Subject: GFS EXPERIMENTAL Froude Number for the greens Model run: BTV_GRID_D2D_GFS_20251006_1200 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 12Z 0.57 2418 35 14 14 0.00 Mon 10/06 15Z 0.43 2414 46 13 13 0.00 Mon 10/06 18Z 0.63 2211 51 10 13 0.00 Mon 10/06 21Z 0.55 2216 49 7 14 0.00 Tue 10/07 00Z 1.10 2421 50 10 13 0.00 Tue 10/07 03Z 1.20 2422 54 18 13 0.00 Tue 10/07 06Z 0.86 2422 56 23 13 0.00 Tue 10/07 09Z 0.67 2419 58 22 13 0.00 Tue 10/07 12Z 0.66 2322 62 24 13 0.00 Tue 10/07 15Z 0.54 2219 65 52 13 0.00 Tue 10/07 18Z 1.27 2222 72 90 12 0.00 Tue 10/07 21Z 0.82 2427 86 92 11 0.18 Wed 10/08 00Z 0.67 2323 91 89 11 0.03 Wed 10/08 03Z 0.84 2329 94 98 10 0.09 Wed 10/08 06Z 0.50 2817 97 99 8 0.40 Wed 10/08 09Z 0.12 3414 85 94 6 0.16 Wed 10/08 12Z 0.12 3412 81 51 4 0.04 Wed 10/08 15Z 0.29 3313 89 13 2 0.00 Wed 10/08 18Z 0.70 3317 81 2 1 0.00 Wed 10/08 21Z 3.95 3322 69 3 0 0.00 Thu 10/09 00Z 0.65 3425 65 5 -1 0.00 Thu 10/09 03Z 0.27 3424 60 7 -3 0.00 Thu 10/09 06Z 0.31 3423 60 8 -4 0.00 Thu 10/09 09Z 0.30 3424 66 8 -5 0.00 Run total areal avg QPF for the greens is: 0.90 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