Subject: NAM12 EXPERIMENTAL Froude Number for the greens Model run: BTV_GRID_D2D_NAM12_20251007_0600 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) === ===== === ==== ==== === === === ==== Tue 10/07 06Z 0.78 2618 60 26 14 0.00 Tue 10/07 09Z 0.58 2515 54 26 14 0.00 Tue 10/07 12Z 0.69 2416 58 14 13 0.00 Tue 10/07 15Z 0.69 2221 65 40 13 0.00 Tue 10/07 18Z 0.92 2226 75 83 14 0.00 Tue 10/07 21Z 0.79 2328 95 92 12 0.05 Wed 10/08 00Z 0.74 2326 96 88 12 0.12 Wed 10/08 03Z 0.71 2133 95 92 12 0.11 Wed 10/08 06Z 0.52 2321 99 98 11 0.52 Wed 10/08 09Z 0.36 3117 97 97 6 0.66 Wed 10/08 12Z 0.14 3418 84 86 6 0.22 Wed 10/08 15Z 0.19 3419 76 26 3 0.00 Wed 10/08 18Z 1.68 3318 81 2 1 0.00 Wed 10/08 21Z 4.14 3320 78 16 1 0.00 Thu 10/09 00Z 1.16 3323 85 50 0 0.01 Thu 10/09 03Z 0.19 3422 89 23 -2 0.00 Thu 10/09 06Z 0.20 3423 77 6 -4 0.00 Thu 10/09 09Z 0.35 3426 65 4 -6 0.00 Thu 10/09 12Z 0.33 3530 72 7 -7 0.00 Thu 10/09 15Z 1.25 3420 75 7 -7 0.00 Thu 10/09 18Z 3.48 3317 69 8 -6 0.00 Thu 10/09 21Z 1.02 3314 61 7 -5 0.00 Fri 10/10 00Z 0.10 3416 40 5 -2 0.00 Fri 10/10 03Z 0.24 3415 57 7 -4 0.00 Fri 10/10 06Z 0.11 3107 28 9 0 0.00 Fri 10/10 09Z 0.19 2809 23 7 1 0.00 Fri 10/10 12Z 0.22 2710 22 7 2 0.00 Fri 10/10 15Z 0.21 2609 21 11 3 0.00 Fri 10/10 18Z 0.21 2408 23 9 3 0.00 Run total areal avg QPF for the greens is: 1.69 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