Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260807_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)
=== ===== === ==== ==== === === === ====
Fri 08/07 18Z 0.44 3004 88 41 16 0.00
Fri 08/07 19Z 0.26 3104 87 44 16 0.04
Fri 08/07 20Z 0.12 3303 86 44 16 0.03
Fri 08/07 21Z 0.09 0102 86 46 17 0.01
Fri 08/07 22Z 0.09 0600 87 47 17 0.02
Fri 08/07 23Z 0.08 2200 86 51 17 0.03
Sat 08/08 00Z 0.08 2301 86 50 17 0.03
Sat 08/08 01Z 0.03 1702 85 50 17 0.01
Sat 08/08 02Z 0.05 1704 85 51 17 0.00
Sat 08/08 03Z 0.04 1806 85 54 16 0.00
Sat 08/08 04Z 0.07 1805 86 60 16 0.00
Sat 08/08 05Z 0.10 2004 89 69 16 0.00
Sat 08/08 06Z 0.11 2203 91 76 16 0.00
Sat 08/08 07Z 0.08 2203 92 82 16 0.03
Sat 08/08 08Z 0.09 2302 92 84 16 0.07
Sat 08/08 09Z 0.09 2202 92 83 16 0.03
Sat 08/08 10Z 0.11 2303 91 80 16 0.02
Sat 08/08 11Z 0.11 2403 91 79 16 0.01
Sat 08/08 12Z 0.09 2203 90 80 16 0.02
Sat 08/08 13Z 0.10 2304 91 82 16 0.01
Sat 08/08 14Z 0.14 2404 91 81 16 0.01
Sat 08/08 15Z 0.10 2303 89 74 16 0.00
Sat 08/08 16Z 0.16 2305 89 72 16 0.00
Sat 08/08 17Z 0.26 2407 88 72 16 0.01
Sat 08/08 18Z 0.39 2509 87 70 16 0.01
Sat 08/08 19Z 0.48 2510 87 64 16 0.00
Sat 08/08 20Z 0.57 2612 88 65 16 0.01
Sat 08/08 21Z 0.56 2613 91 61 16 0.02
Sat 08/08 22Z 0.49 2612 91 61 16 0.06
Sat 08/08 23Z 0.50 2713 89 47 16 0.08
Sun 08/09 00Z 0.52 2714 91 41 16 0.01
Sun 08/09 01Z 0.46 2712 92 41 16 0.01
Sun 08/09 02Z 0.38 2812 90 43 16 0.04
Sun 08/09 03Z 0.36 2811 87 43 16 0.01
Sun 08/09 04Z 0.34 2812 80 36 17 0.01
Sun 08/09 05Z 0.32 2812 73 31 17 0.00
Sun 08/09 06Z 0.31 2811 67 36 17 0.00
Sun 08/09 07Z 0.34 2711 69 44 17 0.00
Sun 08/09 08Z 0.35 2711 75 45 16 0.00
Sun 08/09 09Z 0.37 2612 84 45 16 0.00
Sun 08/09 10Z 0.37 2512 89 42 16 0.00
Sun 08/09 11Z 0.37 2513 92 36 16 0.00
Sun 08/09 12Z 0.37 2513 90 36 16 0.01
Sun 08/09 13Z 0.39 2513 89 34 16 0.00
Sun 08/09 14Z 0.41 2513 91 49 16 0.00
Sun 08/09 15Z 0.46 2513 93 62 15 0.00
Sun 08/09 16Z 0.52 2513 93 67 15 0.00
Sun 08/09 17Z 0.60 2512 94 67 15 0.00
Sun 08/09 18Z 0.58 2511 96 64 15 0.01
Sun 08/09 19Z 0.56 2613 94 64 16 0.21
Sun 08/09 20Z 0.53 2613 93 39 16 0.12
Sun 08/09 21Z 0.57 2715 90 20 16 0.08
Sun 08/09 22Z 0.55 2816 88 23 16 0.03
Sun 08/09 23Z 0.53 2917 81 25 16 0.02
Mon 08/10 00Z 0.47 3017 79 32 15 0.01
Mon 08/10 01Z 0.38 3017 72 35 15 0.01
Mon 08/10 02Z 0.34 3016 76 33 15 0.01
Mon 08/10 03Z 0.33 3116 75 26 15 0.01
Mon 08/10 04Z 0.31 3117 73 29 15 0.01
Mon 08/10 05Z 0.27 3217 69 38 15 0.01
Run total areal avg QPF for the greens is: 1.18 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