Subject: GFS EXPERIMENTAL Froude Number for the greens Model run: BTV_GRID_D2D_GFS_20251006_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) === ===== === ==== ==== === === === ==== Mon 10/06 00Z 0.50 2312 56 38 15 0.00 Mon 10/06 03Z 0.62 2316 55 27 14 0.00 Mon 10/06 06Z 0.72 2320 53 19 14 0.00 Mon 10/06 09Z 0.65 2420 43 17 14 0.00 Mon 10/06 12Z 0.56 2417 36 14 14 0.00 Mon 10/06 15Z 0.41 2413 44 13 13 0.00 Mon 10/06 18Z 0.57 2311 50 11 13 0.00 Mon 10/06 21Z 0.51 2215 48 7 14 0.00 Tue 10/07 00Z 0.91 2320 49 9 13 0.00 Tue 10/07 03Z 1.12 2422 54 16 13 0.00 Tue 10/07 06Z 0.84 2422 54 18 13 0.00 Tue 10/07 09Z 0.68 2419 58 15 13 0.00 Tue 10/07 12Z 0.63 2321 64 26 13 0.00 Tue 10/07 15Z 0.55 2220 69 48 13 0.00 Tue 10/07 18Z 1.20 2223 77 81 12 0.00 Tue 10/07 21Z 0.80 2525 91 98 11 0.25 Wed 10/08 00Z 0.77 2325 93 86 10 0.17 Wed 10/08 03Z 0.75 2325 97 98 10 0.11 Wed 10/08 06Z 0.51 2716 98 98 9 0.35 Wed 10/08 09Z 0.27 3317 91 95 6 0.17 Wed 10/08 12Z 0.26 3316 81 53 4 0.02 Wed 10/08 15Z 0.26 3315 79 7 2 0.00 Wed 10/08 18Z 0.81 3317 72 2 0 0.00 Wed 10/08 21Z 2.80 3321 63 3 0 0.00 Run total areal avg QPF for the greens is: 1.07 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