Subject: NAM3 EXPERIMENTAL Froude Number for the greens Model run: BTV_GRID_D2D_NAM3_20240325_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) === ===== === ==== ==== === === === ==== Mon 03/25 18Z 0.13 1310 40 50 0 0.00 Mon 03/25 19Z 0.15 1311 40 46 0 0.00 Mon 03/25 21Z 0.18 1212 40 42 2 0.00 Mon 03/25 22Z 0.20 1214 36 41 2 0.00 Tue 03/26 00Z 0.28 1220 29 35 4 0.00 Tue 03/26 01Z 0.28 1221 22 35 4 0.00 Tue 03/26 02Z 0.30 1223 18 35 4 0.00 Tue 03/26 05Z 0.28 1324 10 34 6 0.00 Tue 03/26 06Z 0.32 1326 10 32 7 0.00 Tue 03/26 09Z 0.29 1323 54 27 6 0.00 Tue 03/26 10Z 0.30 1324 66 23 7 0.00 Tue 03/26 12Z 0.35 1324 81 24 6 0.00 Tue 03/26 13Z 0.43 1227 83 28 6 0.00 Tue 03/26 14Z 0.46 1229 86 37 6 0.00 Tue 03/26 16Z 0.47 1231 90 38 7 0.00 Tue 03/26 18Z 0.46 1233 92 47 8 0.00 Tue 03/26 21Z 0.31 1428 96 73 7 0.00 Wed 03/27 00Z 0.27 1426 87 77 8 0.00 Wed 03/27 01Z 0.22 1425 87 68 9 0.00 Wed 03/27 06Z 0.03 1826 93 29 9 0.00 Wed 03/27 07Z 0.09 1926 93 25 8 0.00 Wed 03/27 13Z 0.26 2122 72 38 7 0.01 Wed 03/27 14Z 0.21 2119 77 63 7 0.01 Wed 03/27 15Z 0.19 2117 82 88 7 0.01 Wed 03/27 16Z 0.17 2016 84 94 7 0.01 Wed 03/27 17Z 0.16 2017 85 76 7 0.00 Wed 03/27 18Z 0.18 2017 84 88 7 0.01 Wed 03/27 23Z 0.27 2118 82 98 6 0.01 Thu 03/28 00Z 0.27 2118 83 98 5 0.01 Thu 03/28 02Z 0.40 2219 85 90 4 0.01 Thu 03/28 05Z 0.35 2315 94 69 4 0.00 Run total areal avg QPF for the 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