Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260808_0000
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sat 08/08 00Z 0.12 1703 80 75 17 0.00
Sat 08/08 01Z 0.20 2105 83 81 16 0.07
Sat 08/08 02Z 0.24 2207 82 81 16 0.02
Sat 08/08 03Z 0.22 2207 77 87 17 0.00
Sat 08/08 04Z 0.19 2207 75 84 17 0.00
Sat 08/08 05Z 0.18 2107 76 84 17 0.00
Sat 08/08 06Z 0.20 2108 74 79 16 0.00
Sat 08/08 07Z 0.25 2109 77 87 16 0.00
Sat 08/08 08Z 0.30 2209 83 93 16 0.00
Sat 08/08 09Z 0.26 2209 87 84 16 0.00
Sat 08/08 10Z 0.25 2308 90 78 16 0.00
Sat 08/08 11Z 0.27 2309 91 81 16 0.00
Sat 08/08 12Z 0.23 2308 89 84 16 0.00
Sat 08/08 13Z 0.24 2308 90 90 16 0.00
Sat 08/08 14Z 0.25 2308 89 92 16 0.00
Sat 08/08 15Z 0.24 2308 88 89 16 0.00
Sat 08/08 16Z 0.22 2207 88 78 16 0.00
Sat 08/08 17Z 0.28 2208 89 64 16 0.00
Sat 08/08 18Z 0.46 2309 92 64 15 0.00
Sat 08/08 19Z 0.53 2410 92 57 15 0.00
Sat 08/08 20Z 0.50 2410 91 48 16 0.00
Sat 08/08 21Z 0.59 2513 92 52 16 0.00
Sat 08/08 22Z 0.59 2516 91 50 16 0.06
Sat 08/08 23Z 0.44 2613 90 39 17 0.03
Sun 08/09 00Z 0.44 2613 88 45 16 0.01
Sun 08/09 01Z 0.45 2713 88 60 16 0.01
Sun 08/09 02Z 0.42 2713 87 64 16 0.01
Sun 08/09 03Z 0.43 2714 88 67 16 0.01
Sun 08/09 04Z 0.41 2814 87 55 16 0.01
Sun 08/09 05Z 0.41 2815 83 45 16 0.00
Sun 08/09 06Z 0.42 2815 81 52 16 0.00
Sun 08/09 07Z 0.42 2815 82 60 16 0.00
Sun 08/09 08Z 0.39 2814 85 65 16 0.00
Sun 08/09 09Z 0.40 2713 88 68 16 0.00
Sun 08/09 10Z 0.48 2616 92 71 15 0.00
Sun 08/09 11Z 0.55 2617 95 71 15 0.01
Sun 08/09 12Z 0.59 2518 96 34 15 0.02
Sun 08/09 13Z 0.55 2617 94 30 15 0.02
Sun 08/09 14Z 0.53 2717 92 33 15 0.01
Sun 08/09 15Z 0.55 2716 92 28 14 0.01
Sun 08/09 16Z 0.51 2814 88 18 15 0.01
Sun 08/09 17Z 0.49 2814 82 17 15 0.01
Sun 08/09 18Z 0.54 2814 80 10 15 0.01
Sun 08/09 19Z 0.81 2914 79 10 15 0.00
Sun 08/09 20Z 1.92 2913 78 12 14 0.00
Sun 08/09 21Z 1.29 2914 73 18 14 0.00
Sun 08/09 22Z 0.94 2914 68 23 14 0.00
Sun 08/09 23Z 0.67 2915 65 26 14 0.00
Mon 08/10 00Z 0.79 2917 64 31 14 0.00
Mon 08/10 01Z 0.56 3017 61 32 14 0.00
Mon 08/10 02Z 0.41 3016 58 32 15 0.00
Mon 08/10 03Z 0.29 3115 54 28 15 0.00
Mon 08/10 04Z 0.21 3114 51 32 16 0.00
Mon 08/10 05Z 0.19 3215 50 36 16 0.00
Mon 08/10 06Z 0.10 3313 50 35 15 0.00
Mon 08/10 07Z 0.07 3412 53 43 15 0.00
Mon 08/10 08Z 0.05 3411 57 41 14 0.00
Mon 08/10 09Z 0.07 3409 59 46 14 0.00
Mon 08/10 10Z 0.09 3308 62 45 14 0.00
Mon 08/10 11Z 0.11 3206 63 36 14 0.00
Run total areal avg QPF for the Central_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