Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260731_1200
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)
=== ===== === ==== ==== === === === ====
Fri 07/31 12Z 0.04 3507 91 88 11 0.00
Fri 07/31 13Z 0.06 3406 87 84 12 0.00
Fri 07/31 14Z 0.04 3505 86 76 12 0.00
Fri 07/31 15Z 0.12 3305 88 78 12 0.00
Fri 07/31 16Z 0.22 3106 88 80 12 0.00
Fri 07/31 17Z 0.18 3205 86 80 12 0.00
Fri 07/31 18Z 0.21 3205 83 78 13 0.00
Fri 07/31 19Z 0.33 3204 82 74 13 0.00
Fri 07/31 20Z 0.64 3104 81 72 13 0.00
Fri 07/31 21Z 0.44 3105 80 67 13 0.00
Fri 07/31 22Z 0.37 3107 80 65 13 0.00
Fri 07/31 23Z 0.26 3107 82 63 13 0.00
Sat 08/01 00Z 0.14 3205 80 62 14 0.00
Sat 08/01 01Z 0.12 3205 78 61 14 0.00
Sat 08/01 02Z 0.06 3303 75 58 14 0.00
Sat 08/01 03Z 0.10 3103 74 57 14 0.00
Sat 08/01 04Z 0.12 3003 75 55 14 0.00
Sat 08/01 05Z 0.12 3003 75 51 14 0.00
Sat 08/01 06Z 0.11 3003 74 47 14 0.00
Sat 08/01 07Z 0.12 3104 74 44 14 0.00
Sat 08/01 08Z 0.13 3004 75 44 13 0.00
Sat 08/01 09Z 0.17 3005 76 44 13 0.00
Sat 08/01 10Z 0.13 3104 75 44 13 0.00
Sat 08/01 11Z 0.14 3004 75 45 13 0.00
Sat 08/01 12Z 0.14 2903 74 47 13 0.00
Sat 08/01 13Z 0.14 2703 75 44 13 0.00
Sat 08/01 14Z 0.15 2402 77 39 13 0.00
Sat 08/01 15Z 0.31 2303 79 37 13 0.00
Sat 08/01 16Z 0.55 2203 80 33 13 0.00
Sat 08/01 17Z 0.96 2204 80 32 14 0.00
Sat 08/01 18Z 1.17 2204 79 30 14 0.00
Sat 08/01 19Z 0.82 2104 78 28 14 0.00
Sat 08/01 20Z 0.56 2005 76 26 14 0.00
Sat 08/01 21Z 0.36 2005 74 27 15 0.00
Sat 08/01 22Z 0.20 2007 71 26 15 0.00
Sat 08/01 23Z 0.21 2008 70 25 15 0.00
Sun 08/02 00Z 0.20 1909 70 26 15 0.00
Sun 08/02 01Z 0.32 2012 74 29 15 0.00
Sun 08/02 02Z 0.49 2115 78 28 14 0.00
Sun 08/02 03Z 0.50 2117 81 29 14 0.00
Sun 08/02 04Z 0.51 2120 85 41 14 0.00
Sun 08/02 05Z 0.60 2222 91 46 14 0.00
Sun 08/02 06Z 0.56 2221 91 45 14 0.00
Sun 08/02 07Z 0.63 2322 92 47 14 0.00
Sun 08/02 08Z 0.60 2321 90 48 14 0.00
Sun 08/02 09Z 0.49 2318 87 50 15 0.01
Sun 08/02 10Z 0.49 2319 90 56 14 0.01
Sun 08/02 11Z 0.54 2320 90 65 14 0.01
Sun 08/02 12Z 0.55 2320 92 65 14 0.01
Sun 08/02 13Z 0.53 2219 95 66 14 0.01
Sun 08/02 14Z 0.52 2217 93 52 13 0.00
Sun 08/02 15Z 0.54 2216 93 55 14 0.00
Sun 08/02 16Z 0.48 2115 93 55 14 0.00
Sun 08/02 17Z 0.59 2016 91 56 14 0.00
Sun 08/02 18Z 0.95 2018 89 47 14 0.02
Sun 08/02 19Z 0.58 1918 86 36 15 0.00
Sun 08/02 20Z 0.63 1919 87 59 15 0.00
Sun 08/02 21Z 0.80 1921 87 75 15 0.00
Sun 08/02 22Z 0.76 2024 83 89 14 0.08
Sun 08/02 23Z 0.60 2025 74 95 15 0.02
Run total areal avg QPF for the greens is: 0.17 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