Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260224_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)
=== ===== === ==== ==== === === === ====
Tue 02/24 06Z 0.47 3326 87 37 -13 0.00
Tue 02/24 07Z 0.54 3330 91 32 -14 0.00
Tue 02/24 08Z 0.40 3328 92 32 -14 0.00
Tue 02/24 09Z 0.34 3325 92 35 -14 0.00
Tue 02/24 10Z 0.34 3223 92 39 -15 0.00
Tue 02/24 11Z 0.36 3222 93 46 -15 0.00
Tue 02/24 12Z 0.34 3122 93 48 -15 0.00
Tue 02/24 13Z 0.30 3120 93 48 -15 0.00
Tue 02/24 14Z 0.30 3118 92 48 -16 0.00
Tue 02/24 15Z 0.34 3018 92 47 -16 0.00
Tue 02/24 16Z 0.38 3018 91 48 -16 0.00
Tue 02/24 17Z 0.39 3018 89 50 -16 0.00
Tue 02/24 18Z 0.44 3017 87 53 -16 0.00
Tue 02/24 19Z 0.58 3016 87 48 -16 0.00
Tue 02/24 20Z 0.56 3015 85 39 -15 0.00
Tue 02/24 22Z 0.57 2813 84 12 -15 0.00
Tue 02/24 23Z 0.63 2815 84 5 -15 0.00
Wed 02/25 00Z 0.59 2716 84 1 -15 0.00
Wed 02/25 01Z 0.46 2715 80 3 -15 0.00
Wed 02/25 02Z 0.38 2614 76 5 -14 0.00
Wed 02/25 03Z 0.29 2513 66 15 -13 0.00
Wed 02/25 04Z 0.19 2310 52 41 -12 0.00
Wed 02/25 05Z 0.21 2313 49 54 -11 0.00
Wed 02/25 06Z 0.25 2217 41 81 -11 0.00
Wed 02/25 07Z 0.25 2218 35 74 -10 0.00
Wed 02/25 08Z 0.17 2019 45 37 -10 0.00
Wed 02/25 09Z 0.15 1924 54 57 -10 0.00
Wed 02/25 10Z 0.15 1928 70 86 -9 0.00
Wed 02/25 11Z 0.15 1931 85 89 -9 0.00
Wed 02/25 12Z 0.16 1932 91 87 -9 0.01
Wed 02/25 13Z 0.24 2030 92 87 -9 0.04
Wed 02/25 14Z 0.31 2026 93 87 -9 0.06
Wed 02/25 15Z 0.37 2123 94 89 -9 0.04
Wed 02/25 16Z 0.46 2218 95 85 -9 0.03
Wed 02/25 17Z 0.62 2216 94 74 -8 0.01
Wed 02/25 18Z 1.31 2215 92 64 -8 0.00
Wed 02/25 19Z 2.95 2216 90 47 -8 0.00
Wed 02/25 20Z 2.10 2218 92 55 -8 0.00
Wed 02/25 21Z 0.98 2318 94 81 -8 0.00
Wed 02/25 22Z 0.82 2319 94 80 -7 0.00
Wed 02/25 23Z 0.78 2221 95 85 -7 0.01
Thu 02/26 00Z 0.96 2322 94 83 -7 0.01
Thu 02/26 01Z 1.40 2522 94 79 -8 0.03
Thu 02/26 02Z 1.59 2624 94 51 -9 0.02
Thu 02/26 03Z 1.66 2626 87 40 -10 0.01
Thu 02/26 04Z 1.27 2725 84 35 -11 0.01
Thu 02/26 05Z 1.04 2723 82 48 -11 0.00
Thu 02/26 06Z 1.10 2622 87 63 -11 0.00
Thu 02/26 07Z 1.11 2623 89 62 -12 0.00
Thu 02/26 08Z 1.26 2625 89 60 -12 0.00
Thu 02/26 09Z 1.43 2726 82 50 -13 0.00
Thu 02/26 10Z 1.42 2728 74 36 -14 0.00
Thu 02/26 11Z 1.33 2730 73 27 -15 0.00
Thu 02/26 12Z 1.27 2730 70 18 -15 0.00
Thu 02/26 13Z 1.47 2730 72 10 -16 0.00
Thu 02/26 14Z 1.74 2727 77 7 -16 0.00
Thu 02/26 15Z 6.85 2725 80 6 -17 0.00
Thu 02/26 16Z 11.83 2724 83 7 -17 0.00
Thu 02/26 17Z 13.35 2723 82 8 -16 0.00
Run total areal avg QPF for the greens is: 0.28 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