Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260909_1200
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)
=== ===== === ==== ==== === === === ====
Wed 09/09 12Z 0.31 2016 81 62 11 0.00
Wed 09/09 13Z 0.36 2019 79 61 12 0.00
Wed 09/09 14Z 0.36 2019 79 55 12 0.00
Wed 09/09 15Z 0.39 2119 79 46 12 0.00
Wed 09/09 16Z 0.42 2118 82 31 12 0.00
Wed 09/09 17Z 0.40 2019 91 25 13 0.00
Wed 09/09 18Z 0.39 2020 94 41 13 0.01
Wed 09/09 19Z 0.38 2021 93 25 13 0.02
Wed 09/09 20Z 0.38 1922 92 56 13 0.01
Wed 09/09 21Z 0.60 2026 96 88 13 0.01
Wed 09/09 22Z 0.64 2126 96 97 13 0.06
Wed 09/09 23Z 0.72 2129 97 98 13 0.12
Thu 09/10 00Z 0.87 2233 96 98 14 0.10
Thu 09/10 01Z 0.95 2234 96 95 14 0.13
Thu 09/10 02Z 0.87 2236 98 97 16 0.07
Thu 09/10 03Z 1.04 2243 98 93 16 0.22
Thu 09/10 04Z 1.08 2243 97 90 16 0.15
Thu 09/10 05Z 1.13 2342 97 89 16 0.06
Thu 09/10 06Z 1.14 2343 97 91 16 0.13
Thu 09/10 07Z 1.12 2441 98 89 16 0.18
Thu 09/10 08Z 1.11 2536 97 91 15 0.24
Thu 09/10 09Z 0.95 2629 94 87 15 0.19
Thu 09/10 10Z 0.92 2727 94 56 14 0.09
Thu 09/10 11Z 0.88 2726 89 25 14 0.02
Thu 09/10 12Z 0.97 2728 84 25 13 0.01
Thu 09/10 13Z 0.94 2731 71 15 13 0.00
Thu 09/10 14Z 0.99 2730 67 6 13 0.00
Thu 09/10 15Z 1.41 2728 66 5 12 0.00
Thu 09/10 16Z 2.97 2728 63 8 11 0.00
Thu 09/10 17Z 8.89 2727 61 10 11 0.00
Thu 09/10 18Z 16.75 2727 62 10 10 0.00
Thu 09/10 19Z 18.69 2728 60 10 11 0.00
Thu 09/10 20Z 18.09 2728 59 10 11 0.00
Thu 09/10 21Z 11.39 2826 63 9 10 0.00
Thu 09/10 22Z 3.81 2825 73 12 10 0.00
Thu 09/10 23Z 1.96 2925 84 7 9 0.01
Fri 09/11 00Z 1.19 2927 93 8 8 0.01
Fri 09/11 01Z 0.79 3026 96 6 7 0.01
Fri 09/11 02Z 0.73 3026 95 5 6 0.01
Fri 09/11 03Z 0.66 3026 93 5 5 0.01
Fri 09/11 04Z 0.65 3026 91 4 4 0.01
Fri 09/11 05Z 0.61 3025 89 4 4 0.00
Fri 09/11 06Z 0.55 3026 86 2 4 0.00
Fri 09/11 07Z 0.45 3024 85 2 4 0.00
Fri 09/11 08Z 0.40 3124 83 5 5 0.00
Fri 09/11 09Z 0.36 3124 79 4 5 0.00
Fri 09/11 10Z 0.34 3123 74 3 5 0.00
Fri 09/11 11Z 0.34 3023 73 2 6 0.00
Fri 09/11 12Z 0.36 3024 73 2 5 0.00
Fri 09/11 13Z 0.35 3024 68 3 6 0.00
Fri 09/11 14Z 0.34 3124 61 4 6 0.00
Fri 09/11 15Z 0.34 3123 57 4 6 0.00
Fri 09/11 16Z 0.39 3123 56 4 6 0.00
Fri 09/11 17Z 0.46 3022 57 5 6 0.00
Fri 09/11 18Z 0.62 3020 62 5 6 0.00
Fri 09/11 19Z 1.20 2918 63 5 6 0.00
Fri 09/11 20Z 1.64 2918 59 7 6 0.00
Fri 09/11 21Z 1.14 3017 55 9 6 0.00
Fri 09/11 22Z 0.87 2918 54 13 7 0.00
Fri 09/11 23Z 0.79 3019 54 18 7 0.00
Run total areal avg QPF for the Central_Greens is: 1.88 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