Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260507_1800
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)
=== ===== === ==== ==== === === === ====
Thu 05/07 18Z 8.89 2712 68 49 0 0.00
Thu 05/07 19Z 9.95 2714 66 36 0 0.00
Thu 05/07 20Z 10.60 2715 65 38 0 0.00
Thu 05/07 21Z 10.03 2716 64 38 0 0.00
Thu 05/07 22Z 9.97 2816 63 33 0 0.00
Thu 05/07 23Z 6.10 2816 62 35 0 0.00
Fri 05/08 00Z 2.47 2918 62 36 -1 0.00
Fri 05/08 01Z 1.52 2919 65 43 -1 0.00
Fri 05/08 02Z 1.20 2918 69 44 -1 0.00
Fri 05/08 03Z 1.02 3017 71 48 -2 0.00
Fri 05/08 04Z 1.05 2917 74 56 -2 0.00
Fri 05/08 05Z 0.92 2917 76 53 -2 0.00
Fri 05/08 06Z 0.85 3017 77 60 -2 0.00
Fri 05/08 07Z 0.78 3016 76 50 -2 0.00
Fri 05/08 08Z 0.86 3015 75 42 -3 0.00
Fri 05/08 09Z 0.72 2915 72 39 -2 0.00
Fri 05/08 10Z 0.69 2915 71 40 -3 0.00
Fri 05/08 11Z 0.66 2914 69 43 -3 0.00
Fri 05/08 12Z 0.96 2813 69 38 -3 0.00
Fri 05/08 13Z 5.66 2812 68 36 -3 0.00
Fri 05/08 14Z 8.25 2811 66 42 -3 0.00
Fri 05/08 15Z 8.18 2711 66 54 -2 0.00
Fri 05/08 16Z 7.61 2711 66 65 -2 0.00
Fri 05/08 17Z 7.50 2710 65 74 -1 0.00
Fri 05/08 18Z 7.18 2711 65 76 -1 0.00
Fri 05/08 19Z 6.59 2711 68 78 -1 0.00
Fri 05/08 20Z 6.62 2711 67 76 -1 0.00
Fri 05/08 21Z 6.13 2711 70 72 -1 0.00
Fri 05/08 22Z 3.96 2710 70 63 0 0.00
Fri 05/08 23Z 1.67 2710 70 56 0 0.00
Sat 05/09 00Z 0.97 2712 69 47 0 0.00
Sat 05/09 01Z 1.43 2714 70 44 -1 0.00
Sat 05/09 02Z 1.20 2714 70 35 -1 0.00
Sat 05/09 03Z 1.15 2814 69 28 -1 0.00
Sat 05/09 04Z 1.03 2714 69 37 -1 0.00
Sat 05/09 05Z 0.83 2713 67 41 -1 0.00
Sat 05/09 06Z 0.67 2612 68 42 -1 0.00
Sat 05/09 07Z 0.59 2512 65 55 -1 0.00
Sat 05/09 08Z 0.53 2512 59 44 -1 0.00
Sat 05/09 09Z 0.45 2510 57 26 -1 0.00
Sat 05/09 10Z 0.38 2409 54 15 -1 0.00
Sat 05/09 11Z 0.30 2208 50 8 0 0.00
Sat 05/09 12Z 0.25 2109 48 7 0 0.00
Sat 05/09 13Z 0.30 1910 51 6 0 0.00
Sat 05/09 14Z 0.55 1811 59 12 0 0.00
Sat 05/09 15Z 0.64 1812 67 27 0 0.00
Sat 05/09 16Z 0.41 1813 74 45 0 0.01
Sat 05/09 17Z 0.24 1713 78 61 0 0.02
Sat 05/09 18Z 0.42 1614 82 70 0 0.02
Sat 05/09 19Z 0.65 1617 88 76 0 0.04
Sat 05/09 20Z 0.42 1519 92 83 0 0.02
Sat 05/09 21Z 0.17 1619 94 78 1 0.01
Sat 05/09 22Z 0.12 1619 95 77 2 0.01
Sat 05/09 23Z 0.08 1719 96 78 2 0.01
Sun 05/10 00Z 0.08 1819 96 82 3 0.01
Sun 05/10 01Z 0.15 1920 96 68 3 0.01
Sun 05/10 02Z 0.26 2022 97 46 3 0.01
Sun 05/10 03Z 0.32 2021 98 41 3 0.01
Sun 05/10 04Z 0.41 2122 97 43 3 0.01
Sun 05/10 05Z 0.44 2123 94 49 3 0.01
Run total areal avg QPF for the greens is: 0.20 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