Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260808_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 08/08 06Z 0.17 2108 85 88 16 0.00
Sat 08/08 07Z 0.20 2208 86 88 16 0.05
Sat 08/08 08Z 0.20 2506 89 88 15 0.12
Sat 08/08 09Z 0.19 2605 91 87 15 0.04
Sat 08/08 10Z 0.13 2704 91 87 15 0.02
Sat 08/08 11Z 0.08 2802 93 92 15 0.00
Sat 08/08 12Z 0.08 2502 94 92 15 0.00
Sat 08/08 13Z 0.10 2403 96 90 15 0.00
Sat 08/08 14Z 0.15 2305 97 90 15 0.00
Sat 08/08 15Z 0.11 2105 95 85 15 0.00
Sat 08/08 16Z 0.10 2006 95 80 15 0.00
Sat 08/08 17Z 0.20 2109 95 77 15 0.00
Sat 08/08 18Z 0.30 2210 94 72 15 0.00
Sat 08/08 19Z 0.37 2211 91 68 16 0.01
Sat 08/08 20Z 0.45 2311 89 60 16 0.00
Sat 08/08 21Z 0.63 2412 91 55 16 0.00
Sat 08/08 22Z 0.55 2513 93 57 16 0.01
Sat 08/08 23Z 0.45 2412 90 55 16 0.06
Sun 08/09 00Z 0.42 2512 90 64 16 0.01
Sun 08/09 01Z 0.44 2513 91 70 16 0.01
Sun 08/09 02Z 0.52 2515 89 73 16 0.01
Sun 08/09 03Z 0.59 2617 90 64 16 0.02
Sun 08/09 04Z 0.63 2618 92 53 15 0.02
Sun 08/09 05Z 0.58 2718 90 48 16 0.01
Sun 08/09 06Z 0.59 2719 91 44 15 0.00
Sun 08/09 07Z 0.57 2819 90 47 15 0.00
Sun 08/09 08Z 0.55 2818 90 55 15 0.00
Sun 08/09 09Z 0.51 2817 91 42 15 0.01
Sun 08/09 10Z 0.45 2815 89 22 15 0.01
Sun 08/09 11Z 0.40 2814 85 17 15 0.01
Sun 08/09 12Z 0.40 2714 85 20 15 0.01
Sun 08/09 13Z 0.43 2715 85 25 15 0.01
Sun 08/09 14Z 0.49 2815 87 30 14 0.01
Sun 08/09 15Z 0.50 2814 85 16 14 0.01
Sun 08/09 16Z 0.63 2714 85 12 14 0.00
Sun 08/09 17Z 0.77 2714 84 15 14 0.00
Sun 08/09 18Z 1.13 2815 84 19 14 0.02
Sun 08/09 19Z 1.20 2915 81 18 14 0.01
Sun 08/09 20Z 0.91 2914 74 25 14 0.01
Sun 08/09 21Z 0.51 2911 68 32 14 0.00
Sun 08/09 22Z 0.50 2911 68 35 15 0.00
Sun 08/09 23Z 0.39 2910 67 34 15 0.00
Mon 08/10 00Z 0.37 2810 65 35 15 0.00
Mon 08/10 01Z 0.41 2811 66 33 15 0.00
Mon 08/10 02Z 0.38 2811 66 35 15 0.00
Mon 08/10 03Z 0.42 2913 72 42 14 0.00
Mon 08/10 04Z 0.34 2911 71 37 15 0.00
Mon 08/10 05Z 0.29 2911 65 28 15 0.00
Mon 08/10 06Z 0.24 2909 63 20 15 0.00
Mon 08/10 07Z 0.18 2806 59 25 15 0.00
Mon 08/10 08Z 0.15 2605 54 31 16 0.00
Mon 08/10 09Z 0.12 2305 50 30 16 0.00
Mon 08/10 10Z 0.15 2208 48 32 16 0.00
Mon 08/10 11Z 0.19 2209 46 33 16 0.00
Mon 08/10 12Z 0.22 2211 43 33 16 0.00
Mon 08/10 13Z 0.24 2211 40 38 16 0.00
Mon 08/10 14Z 0.28 2312 42 46 15 0.00
Mon 08/10 15Z 0.31 2312 47 64 15 0.00
Mon 08/10 16Z 0.38 2312 55 64 15 0.00
Mon 08/10 17Z 0.46 2212 65 63 15 0.00
Run total areal avg QPF for the greens is: 0.50 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