Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260223_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 02/23 12Z 0.45 0419 80 76 -10 0.00
Mon 02/23 13Z 0.43 0421 69 68 -9 0.00
Mon 02/23 14Z 0.43 0423 57 69 -9 0.00
Mon 02/23 15Z 0.43 0325 47 57 -9 0.00
Mon 02/23 16Z 0.38 0325 49 55 -9 0.00
Mon 02/23 17Z 0.35 0223 58 51 -10 0.00
Mon 02/23 18Z 0.33 0222 67 57 -10 0.00
Mon 02/23 19Z 0.18 0122 69 61 -10 0.00
Mon 02/23 20Z 0.10 0023 74 61 -10 0.00
Mon 02/23 21Z 0.07 3524 75 62 -10 0.00
Mon 02/23 22Z 0.12 3526 78 54 -10 0.00
Mon 02/23 23Z 0.14 3530 77 50 -10 0.01
Tue 02/24 00Z 0.14 3533 83 43 -11 0.00
Tue 02/24 01Z 0.21 3433 90 40 -12 0.00
Tue 02/24 02Z 0.29 3432 92 36 -12 0.00
Tue 02/24 03Z 0.38 3431 93 35 -13 0.01
Tue 02/24 04Z 0.47 3330 95 36 -13 0.01
Tue 02/24 05Z 0.55 3329 95 34 -14 0.01
Tue 02/24 06Z 0.55 3329 95 34 -14 0.01
Tue 02/24 07Z 0.59 3328 95 33 -15 0.01
Tue 02/24 08Z 0.53 3226 95 38 -15 0.01
Tue 02/24 09Z 0.45 3225 92 42 -15 0.01
Tue 02/24 10Z 0.41 3224 92 45 -16 0.01
Tue 02/24 11Z 0.38 3223 92 50 -16 0.01
Tue 02/24 12Z 0.36 3123 91 52 -16 0.01
Tue 02/24 13Z 0.35 3123 91 54 -16 0.00
Tue 02/24 14Z 0.33 3122 90 56 -16 0.00
Tue 02/24 15Z 0.31 3120 89 57 -16 0.00
Tue 02/24 16Z 0.32 3119 89 55 -16 0.00
Tue 02/24 17Z 0.34 3118 88 53 -16 0.00
Tue 02/24 18Z 0.41 3016 88 51 -16 0.00
Tue 02/24 19Z 0.50 2916 89 51 -16 0.00
Tue 02/24 20Z 0.48 2916 87 51 -15 0.00
Tue 02/24 21Z 0.42 2915 84 44 -15 0.00
Tue 02/24 22Z 0.48 2916 85 32 -15 0.00
Tue 02/24 23Z 0.45 2916 86 18 -14 0.00
Wed 02/25 00Z 0.40 2815 83 7 -14 0.00
Wed 02/25 01Z 0.31 2713 79 2 -13 0.00
Wed 02/25 02Z 0.30 2613 77 3 -13 0.00
Wed 02/25 03Z 0.23 2512 69 7 -12 0.00
Wed 02/25 04Z 0.16 2310 57 18 -11 0.00
Wed 02/25 05Z 0.17 2213 50 43 -11 0.00
Wed 02/25 06Z 0.22 2216 43 68 -11 0.00
Wed 02/25 07Z 0.24 2218 34 85 -11 0.00
Wed 02/25 08Z 0.20 2118 46 72 -11 0.00
Wed 02/25 09Z 0.16 2020 60 73 -11 0.00
Wed 02/25 10Z 0.18 1924 69 88 -11 0.00
Wed 02/25 11Z 0.14 1927 84 85 -10 0.01
Wed 02/25 12Z 0.16 1928 91 85 -10 0.03
Wed 02/25 13Z 0.24 2025 92 89 -10 0.03
Wed 02/25 14Z 0.28 2122 94 89 -10 0.01
Wed 02/25 15Z 0.33 2118 95 87 -10 0.01
Wed 02/25 16Z 0.36 2215 94 74 -10 0.01
Wed 02/25 17Z 0.44 2213 93 72 -9 0.00
Wed 02/25 18Z 0.67 2212 92 66 -9 0.00
Wed 02/25 19Z 1.46 2212 89 62 -9 0.00
Wed 02/25 20Z 2.39 2313 87 70 -8 0.00
Wed 02/25 21Z 1.50 2215 88 74 -8 0.00
Wed 02/25 22Z 0.74 2217 92 74 -8 0.00
Wed 02/25 23Z 0.66 2218 93 85 -8 0.00
Run total areal avg QPF for the greens is: 0.21 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