Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260223_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)
=== ===== === ==== ==== === === === ====
Mon 02/23 06Z 0.50 0715 90 72 -9 0.00
Mon 02/23 07Z 0.53 0717 90 56 -9 0.00
Mon 02/23 08Z 0.51 0619 89 64 -9 0.00
Mon 02/23 09Z 0.49 0521 83 69 -9 0.00
Mon 02/23 10Z 0.52 0525 77 69 -8 0.00
Mon 02/23 11Z 0.51 0527 71 61 -8 0.00
Mon 02/23 12Z 0.51 0528 61 56 -7 0.00
Mon 02/23 13Z 0.52 0529 56 60 -8 0.00
Mon 02/23 14Z 0.52 0529 51 60 -8 0.00
Mon 02/23 16Z 0.43 0325 57 66 -9 0.00
Mon 02/23 17Z 0.38 0223 68 71 -10 0.00
Mon 02/23 18Z 0.23 0123 71 72 -10 0.00
Mon 02/23 19Z 0.13 0023 75 66 -10 0.00
Mon 02/23 20Z 0.09 3524 77 62 -10 0.00
Mon 02/23 21Z 0.10 3526 77 59 -10 0.00
Mon 02/23 22Z 0.14 3529 75 48 -10 0.00
Mon 02/23 23Z 0.15 3533 73 38 -11 0.01
Tue 02/24 00Z 0.11 3536 80 28 -12 0.00
Tue 02/24 01Z 0.12 3534 88 21 -13 0.00
Tue 02/24 02Z 0.28 3432 94 17 -13 0.00
Tue 02/24 03Z 0.38 3430 93 12 -13 0.00
Tue 02/24 04Z 0.36 3328 93 11 -13 0.01
Tue 02/24 05Z 0.41 3327 94 12 -14 0.01
Tue 02/24 06Z 0.36 3328 93 12 -14 0.01
Tue 02/24 07Z 0.45 3328 94 13 -15 0.01
Tue 02/24 08Z 0.64 3325 97 16 -16 0.01
Tue 02/24 09Z 0.50 3224 93 17 -16 0.01
Tue 02/24 10Z 0.37 3224 88 19 -15 0.01
Tue 02/24 11Z 0.34 3223 87 27 -16 0.01
Tue 02/24 12Z 0.32 3223 87 33 -16 0.01
Tue 02/24 13Z 0.30 3122 88 41 -16 0.01
Tue 02/24 14Z 0.28 3121 88 45 -16 0.00
Tue 02/24 15Z 0.31 3120 90 44 -16 0.00
Tue 02/24 16Z 0.32 3119 89 52 -16 0.00
Tue 02/24 17Z 0.35 3017 89 57 -16 0.00
Tue 02/24 18Z 0.42 3017 89 57 -16 0.00
Tue 02/24 19Z 0.44 3016 88 54 -15 0.00
Tue 02/24 20Z 0.48 2915 88 57 -15 0.00
Tue 02/24 21Z 0.59 2914 88 51 -15 0.00
Tue 02/24 22Z 0.60 2815 89 37 -15 0.00
Tue 02/24 23Z 0.58 2816 89 18 -15 0.00
Wed 02/25 00Z 0.45 2815 87 7 -14 0.00
Wed 02/25 01Z 0.39 2715 85 3 -14 0.00
Wed 02/25 02Z 0.30 2613 77 4 -13 0.00
Wed 02/25 03Z 0.24 2512 68 11 -13 0.00
Wed 02/25 04Z 0.21 2411 57 29 -12 0.00
Wed 02/25 05Z 0.20 2312 50 50 -12 0.00
Wed 02/25 06Z 0.21 2214 43 66 -12 0.00
Wed 02/25 07Z 0.23 2216 36 85 -11 0.00
Wed 02/25 08Z 0.21 2117 41 85 -11 0.00
Wed 02/25 09Z 0.17 2019 50 87 -10 0.00
Wed 02/25 10Z 0.21 2023 70 88 -11 0.00
Wed 02/25 11Z 0.15 1925 89 85 -10 0.00
Wed 02/25 13Z 0.23 2025 94 87 -10 0.01
Wed 02/25 14Z 0.27 2022 95 69 -10 0.02
Wed 02/25 15Z 0.28 2119 95 53 -9 0.01
Wed 02/25 16Z 0.29 2118 94 46 -9 0.01
Wed 02/25 17Z 0.31 2116 94 43 -8 0.01
Run total areal avg QPF for the greens is: 0.17 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