GFS EXPERIMENTAL Froude Number for the Green Mountains

Ice Storm Warnings and Winter Weather Advisories in effect until 4 PM Today

Ice accumulations of 0.4 to 0.7 inch are expected in the St Lawrence Valley and portions of central/eastern VT, with 0.2 to 0.4 inch elsewhere. Travel will be very difficult, especially during this morning's commute. Isolated to scattered power outages are possible due to the ice. Gusty west to southwest winds 35 to 50 mph develop later today and tonight, with additional power outages possible. Read More >

Subject: GFS EXPERIMENTAL Froude Number for the greens Model run: BTV_GRID_D2D_GFS_20251229_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) === ===== === ==== ==== === === === ==== Mon 12/29 06Z 0.09 1722 97 99 1 0.00 Mon 12/29 09Z 0.12 1921 98 95 2 0.17 Mon 12/29 12Z 0.08 1918 98 99 5 0.15 Mon 12/29 15Z 0.13 2021 97 96 5 0.23 Mon 12/29 18Z 0.21 2022 99 51 2 0.01 Mon 12/29 21Z 0.93 2323 96 60 -3 0.03 Tue 12/30 00Z 1.63 2527 86 74 -9 0.04 Tue 12/30 03Z 1.88 2427 87 91 -12 0.00 Tue 12/30 06Z 3.81 2630 89 96 -15 0.01 Tue 12/30 09Z 3.28 2733 92 88 -18 0.01 Tue 12/30 12Z 9.35 2733 92 92 -20 0.01 Tue 12/30 15Z 9.95 2731 94 92 -21 0.01 Tue 12/30 18Z 11.51 2731 92 85 -21 0.01 Tue 12/30 21Z 2.58 2730 94 93 -20 0.01 Wed 12/31 00Z 2.09 2732 94 88 -19 0.01 Wed 12/31 03Z 1.65 2732 82 60 -19 0.01 Wed 12/31 06Z 1.20 2730 69 45 -18 0.00 Wed 12/31 09Z 1.00 2627 71 78 -16 0.00 Wed 12/31 12Z 0.96 2524 84 93 -15 0.00 Wed 12/31 15Z 1.06 2422 93 94 -15 0.00 Wed 12/31 18Z 1.39 2322 92 93 -13 0.01 Wed 12/31 21Z 1.05 2321 93 99 -12 0.01 Thu 01/01 00Z 0.69 2319 96 99 -12 0.04 Thu 01/01 03Z 0.60 2513 96 99 -13 0.06 Run total areal avg QPF for the greens is: 0.83 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