Subject: GFS EXPERIMENTAL Froude Number for the greens Model run: BTV_GRID_D2D_GFS_20240328_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 03/28 12Z 0.09 2903 99 87 2 0.00 Thu 03/28 15Z 0.09 3005 99 92 1 0.02 Thu 03/28 18Z 0.09 3105 99 63 0 0.01 Thu 03/28 21Z 0.13 3207 99 68 0 0.01 Fri 03/29 00Z 0.16 3309 93 62 -2 0.02 Fri 03/29 03Z 0.26 3314 82 53 -3 0.01 Fri 03/29 06Z 0.27 3418 75 32 -4 0.00 Fri 03/29 09Z 0.25 3318 74 11 -4 0.00 Fri 03/29 12Z 0.28 3321 75 11 -5 0.00 Fri 03/29 15Z 0.71 3217 77 19 -7 0.00 Fri 03/29 18Z 3.31 3123 67 12 -6 0.00 Fri 03/29 21Z 13.54 3127 69 48 -5 0.00 Sat 03/30 00Z 1.73 3132 74 49 -6 0.00 Sat 03/30 03Z 1.34 3132 79 52 -7 0.00 Sat 03/30 06Z 1.24 3130 87 45 -8 0.00 Sat 03/30 09Z 0.97 3129 90 43 -9 0.00 Sat 03/30 12Z 0.77 3125 90 25 -9 0.00 Sat 03/30 15Z 1.56 3021 82 10 -8 0.00 Sat 03/30 18Z 1.78 3018 66 4 -5 0.00 Sat 03/30 21Z 1.59 3014 61 6 -3 0.00 Sun 03/31 00Z 0.66 2914 59 10 -2 0.00 Sun 03/31 03Z 0.44 2911 59 17 -2 0.00 Sun 03/31 06Z 0.34 2909 60 92 -3 0.00 Sun 03/31 09Z 0.36 2809 86 90 -4 0.00 Run total areal avg QPF for the greens is: 0.07 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