Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260731_1200
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 12Z 0.02 3508 93 89 11 0.00
Fri 07/31 13Z 0.03 3407 88 84 12 0.00
Fri 07/31 14Z 0.02 3406 86 73 12 0.00
Fri 07/31 15Z 0.11 3206 89 76 12 0.00
Fri 07/31 16Z 0.23 3107 89 80 12 0.00
Fri 07/31 17Z 0.18 3206 86 81 12 0.00
Fri 07/31 18Z 0.20 3206 83 80 13 0.00
Fri 07/31 19Z 0.32 3205 81 75 13 0.00
Fri 07/31 20Z 0.70 3105 80 72 13 0.00
Fri 07/31 21Z 0.45 3105 78 67 13 0.00
Fri 07/31 22Z 0.36 3107 79 65 13 0.00
Fri 07/31 23Z 0.27 3007 83 65 13 0.00
Sat 08/01 00Z 0.14 3206 83 64 13 0.00
Sat 08/01 01Z 0.13 3206 81 63 13 0.00
Sat 08/01 02Z 0.05 3304 77 59 14 0.00
Sat 08/01 03Z 0.09 3104 77 59 14 0.00
Sat 08/01 04Z 0.13 3004 78 57 14 0.00
Sat 08/01 05Z 0.11 2903 78 49 14 0.00
Sat 08/01 06Z 0.10 3003 78 43 14 0.00
Sat 08/01 07Z 0.09 3104 77 39 14 0.00
Sat 08/01 08Z 0.11 3004 77 38 13 0.00
Sat 08/01 09Z 0.14 3004 78 37 13 0.00
Sat 08/01 10Z 0.11 3004 76 37 13 0.00
Sat 08/01 11Z 0.11 3004 75 37 13 0.00
Sat 08/01 12Z 0.13 2903 75 37 13 0.00
Sat 08/01 13Z 0.14 2703 75 38 13 0.00
Sat 08/01 14Z 0.17 2503 77 38 13 0.00
Sat 08/01 15Z 0.42 2303 79 35 13 0.00
Sat 08/01 16Z 0.76 2203 79 32 13 0.00
Sat 08/01 17Z 1.29 2205 79 31 14 0.00
Sat 08/01 18Z 1.64 2205 79 32 14 0.00
Sat 08/01 19Z 1.23 2105 78 34 14 0.00
Sat 08/01 20Z 0.95 2005 75 31 14 0.00
Sat 08/01 21Z 0.61 1906 71 24 15 0.00
Sat 08/01 22Z 0.32 2008 67 15 15 0.00
Sat 08/01 23Z 0.34 2009 65 12 15 0.00
Sun 08/02 00Z 0.34 2011 66 15 15 0.00
Sun 08/02 01Z 0.51 2013 75 19 15 0.00
Sun 08/02 02Z 0.70 2115 83 24 14 0.00
Sun 08/02 03Z 0.67 2117 86 32 14 0.00
Sun 08/02 04Z 0.60 2120 86 48 15 0.00
Sun 08/02 05Z 0.69 2222 92 46 14 0.00
Sun 08/02 06Z 0.66 2221 92 40 14 0.00
Sun 08/02 07Z 0.71 2322 93 40 14 0.00
Sun 08/02 08Z 0.67 2421 90 41 14 0.01
Sun 08/02 09Z 0.56 2319 87 52 15 0.02
Sun 08/02 10Z 0.59 2321 92 60 14 0.02
Sun 08/02 11Z 0.63 2321 91 65 14 0.02
Sun 08/02 12Z 0.64 2321 92 68 14 0.01
Sun 08/02 13Z 0.61 2220 95 66 14 0.01
Sun 08/02 14Z 0.60 2218 92 39 14 0.01
Sun 08/02 15Z 0.74 2117 94 44 14 0.00
Sun 08/02 16Z 0.67 2116 93 44 14 0.01
Sun 08/02 17Z 0.92 2017 91 46 14 0.00
Sun 08/02 18Z 1.38 2018 89 31 14 0.02
Sun 08/02 19Z 0.91 1919 87 30 15 0.00
Sun 08/02 20Z 1.14 1921 88 53 15 0.00
Sun 08/02 21Z 1.48 2021 85 69 14 0.00
Sun 08/02 22Z 1.11 2023 79 90 14 0.00
Sun 08/02 23Z 0.74 2024 68 96 15 0.00
Run total areal avg QPF for the Central_Greens is: 0.13 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