Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260212_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)
=== ===== === ==== ==== === === === ====
Thu 02/12 00Z 0.82 3122 93 82 -13 0.00
Thu 02/12 01Z 0.70 3225 95 85 -13 0.00
Thu 02/12 02Z 0.57 3225 94 84 -13 0.01
Thu 02/12 03Z 0.48 3224 94 84 -13 0.01
Thu 02/12 04Z 0.44 3324 94 82 -13 0.01
Thu 02/12 05Z 0.43 3323 94 80 -13 0.01
Thu 02/12 06Z 0.43 3323 95 78 -13 0.01
Thu 02/12 07Z 0.45 3324 95 77 -13 0.01
Thu 02/12 08Z 0.46 3324 96 74 -13 0.01
Thu 02/12 09Z 0.37 3323 95 69 -13 0.01
Thu 02/12 10Z 0.30 3323 95 66 -13 0.01
Thu 02/12 11Z 0.27 3323 94 63 -13 0.01
Thu 02/12 12Z 0.24 3323 94 61 -13 0.01
Thu 02/12 13Z 0.21 3422 93 62 -13 0.00
Thu 02/12 14Z 0.19 3421 93 62 -12 0.00
Thu 02/12 15Z 0.21 3321 93 61 -12 0.00
Thu 02/12 16Z 0.25 3321 93 58 -12 0.00
Thu 02/12 17Z 0.28 3321 92 51 -12 0.00
Thu 02/12 18Z 0.29 3321 92 38 -12 0.00
Thu 02/12 19Z 0.31 3320 91 22 -12 0.00
Thu 02/12 20Z 0.32 3320 89 12 -12 0.00
Thu 02/12 21Z 0.32 3321 83 9 -12 0.00
Thu 02/12 22Z 0.28 3322 75 10 -11 0.00
Thu 02/12 23Z 0.22 3323 69 13 -10 0.00
Fri 02/13 00Z 0.15 3423 66 16 -10 0.00
Fri 02/13 01Z 0.11 3423 63 17 -10 0.00
Fri 02/13 02Z 0.09 3423 63 18 -10 0.00
Fri 02/13 03Z 0.09 3422 62 19 -9 0.00
Fri 02/13 04Z 0.10 3421 61 21 -9 0.00
Fri 02/13 05Z 0.11 3420 61 24 -9 0.00
Fri 02/13 06Z 0.12 3420 61 26 -9 0.00
Fri 02/13 07Z 0.13 3319 60 25 -9 0.00
Fri 02/13 08Z 0.14 3319 59 24 -9 0.00
Fri 02/13 09Z 0.17 3319 60 21 -9 0.00
Fri 02/13 10Z 0.19 3219 61 18 -9 0.00
Fri 02/13 11Z 0.21 3219 61 15 -10 0.00
Fri 02/13 12Z 0.24 3119 62 13 -10 0.00
Fri 02/13 13Z 0.27 3120 63 14 -10 0.00
Fri 02/13 14Z 0.28 3119 62 17 -10 0.00
Fri 02/13 15Z 0.29 3018 62 18 -10 0.00
Fri 02/13 16Z 0.30 3017 61 18 -10 0.00
Fri 02/13 17Z 0.31 3016 62 16 -10 0.00
Fri 02/13 18Z 0.34 3016 63 21 -10 0.00
Fri 02/13 19Z 0.37 2916 62 35 -10 0.00
Fri 02/13 20Z 0.39 2916 61 47 -10 0.00
Fri 02/13 21Z 0.42 2816 62 58 -10 0.00
Fri 02/13 22Z 0.51 2718 65 45 -10 0.00
Fri 02/13 23Z 0.48 2718 60 35 -10 0.00
Sat 02/14 00Z 0.43 2718 54 36 -9 0.00
Sat 02/14 02Z 0.39 2718 47 45 -8 0.00
Sat 02/14 03Z 0.40 2718 51 57 -8 0.00
Sat 02/14 04Z 0.42 2719 53 73 -8 0.00
Sat 02/14 05Z 0.41 2618 73 80 -8 0.00
Sat 02/14 06Z 0.42 2618 91 78 -8 0.00
Sat 02/14 07Z 0.44 2718 94 81 -9 0.01
Sat 02/14 08Z 0.39 2817 94 81 -9 0.01
Sat 02/14 09Z 0.35 2815 93 84 -9 0.01
Sat 02/14 10Z 0.33 2814 93 85 -9 0.01
Sat 02/14 11Z 0.33 2814 93 84 -9 0.01
Run total areal avg QPF for the greens is: 0.16 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