Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM EDT Mon Apr 03 2023 Valid 12Z Thu Apr 06 2023 - 12Z Mon Apr 10 2023 ...Heavy rainfall to focus over the western Gulf Coast region... ...Winter cold for the West and North-central U.S. Thursday to starkly contrast summer heat over the East... ...Model Guidance/Predictability Assessment... With the midweek departure of the northern Plains/Upper Midwest blizzard into Ontario, the upper flow pattern over the CONUS becomes rather zonal through late week into the weekend with a parade of inherently low predictable shortwave troughs and impulses before re-amplifying into next week. This overall flow transitions are reasonably depicted among the latest guidance through medium range time scales and preference is for a general blend of best clustered guidance from the ECMWF/CMC/UKMET and GEFS/ECMWF ensemble means, with the 18/00 UTC GFS acting more a less likely outlier. ...Overview and Weather/Hazards Highlights... A deep storm lifts into Ontario into Thursday, with mainly ground blizzard conditions lingering over the Upper Midwest/Great Lakes as the wind field trails the precip shield as they move into Canada. Upper ridging up the Eastern Seaboard shifts offshore Thursday leading to an end to exceptional warmth along the middle and northern sections of the East Coast with the cold front that stalls near the Gulf Coast. The cold post-frontal airmass will moderate as it spreads from the central to eastern states. As this cold front shifts to the Gulf Coast Thursday, the anomalous warmth ahead of it will trigger and widespread showers and strong to severe thunderstorms across the south-central to eastern U.S. along/ahead. Thunderstorms and flash flooding issues look to cross the lower Mississippi Valley before a new focus is made over Texas on Thursday. Accordingly, the experimental Days 4 WPC Excessive Rainfall Outlook (ERO) offers a "Slight Risk" threat area from southwest Louisiana through the Texas coastal Plain. The stalling of the front near the Gulf Coast along with less certain frontal wave enhancements with the ejection of southern stream upper energies should continue to focus convergence/convection and additional potential runoff/flash flooding issues through the weekend. The WPC product suite still tends to limit the northern lift of later week/weekend activity given overall flow. However, increasing northern and southern stream interaction into early next week offers renewed potential for more northward spread along with moderate coastal low development off the Southeast. Out West, the switch to a more zonal flow pattern opens the Pacific Northwest to repeating shortwave troughs and onshore flow. These energetic Pacific systems should favor moderate precipitation across the Pacific Northwest Thursday/Friday set to weaken/lift north over the weekend when a strong upper ridge builds up the West Coast which also ushers in warmer conditions. Cold conditions in the wake of the blizzard persist Thursday over the northern Rockies/Plains with some areas seeing highs and lows 25F below normal, but moderate into Friday. A few record low mins are possible Thursday morning above a fresh snowpack in the Dakotas. The exceptional warmth under the ridge along the Eastern Seaboard should result in dozens of high min records from southern New England to north Florida Thursday morning. 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, 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