Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260731_0600
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)
=== ===== === ==== ==== === === === ====
Fri 07/31 06Z 0.02 3408 82 80 13 0.00
Fri 07/31 07Z 0.09 3311 82 88 13 0.00
Fri 07/31 08Z 0.10 3313 81 94 13 0.00
Fri 07/31 09Z 0.07 3313 81 94 12 0.00
Fri 07/31 10Z 0.06 3413 84 94 12 0.01
Fri 07/31 11Z 0.03 3413 86 90 12 0.01
Fri 07/31 12Z 0.03 3411 88 87 12 0.00
Fri 07/31 13Z 0.03 3411 90 84 12 0.00
Fri 07/31 14Z 0.04 3411 91 81 12 0.00
Fri 07/31 15Z 0.05 3410 92 80 12 0.00
Fri 07/31 16Z 0.06 3308 91 79 12 0.00
Fri 07/31 17Z 0.10 3307 91 75 12 0.00
Fri 07/31 18Z 0.15 3207 89 67 13 0.00
Fri 07/31 19Z 0.28 3108 88 69 13 0.00
Fri 07/31 20Z 0.42 3110 88 64 13 0.00
Fri 07/31 21Z 0.40 3210 90 51 13 0.00
Fri 07/31 22Z 0.26 3211 87 37 13 0.00
Fri 07/31 23Z 0.20 3210 83 33 13 0.00
Sat 08/01 00Z 0.17 3211 80 30 13 0.00
Sat 08/01 01Z 0.14 3311 74 26 14 0.00
Sat 08/01 02Z 0.11 3310 69 24 14 0.00
Sat 08/01 03Z 0.12 3309 68 26 14 0.00
Sat 08/01 04Z 0.09 3307 67 33 14 0.00
Sat 08/01 05Z 0.11 3207 68 39 13 0.00
Sat 08/01 06Z 0.12 3206 69 43 13 0.00
Sat 08/01 07Z 0.13 3105 70 46 13 0.00
Sat 08/01 08Z 0.14 3004 73 42 13 0.00
Sat 08/01 09Z 0.15 2803 76 33 13 0.00
Sat 08/01 10Z 0.15 2503 78 28 12 0.00
Sat 08/01 11Z 0.13 2203 79 24 12 0.00
Sat 08/01 12Z 0.20 2204 79 22 12 0.00
Sat 08/01 13Z 0.24 2205 79 18 12 0.00
Sat 08/01 14Z 0.29 2105 80 15 12 0.00
Sat 08/01 15Z 0.44 2005 81 13 13 0.00
Sat 08/01 16Z 1.02 2005 82 14 13 0.00
Sat 08/01 17Z 1.19 2006 81 13 13 0.00
Sat 08/01 18Z 1.29 2005 80 12 13 0.00
Sat 08/01 19Z 0.99 2005 77 13 14 0.00
Sat 08/01 20Z 0.32 1905 75 14 14 0.00
Sat 08/01 21Z 0.19 1806 73 14 14 0.00
Sat 08/01 22Z 0.21 1809 75 15 14 0.00
Sat 08/01 23Z 0.21 1811 78 18 14 0.00
Sun 08/02 00Z 0.26 1812 81 25 14 0.00
Sun 08/02 01Z 0.31 1914 83 38 14 0.00
Sun 08/02 02Z 0.36 1915 85 55 14 0.00
Sun 08/02 03Z 0.38 1916 89 59 14 0.00
Sun 08/02 04Z 0.34 1917 93 62 14 0.00
Sun 08/02 05Z 0.30 1917 93 52 14 0.00
Sun 08/02 06Z 0.36 2018 93 50 14 0.00
Sun 08/02 07Z 0.39 2119 89 42 14 0.00
Sun 08/02 08Z 0.33 2117 87 29 15 0.00
Sun 08/02 09Z 0.38 2118 95 24 14 0.00
Sun 08/02 10Z 0.37 2117 97 20 14 0.01
Sun 08/02 11Z 0.39 2118 97 28 14 0.02
Sun 08/02 12Z 0.37 2117 92 21 14 0.01
Sun 08/02 13Z 0.31 2017 88 15 14 0.00
Sun 08/02 14Z 0.35 2017 90 15 14 0.00
Sun 08/02 15Z 0.37 2016 93 13 14 0.00
Sun 08/02 16Z 0.37 2015 95 9 13 0.00
Sun 08/02 17Z 0.38 1914 94 10 14 0.00
Run total areal avg QPF for the Central_Greens is: 0.06 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