Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260801_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)
=== ===== === ==== ==== === === === ====
Sat 08/01 12Z 0.15 2304 85 69 14 0.00
Sat 08/01 13Z 0.14 2105 86 61 14 0.00
Sat 08/01 14Z 0.22 2206 87 50 14 0.00
Sat 08/01 15Z 0.45 2105 86 36 14 0.00
Sat 08/01 16Z 1.07 2106 82 29 14 0.00
Sat 08/01 17Z 1.55 2206 77 31 15 0.00
Sat 08/01 18Z 1.94 2306 75 24 15 0.00
Sat 08/01 19Z 1.66 2205 72 18 15 0.00
Sat 08/01 20Z 1.49 2105 70 16 16 0.00
Sat 08/01 21Z 0.79 2105 69 16 16 0.00
Sat 08/01 22Z 0.36 2006 68 17 16 0.00
Sat 08/01 23Z 0.21 2007 67 19 16 0.00
Sun 08/02 00Z 0.23 2009 67 23 16 0.00
Sun 08/02 01Z 0.37 2011 71 33 16 0.00
Sun 08/02 02Z 0.46 2015 73 39 15 0.00
Sun 08/02 03Z 0.49 2118 75 47 15 0.00
Sun 08/02 04Z 0.55 2119 78 48 15 0.00
Sun 08/02 05Z 0.55 2120 82 37 15 0.00
Sun 08/02 06Z 0.54 2121 82 48 15 0.00
Sun 08/02 07Z 0.58 2221 79 51 15 0.00
Sun 08/02 08Z 0.60 2222 79 37 15 0.00
Sun 08/02 09Z 0.61 2222 78 40 15 0.00
Sun 08/02 10Z 0.65 2222 82 43 15 0.00
Sun 08/02 11Z 0.61 2221 83 40 14 0.00
Sun 08/02 12Z 0.52 2219 85 42 14 0.00
Sun 08/02 13Z 0.50 2219 88 40 14 0.00
Sun 08/02 14Z 0.45 2118 87 39 14 0.00
Sun 08/02 15Z 0.45 2016 89 30 14 0.00
Sun 08/02 16Z 0.39 1916 90 34 14 0.00
Sun 08/02 17Z 0.42 1918 90 30 14 0.01
Sun 08/02 18Z 0.63 1920 87 34 14 0.01
Sun 08/02 19Z 0.65 1922 85 27 15 0.01
Sun 08/02 20Z 0.36 1923 83 27 15 0.01
Sun 08/02 21Z 0.21 1823 87 37 15 0.00
Sun 08/02 22Z 0.24 1925 88 54 15 0.01
Sun 08/02 23Z 0.24 1925 80 52 15 0.01
Mon 08/03 00Z 0.20 1926 74 49 16 0.00
Mon 08/03 01Z 0.21 1926 69 39 16 0.00
Mon 08/03 02Z 0.24 1926 68 36 16 0.00
Mon 08/03 03Z 0.26 1926 73 37 16 0.00
Mon 08/03 04Z 0.27 1926 85 60 16 0.00
Mon 08/03 05Z 0.25 1926 93 76 16 0.01
Mon 08/03 06Z 0.23 1926 96 73 16 0.02
Mon 08/03 07Z 0.25 1928 96 76 16 0.02
Mon 08/03 08Z 0.33 2029 93 86 16 0.03
Mon 08/03 09Z 0.31 2029 88 92 16 0.02
Mon 08/03 10Z 0.31 2029 83 85 16 0.01
Mon 08/03 11Z 0.34 2030 89 90 16 0.01
Mon 08/03 12Z 0.45 2028 98 98 16 0.05
Mon 08/03 13Z 0.46 2124 95 89 16 0.34
Mon 08/03 14Z 0.53 2220 92 79 15 0.24
Mon 08/03 15Z 0.64 2320 96 84 15 0.02
Mon 08/03 16Z 0.72 2420 98 81 15 0.02
Mon 08/03 17Z 0.81 2618 98 80 14 0.02
Mon 08/03 18Z 0.72 2719 97 69 14 0.09
Mon 08/03 19Z 0.63 2818 95 48 14 0.05
Mon 08/03 20Z 0.52 3018 94 31 14 0.02
Mon 08/03 21Z 0.43 3118 91 21 14 0.01
Mon 08/03 22Z 0.31 3218 84 14 13 0.00
Mon 08/03 23Z 0.28 3318 81 8 13 0.00
Run total areal avg QPF for the greens is: 1.04 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