Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260525_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)
=== ===== === ==== ==== === === === ====
Mon 05/25 12Z 0.29 2414 99 93 8 0.00
Mon 05/25 13Z 0.37 2615 98 92 8 0.03
Mon 05/25 14Z 0.40 2717 98 88 8 0.02
Mon 05/25 15Z 0.36 2916 97 77 8 0.01
Mon 05/25 16Z 0.43 2918 97 71 8 0.01
Mon 05/25 17Z 0.49 3020 95 66 8 0.01
Mon 05/25 18Z 0.56 3020 93 50 8 0.00
Mon 05/25 19Z 0.64 2918 94 31 8 0.00
Mon 05/25 20Z 0.74 2918 96 19 8 0.01
Mon 05/25 21Z 0.68 2918 94 11 8 0.01
Mon 05/25 22Z 0.63 2918 89 7 9 0.01
Mon 05/25 23Z 0.57 2918 80 6 9 0.01
Tue 05/26 00Z 0.55 2919 71 5 9 0.00
Tue 05/26 01Z 0.57 2920 65 7 9 0.00
Tue 05/26 02Z 0.59 3021 63 9 9 0.00
Tue 05/26 03Z 0.63 3022 61 10 9 0.00
Tue 05/26 04Z 0.70 3123 65 13 9 0.00
Tue 05/26 05Z 0.81 3023 71 15 9 0.00
Tue 05/26 06Z 0.87 3023 71 18 9 0.00
Tue 05/26 07Z 0.76 3023 70 18 9 0.00
Tue 05/26 08Z 0.62 3023 72 19 10 0.00
Tue 05/26 09Z 0.54 3022 72 20 10 0.01
Tue 05/26 10Z 0.51 3122 74 20 10 0.01
Tue 05/26 11Z 0.47 3120 79 19 10 0.00
Tue 05/26 12Z 0.47 3019 79 20 10 0.00
Tue 05/26 13Z 0.45 3017 77 17 10 0.00
Tue 05/26 14Z 0.48 3015 75 29 11 0.00
Tue 05/26 15Z 0.59 2914 73 49 11 0.00
Tue 05/26 16Z 0.71 2813 70 60 11 0.00
Tue 05/26 17Z 0.98 2712 69 70 12 0.00
Tue 05/26 18Z 2.71 2613 73 61 12 0.00
Tue 05/26 19Z 4.31 2515 73 52 12 0.00
Tue 05/26 20Z 3.85 2417 71 40 12 0.00
Tue 05/26 21Z 3.15 2319 72 33 13 0.00
Tue 05/26 22Z 1.78 2321 69 31 13 0.00
Tue 05/26 23Z 1.30 2325 62 31 13 0.00
Wed 05/27 00Z 1.49 2428 60 29 13 0.00
Wed 05/27 01Z 1.57 2431 62 31 13 0.00
Wed 05/27 02Z 1.39 2532 62 35 13 0.00
Wed 05/27 03Z 1.22 2532 56 44 13 0.00
Wed 05/27 04Z 1.20 2633 54 58 13 0.00
Wed 05/27 05Z 1.23 2732 53 65 13 0.00
Wed 05/27 06Z 1.19 2730 59 60 12 0.00
Wed 05/27 07Z 1.06 2828 68 60 12 0.00
Wed 05/27 08Z 0.96 2826 72 61 11 0.00
Wed 05/27 09Z 0.87 2825 82 60 11 0.00
Wed 05/27 10Z 0.79 2824 86 60 11 0.00
Wed 05/27 11Z 0.70 2822 87 55 11 0.01
Wed 05/27 12Z 0.66 2820 88 55 10 0.01
Wed 05/27 13Z 0.59 2818 90 57 10 0.01
Wed 05/27 14Z 0.60 2817 91 46 10 0.01
Wed 05/27 15Z 0.67 2816 88 44 10 0.01
Wed 05/27 16Z 0.92 2815 89 45 10 0.01
Wed 05/27 17Z 1.66 2914 89 39 10 0.01
Wed 05/27 18Z 0.74 2913 90 39 10 0.01
Wed 05/27 19Z 0.64 3013 88 35 10 0.01
Wed 05/27 20Z 0.98 3113 87 32 9 0.01
Wed 05/27 21Z 0.89 3113 85 25 9 0.00
Wed 05/27 22Z 0.66 3214 84 19 9 0.00
Wed 05/27 23Z 0.43 3316 86 17 8 0.00
Run total areal avg QPF for the greens is: 0.24 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