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Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260802_1200
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 08/02 12Z 0.26 2014 80 64 15 0.00
Sun 08/02 13Z 0.28 2015 80 59 15 0.00
Sun 08/02 14Z 0.26 2014 83 53 15 0.00
Sun 08/02 15Z 0.30 1913 89 61 15 0.00
Sun 08/02 16Z 0.20 1813 92 69 15 0.01
Sun 08/02 17Z 0.37 1915 92 78 15 0.10
Sun 08/02 18Z 0.34 1916 93 79 15 0.10
Sun 08/02 19Z 0.26 1817 92 59 15 0.08
Sun 08/02 20Z 0.29 1819 89 41 15 0.01
Sun 08/02 21Z 0.21 1821 87 24 15 0.01
Sun 08/02 22Z 0.12 1823 86 17 16 0.00
Sun 08/02 23Z 0.12 1824 85 17 16 0.00
Mon 08/03 00Z 0.11 1824 85 21 15 0.00
Mon 08/03 01Z 0.11 1825 83 48 15 0.00
Mon 08/03 02Z 0.15 1825 80 77 15 0.01
Mon 08/03 03Z 0.18 1925 79 93 15 0.01
Mon 08/03 04Z 0.15 1924 80 93 15 0.01
Mon 08/03 05Z 0.17 1925 82 93 15 0.01
Mon 08/03 06Z 0.28 1927 88 94 15 0.01
Mon 08/03 07Z 0.21 1926 88 84 15 0.05
Mon 08/03 08Z 0.20 1926 81 84 16 0.01
Mon 08/03 09Z 0.13 1826 83 87 16 0.01
Mon 08/03 10Z 0.11 1828 89 93 16 0.02
Mon 08/03 11Z 0.14 1830 97 95 16 0.10
Mon 08/03 12Z 0.25 1931 96 83 16 0.15
Mon 08/03 13Z 0.43 2031 95 75 16 0.05
Mon 08/03 14Z 0.50 2029 98 74 16 0.02
Mon 08/03 15Z 0.69 2228 99 77 16 0.03
Mon 08/03 16Z 0.67 2223 99 81 16 0.04
Mon 08/03 17Z 0.72 2321 97 81 16 0.08
Mon 08/03 18Z 0.62 2417 96 88 15 0.11
Mon 08/03 19Z 0.62 2417 93 82 15 0.20
Mon 08/03 20Z 0.67 2418 95 69 15 0.04
Mon 08/03 21Z 0.88 2624 98 78 14 0.14
Mon 08/03 22Z 0.88 2828 97 71 12 0.10
Mon 08/03 23Z 0.76 3028 95 52 11 0.05
Tue 08/04 00Z 0.54 3230 94 42 11 0.04
Tue 08/04 01Z 0.46 3228 93 25 11 0.01
Tue 08/04 02Z 0.46 3226 89 20 10 0.00
Tue 08/04 03Z 0.55 3124 87 10 10 0.00
Tue 08/04 04Z 0.65 3125 85 5 11 0.01
Tue 08/04 05Z 0.73 3023 84 4 11 0.00
Tue 08/04 06Z 0.81 3023 83 4 10 0.00
Tue 08/04 07Z 0.83 3023 79 4 11 0.00
Tue 08/04 08Z 0.76 3023 76 3 11 0.00
Tue 08/04 09Z 0.75 3022 71 2 11 0.00
Tue 08/04 10Z 0.60 3021 64 2 12 0.00
Tue 08/04 11Z 0.50 3020 58 2 13 0.00
Tue 08/04 12Z 0.45 3020 55 1 13 0.00
Tue 08/04 13Z 0.42 3018 54 1 13 0.00
Tue 08/04 14Z 0.38 3117 54 1 13 0.00
Tue 08/04 15Z 0.36 3014 54 1 13 0.00
Tue 08/04 16Z 0.31 3011 51 2 13 0.00
Tue 08/04 17Z 0.29 3010 49 3 14 0.00
Tue 08/04 18Z 0.23 2907 46 5 14 0.00
Tue 08/04 19Z 0.21 2906 43 10 15 0.00
Tue 08/04 20Z 0.21 2705 41 15 16 0.00
Tue 08/04 21Z 0.19 2605 38 19 16 0.00
Tue 08/04 22Z 0.16 2605 37 24 16 0.00
Tue 08/04 23Z 0.17 2505 37 26 17 0.00
Run total areal avg QPF for the greens is: 1.62 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