NAM12 EXPERIMENTAL Froude Number for the Green Mountains

Lake Effect Snow continues through friday, followed by extreme cold for the weekend.

An Extreme Cold Warning is in effect for northern New York and Vermont from Friday evening through Saturday morning. Dangerously cold wind chills of -20F to -40F are expected. In addition, a Winter Weather Advisory remains in effect for southern St Lawrence County through Friday. A lake effect band will produce 3 to 9 inches of snow in the Advisory area, mainly along and south of Route 3. Read More >

Subject: NAM12 EXPERIMENTAL Froude Number for the greens Model run: BTV_GRID_D2D_NAM12_20260122_1800 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 18Z 1.05 2419 90 79 -9 0.00 Thu 01/22 21Z 17.05 2630 79 69 -11 0.04 Fri 01/23 00Z 2.26 2625 73 83 -13 0.00 Fri 01/23 03Z 2.20 2528 90 55 -14 0.01 Fri 01/23 06Z 3.09 2627 81 38 -16 0.00 Fri 01/23 09Z 1.49 2625 79 39 -18 0.00 Fri 01/23 12Z 1.30 2524 80 51 -18 0.00 Fri 01/23 15Z 8.33 2524 89 66 -18 0.00 Fri 01/23 18Z 8.42 2721 82 72 -20 0.01 Fri 01/23 21Z 7.08 2820 82 79 -21 0.01 Sat 01/24 00Z 3.87 2925 82 79 -23 0.02 Sat 01/24 03Z 14.04 2930 78 44 -26 0.01 Sat 01/24 06Z 3.08 3029 77 31 -28 0.00 Sat 01/24 09Z 0.67 3030 68 34 -27 0.00 Sat 01/24 12Z 0.41 3128 61 26 -25 0.00 Sat 01/24 15Z 0.36 3126 53 17 -24 0.00 Sat 01/24 18Z 0.41 3023 49 17 -24 0.00 Sat 01/24 21Z 0.49 3022 51 13 -24 0.00 Sun 01/25 00Z 0.35 3122 43 11 -22 0.00 Sun 01/25 03Z 0.23 3120 43 9 -20 0.00 Sun 01/25 06Z 0.21 3116 39 8 -19 0.00 Sun 01/25 09Z 0.18 3115 35 13 -18 0.00 Sun 01/25 12Z 0.15 3112 30 53 -17 0.00 Sun 01/25 15Z 0.18 3115 35 25 -18 0.00 Sun 01/25 18Z 0.03 0005 28 74 -16 0.00 Sun 01/25 21Z 0.16 0509 26 68 -15 0.00 Mon 01/26 00Z 0.29 0914 27 68 -15 0.00 Mon 01/26 03Z 0.39 1121 54 80 -15 0.01 Mon 01/26 06Z 0.41 1122 77 86 -14 0.05 Run total areal avg QPF for the greens is: 0.16 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