####018005157#### FXUS02 KWBC 051852 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 252 PM EDT Sun May 5 2024 Valid 12Z Wed May 08 2024 - 12Z Sun May 12 2024 ...Mid-South/Ohio Valley Excessive Rain/Severe Threat midweek shifts to the Central Gulf Coast States/Appalachians Thursday... ...Guidance/Predictability Assessment... Latest guidance continues to show good agreement for the overall synoptic pattern, but offer plenty of uncertainties in the details, especially later in the period. The biggest area of concern during the period is with an upper low as it ejects out of the Northern Plains into the Great Lakes/Northeast. There are uncertainties with the speed of this trough early in the period, and then with the evolution of additional energy dropping into the trough from central Canada around late week/next weekend. On the large scale at least, the guidance all suggests that the pattern across the CONUS will shift from a West trough-East ridge mid-week to West ridge- East trough set up by next weekend. A general blend of the deterministic solutions worked as a good starting point for the Wed-Fri WPC forecast, incorporating more ensemble mean guidance by next weekend to mitigate the differences across mainly the Eastern U.S. next week. This maintains good continuity with the previous WPC forecast as well. ...Weather/Hazards Highlights... Amplified upper trough/low energies will shift slowly from the northern Plains midweek to the East next weekend along with a main/reforming parent surface lows then moderate coastal low. There will be higher elevation snows back over the north-central Rockies into mid-late week on the backside of the main trough/low as depicted in the WPC Winter Weather Outlook. Rainfall on the west side of the strong surface low could be heavy across eastern Montana given upper-level support. However, this region is not particularly sensitive to flooding concerns, and instability should be limited wrapping around the low. A WPC Excessive Rainfall Outlook (ERO) Marginal Risk area remains in place Day 4/Wednesday for this area given the potential for heavy rainfall which should start towards the end of the short range period. Meanwhile, an associated lead and wavy/trailing frontal system will gradually work downstream across the central and eastern states to intercept and pool return flow instability and moisture. This will set the stage for a widespread and generally broad comma shaped area of rainfall to include a threat for excessive rainfall and strong to severe thunderstorms for areas near the Mid-South and Ohio Valley midweek and the Central Gulf Coast States to Appalachians into the Southeast Thursday into Friday. A Marginal Risk and embedded Slight Risk ERO is in place from the Mid-Mississippi Valley through the Ohio Valley states for Day 4/Wednesday. These risks shift to the lower Mississippi Valley through the northern central Gulf Coast states to the Appalachians Day 5/Thursday as fronts push farther toward the east and northeast and interact with pooling moisture and instability. The Storm Prediction Center highlights a broad area of the Midwest to Mississippi Valley/parts of the Southern Plains for severe weather potential into midweek. A favorable pattern will continue for rain and thunderstorms across the Southeast with the trailing cold front and broadly across the East next weekend. Downstream energy track may also lead to a moderate New England coastal low. Expect much cooler than normal temperatures for parts of the West Wednesday/Thursday under upper troughing. Meanwhile, mean upper ridging will favor quite warm temperatures from the South through the Appalachians/Mid- Atlantic to threaten record seasonal values. 90s are forecast across the southern tier, with potential for south Texas excessive heat with temperatures over 100F and higher heat indices. Temperatures broadly cool later week into next weekend across the East, while warming across the West underneath a building upper ridge. Santorelli/Schichtel 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 $$