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Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260703_0000
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 00Z 1.02 2621 76 63 20 0.00
Fri 07/03 01Z 1.17 2725 75 64 20 0.00
Fri 07/03 02Z 1.23 2827 82 70 19 0.00
Fri 07/03 03Z 1.03 2826 86 65 19 0.00
Fri 07/03 04Z 0.84 2925 86 72 19 0.01
Fri 07/03 05Z 0.84 2926 88 57 18 0.02
Fri 07/03 06Z 0.86 3025 89 45 18 0.00
Fri 07/03 07Z 0.81 3024 88 37 17 0.00
Fri 07/03 08Z 0.82 3023 87 24 17 0.00
Fri 07/03 09Z 0.79 3023 86 17 17 0.00
Fri 07/03 10Z 0.67 3023 82 13 17 0.00
Fri 07/03 11Z 0.54 3022 75 11 17 0.00
Fri 07/03 12Z 0.46 3120 73 16 17 0.00
Fri 07/03 13Z 0.43 3018 70 19 18 0.00
Fri 07/03 14Z 0.45 3016 68 19 17 0.00
Fri 07/03 15Z 0.55 2915 69 34 17 0.00
Fri 07/03 16Z 0.72 2816 69 54 18 0.00
Fri 07/03 17Z 1.47 2817 74 47 17 0.00
Fri 07/03 18Z 7.55 2718 74 52 17 0.00
Fri 07/03 19Z 8.27 2818 67 55 18 0.00
Fri 07/03 20Z 8.14 2817 64 62 18 0.00
Fri 07/03 21Z 6.62 2817 65 68 18 0.00
Fri 07/03 22Z 2.44 2716 68 74 18 0.00
Fri 07/03 23Z 1.77 2718 71 83 18 0.00
Sat 07/04 00Z 1.22 2720 79 79 18 0.04
Sat 07/04 01Z 1.04 2618 82 85 17 0.00
Sat 07/04 02Z 0.85 2720 87 90 17 0.05
Sat 07/04 03Z 0.81 2721 92 84 16 0.01
Sat 07/04 04Z 0.61 2820 93 74 17 0.02
Sat 07/04 05Z 0.54 2920 88 74 17 0.01
Sat 07/04 06Z 0.53 3022 87 69 16 0.01
Sat 07/04 07Z 0.51 3122 87 55 16 0.01
Sat 07/04 08Z 0.54 3022 89 47 15 0.01
Sat 07/04 09Z 0.55 3123 89 47 15 0.01
Sat 07/04 10Z 0.52 3124 89 44 15 0.01
Sat 07/04 11Z 0.54 3125 90 53 14 0.01
Sat 07/04 12Z 0.53 3125 89 47 14 0.01
Sat 07/04 13Z 0.53 3123 85 40 13 0.01
Sat 07/04 14Z 0.57 3123 84 36 13 0.00
Sat 07/04 15Z 0.53 3220 82 26 12 0.00
Sat 07/04 16Z 0.60 3220 81 27 12 0.00
Sat 07/04 17Z 0.88 3217 75 24 12 0.00
Sat 07/04 18Z 2.24 3217 71 18 12 0.00
Sat 07/04 19Z 2.60 3116 73 16 12 0.00
Sat 07/04 20Z 2.96 3115 74 13 12 0.00
Sat 07/04 21Z 2.22 3114 75 13 12 0.00
Sat 07/04 22Z 2.04 3115 73 11 12 0.00
Sat 07/04 23Z 1.25 3116 69 12 12 0.00
Sun 07/05 00Z 1.13 3117 66 13 12 0.00
Sun 07/05 01Z 1.07 3118 65 13 12 0.00
Sun 07/05 02Z 1.09 3218 64 10 12 0.00
Sun 07/05 03Z 0.96 3217 65 9 12 0.00
Sun 07/05 04Z 0.61 3216 64 8 11 0.00
Sun 07/05 05Z 0.39 3315 59 6 12 0.00
Sun 07/05 06Z 0.27 3313 54 5 12 0.00
Sun 07/05 07Z 0.22 3311 52 5 12 0.00
Sun 07/05 08Z 0.14 3309 50 4 12 0.00
Sun 07/05 09Z 0.14 3307 47 3 12 0.00
Sun 07/05 10Z 0.20 3207 47 3 12 0.00
Sun 07/05 11Z 0.23 3207 47 4 11 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