Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260203_1800
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Tue 02/03 18Z 0.21 2504 83 56 -11 0.00
Tue 02/03 19Z 0.30 2505 81 71 -11 0.00
Tue 02/03 20Z 0.28 2506 81 77 -11 0.00
Tue 02/03 21Z 0.25 2606 80 70 -11 0.00
Tue 02/03 22Z 0.23 2607 83 68 -11 0.00
Tue 02/03 23Z 0.28 2708 86 83 -12 0.00
Wed 02/04 00Z 0.31 2709 90 82 -12 0.00
Wed 02/04 01Z 0.43 2711 93 77 -12 0.00
Wed 02/04 02Z 0.50 2712 91 86 -12 0.00
Wed 02/04 04Z 0.71 2716 82 51 -13 0.00
Wed 02/04 05Z 0.76 2617 86 49 -13 0.00
Wed 02/04 06Z 0.71 2717 91 46 -13 0.00
Wed 02/04 07Z 0.64 2716 92 47 -13 0.00
Wed 02/04 08Z 0.57 2715 91 53 -14 0.00
Wed 02/04 09Z 0.60 2814 92 54 -14 0.01
Wed 02/04 10Z 0.69 2715 90 48 -15 0.01
Wed 02/04 11Z 0.47 2713 84 60 -15 0.01
Wed 02/04 12Z 0.29 2811 78 62 -15 0.00
Wed 02/04 13Z 0.22 3013 74 58 -14 0.00
Wed 02/04 14Z 0.20 3115 73 56 -14 0.00
Wed 02/04 15Z 0.24 3117 79 54 -14 0.00
Wed 02/04 16Z 0.30 3118 86 43 -14 0.00
Wed 02/04 17Z 0.39 3117 89 47 -14 0.00
Wed 02/04 18Z 0.50 3016 85 43 -14 0.00
Wed 02/04 19Z 0.56 3015 86 35 -14 0.00
Wed 02/04 20Z 0.46 3015 87 31 -13 0.00
Wed 02/04 21Z 0.33 3114 87 28 -13 0.00
Wed 02/04 23Z 0.29 3114 89 30 -12 0.00
Thu 02/05 00Z 0.25 3115 87 31 -12 0.00
Thu 02/05 01Z 0.23 3115 85 31 -12 0.00
Thu 02/05 02Z 0.20 3114 82 32 -12 0.00
Thu 02/05 03Z 0.19 3113 80 32 -12 0.00
Thu 02/05 04Z 0.18 3011 79 31 -12 0.00
Thu 02/05 05Z 0.19 3011 79 31 -12 0.00
Thu 02/05 06Z 0.20 2910 79 31 -12 0.00
Thu 02/05 07Z 0.21 2811 81 32 -12 0.00
Thu 02/05 08Z 0.23 2812 82 32 -12 0.00
Thu 02/05 09Z 0.25 2913 83 31 -13 0.00
Thu 02/05 10Z 0.24 2914 82 31 -13 0.00
Thu 02/05 11Z 0.24 3015 82 62 -13 0.00
Thu 02/05 12Z 0.25 3017 83 70 -13 0.00
Thu 02/05 13Z 0.24 3118 81 52 -13 0.00
Thu 02/05 14Z 0.24 3118 80 10 -14 0.00
Thu 02/05 15Z 0.23 3117 79 4 -14 0.00
Thu 02/05 16Z 0.22 3117 78 3 -14 0.00
Thu 02/05 17Z 0.24 3116 77 4 -15 0.00
Thu 02/05 18Z 0.26 3115 75 4 -15 0.00
Thu 02/05 19Z 0.24 3215 70 4 -15 0.00
Thu 02/05 20Z 0.21 3215 66 2 -14 0.00
Thu 02/05 21Z 0.19 3215 63 3 -14 0.00
Thu 02/05 22Z 0.16 3215 60 5 -13 0.00
Thu 02/05 23Z 0.12 3316 55 5 -12 0.00
Fri 02/06 00Z 0.08 3315 51 6 -12 0.00
Fri 02/06 01Z 0.05 3313 47 6 -11 0.00
Fri 02/06 02Z 0.04 3412 42 6 -11 0.00
Fri 02/06 03Z 0.02 3409 38 6 -10 0.00
Fri 02/06 04Z 0.02 3407 36 7 -10 0.00
Fri 02/06 05Z 0.02 3307 33 8 -10 0.00
Run total areal avg QPF for the Central_Greens is: 0.03 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