Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260228_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)
=== ===== === ==== ==== === === === ====
Sat 02/28 12Z 0.49 2135 70 50 -1 0.00
Sat 02/28 13Z 0.56 2138 70 64 -1 0.00
Sat 02/28 14Z 0.54 2139 70 83 0 0.00
Sat 02/28 15Z 0.63 2141 72 91 0 0.00
Sat 02/28 16Z 0.65 2139 81 96 0 0.01
Sat 02/28 17Z 0.76 2238 88 96 -1 0.02
Sat 02/28 18Z 0.75 2236 88 92 0 0.01
Sat 02/28 19Z 0.79 2333 90 72 -1 0.01
Sat 02/28 20Z 0.85 2430 91 65 -1 0.01
Sat 02/28 21Z 0.97 2528 92 45 -2 0.00
Sat 02/28 22Z 1.03 2527 90 25 -3 0.01
Sat 02/28 23Z 0.91 2624 88 23 -3 0.01
Sun 03/01 00Z 0.81 2723 84 23 -4 0.01
Sun 03/01 01Z 0.65 2821 77 25 -5 0.01
Sun 03/01 02Z 0.46 2918 74 32 -5 0.01
Sun 03/01 03Z 0.33 3015 69 42 -6 0.00
Sun 03/01 04Z 0.28 3014 69 52 -6 0.00
Sun 03/01 05Z 0.27 3014 74 75 -7 0.00
Sun 03/01 06Z 0.27 3015 75 84 -8 0.00
Sun 03/01 07Z 0.25 3115 73 93 -9 0.00
Sun 03/01 08Z 0.27 3116 74 92 -10 0.00
Sun 03/01 09Z 0.25 3115 82 89 -11 0.00
Sun 03/01 10Z 0.25 3115 84 86 -12 0.00
Sun 03/01 11Z 0.21 3215 83 83 -13 0.00
Sun 03/01 12Z 0.20 3215 79 85 -13 0.00
Sun 03/01 13Z 0.23 3115 75 87 -14 0.00
Sun 03/01 14Z 0.29 3116 72 85 -15 0.00
Sun 03/01 15Z 0.30 3116 64 82 -15 0.00
Sun 03/01 16Z 0.36 3117 59 79 -16 0.00
Sun 03/01 17Z 0.40 3118 56 61 -16 0.00
Sun 03/01 18Z 0.46 3118 60 47 -17 0.00
Sun 03/01 19Z 0.61 3118 66 27 -18 0.00
Sun 03/01 20Z 0.58 3118 67 24 -18 0.00
Sun 03/01 21Z 0.58 3118 68 19 -18 0.00
Sun 03/01 22Z 0.60 3119 70 17 -19 0.00
Sun 03/01 23Z 0.58 3120 70 14 -19 0.00
Mon 03/02 00Z 0.55 3121 66 13 -20 0.00
Mon 03/02 01Z 0.50 3121 63 13 -20 0.00
Mon 03/02 02Z 0.45 3121 61 14 -20 0.00
Mon 03/02 03Z 0.39 3120 58 15 -20 0.00
Mon 03/02 05Z 0.34 3119 52 15 -20 0.00
Mon 03/02 06Z 0.33 3119 47 14 -20 0.00
Mon 03/02 07Z 0.30 3118 42 14 -20 0.00
Mon 03/02 08Z 0.31 3118 42 13 -20 0.00
Mon 03/02 09Z 0.31 3117 42 12 -20 0.00
Mon 03/02 10Z 0.32 3017 42 12 -20 0.00
Mon 03/02 11Z 0.33 3018 42 12 -20 0.00
Mon 03/02 12Z 0.35 3018 42 15 -20 0.00
Mon 03/02 13Z 0.37 2918 42 16 -20 0.00
Mon 03/02 14Z 0.36 2917 44 19 -20 0.00
Mon 03/02 15Z 0.38 2916 46 17 -20 0.00
Mon 03/02 16Z 0.38 2914 45 20 -19 0.00
Mon 03/02 17Z 0.38 2913 42 19 -19 0.00
Mon 03/02 18Z 0.38 2912 43 19 -18 0.00
Mon 03/02 19Z 0.36 2811 43 22 -17 0.00
Mon 03/02 20Z 0.35 2711 45 15 -16 0.00
Mon 03/02 21Z 0.35 2712 47 28 -15 0.00
Mon 03/02 22Z 0.36 2613 48 43 -14 0.00
Mon 03/02 23Z 0.35 2514 45 49 -13 0.00
Run total areal avg QPF for the greens is: 0.11 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