Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260216_0600
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)
=== ===== === ==== ==== === === === ====
Mon 02/16 06Z 0.06 1815 66 46 -6 0.00
Mon 02/16 07Z 0.08 1816 69 51 -6 0.00
Mon 02/16 08Z 0.07 1816 70 54 -6 0.00
Mon 02/16 09Z 0.07 1914 71 58 -5 0.00
Mon 02/16 10Z 0.07 1912 72 71 -5 0.00
Mon 02/16 11Z 0.07 1912 73 82 -5 0.00
Mon 02/16 12Z 0.05 1911 75 84 -4 0.00
Mon 02/16 13Z 0.04 1811 78 86 -4 0.00
Mon 02/16 16Z 0.08 2009 83 71 -4 0.00
Mon 02/16 17Z 0.06 1908 84 63 -4 0.00
Mon 02/16 18Z 0.05 1908 85 59 -4 0.00
Mon 02/16 19Z 0.03 1808 84 53 -4 0.00
Mon 02/16 22Z 0.05 1909 85 42 -4 0.00
Mon 02/16 23Z 0.06 1911 85 36 -3 0.00
Tue 02/17 00Z 0.09 1912 85 31 -3 0.00
Tue 02/17 01Z 0.15 2113 87 30 -2 0.00
Tue 02/17 02Z 0.18 2114 90 36 -2 0.00
Tue 02/17 03Z 0.20 2115 91 43 -2 0.00
Tue 02/17 04Z 0.25 2217 92 80 -3 0.00
Tue 02/17 05Z 0.27 2217 93 89 -3 0.00
Tue 02/17 06Z 0.28 2217 94 90 -3 0.00
Tue 02/17 07Z 0.26 2216 93 90 -3 0.00
Tue 02/17 08Z 0.27 2217 93 96 -3 0.00
Tue 02/17 09Z 0.26 2117 95 97 -3 0.00
Tue 02/17 10Z 0.25 2117 95 97 -3 0.01
Tue 02/17 11Z 0.23 2116 95 97 -2 0.01
Tue 02/17 12Z 0.27 2216 96 92 -3 0.00
Tue 02/17 13Z 0.27 2215 97 80 -3 0.01
Tue 02/17 14Z 0.30 2314 98 74 -3 0.01
Tue 02/17 15Z 0.32 2513 98 60 -3 0.01
Tue 02/17 16Z 0.34 2613 98 48 -3 0.01
Tue 02/17 17Z 0.31 2711 98 37 -3 0.01
Tue 02/17 18Z 0.31 2811 98 38 -3 0.01
Tue 02/17 19Z 0.37 2913 98 37 -3 0.02
Tue 02/17 20Z 0.38 2913 98 20 -3 0.01
Tue 02/17 21Z 0.42 2915 98 13 -3 0.01
Tue 02/17 22Z 0.44 2815 97 16 -4 0.01
Tue 02/17 23Z 0.51 2816 94 16 -4 0.00
Wed 02/18 00Z 0.52 2918 88 16 -3 0.00
Wed 02/18 01Z 0.45 2919 76 15 -3 0.01
Wed 02/18 02Z 0.43 2919 66 13 -3 0.01
Wed 02/18 03Z 0.44 2920 61 14 -3 0.01
Wed 02/18 04Z 0.44 2920 58 18 -3 0.01
Wed 02/18 05Z 0.45 2921 57 17 -4 0.01
Wed 02/18 06Z 0.46 2921 56 16 -4 0.01
Wed 02/18 07Z 0.42 3021 54 14 -4 0.01
Wed 02/18 08Z 0.38 3020 52 15 -4 0.01
Wed 02/18 09Z 0.31 3019 49 21 -4 0.01
Wed 02/18 10Z 0.30 3018 46 34 -3 0.01
Wed 02/18 11Z 0.26 3016 42 38 -3 0.01
Wed 02/18 12Z 0.22 2913 41 44 -3 0.01
Wed 02/18 13Z 0.20 2911 40 60 -3 0.01
Wed 02/18 14Z 0.16 2808 40 65 -3 0.00
Wed 02/18 15Z 0.13 2606 47 67 -3 0.00
Wed 02/18 16Z 0.12 2506 57 80 -3 0.00
Wed 02/18 17Z 0.10 2405 68 84 -3 0.00
Run total areal avg QPF for the greens is: 0.26 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