Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260203_1800
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 02/03 18Z 0.17 2504 83 57 -11 0.00
Tue 02/03 19Z 0.25 2505 82 66 -11 0.00
Tue 02/03 20Z 0.24 2505 81 70 -12 0.00
Tue 02/03 21Z 0.22 2606 81 67 -12 0.00
Tue 02/03 22Z 0.21 2606 83 67 -12 0.00
Tue 02/03 23Z 0.26 2607 85 80 -12 0.00
Wed 02/04 00Z 0.27 2707 89 83 -12 0.00
Wed 02/04 01Z 0.34 2709 91 81 -12 0.00
Wed 02/04 02Z 0.39 2709 91 88 -12 0.00
Wed 02/04 04Z 0.54 2712 85 64 -13 0.00
Wed 02/04 05Z 0.58 2612 87 59 -13 0.00
Wed 02/04 06Z 0.56 2713 91 57 -13 0.00
Wed 02/04 07Z 0.54 2713 93 58 -13 0.00
Wed 02/04 08Z 0.53 2713 92 63 -13 0.00
Wed 02/04 09Z 0.55 2713 92 66 -14 0.01
Wed 02/04 10Z 0.60 2714 90 62 -15 0.01
Wed 02/04 11Z 0.42 2712 85 68 -15 0.01
Wed 02/04 12Z 0.29 2811 80 69 -14 0.01
Wed 02/04 13Z 0.27 3013 78 65 -14 0.00
Wed 02/04 14Z 0.31 3115 80 62 -14 0.00
Wed 02/04 15Z 0.38 3118 85 58 -14 0.00
Wed 02/04 16Z 0.45 3018 89 49 -14 0.00
Wed 02/04 17Z 0.52 3018 90 53 -14 0.00
Wed 02/04 18Z 0.58 3017 87 47 -14 0.00
Wed 02/04 19Z 0.58 3016 89 41 -14 0.00
Wed 02/04 20Z 0.52 3016 90 37 -13 0.00
Wed 02/04 21Z 0.43 3016 90 34 -13 0.00
Wed 02/04 23Z 0.39 3016 89 35 -12 0.00
Thu 02/05 00Z 0.35 3016 87 36 -12 0.00
Thu 02/05 01Z 0.32 3116 84 36 -12 0.00
Thu 02/05 02Z 0.29 3115 82 36 -12 0.00
Thu 02/05 03Z 0.27 3014 81 37 -12 0.00
Thu 02/05 04Z 0.25 3013 79 37 -12 0.00
Thu 02/05 05Z 0.26 2913 79 37 -12 0.00
Thu 02/05 06Z 0.27 2913 81 37 -12 0.00
Thu 02/05 07Z 0.29 2813 82 36 -12 0.00
Thu 02/05 08Z 0.32 2814 84 36 -13 0.00
Thu 02/05 09Z 0.34 2916 86 37 -13 0.00
Thu 02/05 10Z 0.34 2916 85 44 -13 0.00
Thu 02/05 11Z 0.36 2917 85 66 -14 0.00
Thu 02/05 12Z 0.37 3019 85 71 -14 0.00
Thu 02/05 13Z 0.36 3019 85 45 -14 0.00
Thu 02/05 14Z 0.36 3119 84 7 -15 0.00
Thu 02/05 15Z 0.35 3118 84 4 -15 0.00
Thu 02/05 16Z 0.34 3117 83 3 -15 0.00
Thu 02/05 17Z 0.36 3116 82 4 -15 0.00
Thu 02/05 18Z 0.36 3116 80 4 -15 0.00
Thu 02/05 19Z 0.32 3115 74 4 -15 0.00
Thu 02/05 20Z 0.30 3115 69 3 -15 0.00
Thu 02/05 21Z 0.26 3115 65 3 -14 0.00
Thu 02/05 22Z 0.23 3215 61 5 -14 0.00
Thu 02/05 23Z 0.18 3215 54 5 -13 0.00
Fri 02/06 00Z 0.14 3314 49 6 -12 0.00
Fri 02/06 01Z 0.10 3312 46 6 -12 0.00
Fri 02/06 02Z 0.07 3311 41 6 -11 0.00
Fri 02/06 03Z 0.05 3409 37 7 -11 0.00
Fri 02/06 04Z 0.05 3307 35 7 -11 0.00
Fri 02/06 05Z 0.04 3306 33 8 -10 0.00
Run total areal avg QPF for the greens is: 0.04 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