Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260919_0600
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 09/19 06Z 0.07 0014 75 7 4 0.00
Sat 09/19 07Z 0.05 0014 71 6 4 0.00
Sat 09/19 08Z 0.04 0013 65 6 4 0.00
Sat 09/19 09Z 0.03 0011 59 6 5 0.00
Sat 09/19 10Z 0.03 3510 54 6 6 0.00
Sat 09/19 11Z 0.02 3510 51 6 6 0.00
Sat 09/19 12Z 0.02 0009 47 6 6 0.00
Sat 09/19 13Z 0.02 0008 45 6 6 0.00
Sat 09/19 14Z 0.02 0006 46 6 6 0.00
Sat 09/19 15Z 0.02 0004 50 6 6 0.00
Sat 09/19 16Z 0.02 0002 56 5 5 0.00
Sat 09/19 17Z 0.02 0001 62 5 5 0.00
Sat 09/19 18Z 0.03 3000 67 5 5 0.00
Sat 09/19 19Z 0.05 1901 70 5 5 0.00
Sat 09/19 20Z 0.10 2401 71 5 5 0.00
Sat 09/19 21Z 0.06 2301 68 5 6 0.00
Sat 09/19 22Z 0.04 2002 65 5 6 0.00
Sat 09/19 23Z 0.03 1805 63 5 6 0.00
Sun 09/20 00Z 0.06 1907 60 5 6 0.00
Sun 09/20 01Z 0.08 1908 58 5 6 0.00
Sun 09/20 02Z 0.04 1810 57 6 7 0.00
Sun 09/20 03Z 0.11 1912 62 6 6 0.00
Sun 09/20 04Z 0.20 2015 68 7 6 0.00
Sun 09/20 05Z 0.24 2017 76 9 6 0.00
Sun 09/20 06Z 0.29 2018 82 9 6 0.00
Sun 09/20 07Z 0.27 2118 86 8 6 0.00
Sun 09/20 08Z 0.28 2118 88 11 6 0.00
Sun 09/20 09Z 0.26 2018 91 16 6 0.00
Sun 09/20 10Z 0.24 2018 94 28 6 0.01
Sun 09/20 11Z 0.19 2017 95 43 6 0.01
Sun 09/20 12Z 0.15 1918 96 67 6 0.01
Sun 09/20 13Z 0.14 1919 96 85 7 0.02
Sun 09/20 14Z 0.14 1920 97 98 7 0.03
Sun 09/20 15Z 0.11 1921 97 99 7 0.05
Sun 09/20 16Z 0.09 1922 98 99 8 0.09
Sun 09/20 17Z 0.12 1923 98 99 8 0.14
Sun 09/20 18Z 0.13 1923 98 99 8 0.14
Sun 09/20 19Z 0.15 1923 98 98 8 0.14
Sun 09/20 20Z 0.15 1921 98 99 8 0.15
Sun 09/20 21Z 0.13 1919 98 96 8 0.11
Sun 09/20 22Z 0.11 1915 99 92 8 0.10
Sun 09/20 23Z 0.08 1911 98 74 8 0.07
Mon 09/21 00Z 0.08 2007 99 64 7 0.04
Mon 09/21 01Z 0.07 2402 99 60 7 0.03
Mon 09/21 02Z 0.04 3303 99 58 6 0.01
Mon 09/21 03Z 0.03 0006 98 41 6 0.01
Mon 09/21 04Z 0.05 0108 96 40 6 0.00
Mon 09/21 05Z 0.04 0009 93 23 6 0.00
Mon 09/21 06Z 0.04 0011 91 10 6 0.00
Mon 09/21 07Z 0.04 0014 87 2 5 0.00
Mon 09/21 08Z 0.03 0017 82 2 5 0.00
Mon 09/21 09Z 0.04 0018 83 2 5 0.01
Mon 09/21 10Z 0.05 0019 82 3 4 0.01
Mon 09/21 11Z 0.06 0019 83 3 4 0.01
Mon 09/21 12Z 0.07 0019 82 3 3 0.00
Mon 09/21 13Z 0.07 0018 82 2 3 0.00
Mon 09/21 14Z 0.06 3517 77 2 3 0.00
Mon 09/21 15Z 0.04 0018 71 1 4 0.00
Mon 09/21 16Z 0.04 0017 65 1 4 0.00
Mon 09/21 17Z 0.05 0016 60 1 4 0.00
Run total areal avg QPF for the greens is: 1.19 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