Subject: GFS EXPERIMENTAL Froude Number for the greens Model run: BTV_GRID_D2D_GFS_20251017_0000 Using the MB925 to MB850 layer. Assumes greens are orthogonal to 270 degree winds. 925-850 mb Layer Average Wind/RH. Avg QPF over the greens. Date Time Wind RH% 700 850T QPF Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in) === ===== === ==== ==== === === === ==== Fri 10/17 00Z 0.08 3528 56 68 -1 0.00 Fri 10/17 03Z 0.12 0022 64 62 -1 0.00 Fri 10/17 06Z 0.14 0116 75 49 0 0.00 Fri 10/17 09Z 0.05 0015 75 45 0 0.00 Fri 10/17 12Z 0.03 3514 74 35 0 0.00 Fri 10/17 15Z 0.06 3512 74 18 0 0.00 Fri 10/17 18Z 0.22 3410 70 11 0 0.00 Fri 10/17 21Z 0.11 3411 62 8 1 0.00 Sat 10/18 00Z 0.07 3410 47 11 2 0.00 Sat 10/18 03Z 0.03 3508 42 20 2 0.00 Sat 10/18 06Z 0.05 3406 38 29 3 0.00 Sat 10/18 09Z 0.04 3406 35 45 3 0.00 Sat 10/18 12Z 0.03 3404 32 68 5 0.00 Sat 10/18 15Z 0.05 2902 32 85 5 0.00 Sat 10/18 18Z 0.05 2402 37 80 7 0.00 Sat 10/18 21Z 0.08 2104 45 74 8 0.00 Sun 10/19 00Z 0.08 2006 51 84 10 0.00 Sun 10/19 03Z 0.13 2109 57 95 10 0.00 Sun 10/19 06Z 0.16 2113 65 68 10 0.00 Sun 10/19 09Z 0.19 2115 58 56 11 0.00 Sun 10/19 12Z 0.14 2013 55 48 11 0.00 Sun 10/19 15Z 0.08 1917 56 49 12 0.00 Sun 10/19 18Z 0.04 1818 59 43 11 0.00 Sun 10/19 21Z 0.04 1724 65 44 10 0.00 Run total areal avg QPF for the greens is: 0.00 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