heavy rainfall and severe weather for some from the upper Mississippi Valley/Great Lakes into the East. The upper trough will dig into the central and eastern U.S. next weekend as height rise again out West. Tropical moisture will also increase rain/thunderstorm chances across Florida late this week and into the weekend. ...Guidance Evaluation/Preferences... Model guidance has trended stronger with a closed low across the northern High Plains into the Upper Mississippi Valley Thursday and Friday, but show relatively good agreement on this feature, with mainly just some minor timing differences as the low lifts into central Canada and the amplified trough slides into the Ohio Valley/Northeast on Saturday. For the first half of the period, a general model compromise worked well. After this, model guidance begins to show much more uncertainty surrounding a couple of shortwaves through the West Sunday/Monday. The ECMWF is stronger with an initial shortwave dropping down behind the eastern trough tending to amplify this feature more than the other guidance resulting in a stronger ridge over the West. Meanwhile, the GFS and the CMC are weaker with this first shortwave which allows for a weakness to round the top of a Pacific upper high and slide into the West. The WPC blend trended towards the ensemble means which seemed to side more with the GFS and CMC vs the ECMWF, but still incorporated some minor amounts of the ECMWF and GFS for added flow definition. ...Weather/Threat Highlights... Initial ridging across the southern Plains and rising heights farther east over the Deep South will continue to promote a broad area of heat across much of the southern U.S. during the period. The greatest and most lasting anomalies through the period should be over Texas (persisting from the short range time frame) where some locations could see highs up to 15-25F above normal, with numerous daily record highs likely. The heat across Texas should finally begin to moderate by next weekend as troughing presses through the West. However, warm to hot temperatures are also forecast for the southeastern quadrant of the U.S. with potential for daily record highs, and warmer than average temperatures by 10-20F should expand in coverage across the Ohio Valley to Eastern Seaboard by later in the week. A warm front lifting through the Mid-Mississippi Valley and Ohio Valley will provide a focus for multiple areas of showers and storms/convective complexes during the middle to latter part of the week. The ingredients are in place for heavy rainfall, though the specifics of coverage and amounts are uncertain, but at least a localized flood threat is likely especially if heavy rain falls in areas that are sensitive to additional rainfall. Then organized rainfall, heavy at times, is likely along a frontal boundary through the north-central U.S. around Thursday with potential for at least localized flood and flash flood threats given wet antecedent conditions across that region. Storms that could be severe are forecast to shift from the Upper Midwest into parts of the Ohio and Mississippi Valleys along this front Thursday into Friday. Additionally, tropical moisture increasing across the Florida peninsula late this week could lead to a more rainy pattern for the Sunshine State. After a couple of initial fronts crossing the Northwest, the main well-defined front ahead of the deepening trough will bring unseasonably cool temperatures to the Northwest and expanding into the northern Rockies and High Plains by late week. This will also provide support for a notable round of precipitation, with lowering snow levels in the Cascades to Northern Rockies as the week progresses, with some chance of snow even into northern parts of the High Plains, though with very low confidence at this point. 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