Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260909_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)
=== ===== === ==== ==== === === === ====
Wed 09/09 00Z 0.03 3405 74 0 11 0.00
Wed 09/09 01Z 0.02 3503 68 0 11 0.00
Wed 09/09 02Z 0.05 0302 66 1 11 0.00
Wed 09/09 03Z 0.04 1302 64 0 11 0.00
Wed 09/09 04Z 0.02 1704 65 1 11 0.00
Wed 09/09 05Z 0.07 1906 64 0 11 0.00
Wed 09/09 06Z 0.11 2007 71 1 11 0.00
Wed 09/09 07Z 0.13 2008 83 11 10 0.00
Wed 09/09 08Z 0.15 2010 93 70 10 0.00
Wed 09/09 09Z 0.20 2012 96 84 10 0.00
Wed 09/09 10Z 0.24 2113 96 73 11 0.01
Wed 09/09 11Z 0.27 2114 94 65 11 0.00
Wed 09/09 12Z 0.33 2216 93 61 12 0.01
Wed 09/09 13Z 0.38 2218 91 57 12 0.00
Wed 09/09 14Z 0.41 2219 92 60 12 0.01
Wed 09/09 15Z 0.41 2219 93 55 12 0.00
Wed 09/09 16Z 0.43 2219 89 44 12 0.00
Wed 09/09 17Z 0.48 2120 84 30 12 0.00
Wed 09/09 18Z 0.52 2021 83 9 12 0.00
Wed 09/09 19Z 0.60 2021 89 11 12 0.00
Wed 09/09 20Z 0.68 2024 93 76 12 0.02
Wed 09/09 21Z 0.47 2022 94 99 12 0.09
Wed 09/09 22Z 0.47 2026 97 98 13 0.15
Wed 09/09 23Z 0.58 2030 99 98 14 0.14
Thu 09/10 00Z 0.79 2235 99 96 14 0.24
Thu 09/10 01Z 0.91 2238 99 98 15 0.26
Thu 09/10 02Z 1.05 2242 98 95 15 0.22
Thu 09/10 03Z 1.22 2343 98 97 15 0.22
Thu 09/10 04Z 1.16 2342 97 97 15 0.14
Thu 09/10 05Z 1.23 2346 97 96 15 0.23
Thu 09/10 06Z 1.16 2344 97 87 15 0.17
Thu 09/10 07Z 1.10 2442 97 94 15 0.15
Thu 09/10 08Z 1.03 2539 98 93 15 0.19
Thu 09/10 09Z 0.99 2635 98 62 15 0.12
Thu 09/10 10Z 0.99 2632 97 32 14 0.07
Thu 09/10 11Z 0.99 2729 93 31 13 0.03
Thu 09/10 12Z 1.11 2729 92 18 12 0.02
Thu 09/10 13Z 1.05 2730 77 20 12 0.01
Thu 09/10 14Z 1.42 2731 79 8 11 0.00
Thu 09/10 15Z 3.10 2729 81 9 10 0.00
Thu 09/10 16Z 10.31 2728 76 7 10 0.00
Thu 09/10 17Z 12.36 2728 72 6 9 0.00
Thu 09/10 18Z 15.12 2727 79 4 9 0.00
Thu 09/10 19Z 13.05 2728 83 5 9 0.00
Thu 09/10 20Z 11.08 2829 86 7 8 0.01
Thu 09/10 21Z 2.80 2828 90 6 7 0.01
Thu 09/10 22Z 1.53 2929 92 7 6 0.01
Thu 09/10 23Z 1.10 2928 94 7 5 0.01
Fri 09/11 00Z 1.11 3028 94 9 4 0.01
Fri 09/11 01Z 0.88 3029 92 8 3 0.00
Fri 09/11 02Z 0.82 3029 92 5 3 0.00
Fri 09/11 03Z 0.76 3029 91 8 2 0.00
Fri 09/11 04Z 0.73 3031 90 5 2 0.00
Fri 09/11 05Z 0.61 3132 88 1 2 0.00
Fri 09/11 06Z 0.48 3130 87 1 2 0.00
Fri 09/11 07Z 0.44 3129 85 1 3 0.00
Fri 09/11 08Z 0.36 3128 80 1 4 0.00
Fri 09/11 09Z 0.33 3128 75 3 5 0.00
Fri 09/11 10Z 0.31 3127 72 3 5 0.00
Fri 09/11 11Z 0.32 3127 70 5 4 0.00
Run total areal avg QPF for the Central_Greens is: 2.55 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