Prognostic Meteorological Discussion
Issued by NWS
Issued by NWS
468 FXUS02 KWBC 050712 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 312 AM 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... Recent guidance cycles have shown good agreement for the overall synoptic pattern, albeit with local uncertainties. A blend of best clustered guidance from the GFS/ECMWF models and to a lesser extent more run to run varied UKMET/Canadian runs Wednesday-Friday tends to mitigate smaller scale issues consistent with uncertainty and has good ensemble and NBM support and continuity. By next weekend there remain significant differences between model guidance and run to run continuity on how far south and east the lingering Plains energy works into the Great Lakes/Northeast. There is also uncertainty out West with the evolution of energy around the Great Basin and a blocky upper ridge/high Rex type pattern to the north. Accordingly, the WPC blend has again trended to more compatable and run to run consistent GEFS/ECMWF/Canadian ensemble means. This maintains maximum WPC product continuity. ...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 protracted heavy rain. 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 remains from the Mid- Mississippi Valley through the Ohio Valley states Day 4/Wednesday 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 South with the trailing cold front and broadly onward across the East where dowsstream energy track may support moderate late next week coastal low development off the Northeast to monitor. 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. 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 $$