Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260419_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)
=== ===== === ==== ==== === === === ====
Sun 04/19 18Z 0.43 3017 97 90 -5 0.00
Sun 04/19 19Z 0.66 3019 93 88 -6 0.00
Sun 04/19 20Z 0.83 2920 93 87 -6 0.01
Sun 04/19 21Z 0.81 3018 93 78 -6 0.02
Sun 04/19 22Z 0.90 2917 92 29 -6 0.00
Sun 04/19 23Z 0.93 2818 94 35 -6 0.00
Mon 04/20 00Z 1.15 2821 93 46 -6 0.01
Mon 04/20 01Z 1.47 2823 91 53 -6 0.01
Mon 04/20 02Z 1.56 2925 90 59 -6 0.02
Mon 04/20 03Z 1.43 2925 84 25 -7 0.00
Mon 04/20 04Z 1.42 2825 74 32 -7 0.00
Mon 04/20 05Z 1.33 2824 69 46 -7 0.00
Mon 04/20 06Z 1.16 2822 72 42 -7 0.00
Mon 04/20 07Z 1.16 2821 76 38 -7 0.00
Mon 04/20 08Z 0.99 2819 82 46 -8 0.00
Mon 04/20 09Z 0.80 2817 86 54 -8 0.00
Mon 04/20 10Z 0.72 2816 87 55 -8 0.00
Mon 04/20 11Z 0.63 2914 91 53 -9 0.00
Mon 04/20 12Z 0.55 2912 93 61 -9 0.01
Mon 04/20 13Z 0.50 3011 94 53 -9 0.01
Mon 04/20 14Z 0.85 3111 92 48 -10 0.01
Mon 04/20 15Z 1.47 3111 88 52 -10 0.00
Mon 04/20 16Z 3.24 3110 83 52 -10 0.00
Mon 04/20 17Z 4.39 3010 74 53 -9 0.00
Mon 04/20 18Z 5.30 3011 67 52 -9 0.00
Mon 04/20 19Z 6.09 3011 62 48 -9 0.00
Mon 04/20 20Z 6.27 3011 59 39 -9 0.00
Mon 04/20 21Z 5.67 3111 59 39 -9 0.00
Mon 04/20 22Z 4.34 3111 59 33 -9 0.00
Mon 04/20 23Z 2.60 3111 58 26 -9 0.00
Tue 04/21 00Z 1.35 3112 57 22 -9 0.00
Tue 04/21 01Z 1.16 3212 56 16 -9 0.00
Tue 04/21 02Z 1.18 3213 55 13 -9 0.00
Tue 04/21 03Z 1.50 3214 53 11 -10 0.00
Tue 04/21 04Z 1.29 3213 51 10 -10 0.00
Tue 04/21 05Z 1.15 3213 50 11 -10 0.00
Tue 04/21 06Z 0.93 3212 49 13 -10 0.00
Tue 04/21 07Z 0.71 3111 48 13 -10 0.00
Tue 04/21 08Z 0.58 3110 48 12 -10 0.00
Tue 04/21 09Z 0.52 3108 48 13 -10 0.00
Tue 04/21 10Z 0.44 3007 47 14 -10 0.00
Tue 04/21 11Z 0.38 2906 47 13 -10 0.00
Tue 04/21 12Z 0.51 2704 46 12 -10 0.00
Tue 04/21 13Z 1.49 2404 46 11 -10 0.00
Tue 04/21 14Z 2.04 2304 44 11 -9 0.00
Tue 04/21 15Z 2.70 2205 42 11 -9 0.00
Tue 04/21 16Z 2.86 2206 40 12 -8 0.00
Tue 04/21 17Z 3.51 2207 39 18 -7 0.00
Tue 04/21 18Z 3.85 2307 38 44 -6 0.00
Tue 04/21 19Z 3.34 2306 37 73 -6 0.00
Tue 04/21 20Z 2.96 2306 37 88 -5 0.00
Tue 04/21 21Z 2.05 2206 37 85 -5 0.00
Tue 04/21 22Z 1.09 2206 37 76 -5 0.00
Tue 04/21 23Z 0.30 2107 37 66 -4 0.00
Wed 04/22 00Z 0.27 2009 38 62 -4 0.00
Wed 04/22 01Z 0.30 2011 40 71 -4 0.00
Wed 04/22 02Z 0.39 2113 42 82 -4 0.00
Wed 04/22 03Z 0.49 2115 44 90 -4 0.00
Wed 04/22 04Z 0.51 2117 47 92 -4 0.00
Wed 04/22 05Z 0.52 2117 50 89 -4 0.00
Run total areal avg QPF for the greens is: 0.10 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