Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260102_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)
=== ===== === ==== ==== === === === ====
Fri 01/02 18Z 1.70 2713 85 34 -18 0.00
Fri 01/02 19Z 2.11 2715 89 35 -18 0.00
Fri 01/02 20Z 1.23 2716 92 38 -17 0.00
Fri 01/02 21Z 1.39 2719 91 40 -17 0.00
Fri 01/02 22Z 1.31 2721 86 35 -17 0.00
Fri 01/02 23Z 1.32 2723 83 26 -17 0.00
Sat 01/03 00Z 1.44 2724 84 26 -17 0.00
Sat 01/03 01Z 1.57 2825 87 44 -17 0.00
Sat 01/03 02Z 1.39 2826 87 71 -17 0.00
Sat 01/03 03Z 1.40 2827 86 75 -18 0.01
Sat 01/03 04Z 1.73 2828 89 72 -18 0.00
Sat 01/03 05Z 1.54 2929 84 69 -18 0.00
Sat 01/03 06Z 1.14 2929 83 67 -18 0.00
Sat 01/03 07Z 1.12 2829 87 70 -18 0.00
Sat 01/03 08Z 1.12 2829 89 68 -18 0.00
Sat 01/03 09Z 0.97 2928 91 63 -18 0.00
Sat 01/03 10Z 0.93 2827 93 53 -18 0.00
Sat 01/03 11Z 0.87 2826 94 40 -18 0.00
Sat 01/03 12Z 0.83 2825 94 33 -17 0.00
Sat 01/03 13Z 0.85 2823 95 38 -17 0.00
Sat 01/03 14Z 0.95 2823 95 43 -18 0.01
Sat 01/03 15Z 1.03 2822 94 51 -18 0.00
Sat 01/03 16Z 0.99 2721 94 54 -18 0.00
Sat 01/03 17Z 1.15 2721 93 40 -18 0.00
Sat 01/03 18Z 1.13 2722 92 33 -17 0.00
Sat 01/03 19Z 1.07 2722 91 24 -17 0.00
Sat 01/03 20Z 0.99 2721 91 18 -16 0.00
Sat 01/03 21Z 0.92 2721 93 22 -16 0.00
Sat 01/03 22Z 1.05 2722 94 56 -16 0.00
Sat 01/03 23Z 1.02 2722 93 76 -16 0.00
Sun 01/04 00Z 1.02 2721 94 79 -16 0.00
Sun 01/04 01Z 1.05 2722 95 76 -16 0.00
Sun 01/04 02Z 0.94 2721 95 77 -16 0.00
Sun 01/04 03Z 0.91 2721 94 78 -16 0.00
Sun 01/04 04Z 0.78 2720 92 77 -16 0.00
Sun 01/04 05Z 0.70 2820 91 78 -16 0.00
Sun 01/04 06Z 0.63 2819 91 77 -16 0.00
Sun 01/04 07Z 0.64 2818 92 77 -16 0.00
Sun 01/04 08Z 0.58 2817 91 78 -17 0.00
Sun 01/04 09Z 0.51 2817 88 78 -16 0.00
Sun 01/04 10Z 0.47 2818 84 72 -16 0.00
Sun 01/04 11Z 0.47 2919 83 69 -16 0.00
Sun 01/04 12Z 0.47 2920 83 62 -16 0.00
Sun 01/04 13Z 0.45 2921 83 55 -16 0.00
Sun 01/04 14Z 0.43 2920 84 41 -16 0.00
Sun 01/04 15Z 0.46 2919 88 40 -17 0.00
Sun 01/04 16Z 0.51 2918 89 47 -17 0.00
Sun 01/04 17Z 0.57 2918 88 52 -18 0.00
Sun 01/04 18Z 0.65 2918 87 58 -18 0.00
Sun 01/04 19Z 0.72 2918 89 52 -19 0.00
Sun 01/04 20Z 0.64 2919 91 44 -19 0.00
Sun 01/04 21Z 0.60 3019 91 43 -20 0.00
Sun 01/04 22Z 0.65 3021 91 46 -21 0.00
Sun 01/04 23Z 0.65 3123 89 58 -21 0.00
Mon 01/05 00Z 0.55 3123 87 60 -21 0.00
Mon 01/05 01Z 0.47 3123 84 60 -21 0.00
Mon 01/05 02Z 0.49 3123 82 60 -22 0.00
Mon 01/05 03Z 0.53 3124 82 47 -22 0.00
Mon 01/05 04Z 0.50 3124 81 35 -22 0.00
Mon 01/05 05Z 0.49 3124 82 29 -22 0.00
Run total areal avg QPF for the greens is: 0.02 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