Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260324_1800
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 03/24 18Z 2.99 2506 77 6 -9 0.00
Tue 03/24 19Z 2.99 2308 70 5 -8 0.00
Tue 03/24 20Z 2.33 2210 64 5 -7 0.00
Tue 03/24 21Z 1.66 2213 61 9 -7 0.00
Tue 03/24 22Z 1.24 2318 61 13 -7 0.00
Tue 03/24 23Z 1.21 2422 63 14 -7 0.00
Wed 03/25 00Z 1.56 2426 69 17 -7 0.00
Wed 03/25 01Z 2.54 2528 70 59 -7 0.00
Wed 03/25 02Z 3.21 2628 63 86 -8 0.00
Wed 03/25 03Z 2.04 2728 79 86 -8 0.00
Wed 03/25 04Z 1.30 2729 87 85 -8 0.00
Wed 03/25 05Z 1.03 2829 90 21 -8 0.00
Wed 03/25 06Z 0.97 2828 89 13 -8 0.00
Wed 03/25 07Z 0.97 2827 88 10 -8 0.00
Wed 03/25 08Z 0.87 2925 90 12 -9 0.00
Wed 03/25 09Z 0.76 2922 90 13 -9 0.01
Wed 03/25 10Z 0.66 3021 87 13 -8 0.00
Wed 03/25 11Z 0.58 2919 85 15 -9 0.00
Wed 03/25 12Z 0.56 2918 85 19 -9 0.00
Wed 03/25 13Z 0.60 2917 85 16 -9 0.00
Wed 03/25 14Z 0.49 2815 81 10 -8 0.00
Wed 03/25 15Z 0.47 2814 79 7 -8 0.00
Wed 03/25 16Z 0.47 2713 78 5 -8 0.00
Wed 03/25 17Z 0.44 2713 74 4 -7 0.00
Wed 03/25 18Z 0.43 2713 67 3 -6 0.00
Wed 03/25 19Z 0.37 2711 56 7 -5 0.00
Wed 03/25 20Z 0.37 2609 49 11 -5 0.00
Wed 03/25 21Z 0.37 2408 45 13 -4 0.00
Wed 03/25 22Z 0.32 2209 43 8 -4 0.00
Wed 03/25 23Z 0.30 2012 42 8 -4 0.00
Thu 03/26 00Z 0.37 2016 38 10 -3 0.00
Thu 03/26 01Z 0.49 2020 54 68 -3 0.00
Thu 03/26 02Z 0.67 2024 68 91 -3 0.00
Thu 03/26 03Z 0.97 2128 74 94 -3 0.00
Thu 03/26 04Z 0.94 2228 86 90 -3 0.00
Thu 03/26 05Z 0.77 2128 83 83 -1 0.00
Thu 03/26 06Z 0.78 2131 85 76 -1 0.00
Thu 03/26 07Z 0.74 2232 85 61 0 0.00
Thu 03/26 08Z 0.67 2232 82 75 0 0.00
Thu 03/26 09Z 0.64 2232 78 92 1 0.00
Thu 03/26 10Z 0.59 2330 77 89 1 0.00
Thu 03/26 11Z 0.59 2330 76 91 2 0.00
Thu 03/26 12Z 0.57 2329 77 92 2 0.00
Thu 03/26 13Z 0.61 2331 80 89 2 0.00
Thu 03/26 14Z 0.66 2332 83 91 3 0.00
Thu 03/26 15Z 0.72 2334 85 93 3 0.00
Thu 03/26 16Z 0.77 2236 83 90 4 0.00
Thu 03/26 17Z 0.81 2337 82 91 5 0.00
Thu 03/26 18Z 0.85 2237 83 95 5 0.01
Thu 03/26 19Z 0.98 2239 86 92 5 0.01
Thu 03/26 20Z 1.09 2238 85 87 6 0.00
Thu 03/26 21Z 1.18 2238 84 82 7 0.00
Thu 03/26 22Z 1.11 2240 85 87 7 0.00
Thu 03/26 23Z 0.99 2243 89 95 8 0.01
Fri 03/27 00Z 0.96 2244 94 93 8 0.05
Fri 03/27 01Z 1.07 2246 96 91 7 0.09
Fri 03/27 02Z 1.08 2344 97 91 8 0.14
Fri 03/27 03Z 1.02 2438 97 95 7 0.22
Fri 03/27 04Z 0.94 2629 98 96 6 0.23
Fri 03/27 05Z 0.93 2827 98 97 4 0.17
Run total areal avg QPF for the Central_Greens is: 0.94 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