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Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260802_0000
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sun 08/02 00Z 0.31 2107 75 14 15 0.00
Sun 08/02 01Z 0.33 2108 73 14 15 0.00
Sun 08/02 02Z 0.36 2010 72 25 15 0.00
Sun 08/02 03Z 0.40 2012 73 40 15 0.00
Sun 08/02 04Z 0.55 2015 75 56 15 0.00
Sun 08/02 05Z 0.71 2119 85 68 15 0.00
Sun 08/02 06Z 0.56 2121 91 70 15 0.02
Sun 08/02 07Z 0.48 2123 88 75 15 0.01
Sun 08/02 08Z 0.47 2123 85 76 16 0.00
Sun 08/02 09Z 0.55 2223 90 84 15 0.00
Sun 08/02 10Z 0.64 2322 91 77 14 0.00
Sun 08/02 11Z 0.60 2222 87 64 15 0.00
Sun 08/02 12Z 0.51 2219 86 61 15 0.00
Sun 08/02 13Z 0.45 2217 87 45 15 0.00
Sun 08/02 14Z 0.55 2117 91 53 14 0.00
Sun 08/02 15Z 0.48 2116 96 87 14 0.01
Sun 08/02 16Z 0.41 2114 93 85 14 0.04
Sun 08/02 17Z 0.56 2115 92 78 14 0.00
Sun 08/02 18Z 0.54 2015 92 71 15 0.00
Sun 08/02 19Z 0.63 1916 91 49 15 0.03
Sun 08/02 20Z 0.72 2017 88 46 15 0.05
Sun 08/02 21Z 0.78 1916 87 21 15 0.00
Sun 08/02 22Z 0.51 1919 77 35 15 0.00
Sun 08/02 23Z 0.42 1921 76 47 15 0.00
Mon 08/03 00Z 0.34 1920 77 61 15 0.00
Mon 08/03 01Z 0.30 1920 78 61 15 0.00
Mon 08/03 02Z 0.31 1920 77 81 15 0.01
Mon 08/03 03Z 0.25 1921 68 80 16 0.00
Mon 08/03 04Z 0.27 1920 62 91 16 0.00
Mon 08/03 05Z 0.29 1921 66 85 16 0.00
Mon 08/03 06Z 0.35 2022 85 64 15 0.00
Mon 08/03 07Z 0.28 1920 93 48 15 0.01
Mon 08/03 08Z 0.28 1922 89 90 16 0.01
Mon 08/03 09Z 0.25 1919 81 94 16 0.02
Mon 08/03 10Z 0.17 1820 81 88 17 0.01
Mon 08/03 11Z 0.17 1823 86 85 17 0.00
Mon 08/03 12Z 0.22 1825 91 79 17 0.01
Mon 08/03 13Z 0.31 1926 95 78 17 0.01
Mon 08/03 14Z 0.37 1926 96 82 17 0.01
Mon 08/03 15Z 0.42 2024 98 83 17 0.05
Mon 08/03 16Z 0.45 2022 98 73 17 0.10
Mon 08/03 17Z 0.48 2020 98 74 17 0.06
Mon 08/03 18Z 0.46 2020 97 84 17 0.13
Mon 08/03 19Z 0.74 2023 97 71 17 0.04
Mon 08/03 20Z 0.64 2025 95 54 17 0.01
Mon 08/03 21Z 0.73 2224 91 68 17 0.23
Mon 08/03 22Z 0.75 2523 93 35 15 0.16
Mon 08/03 23Z 0.92 2524 96 47 13 0.02
Tue 08/04 00Z 0.78 2623 96 63 13 0.02
Tue 08/04 01Z 0.67 2622 97 65 13 0.02
Tue 08/04 02Z 0.60 2822 98 57 12 0.04
Tue 08/04 03Z 0.54 3025 98 78 11 0.04
Tue 08/04 04Z 0.37 3229 98 78 11 0.04
Tue 08/04 05Z 0.18 3332 96 76 12 0.02
Tue 08/04 06Z 0.16 3332 89 48 12 0.01
Tue 08/04 07Z 0.14 3330 81 10 12 0.01
Tue 08/04 08Z 0.12 3327 77 1 12 0.00
Tue 08/04 09Z 0.17 3325 79 2 12 0.00
Tue 08/04 10Z 0.15 3323 73 2 12 0.00
Tue 08/04 11Z 0.11 3321 60 2 13 0.00
Run total areal avg QPF for the Central_Greens is: 1.25 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