Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260506_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)
=== ===== === ==== ==== === === === ====
Wed 05/06 12Z 0.13 2012 95 96 6 0.00
Wed 05/06 13Z 0.24 2016 97 96 6 0.05
Wed 05/06 14Z 0.25 2017 98 96 6 0.07
Wed 05/06 15Z 0.25 2017 98 98 7 0.08
Wed 05/06 16Z 0.21 2016 99 99 7 0.12
Wed 05/06 17Z 0.22 2015 99 99 6 0.16
Wed 05/06 18Z 0.13 2011 99 99 7 0.16
Wed 05/06 19Z 0.11 1911 98 99 8 0.18
Wed 05/06 20Z 0.24 2412 99 99 7 0.16
Wed 05/06 21Z 0.28 2713 98 97 6 0.07
Wed 05/06 22Z 0.25 3014 97 97 5 0.03
Wed 05/06 23Z 0.22 3113 95 96 4 0.01
Thu 05/07 00Z 0.24 3113 92 97 3 0.00
Thu 05/07 01Z 0.26 3013 88 93 3 0.00
Thu 05/07 02Z 0.29 3014 82 84 2 0.00
Thu 05/07 03Z 0.29 3014 81 77 2 0.00
Thu 05/07 04Z 0.29 3013 81 49 2 0.00
Thu 05/07 05Z 0.32 3013 82 54 1 0.00
Thu 05/07 06Z 0.40 3014 86 44 0 0.00
Thu 05/07 07Z 0.41 3014 86 47 0 0.00
Thu 05/07 08Z 0.49 2916 89 52 0 0.00
Thu 05/07 09Z 0.47 2915 90 46 0 0.00
Thu 05/07 10Z 0.50 2815 92 42 0 0.00
Thu 05/07 11Z 0.52 2815 93 47 -1 0.00
Thu 05/07 12Z 0.57 2816 89 36 -1 0.01
Thu 05/07 13Z 0.46 2812 75 28 -1 0.00
Thu 05/07 14Z 0.65 2711 74 21 -2 0.00
Thu 05/07 15Z 2.35 2711 76 21 -2 0.00
Thu 05/07 16Z 6.64 2812 78 23 -2 0.00
Thu 05/07 17Z 7.77 2812 76 25 -1 0.00
Thu 05/07 18Z 7.93 2812 74 26 -1 0.00
Thu 05/07 19Z 8.64 2813 72 26 0 0.00
Thu 05/07 20Z 8.53 2813 69 27 0 0.00
Thu 05/07 21Z 9.10 2814 66 30 0 0.00
Thu 05/07 22Z 7.78 2914 63 30 0 0.00
Thu 05/07 23Z 5.49 2916 63 34 0 0.00
Fri 05/08 00Z 2.64 2918 64 32 -1 0.00
Fri 05/08 01Z 1.96 3020 71 24 -1 0.00
Fri 05/08 02Z 1.70 3021 72 26 -2 0.00
Fri 05/08 03Z 1.50 3021 75 29 -2 0.00
Fri 05/08 04Z 1.19 2921 76 31 -2 0.00
Fri 05/08 05Z 0.98 3021 77 40 -2 0.00
Fri 05/08 06Z 0.88 3020 73 49 -2 0.00
Fri 05/08 07Z 0.74 3018 73 60 -2 0.00
Fri 05/08 08Z 0.72 3018 74 60 -3 0.00
Fri 05/08 09Z 0.71 3018 74 58 -3 0.00
Fri 05/08 10Z 0.69 2917 76 52 -3 0.00
Fri 05/08 11Z 0.66 2916 77 52 -3 0.00
Fri 05/08 12Z 0.68 2916 79 54 -3 0.00
Fri 05/08 13Z 1.86 2915 80 54 -3 0.00
Fri 05/08 14Z 6.24 2913 80 58 -3 0.00
Fri 05/08 15Z 8.30 2812 76 65 -3 0.00
Fri 05/08 16Z 8.00 2713 77 73 -2 0.00
Fri 05/08 17Z 8.72 2713 73 73 -2 0.00
Fri 05/08 18Z 7.38 2714 74 68 -2 0.00
Fri 05/08 19Z 9.37 2814 70 63 -2 0.00
Fri 05/08 20Z 7.98 2814 71 51 -2 0.00
Fri 05/08 21Z 7.98 2813 67 39 -1 0.00
Fri 05/08 22Z 7.51 2813 67 38 -1 0.00
Fri 05/08 23Z 4.55 2713 66 36 -1 0.00
Run total areal avg QPF for the greens is: 1.10 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