Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260818_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)
=== ===== === ==== ==== === === === ====
Tue 08/18 00Z 0.06 3405 93 94 14 0.00
Tue 08/18 01Z 0.05 3506 90 95 14 0.06
Tue 08/18 02Z 0.06 0008 88 93 14 0.01
Tue 08/18 03Z 0.10 0009 87 81 14 0.00
Tue 08/18 04Z 0.11 0108 87 44 14 0.00
Tue 08/18 05Z 0.09 0107 85 20 14 0.00
Tue 08/18 06Z 0.10 0206 84 15 14 0.00
Tue 08/18 07Z 0.10 0305 83 17 14 0.00
Tue 08/18 08Z 0.07 0303 83 24 14 0.00
Tue 08/18 09Z 0.04 0103 83 35 14 0.00
Tue 08/18 10Z 0.03 0002 82 51 14 0.00
Tue 08/18 11Z 0.03 3503 80 52 13 0.00
Tue 08/18 12Z 0.03 3403 79 46 13 0.00
Tue 08/18 13Z 0.04 3202 79 39 13 0.00
Tue 08/18 14Z 0.04 3203 80 27 13 0.00
Tue 08/18 15Z 0.05 3203 82 22 13 0.00
Tue 08/18 16Z 0.03 3403 83 14 13 0.00
Tue 08/18 17Z 0.06 3202 85 12 13 0.00
Tue 08/18 18Z 0.07 3401 86 8 13 0.01
Tue 08/18 19Z 0.11 3202 85 5 13 0.01
Tue 08/18 20Z 0.30 3004 82 5 13 0.00
Tue 08/18 21Z 0.32 3004 80 7 13 0.00
Tue 08/18 22Z 0.18 3105 78 12 13 0.00
Tue 08/18 23Z 0.10 3103 77 11 13 0.00
Wed 08/19 00Z 0.11 2903 77 10 13 0.00
Wed 08/19 01Z 0.18 2804 77 16 13 0.00
Wed 08/19 02Z 0.21 2905 78 18 13 0.00
Wed 08/19 03Z 0.17 2904 80 13 13 0.00
Wed 08/19 04Z 0.17 2803 82 7 12 0.00
Wed 08/19 05Z 0.24 2805 85 6 12 0.00
Wed 08/19 06Z 0.20 2805 88 9 12 0.00
Wed 08/19 07Z 0.16 2904 90 12 12 0.00
Wed 08/19 08Z 0.16 2804 93 8 12 0.00
Wed 08/19 09Z 0.09 2902 93 10 11 0.00
Wed 08/19 10Z 0.14 2503 92 14 11 0.00
Wed 08/19 11Z 0.22 2505 92 15 11 0.00
Wed 08/19 12Z 0.19 2404 91 17 11 0.00
Wed 08/19 13Z 0.28 2505 92 19 11 0.00
Wed 08/19 14Z 0.30 2405 93 21 11 0.00
Wed 08/19 15Z 0.35 2405 91 22 11 0.00
Wed 08/19 16Z 0.51 2406 88 29 11 0.00
Wed 08/19 17Z 0.63 2406 82 44 12 0.00
Wed 08/19 18Z 0.48 2405 74 67 13 0.00
Wed 08/19 19Z 0.61 2407 70 79 13 0.00
Wed 08/19 20Z 0.39 2407 69 77 13 0.00
Wed 08/19 21Z 0.42 2408 69 87 13 0.00
Wed 08/19 22Z 0.47 2509 73 90 13 0.00
Wed 08/19 23Z 0.54 2410 83 89 13 0.00
Thu 08/20 00Z 0.64 2413 87 79 13 0.00
Thu 08/20 01Z 0.71 2415 90 73 13 0.00
Thu 08/20 02Z 0.76 2516 91 72 13 0.00
Thu 08/20 03Z 0.57 2615 88 64 13 0.00
Thu 08/20 04Z 0.54 2615 90 68 13 0.00
Thu 08/20 05Z 0.46 2714 90 70 13 0.00
Thu 08/20 06Z 0.36 2711 91 59 12 0.00
Thu 08/20 07Z 0.31 2810 92 64 12 0.00
Thu 08/20 08Z 0.29 2910 94 56 11 0.00
Thu 08/20 09Z 0.29 2910 95 58 11 0.00
Thu 08/20 10Z 0.22 3008 94 44 11 0.00
Thu 08/20 11Z 0.20 3009 92 32 11 0.00
Run total areal avg QPF for the Central_Greens is: 0.09 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