Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens Model run: BTV_GRID_D2D_NAM3_20240816_1200 Using the MB925 to MB850 layer. Assumes Central_Greens are orthogonal to 260 degree winds. 925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens. Date Time Wind RH% 700 850T QPF Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in) === ===== === ==== ==== === === === ==== Fri 08/16 12Z 0.05 0006 84 53 13 0.00 Fri 08/16 13Z 0.09 0205 84 53 13 0.00 Fri 08/16 14Z 0.09 0303 86 54 13 0.00 Fri 08/16 15Z 0.06 0401 88 55 13 0.00 Fri 08/16 16Z 0.05 0800 88 56 13 0.01 Fri 08/16 17Z 0.08 1101 88 58 14 0.04 Fri 08/16 18Z 0.16 1202 88 61 14 0.05 Fri 08/16 19Z 0.25 1303 88 64 14 0.05 Fri 08/16 20Z 0.31 1304 86 66 14 0.04 Fri 08/16 21Z 0.22 1405 84 61 14 0.03 Fri 08/16 22Z 0.14 1506 83 57 14 0.00 Fri 08/16 23Z 0.12 1509 83 52 15 0.00 Sat 08/17 00Z 0.07 1611 82 46 15 0.00 Sat 08/17 01Z 0.04 1712 82 43 15 0.00 Sat 08/17 02Z 0.13 1813 84 45 14 0.00 Sat 08/17 03Z 0.18 1913 86 41 14 0.00 Sat 08/17 04Z 0.24 2012 87 38 14 0.00 Sat 08/17 05Z 0.32 2113 89 38 14 0.00 Sat 08/17 06Z 0.31 2114 93 35 14 0.00 Sat 08/17 07Z 0.25 2012 90 33 14 0.00 Sat 08/17 08Z 0.25 2014 91 31 14 0.00 Sat 08/17 09Z 0.24 2015 91 21 14 0.00 Sat 08/17 10Z 0.28 2016 89 26 13 0.00 Sat 08/17 11Z 0.24 1916 84 20 13 0.00 Sat 08/17 12Z 0.21 1916 81 17 14 0.00 Sat 08/17 13Z 0.19 1916 81 24 14 0.00 Sat 08/17 14Z 0.20 1916 82 33 14 0.00 Sat 08/17 15Z 0.21 1916 80 45 14 0.00 Sat 08/17 16Z 0.19 1817 80 60 14 0.00 Sat 08/17 17Z 0.19 1818 81 79 14 0.00 Sat 08/17 18Z 0.17 1819 77 90 14 0.00 Sat 08/17 19Z 0.17 1819 81 94 14 0.00 Sat 08/17 20Z 0.22 1819 81 95 14 0.00 Sat 08/17 21Z 0.31 1818 82 95 13 0.00 Sat 08/17 22Z 0.16 1719 81 96 13 0.00 Sat 08/17 23Z 0.13 1721 81 92 13 0.00 Sun 08/18 00Z 0.18 1823 84 93 13 0.00 Sun 08/18 01Z 0.25 1823 87 93 12 0.00 Sun 08/18 02Z 0.36 1923 92 92 12 0.01 Sun 08/18 03Z 0.31 1923 89 93 12 0.02 Sun 08/18 04Z 0.23 1824 88 89 12 0.05 Sun 08/18 05Z 0.16 1825 90 83 12 0.06 Sun 08/18 06Z 0.17 1824 87 84 12 0.03 Sun 08/18 07Z 0.19 1825 85 88 12 0.03 Sun 08/18 08Z 0.22 1827 84 91 12 0.01 Sun 08/18 09Z 0.13 1726 84 91 12 0.03 Sun 08/18 10Z 0.10 1727 83 94 12 0.01 Sun 08/18 11Z 0.10 1726 82 89 12 0.04 Sun 08/18 12Z 0.14 1727 80 93 12 0.01 Sun 08/18 13Z 0.16 1828 81 94 12 0.01 Sun 08/18 14Z 0.14 1728 81 89 12 0.02 Sun 08/18 15Z 0.14 1727 82 90 12 0.01 Sun 08/18 16Z 0.13 1725 81 93 12 0.01 Sun 08/18 17Z 0.16 1825 81 89 13 0.00 Sun 08/18 18Z 0.13 1724 80 89 13 0.00 Sun 08/18 19Z 0.13 1723 86 90 13 0.00 Sun 08/18 20Z 0.09 1721 89 90 13 0.00 Sun 08/18 21Z 0.09 1622 91 95 13 0.01 Sun 08/18 22Z 0.10 1622 95 91 13 0.01 Sun 08/18 23Z 0.10 1624 96 89 13 0.01 Run total areal avg QPF for the Central_Greens is: 0.60 inches. Froude Number (Frd#): Frd# < 0.5 Flow is subcritical and blocked. Upslope clouds/precip backed farther upwind of and up to mtn crest. W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes. Gap winds possible. Frd# 0.5-1 Flow is subcritical/slow moving/blocked. Upslope clouds/precip falls immediately upwind of mtn crest. W Upslope snow favors western slopes to the Green Mt. spine including: Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln. Gap winds possible. Frd# 1-2 Flow is critical. With strong winds, Mountain waves/downslope winds possible. Precip falls close to mountain ridge crests and on lee side. W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom. Froude > 2 Flow is supercritical/unblocked(rapid flow). Air flows freely over terrain. Persistent upslope snow not favored. Scattered snow showers and flurries. Relative Humidity (RH): 925-850 mb RH > 90% needed for upslope precipitation. with 700mb RH > 70% favors upslope snow. with 700mb RH > 90% greater amounts of W upslope snow possible. 850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1) T > -11 10-15:1 T -11 to -15 25-35:1 T < -15 15-20:1