Extended Forecast Discussion NWS Weather Prediction Center College Park MD 250 PM EDT Sun Apr 02 2023 Valid 12Z Wed Apr 05 2023 - 12Z Sun Apr 09 2023 ...Blizzard continues in the Upper Midwest Wednesday night... ...Heavy rainfall and strong thunderstorms over portions of the Tennessee Valley, Lower Mississippi Valley, and western Gulf Coast states... ...Winter cold for the West and North-central U.S. through midweek week to starkly contrast summer heat that shifts off the East Coast Thursday... ...Model Guidance/Predictability Assessment... With the departure of the northern Plains/Upper Midwest blizzard into Ontario Wednesday night, the upper flow pattern over the CONUS becomes rather zonal with a parade of inherently low predictable shortwave troughs and impulses across the northern tier states. This flow transition is in good agreement among the latest global guidance with Days 4/5 model preference a general blend of the 06Z GFS and the 00Z ECMWF/CMC/UKMET. 12Z versions of these models maintain the good agreement. Forecast spread among these itinerant features increases Friday with the number, position, and strength of these features in question. This lends a transition to a preference for the more run to run consistent GEFS/ECENS ensemble means along with the 06Z GFS/00Z ECMWF for some detail. There is a general southwestern trend to heavy QPF, on Thursday, mainly over Texas as reflected in the updated Excessive Rain Outlooks (EROs) for Days 4/5. ...Overview and Weather/Hazards Highlights... The blizzard causing upper low lifts into Ontario Wednesday night with mainly ground blizzard conditions continuing over the Upper Midwest as the wind field trails the precip shield as they move into Canada. Upper ridging up the Eastern Seaboard shifts offshore Thursday, bringing an end to exceptional warmth along the middle and northern sections of the East Coast with the cold front that stalls along the Gulf Coast. Behind that cold front is anomalous cold air that moderates as it spreads east from the northern Plains. As the cold front shifts to the Gulf Coast Wednesday night/Thursday, the anomalous warmth ahead of it will trigger and widespread showers and strong to severe thunderstorms across the east-central to eastern U.S. along/ahead. Thunderstorms and flash flooding issues look to cross the lower Mississippi Valley, spread into the Tennessee Valley Wednesday night before a new focus is made over Texas on Thursday. Accordingly, the experimental Days 4/5 WPC EROs offers a "Slight Risk" threat area over the lower Mississippi Valley to portions of the Tennessee Valley on Day 4 and southwest Louisiana into central Texas for Day 5. The stalling of the front near the Gulf Coast into the weekend 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. The WPC product suite tends to limit the northern lift of the later week/weekend activity given northern tier zonal flow amplification. 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 Wednesday night into Saturday 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 into Friday over the northern Rockies/Plains with some areas seeing highs and lows 25F below normal. 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. Jackson 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