GFS EXPERIMENTAL Froude Number for the Green Mountains

Winter Weather Advisory in Effect Across Southeastern St. Lawrence County Today, then Cold Weather Friday Night and Saturday

Rounds of lake effect snow are expected today into tomorrow in southeastern St. Lawrence County with periods of localized heavy snow. Snowfall rates may exceed 1"/hour at times, and gusty winds 35 mph during falling snow will result in low visibility. Then, cold temperatures and gusty winds will occur Friday night and Saturday across northern New York and Vermont. Read More >

Subject: GFS EXPERIMENTAL Froude Number for the greens Model run: BTV_GRID_D2D_GFS_20260122_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) === ===== === ==== ==== === === === ==== Thu 01/22 12Z 0.86 2330 90 94 -8 0.00 Thu 01/22 15Z 1.19 2427 88 87 -10 0.01 Thu 01/22 18Z 1.59 2428 89 98 -9 0.02 Thu 01/22 21Z 5.76 2635 78 39 -12 0.04 Fri 01/23 00Z 1.52 2630 81 49 -14 0.00 Fri 01/23 03Z 1.34 2626 81 44 -15 0.00 Fri 01/23 06Z 1.48 2630 90 44 -17 0.01 Fri 01/23 09Z 1.58 2726 83 57 -19 0.01 Fri 01/23 12Z 1.13 2523 93 72 -19 0.01 Fri 01/23 15Z 2.26 2624 95 90 -19 0.01 Fri 01/23 18Z 6.50 2726 91 66 -20 0.02 Fri 01/23 21Z 2.77 2825 92 90 -22 0.01 Sat 01/24 00Z 3.57 2929 96 88 -25 0.01 Sat 01/24 03Z 5.19 3032 92 53 -28 0.00 Sat 01/24 06Z 0.87 3030 91 50 -28 0.00 Sat 01/24 09Z 0.48 3125 90 41 -27 0.00 Sat 01/24 12Z 0.38 3024 84 28 -26 0.00 Sat 01/24 15Z 0.37 3021 81 25 -25 0.00 Sat 01/24 18Z 0.41 3018 82 27 -25 0.00 Sat 01/24 21Z 0.46 2918 85 19 -25 0.00 Sun 01/25 00Z 0.36 3019 80 17 -24 0.00 Sun 01/25 03Z 0.27 3117 74 17 -22 0.00 Sun 01/25 06Z 0.22 3115 64 18 -21 0.00 Sun 01/25 09Z 0.19 3013 54 22 -20 0.00 Run total areal avg QPF for the greens is: 0.15 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