Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens Model run: BTV_GRID_D2D_NAM3_20250917_0600 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) === ===== === ==== ==== === === === ==== Wed 09/17 06Z 0.16 1207 72 17 11 0.00 Wed 09/17 07Z 0.15 1207 70 18 11 0.00 Wed 09/17 08Z 0.17 1208 66 18 11 0.00 Wed 09/17 09Z 0.16 1208 61 17 11 0.00 Wed 09/17 10Z 0.15 1208 55 16 12 0.00 Wed 09/17 11Z 0.15 1209 48 16 12 0.00 Wed 09/17 12Z 0.11 1308 42 14 12 0.00 Wed 09/17 13Z 0.09 1407 38 14 13 0.00 Wed 09/17 14Z 0.08 1408 35 14 13 0.00 Wed 09/17 15Z 0.04 1507 35 19 13 0.00 Wed 09/17 16Z 0.02 1606 37 24 13 0.00 Wed 09/17 17Z 0.02 1704 41 26 13 0.00 Wed 09/17 18Z 0.03 1703 46 30 13 0.00 Wed 09/17 19Z 0.05 1703 51 32 12 0.00 Wed 09/17 20Z 0.07 1902 54 37 12 0.00 Wed 09/17 21Z 0.03 1802 55 32 12 0.00 Wed 09/17 22Z 0.03 1703 54 30 12 0.00 Wed 09/17 23Z 0.05 1804 51 32 13 0.00 Thu 09/18 00Z 0.07 1905 47 34 13 0.00 Thu 09/18 01Z 0.09 1906 45 36 13 0.00 Thu 09/18 02Z 0.11 2007 44 34 13 0.00 Thu 09/18 03Z 0.16 2108 45 37 14 0.00 Thu 09/18 04Z 0.19 2209 49 42 14 0.00 Thu 09/18 05Z 0.23 2310 49 45 13 0.00 Thu 09/18 06Z 0.26 2410 47 42 13 0.00 Thu 09/18 07Z 0.29 2411 48 39 13 0.00 Thu 09/18 08Z 0.27 2510 46 33 13 0.00 Thu 09/18 09Z 0.26 2510 48 30 13 0.00 Thu 09/18 10Z 0.26 2609 51 28 13 0.00 Thu 09/18 11Z 0.22 2708 51 26 12 0.00 Thu 09/18 12Z 0.20 2707 53 19 12 0.00 Thu 09/18 13Z 0.19 2707 55 11 12 0.00 Thu 09/18 14Z 0.17 2705 55 11 12 0.00 Thu 09/18 15Z 0.20 2606 57 18 12 0.00 Thu 09/18 16Z 0.26 2606 56 23 12 0.00 Thu 09/18 17Z 0.39 2607 53 25 12 0.00 Thu 09/18 18Z 0.48 2608 51 37 13 0.00 Thu 09/18 19Z 0.51 2708 55 45 13 0.00 Thu 09/18 20Z 0.74 2709 60 61 12 0.00 Thu 09/18 21Z 1.13 2712 66 62 12 0.00 Thu 09/18 22Z 1.02 2715 73 52 12 0.00 Thu 09/18 23Z 0.86 2816 83 45 12 0.00 Fri 09/19 00Z 0.71 2918 91 40 11 0.01 Fri 09/19 01Z 0.67 2918 91 51 11 0.00 Fri 09/19 02Z 0.55 3019 94 61 11 0.01 Fri 09/19 03Z 0.42 3120 95 59 11 0.01 Fri 09/19 04Z 0.28 3220 95 53 10 0.01 Fri 09/19 05Z 0.26 3220 96 51 10 0.01 Fri 09/19 06Z 0.27 3219 97 47 9 0.01 Fri 09/19 07Z 0.30 3220 96 45 8 0.01 Fri 09/19 08Z 0.27 3220 96 41 8 0.01 Fri 09/19 09Z 0.22 3220 94 31 8 0.00 Fri 09/19 10Z 0.19 3220 88 23 8 0.00 Fri 09/19 11Z 0.16 3220 76 35 8 0.00 Fri 09/19 12Z 0.12 3321 66 36 7 0.00 Fri 09/19 13Z 0.09 3320 56 29 7 0.00 Fri 09/19 14Z 0.08 3319 51 14 7 0.00 Fri 09/19 15Z 0.09 3318 48 11 7 0.00 Fri 09/19 16Z 0.09 3317 44 7 6 0.00 Fri 09/19 17Z 0.09 3317 40 3 6 0.00 Run total areal avg QPF for the Central_Greens is: 0.08 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