Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260911_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)
=== ===== === ==== ==== === === === ====
Fri 09/11 12Z 0.32 3118 86 4 6 0.00
Fri 09/11 13Z 0.34 3119 82 5 6 0.00
Fri 09/11 14Z 0.35 3118 82 6 6 0.00
Fri 09/11 15Z 0.36 3117 80 8 6 0.00
Fri 09/11 16Z 0.39 3116 75 11 6 0.00
Fri 09/11 17Z 0.46 3016 77 14 6 0.00
Fri 09/11 18Z 0.46 3015 76 16 6 0.00
Fri 09/11 19Z 0.51 3015 74 18 7 0.00
Fri 09/11 20Z 0.59 2915 76 18 7 0.00
Fri 09/11 21Z 0.56 3016 73 18 7 0.00
Fri 09/11 22Z 0.48 3016 70 19 7 0.00
Fri 09/11 23Z 0.35 3116 65 20 8 0.00
Sat 09/12 00Z 0.29 3116 62 23 8 0.00
Sat 09/12 01Z 0.22 3216 57 26 9 0.00
Sat 09/12 02Z 0.15 3215 51 32 10 0.00
Sat 09/12 03Z 0.12 3214 47 35 11 0.00
Sat 09/12 04Z 0.08 3313 43 34 11 0.00
Sat 09/12 05Z 0.05 3311 40 34 11 0.00
Sat 09/12 06Z 0.03 3409 37 33 12 0.00
Sat 09/12 07Z 0.02 3406 35 33 12 0.00
Sat 09/12 08Z 0.02 3404 33 33 12 0.00
Sat 09/12 09Z 0.02 3403 33 31 12 0.00
Sat 09/12 10Z 0.02 0002 33 30 12 0.00
Sat 09/12 11Z 0.02 1000 32 28 12 0.00
Sat 09/12 12Z 0.02 1803 32 28 12 0.00
Sat 09/12 13Z 0.04 1806 34 24 12 0.00
Sat 09/12 14Z 0.08 1907 36 22 12 0.00
Sat 09/12 15Z 0.12 2008 39 22 12 0.00
Sat 09/12 16Z 0.17 2109 42 24 12 0.00
Sat 09/12 17Z 0.20 2010 43 27 12 0.00
Sat 09/12 18Z 0.20 2011 44 27 12 0.00
Sat 09/12 19Z 0.20 1911 47 23 12 0.00
Sat 09/12 20Z 0.24 1912 51 15 12 0.00
Sat 09/12 21Z 0.26 1914 53 6 12 0.00
Sat 09/12 22Z 0.29 2016 52 7 13 0.00
Sat 09/12 23Z 0.34 2017 55 7 13 0.00
Sun 09/13 00Z 0.38 2119 63 22 13 0.00
Sun 09/13 01Z 0.38 2120 73 71 13 0.00
Sun 09/13 02Z 0.43 2122 82 84 13 0.00
Sun 09/13 03Z 0.48 2223 89 98 13 0.01
Sun 09/13 04Z 0.42 2121 91 80 13 0.01
Sun 09/13 05Z 0.42 2122 98 88 13 0.06
Sun 09/13 06Z 0.43 2124 97 85 13 0.14
Sun 09/13 07Z 0.44 2224 96 89 14 0.05
Sun 09/13 08Z 0.44 2223 97 96 14 0.05
Sun 09/13 09Z 0.40 2221 95 92 14 0.10
Sun 09/13 10Z 0.36 2220 95 93 14 0.05
Sun 09/13 11Z 0.42 2124 96 93 14 0.07
Sun 09/13 12Z 0.43 2123 97 94 14 0.19
Sun 09/13 13Z 0.44 2126 98 92 14 0.15
Sun 09/13 14Z 0.44 2126 99 94 14 0.25
Sun 09/13 15Z 0.52 2223 99 86 13 0.08
Sun 09/13 16Z 0.49 2419 98 73 14 0.03
Sun 09/13 17Z 0.42 2515 94 51 14 0.01
Sun 09/13 18Z 0.45 2615 91 39 14 0.00
Sun 09/13 19Z 0.46 2613 90 40 14 0.00
Sun 09/13 20Z 0.56 2614 92 39 14 0.00
Sun 09/13 21Z 0.70 2617 96 26 14 0.01
Sun 09/13 22Z 0.82 2619 95 22 14 0.04
Sun 09/13 23Z 0.76 2721 91 25 13 0.02
Run total areal avg QPF for the Central_Greens is: 1.32 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