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Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260320_0600
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)
=== ===== === ==== ==== === === === ====
Fri 03/20 06Z 0.55 2516 89 8 -6 0.00
Fri 03/20 07Z 0.67 2619 91 9 -7 0.00
Fri 03/20 08Z 0.62 2718 92 12 -7 0.00
Fri 03/20 09Z 0.56 2719 90 16 -7 0.00
Fri 03/20 10Z 0.55 2819 86 25 -6 0.00
Fri 03/20 11Z 0.41 2816 80 34 -5 0.00
Fri 03/20 12Z 0.28 2712 70 23 -3 0.00
Fri 03/20 13Z 0.22 2609 63 9 -3 0.00
Fri 03/20 14Z 0.25 2410 69 32 -4 0.00
Fri 03/20 15Z 0.23 2112 68 41 -3 0.00
Fri 03/20 16Z 0.31 2116 71 79 -3 0.00
Fri 03/20 17Z 0.33 2019 82 93 -2 0.00
Fri 03/20 18Z 0.25 1927 94 96 0 0.01
Fri 03/20 19Z 0.26 1931 93 91 2 0.03
Fri 03/20 20Z 0.46 2031 98 97 0 0.16
Fri 03/20 21Z 0.62 2134 98 96 1 0.17
Fri 03/20 22Z 0.88 2337 98 96 1 0.15
Fri 03/20 23Z 1.00 2437 98 92 1 0.13
Sat 03/21 00Z 1.02 2434 98 61 1 0.11
Sat 03/21 01Z 0.99 2530 98 7 0 0.08
Sat 03/21 02Z 0.93 2627 98 8 0 0.04
Sat 03/21 03Z 0.80 2724 98 9 0 0.03
Sat 03/21 04Z 0.64 2822 97 16 -1 0.02
Sat 03/21 05Z 0.39 2917 94 20 -2 0.01
Sat 03/21 06Z 0.31 2916 92 38 -2 0.01
Sat 03/21 07Z 0.24 3016 90 45 -2 0.01
Sat 03/21 08Z 0.20 3116 90 47 -3 0.00
Sat 03/21 09Z 0.15 3216 88 54 -3 0.00
Sat 03/21 10Z 0.14 3217 87 59 -4 0.00
Sat 03/21 11Z 0.16 3220 89 54 -5 0.00
Sat 03/21 12Z 0.16 3321 90 37 -6 0.00
Sat 03/21 13Z 0.15 3320 89 11 -7 0.00
Sat 03/21 14Z 0.16 3318 87 8 -7 0.00
Sat 03/21 15Z 0.23 3217 88 11 -8 0.00
Sat 03/21 16Z 0.30 3317 87 13 -8 0.00
Sat 03/21 17Z 0.27 3315 82 14 -7 0.00
Sat 03/21 18Z 0.45 3314 79 16 -7 0.00
Sat 03/21 19Z 0.68 3213 77 20 -7 0.00
Sat 03/21 20Z 0.50 3212 73 23 -7 0.00
Sat 03/21 21Z 0.20 3311 67 27 -7 0.00
Sat 03/21 22Z 0.12 3310 60 27 -6 0.00
Sat 03/21 23Z 0.10 3308 54 28 -6 0.00
Sun 03/22 00Z 0.08 3308 50 29 -6 0.00
Sun 03/22 01Z 0.08 3206 49 38 -6 0.00
Sun 03/22 02Z 0.11 3004 52 62 -6 0.00
Sun 03/22 03Z 0.12 2803 57 88 -6 0.00
Sun 03/22 04Z 0.11 2104 61 93 -5 0.00
Sun 03/22 05Z 0.11 2007 64 96 -5 0.00
Sun 03/22 06Z 0.17 2009 69 95 -5 0.00
Sun 03/22 07Z 0.21 2012 74 96 -5 0.00
Sun 03/22 08Z 0.31 2016 87 94 -6 0.00
Sun 03/22 09Z 0.27 2015 95 93 -6 0.05
Sun 03/22 10Z 0.23 1918 96 92 -5 0.07
Sun 03/22 11Z 0.26 1922 96 93 -4 0.06
Sun 03/22 12Z 0.22 1926 97 96 -3 0.05
Sun 03/22 13Z 0.26 1929 97 98 -2 0.08
Sun 03/22 14Z 0.25 1928 98 99 -1 0.11
Sun 03/22 15Z 0.31 1927 98 99 -2 0.11
Sun 03/22 16Z 0.34 2023 98 98 0 0.09
Sun 03/22 17Z 0.36 2121 99 98 0 0.10
Run total areal avg QPF for the Central_Greens is: 1.68 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