Extended Forecast Discussion NWS Weather Prediction Center College Park MD 132 PM EST Wed Feb 19 2020 Valid 12Z Sat Feb 22 2020 - 12Z Wed Feb 26 2020 ...A dynamic storm affects the Southwest to the Northeast Saturday to Tuesday night, followed by a wintry Northwest to Midwest storm Sunday to Wednesday... ...Guidance/Predictability Assessment... A low over the southern CA Saturday shifts east to the central Great Plains through Sunday before it is drawn into a northern stream over the Great Lakes Monday. A renewed surface low may develop near the Northeastern Seaboard Tuesday ahead of this combined trough. The next system is a sharp trough that reaches the Pacific Northwest Sunday and shifts southeast to the central Plains through Monday night before it likely shifts east. There is good agreement among deterministic global models (06Z GFS and 00Z ECMWF/UKMET/CMC) through Day 4 across the CONUS before the CMC speeds up the wave from the Southwest over the central Plains. The GFS is the fastest solution with the Northwest trough which results in a more amplified trough down the Inter-Mountain West on Day 5. However, by this time the 06Z GEFS mean is in better alignment with the 00Z ECENS mean, so those become the dominant preference for Days 6 and 7. Overall a notably slower solution with these systems is seen with this blend compared to previous forecasts. ...Weather Pattern and Hazard Highlights... System #1: The center of the expansive and mainly dry high pressure will shift east off the Southeast Coast on Saturday ahead of the southern stream system progressing from southern CA to the south-central Plains through Sunday. A swath of moderate precipitation northern Four Corners/Central Rockies Saturday night into Sunday will include heavy mountain snows. Precipitation will then spread across the Mid MS/TN Valleys/southern Appalachians Sunday night through Monday as height falls and main surface system tracks east-northeastward. A bit of a northward shift in guidance now suggests that Gulf of Mexico laden air will be focused in locally moderate to heavy rainfall mainly just north/west of areas that are particularly sensitive due to ongoing runoff issues. This will be a fairly warm system, but there is a risk for snow/ice on the northern periphery (particularly for the Northeast should the secondary low develop near the Northeastern Seaboard Tuesday as indicated by recent ECMWF runs) of the growing precipitation shield as the ambient/cold high pressure dome recedes. System #2: The northern stream upper trough/surface system moving into the Northwest Sunday will dig through the Great Basin and Rockies Sunday will bring enhanced rain with heavy mountain snow and unsettled flow to the Pacific Northwest. The heavy snow risk is for the Cascades, north-central Great Basin/northern with slow system progression and reinforcement. Downstream progression over the east-central states into next midweek offers an emerging pattern for moderate lead precipitation, but there would especially be a threat of heavy wrapback snows over the cooled north-central Plains with upper level support. Below normal weather continues under the sprawling high over the Southeast Saturday with temperatures 10 to 15 degrees below normal along the Gulf/Florida/Carolina coasts. Above normal temperatures spread east with the first system, then much below normal temperatures spread southeast with the second system. Temperatures 15 to 25 degrees below normal (primarily for max temps) are forecast for the Rockies Tuesday, expanding to the Great Plains Wednesday. Jackson Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml