Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260719_1800
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 07/19 18Z 5.53 3216 78 10 8 0.00
Sun 07/19 19Z 5.61 3117 76 9 8 0.00
Sun 07/19 20Z 7.39 3018 77 11 8 0.00
Sun 07/19 21Z 7.54 3018 74 12 9 0.00
Sun 07/19 22Z 6.40 3018 70 11 9 0.00
Sun 07/19 23Z 3.72 3019 71 10 9 0.00
Mon 07/20 00Z 2.68 3021 75 9 8 0.00
Mon 07/20 01Z 1.75 3122 78 7 8 0.00
Mon 07/20 02Z 1.20 3123 81 6 8 0.00
Mon 07/20 03Z 1.08 3123 83 6 7 0.00
Mon 07/20 04Z 0.86 3123 82 7 7 0.00
Mon 07/20 05Z 0.71 3123 84 19 7 0.00
Mon 07/20 06Z 0.60 3123 84 17 8 0.00
Mon 07/20 07Z 0.50 3122 86 12 8 0.00
Mon 07/20 08Z 0.47 3120 85 14 8 0.00
Mon 07/20 09Z 0.40 3118 83 19 8 0.00
Mon 07/20 10Z 0.33 3116 80 22 8 0.00
Mon 07/20 11Z 0.31 3115 75 32 8 0.00
Mon 07/20 12Z 0.30 3114 73 42 8 0.00
Mon 07/20 13Z 0.31 3011 73 45 8 0.00
Mon 07/20 14Z 0.37 3009 73 44 8 0.00
Mon 07/20 15Z 0.71 2907 72 49 8 0.00
Mon 07/20 16Z 1.15 2805 71 53 9 0.00
Mon 07/20 17Z 1.44 2505 67 49 10 0.00
Mon 07/20 18Z 1.74 2406 66 47 10 0.00
Mon 07/20 19Z 2.11 2307 67 47 11 0.00
Mon 07/20 20Z 2.46 2308 70 49 11 0.00
Mon 07/20 21Z 1.82 2208 71 46 11 0.00
Mon 07/20 22Z 0.81 2209 71 39 11 0.00
Mon 07/20 23Z 0.45 2111 68 31 12 0.00
Tue 07/21 00Z 0.39 2113 61 23 12 0.00
Tue 07/21 01Z 0.34 2014 53 24 13 0.00
Tue 07/21 02Z 0.36 2016 55 21 13 0.00
Tue 07/21 03Z 0.43 2118 57 15 13 0.00
Tue 07/21 04Z 0.50 2121 59 14 13 0.00
Tue 07/21 05Z 0.62 2123 63 13 12 0.00
Tue 07/21 06Z 0.68 2224 70 11 12 0.00
Tue 07/21 07Z 0.70 2225 70 9 12 0.00
Tue 07/21 08Z 0.57 2124 72 6 12 0.00
Tue 07/21 09Z 0.55 2124 81 3 12 0.00
Tue 07/21 10Z 0.56 2125 89 2 12 0.00
Tue 07/21 11Z 0.56 2125 91 1 12 0.00
Tue 07/21 12Z 0.47 2024 95 2 12 0.00
Tue 07/21 13Z 0.41 2025 98 11 12 0.01
Tue 07/21 14Z 0.41 2025 98 30 12 0.02
Tue 07/21 15Z 0.37 1925 97 33 12 0.01
Tue 07/21 16Z 0.37 1924 97 51 12 0.01
Tue 07/21 17Z 0.26 1823 95 66 13 0.00
Tue 07/21 18Z 0.19 1823 94 53 13 0.00
Tue 07/21 19Z 0.12 1724 93 74 13 0.01
Tue 07/21 20Z 0.08 1625 93 87 13 0.03
Tue 07/21 21Z 0.12 1626 91 51 14 0.02
Tue 07/21 22Z 0.10 1628 92 58 14 0.02
Tue 07/21 23Z 0.09 1628 92 66 15 0.01
Wed 07/22 00Z 0.06 1726 96 62 15 0.00
Wed 07/22 01Z 0.16 1826 95 85 15 0.09
Wed 07/22 02Z 0.21 1825 91 62 15 0.19
Wed 07/22 03Z 0.39 2025 90 58 14 0.02
Wed 07/22 04Z 0.48 2223 85 60 14 0.01
Wed 07/22 05Z 0.59 2226 80 61 14 0.00
Run total areal avg QPF for the Central_Greens is: 0.45 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