Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260508_0000
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)
=== ===== === ==== ==== === === === ====
Fri 05/08 00Z 0.67 2913 64 45 0 0.00
Fri 05/08 01Z 0.86 2915 62 49 -1 0.00
Fri 05/08 02Z 1.07 2916 59 47 -1 0.00
Fri 05/08 03Z 1.70 2917 61 48 -1 0.00
Fri 05/08 04Z 1.41 2918 68 58 -2 0.00
Fri 05/08 05Z 0.97 2818 72 65 -2 0.00
Fri 05/08 06Z 0.89 2919 73 60 -2 0.00
Fri 05/08 07Z 0.87 2920 72 54 -2 0.00
Fri 05/08 08Z 0.87 2920 73 56 -3 0.00
Fri 05/08 09Z 0.88 2920 72 56 -3 0.00
Fri 05/08 10Z 0.85 2919 70 55 -3 0.00
Fri 05/08 11Z 0.89 2917 69 57 -3 0.00
Fri 05/08 12Z 1.22 2916 69 59 -3 0.00
Fri 05/08 13Z 5.64 2813 68 64 -3 0.00
Fri 05/08 14Z 7.94 2811 66 63 -3 0.00
Fri 05/08 15Z 7.57 2710 65 62 -2 0.00
Fri 05/08 16Z 7.32 2610 65 62 -2 0.00
Fri 05/08 17Z 7.35 2610 64 71 -1 0.00
Fri 05/08 18Z 6.84 2610 68 82 -1 0.00
Fri 05/08 19Z 6.36 2612 72 88 -1 0.00
Fri 05/08 20Z 5.25 2612 75 84 -1 0.00
Fri 05/08 21Z 5.26 2712 72 76 -1 0.00
Fri 05/08 22Z 4.06 2711 71 69 -1 0.00
Fri 05/08 23Z 2.38 2811 70 60 -1 0.00
Sat 05/09 00Z 1.03 2812 71 47 -1 0.00
Sat 05/09 01Z 1.21 2813 72 43 -1 0.00
Sat 05/09 02Z 1.38 2814 71 39 -2 0.00
Sat 05/09 03Z 1.46 2815 69 32 -2 0.00
Sat 05/09 04Z 1.08 2815 68 31 -2 0.00
Sat 05/09 05Z 0.79 2814 67 34 -2 0.00
Sat 05/09 06Z 0.67 2813 66 32 -2 0.00
Sat 05/09 07Z 0.62 2812 65 25 -2 0.00
Sat 05/09 08Z 0.57 2710 62 16 -2 0.00
Sat 05/09 09Z 0.56 2609 62 12 -2 0.00
Sat 05/09 10Z 0.45 2508 62 8 -1 0.00
Sat 05/09 11Z 0.34 2307 62 7 -1 0.00
Sat 05/09 12Z 0.35 2108 59 9 -1 0.00
Sat 05/09 13Z 0.43 1910 58 12 -1 0.00
Sat 05/09 14Z 0.38 1812 56 25 -1 0.00
Sat 05/09 15Z 0.88 1713 57 40 0 0.00
Sat 05/09 16Z 0.81 1714 67 53 0 0.00
Sat 05/09 17Z 0.77 1716 78 71 0 0.02
Sat 05/09 18Z 0.55 1719 84 80 0 0.03
Sat 05/09 19Z 0.17 1721 89 84 0 0.02
Sat 05/09 20Z 0.04 1722 94 91 0 0.02
Sat 05/09 21Z 0.05 1822 96 88 1 0.01
Sat 05/09 22Z 0.06 1822 96 75 2 0.01
Sat 05/09 23Z 0.14 1923 97 68 2 0.01
Sun 05/10 00Z 0.20 2024 97 37 3 0.02
Sun 05/10 01Z 0.26 2023 98 40 3 0.02
Sun 05/10 02Z 0.31 2123 97 61 3 0.01
Sun 05/10 03Z 0.38 2124 95 76 4 0.01
Sun 05/10 04Z 0.44 2125 93 72 5 0.01
Sun 05/10 05Z 0.46 2127 88 76 5 0.01
Sun 05/10 06Z 0.68 2232 93 90 5 0.01
Sun 05/10 07Z 0.80 2330 91 90 4 0.04
Sun 05/10 08Z 0.89 2427 93 79 3 0.03
Sun 05/10 09Z 0.86 2526 88 68 3 0.02
Sun 05/10 10Z 0.80 2525 74 63 3 0.01
Sun 05/10 11Z 0.72 2623 62 38 3 0.01
Run total areal avg QPF for the greens is: 0.32 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