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Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260802_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 08/02 00Z 0.20 2106 76 28 15 0.00
Sun 08/02 01Z 0.18 2007 74 27 15 0.00
Sun 08/02 02Z 0.19 1909 74 32 15 0.00
Sun 08/02 03Z 0.24 2012 74 42 15 0.00
Sun 08/02 04Z 0.38 2014 75 53 15 0.00
Sun 08/02 05Z 0.52 2118 82 64 15 0.00
Sun 08/02 06Z 0.48 2120 87 68 15 0.01
Sun 08/02 07Z 0.41 2122 87 67 15 0.00
Sun 08/02 08Z 0.39 2122 85 69 15 0.00
Sun 08/02 09Z 0.45 2123 86 82 15 0.00
Sun 08/02 10Z 0.51 2222 88 80 15 0.00
Sun 08/02 11Z 0.51 2221 88 71 15 0.00
Sun 08/02 12Z 0.46 2219 87 68 15 0.00
Sun 08/02 13Z 0.41 2216 88 53 15 0.00
Sun 08/02 14Z 0.44 2116 92 50 14 0.00
Sun 08/02 15Z 0.43 2115 95 72 14 0.01
Sun 08/02 16Z 0.34 2115 93 83 14 0.03
Sun 08/02 17Z 0.38 2015 92 79 14 0.01
Sun 08/02 18Z 0.38 2017 92 70 15 0.00
Sun 08/02 19Z 0.45 2017 90 59 15 0.02
Sun 08/02 20Z 0.50 2017 88 56 15 0.03
Sun 08/02 21Z 0.51 2017 87 34 15 0.00
Sun 08/02 22Z 0.29 1917 81 33 15 0.00
Sun 08/02 23Z 0.24 1919 81 39 15 0.00
Mon 08/03 00Z 0.22 1920 78 60 15 0.00
Mon 08/03 01Z 0.20 1920 79 72 15 0.00
Mon 08/03 02Z 0.22 1921 78 83 15 0.00
Mon 08/03 03Z 0.18 1921 71 84 15 0.00
Mon 08/03 04Z 0.17 1921 65 90 15 0.00
Mon 08/03 05Z 0.18 1922 67 86 16 0.00
Mon 08/03 06Z 0.24 1923 76 74 15 0.00
Mon 08/03 07Z 0.21 1922 85 64 15 0.01
Mon 08/03 08Z 0.19 1922 86 89 16 0.01
Mon 08/03 09Z 0.17 1921 83 94 15 0.02
Mon 08/03 10Z 0.09 1821 80 90 16 0.01
Mon 08/03 11Z 0.08 1823 82 89 17 0.00
Mon 08/03 12Z 0.09 1825 87 84 17 0.01
Mon 08/03 13Z 0.15 1926 93 82 17 0.01
Mon 08/03 14Z 0.19 1927 96 80 17 0.01
Mon 08/03 15Z 0.26 1925 98 84 16 0.04
Mon 08/03 16Z 0.31 2023 98 79 17 0.15
Mon 08/03 17Z 0.36 2022 98 81 17 0.07
Mon 08/03 18Z 0.34 2020 96 85 17 0.13
Mon 08/03 19Z 0.41 1921 97 77 17 0.04
Mon 08/03 20Z 0.36 1921 96 63 17 0.05
Mon 08/03 21Z 0.61 2221 93 74 17 0.43
Mon 08/03 22Z 0.73 2523 94 37 15 0.37
Mon 08/03 23Z 0.84 2524 94 58 14 0.02
Tue 08/04 00Z 0.74 2623 96 68 13 0.04
Tue 08/04 01Z 0.60 2720 98 69 13 0.03
Tue 08/04 02Z 0.50 2919 98 67 13 0.05
Tue 08/04 03Z 0.50 3123 98 83 12 0.05
Tue 08/04 04Z 0.40 3330 98 85 11 0.07
Tue 08/04 05Z 0.30 3332 94 69 12 0.03
Tue 08/04 06Z 0.26 3431 87 33 12 0.01
Tue 08/04 07Z 0.23 3429 82 8 12 0.01
Tue 08/04 08Z 0.23 3426 80 2 12 0.01
Tue 08/04 09Z 0.28 3324 82 2 11 0.00
Tue 08/04 10Z 0.24 3322 73 2 12 0.00
Tue 08/04 11Z 0.21 3321 60 2 12 0.00
Run total areal avg QPF for the greens is: 1.79 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