Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EST Thu Feb 27 2020 Valid 12Z Sun Mar 01 2020 - 12Z Thu Mar 05 2020 ...Heavy rainfall threat in the East next week... ...Overview... Troughing over California on Sunday will swing through the Southwest/Four Corners as a briefly closed low before lifting northeastward through the mid-Mississippi Valley into the Northeast as it merges back into the flow. Additional height falls are possible through the interior West Wednesday between two ridges over the eastern Pacific and over Cuba. This would support a heavy rainfall threat along the height gradient out of the Lower Mississippi Valley northeastward next week Mon-Wed. ...Guidance/Predictability Assessment... Split flow out of the Pacific adds uncertainty to the forecast next week with the East in the confluent flow region. Speed of the exiting and weakening closed low out of southern California on Monday was fairly well-clustered outside the 12Z Canadian (through the 18Z guidance). GFS has finally come into better agreement with the more steadfast (but previously likely overdeveloped) ECMWF with secondary area of height falls out of the central Rockies next Wed which will act to broaden the trough on either side of 100W. To the north, timing, track, and depth differences seen among the models suggested a blended/consensus solution there, but even that was stratified between the deterministic models and the ensemble members. This was further continued with the southern portion of the cold front back into Texas and how sfc waves developed and moved toward the Great Lakes. Needless to say, confidence in specifics was lacking despite the good synoptic agreement. A deterministic blend sufficed to start the forecast period (Sun-Tue) before trending sharply to a 50/50 deterministic/ensemble blend that favored the 12Z ECMWF over the GFS or Canadian. This forged a balance between the still unstable ensemble means and perhaps somewhat more stable ECMWF (loosely speaking) with the track/depth of the lead/secondary surface lows out of Texas next Tue-Wed. ...Weather/Hazard Highlights... Main focus will be the potentially heavy rain event along a couple boundaries early in the week. Southerly surface flow out of the Gulf Sunday will set the stage for the front to realize the moisture potential as it pushes into Arkansas late Monday or early Tuesday. Precipitable water anomalies of +2 to +3 (actual values around 1.50 inches) for a couple days supports a swath of multi-inch totals from near the ArkLaTex northeastward through the Ohio and Tennessee Valleys. System should push off the East Coast by next Thursday with just a trailing boundary on its heels. Guidance continues to indicate that any winter weather with this system will be confined to fairly far northern latitudes in the eastern half of the lower 48. Precipitation over the West will center on Sunday over the central Rockies as the cold front sinks southward and then Mon-Tue as another front moves through the Pacific Northwest. Depending on specifics, favored terrain may see a brief period of heavier precip in this event. Guidance spread for the eventual amplitude of flow aloft later in the week keeps confidence low regarding the southward extent and amount of moisture across the Great Basin and Four Corners states. Milder air in the central states on Sun (about 5-10F above normal) will continue eastward with time and lead to a pronounced warming trend over the East next week. Especially by next Tue-Wed the eastern half of the country should see one or more days of lows 15-25F above normal and highs 5-15F above normal as many areas may see overnight low temperatures near their average daytime high. Mean troughing aloft that moves into the western-central U.S. should bring moderately cool readings across the West and into the Rockies/High Plains from Sun-Thu. Fracasso 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