Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260510_0000
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)
=== ===== === ==== ==== === === === ====
Sun 05/10 00Z 0.06 1817 97 46 2 0.00
Sun 05/10 01Z 0.10 1820 95 34 3 0.01
Sun 05/10 02Z 0.15 1921 94 32 3 0.01
Sun 05/10 03Z 0.16 1922 94 29 3 0.01
Sun 05/10 04Z 0.27 2024 95 31 3 0.01
Sun 05/10 05Z 0.33 2024 93 32 4 0.00
Sun 05/10 06Z 0.40 2125 92 48 4 0.00
Sun 05/10 07Z 0.42 2225 91 57 5 0.01
Sun 05/10 08Z 0.51 2225 93 70 5 0.01
Sun 05/10 09Z 0.59 2323 92 88 4 0.04
Sun 05/10 10Z 0.56 2322 93 83 5 0.02
Sun 05/10 11Z 0.55 2322 93 64 5 0.01
Sun 05/10 12Z 0.54 2322 92 49 5 0.00
Sun 05/10 13Z 0.57 2322 91 58 5 0.01
Sun 05/10 14Z 0.63 2421 90 63 4 0.01
Sun 05/10 15Z 0.69 2420 88 74 4 0.01
Sun 05/10 16Z 1.02 2419 91 77 3 0.00
Sun 05/10 17Z 1.22 2416 89 60 3 0.01
Sun 05/10 18Z 1.78 2514 88 26 3 0.01
Sun 05/10 19Z 4.38 2514 86 23 3 0.01
Sun 05/10 20Z 5.88 2616 73 22 3 0.01
Sun 05/10 21Z 8.85 2617 61 20 3 0.00
Sun 05/10 22Z 9.64 2718 47 20 3 0.00
Sun 05/10 23Z 4.10 2819 51 21 2 0.00
Mon 05/11 00Z 1.74 2820 54 27 1 0.00
Mon 05/11 01Z 1.46 2921 59 28 0 0.00
Mon 05/11 02Z 1.29 2921 63 28 0 0.00
Mon 05/11 03Z 1.13 2920 71 32 0 0.00
Mon 05/11 04Z 1.04 3019 77 31 -1 0.00
Mon 05/11 05Z 0.98 3019 79 30 -2 0.00
Mon 05/11 06Z 0.75 3018 82 27 -2 0.00
Mon 05/11 07Z 0.66 3116 83 21 -2 0.00
Mon 05/11 08Z 0.55 3114 83 20 -2 0.00
Mon 05/11 09Z 0.47 3113 83 19 -3 0.00
Mon 05/11 10Z 0.42 3111 83 20 -3 0.00
Mon 05/11 11Z 0.41 3010 85 22 -3 0.00
Mon 05/11 12Z 0.47 2909 88 23 -3 0.00
Mon 05/11 13Z 0.59 2909 87 28 -3 0.00
Mon 05/11 14Z 2.02 2809 83 33 -3 0.00
Mon 05/11 15Z 3.49 2809 76 37 -3 0.00
Mon 05/11 16Z 4.36 2910 77 46 -2 0.01
Mon 05/11 17Z 5.00 2910 75 52 -2 0.00
Mon 05/11 18Z 4.43 2811 73 70 -2 0.01
Mon 05/11 19Z 4.17 2911 70 62 -1 0.00
Mon 05/11 20Z 4.39 2912 71 82 -1 0.01
Mon 05/11 21Z 3.45 3012 70 82 -1 0.00
Mon 05/11 22Z 2.57 3013 77 75 -2 0.00
Mon 05/11 23Z 0.98 3115 77 70 -2 0.01
Tue 05/12 00Z 0.68 3117 74 63 -2 0.00
Tue 05/12 01Z 0.81 3218 77 59 -3 0.00
Tue 05/12 02Z 0.73 3218 78 58 -3 0.00
Tue 05/12 03Z 0.84 3219 79 45 -3 0.00
Tue 05/12 04Z 0.80 3219 77 43 -4 0.00
Tue 05/12 05Z 0.70 3220 74 43 -4 0.00
Tue 05/12 06Z 0.60 3219 72 33 -4 0.00
Tue 05/12 07Z 0.52 3319 73 29 -4 0.00
Tue 05/12 08Z 0.50 3317 73 37 -5 0.00
Tue 05/12 09Z 0.47 3216 73 48 -5 0.00
Tue 05/12 10Z 0.46 3215 73 46 -5 0.00
Tue 05/12 11Z 0.53 3215 74 30 -6 0.00
Run total areal avg QPF for the greens is: 0.24 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