Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260512_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)
=== ===== === ==== ==== === === === ====
Tue 05/12 12Z 0.48 3210 81 49 -3 0.00
Tue 05/12 13Z 1.70 3111 80 38 -3 0.00
Tue 05/12 14Z 4.88 3112 79 35 -3 0.00
Tue 05/12 15Z 6.42 3012 74 35 -3 0.00
Tue 05/12 16Z 6.48 3011 72 38 -3 0.00
Tue 05/12 17Z 6.78 2912 76 37 -2 0.00
Tue 05/12 18Z 6.55 3011 76 34 -2 0.00
Tue 05/12 19Z 6.53 2911 74 31 -1 0.00
Tue 05/12 20Z 5.59 3010 71 28 -1 0.00
Tue 05/12 21Z 4.62 3009 69 26 0 0.00
Tue 05/12 22Z 3.07 3008 68 26 0 0.00
Tue 05/12 23Z 1.11 2908 67 27 0 0.00
Wed 05/13 00Z 0.68 2909 67 27 0 0.00
Wed 05/13 01Z 0.60 2808 68 26 0 0.00
Wed 05/13 02Z 0.52 2707 67 23 0 0.00
Wed 05/13 03Z 0.46 2607 67 19 0 0.00
Wed 05/13 04Z 0.45 2407 67 17 0 0.00
Wed 05/13 05Z 0.38 2208 66 15 0 0.00
Wed 05/13 06Z 0.33 2208 64 12 0 0.00
Wed 05/13 07Z 0.34 2110 62 19 0 0.00
Wed 05/13 08Z 0.35 2112 62 43 0 0.00
Wed 05/13 09Z 0.42 2113 66 85 0 0.00
Wed 05/13 10Z 0.27 2013 73 96 0 0.00
Wed 05/13 11Z 0.15 1914 77 98 1 0.00
Wed 05/13 12Z 0.11 1916 83 98 2 0.00
Wed 05/13 13Z 0.10 1819 89 97 2 0.02
Wed 05/13 14Z 0.13 1821 94 95 3 0.04
Wed 05/13 15Z 0.14 1823 93 97 3 0.06
Wed 05/13 16Z 0.08 1827 93 98 4 0.06
Wed 05/13 17Z 0.14 1830 94 98 4 0.05
Wed 05/13 18Z 0.22 1931 95 96 5 0.05
Wed 05/13 19Z 0.27 2029 94 96 5 0.04
Wed 05/13 20Z 0.23 1927 90 93 6 0.02
Wed 05/13 21Z 0.21 1927 92 96 6 0.02
Wed 05/13 22Z 0.20 1929 95 97 6 0.05
Wed 05/13 23Z 0.21 1930 94 94 6 0.04
Thu 05/14 00Z 0.25 1932 92 86 6 0.02
Thu 05/14 01Z 0.30 1933 91 77 6 0.00
Thu 05/14 02Z 0.34 2033 89 84 6 0.00
Thu 05/14 03Z 0.37 2033 89 81 6 0.01
Thu 05/14 04Z 0.37 2033 88 76 6 0.01
Thu 05/14 05Z 0.36 2031 85 77 6 0.00
Thu 05/14 06Z 0.32 2030 81 79 6 0.00
Thu 05/14 07Z 0.26 1928 85 86 5 0.01
Thu 05/14 08Z 0.16 1925 91 91 5 0.01
Thu 05/14 09Z 0.12 1923 93 97 5 0.05
Thu 05/14 10Z 0.06 1822 96 97 5 0.06
Thu 05/14 11Z 0.05 1821 97 94 5 0.06
Thu 05/14 12Z 0.08 1719 98 95 5 0.05
Thu 05/14 13Z 0.12 1619 98 94 5 0.04
Thu 05/14 14Z 0.23 1519 98 95 5 0.03
Thu 05/14 15Z 0.34 1520 98 93 5 0.03
Thu 05/14 16Z 0.37 1419 97 85 5 0.05
Thu 05/14 17Z 0.45 1316 97 79 5 0.04
Thu 05/14 18Z 0.60 1215 98 74 5 0.03
Thu 05/14 19Z 0.68 1015 97 80 5 0.04
Thu 05/14 20Z 0.77 0816 97 84 5 0.04
Thu 05/14 21Z 0.89 0817 94 87 5 0.06
Thu 05/14 22Z 0.81 0719 89 87 5 0.04
Thu 05/14 23Z 0.66 0619 90 88 5 0.04
Run total areal avg QPF for the greens is: 1.17 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