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Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260703_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)
=== ===== === ==== ==== === === === ====
Fri 07/03 06Z 0.68 3023 87 55 18 0.00
Fri 07/03 07Z 0.76 3025 87 58 17 0.00
Fri 07/03 08Z 0.74 3024 85 56 17 0.00
Fri 07/03 09Z 0.72 3023 84 49 17 0.00
Fri 07/03 10Z 0.63 3022 79 40 17 0.00
Fri 07/03 11Z 0.59 3023 75 30 17 0.00
Fri 07/03 12Z 0.55 3021 73 25 17 0.00
Fri 07/03 13Z 0.56 2920 73 22 17 0.00
Fri 07/03 14Z 0.61 2919 72 20 17 0.00
Fri 07/03 15Z 0.69 2919 73 23 17 0.00
Fri 07/03 16Z 0.85 2917 74 29 17 0.00
Fri 07/03 17Z 1.96 2816 76 38 17 0.00
Fri 07/03 18Z 6.01 2716 79 48 17 0.00
Fri 07/03 19Z 8.77 2716 74 53 17 0.00
Fri 07/03 20Z 9.39 2718 69 61 18 0.00
Fri 07/03 21Z 6.40 2818 69 64 18 0.00
Fri 07/03 22Z 2.74 2818 70 65 18 0.00
Fri 07/03 23Z 1.44 2818 72 60 17 0.00
Sat 07/04 00Z 1.17 2918 72 63 17 0.00
Sat 07/04 01Z 1.06 2918 74 63 17 0.00
Sat 07/04 02Z 0.98 2919 78 62 17 0.00
Sat 07/04 03Z 0.82 2920 77 62 17 0.02
Sat 07/04 04Z 0.81 2921 77 63 17 0.00
Sat 07/04 05Z 0.68 3023 81 61 16 0.00
Sat 07/04 06Z 0.60 3122 83 58 16 0.01
Sat 07/04 07Z 0.58 3122 86 58 16 0.00
Sat 07/04 08Z 0.56 3121 90 62 15 0.00
Sat 07/04 09Z 0.58 3022 91 60 15 0.01
Sat 07/04 10Z 0.56 3021 90 59 15 0.01
Sat 07/04 11Z 0.60 3022 93 66 14 0.01
Sat 07/04 12Z 0.58 3121 94 66 14 0.01
Sat 07/04 13Z 0.57 3121 94 60 13 0.01
Sat 07/04 14Z 0.54 3121 92 54 13 0.01
Sat 07/04 15Z 0.53 3119 88 50 13 0.01
Sat 07/04 16Z 0.59 3119 86 54 12 0.01
Sat 07/04 17Z 0.90 3018 84 42 12 0.01
Sat 07/04 18Z 1.15 3117 81 33 12 0.00
Sat 07/04 19Z 1.25 3117 80 24 12 0.00
Sat 07/04 20Z 1.30 3117 76 17 12 0.00
Sat 07/04 21Z 1.46 3117 73 13 12 0.00
Sat 07/04 22Z 1.34 3116 70 10 12 0.00
Sat 07/04 23Z 0.83 3216 67 6 12 0.00
Sun 07/05 00Z 0.53 3216 66 5 12 0.00
Sun 07/05 01Z 0.51 3316 65 4 12 0.00
Sun 07/05 02Z 0.43 3315 65 5 12 0.00
Sun 07/05 03Z 0.27 3414 63 5 12 0.00
Sun 07/05 04Z 0.16 3411 62 5 12 0.00
Sun 07/05 05Z 0.14 3410 62 6 12 0.00
Sun 07/05 06Z 0.09 3508 61 7 12 0.00
Sun 07/05 07Z 0.08 0006 61 7 12 0.00
Sun 07/05 08Z 0.07 0104 61 7 11 0.00
Sun 07/05 09Z 0.07 0302 61 7 11 0.00
Sun 07/05 10Z 0.06 0701 60 7 11 0.00
Sun 07/05 11Z 0.06 1301 60 7 11 0.00
Sun 07/05 12Z 0.05 1702 59 10 12 0.00
Sun 07/05 13Z 0.05 1702 60 14 11 0.00
Sun 07/05 14Z 0.07 1401 63 12 11 0.00
Sun 07/05 15Z 0.18 1402 69 8 11 0.00
Sun 07/05 16Z 0.29 1401 73 7 11 0.00
Sun 07/05 17Z 0.37 1300 75 7 11 0.00
Run total areal avg QPF for the greens is: 0.12 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