Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260509_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 05/09 06Z 0.60 2512 60 49 0 0.00
Sat 05/09 07Z 0.76 2512 58 44 0 0.00
Sat 05/09 08Z 0.62 2511 55 42 0 0.00
Sat 05/09 09Z 0.49 2509 50 38 0 0.00
Sat 05/09 10Z 0.45 2309 50 41 0 0.00
Sat 05/09 11Z 0.34 2110 52 42 0 0.00
Sat 05/09 12Z 0.27 1912 57 41 0 0.00
Sat 05/09 13Z 0.24 1812 64 41 0 0.00
Sat 05/09 14Z 0.53 1712 68 49 0 0.00
Sat 05/09 15Z 1.08 1613 73 60 1 0.00
Sat 05/09 16Z 1.26 1615 78 67 1 0.00
Sat 05/09 17Z 1.02 1617 84 72 1 0.01
Sat 05/09 18Z 0.87 1619 88 74 1 0.03
Sat 05/09 19Z 0.96 1620 91 74 1 0.03
Sat 05/09 20Z 0.22 1620 94 73 1 0.03
Sat 05/09 21Z 0.08 1719 96 73 2 0.01
Sat 05/09 22Z 0.08 1718 95 78 3 0.01
Sat 05/09 23Z 0.09 1818 95 76 3 0.01
Sun 05/10 00Z 0.10 1820 95 63 3 0.01
Sun 05/10 01Z 0.20 1922 97 53 3 0.01
Sun 05/10 02Z 0.27 2024 96 30 3 0.01
Sun 05/10 03Z 0.30 2025 95 20 4 0.01
Sun 05/10 04Z 0.41 2126 93 22 4 0.01
Sun 05/10 05Z 0.34 2026 86 21 5 0.01
Sun 05/10 06Z 0.35 2127 81 35 6 0.01
Sun 05/10 07Z 0.50 2130 84 66 6 0.01
Sun 05/10 08Z 0.58 2229 85 85 6 0.00
Sun 05/10 09Z 0.64 2328 91 93 5 0.01
Sun 05/10 10Z 0.74 2427 95 83 4 0.03
Sun 05/10 11Z 0.85 2524 94 67 3 0.03
Sun 05/10 12Z 0.88 2622 93 69 2 0.01
Sun 05/10 13Z 1.06 2621 86 60 1 0.02
Sun 05/10 14Z 2.44 2519 79 39 1 0.02
Sun 05/10 15Z 5.75 2518 78 11 1 0.00
Sun 05/10 16Z 7.68 2517 72 12 1 0.00
Sun 05/10 17Z 11.24 2517 59 16 1 0.00
Sun 05/10 18Z 11.78 2516 50 20 2 0.00
Sun 05/10 19Z 11.77 2616 45 21 2 0.00
Sun 05/10 20Z 11.63 2616 45 22 2 0.00
Sun 05/10 21Z 11.28 2616 48 23 2 0.00
Sun 05/10 22Z 9.33 2716 53 21 1 0.00
Sun 05/10 23Z 5.68 2718 57 22 1 0.00
Mon 05/11 00Z 2.13 2721 59 20 0 0.00
Mon 05/11 01Z 1.61 2821 58 21 0 0.00
Mon 05/11 02Z 1.55 2823 60 22 -1 0.00
Mon 05/11 03Z 1.24 2821 70 20 -2 0.00
Mon 05/11 04Z 1.02 2921 78 22 -2 0.00
Mon 05/11 05Z 0.93 2921 78 23 -3 0.00
Mon 05/11 06Z 0.84 2919 80 22 -3 0.00
Mon 05/11 07Z 0.72 3018 76 21 -3 0.00
Mon 05/11 08Z 0.67 3017 75 21 -3 0.00
Mon 05/11 09Z 0.62 2916 75 21 -3 0.00
Mon 05/11 10Z 0.62 2915 74 21 -3 0.00
Mon 05/11 11Z 0.65 2915 74 21 -4 0.00
Mon 05/11 12Z 0.75 2815 72 22 -4 0.00
Mon 05/11 13Z 2.27 2814 70 21 -4 0.00
Mon 05/11 14Z 5.84 2812 71 25 -4 0.00
Mon 05/11 15Z 6.84 2811 70 26 -3 0.00
Mon 05/11 16Z 6.96 2811 66 26 -3 0.00
Mon 05/11 17Z 6.44 2810 65 26 -2 0.00
Run total areal avg QPF for the greens is: 0.33 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