Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260911_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)
=== ===== === ==== ==== === === === ====
Fri 09/11 18Z 0.81 3011 85 10 7 0.00
Fri 09/11 19Z 0.58 3013 81 14 7 0.00
Fri 09/11 20Z 0.54 3014 80 18 7 0.00
Fri 09/11 21Z 0.49 3015 78 20 8 0.00
Fri 09/11 22Z 0.40 3115 72 19 8 0.00
Fri 09/11 23Z 0.35 3116 66 17 9 0.00
Sat 09/12 00Z 0.29 3115 62 16 9 0.00
Sat 09/12 01Z 0.23 3216 57 18 10 0.00
Sat 09/12 02Z 0.16 3214 53 22 10 0.00
Sat 09/12 03Z 0.11 3212 51 27 11 0.00
Sat 09/12 04Z 0.07 3310 48 31 11 0.00
Sat 09/12 05Z 0.06 3308 45 34 11 0.00
Sat 09/12 06Z 0.05 3205 42 35 11 0.00
Sat 09/12 07Z 0.05 3103 39 36 12 0.00
Sat 09/12 08Z 0.05 3003 36 36 12 0.00
Sat 09/12 09Z 0.06 2802 34 36 12 0.00
Sat 09/12 10Z 0.04 2601 33 35 12 0.00
Sat 09/12 11Z 0.04 2002 33 34 12 0.00
Sat 09/12 12Z 0.03 1804 34 33 12 0.00
Sat 09/12 13Z 0.05 1806 35 30 12 0.00
Sat 09/12 14Z 0.09 1909 39 28 12 0.00
Sat 09/12 15Z 0.16 2010 45 25 12 0.00
Sat 09/12 16Z 0.20 2010 52 20 11 0.00
Sat 09/12 17Z 0.19 2011 55 16 12 0.00
Sat 09/12 18Z 0.19 1910 60 15 12 0.00
Sat 09/12 19Z 0.23 1912 65 13 12 0.00
Sat 09/12 20Z 0.24 1913 67 9 12 0.00
Sat 09/12 21Z 0.31 2015 69 4 12 0.00
Sat 09/12 22Z 0.32 2016 65 5 12 0.00
Sat 09/12 23Z 0.34 2017 63 12 12 0.00
Sun 09/13 00Z 0.38 2118 66 22 13 0.00
Sun 09/13 01Z 0.40 2119 72 18 13 0.00
Sun 09/13 02Z 0.45 2120 79 28 13 0.00
Sun 09/13 03Z 0.44 2220 81 42 13 0.00
Sun 09/13 04Z 0.45 2220 85 54 13 0.00
Sun 09/13 05Z 0.46 2222 90 69 13 0.00
Sun 09/13 06Z 0.43 2223 96 94 13 0.05
Sun 09/13 07Z 0.46 2224 96 92 13 0.14
Sun 09/13 08Z 0.46 2323 94 91 14 0.02
Sun 09/13 09Z 0.43 2223 95 87 14 0.02
Sun 09/13 10Z 0.43 2223 97 91 14 0.04
Sun 09/13 11Z 0.45 2322 97 82 14 0.05
Sun 09/13 12Z 0.44 2321 97 89 14 0.05
Sun 09/13 13Z 0.42 2220 96 93 14 0.08
Sun 09/13 14Z 0.45 2221 97 87 14 0.10
Sun 09/13 15Z 0.50 2321 98 81 14 0.19
Sun 09/13 16Z 0.49 2220 95 63 14 0.07
Sun 09/13 17Z 0.46 2220 96 55 14 0.01
Sun 09/13 18Z 0.40 2218 95 48 14 0.01
Sun 09/13 19Z 0.38 2215 95 43 14 0.01
Sun 09/13 20Z 0.41 2314 91 51 14 0.01
Sun 09/13 21Z 0.42 2413 89 49 14 0.00
Sun 09/13 22Z 0.50 2615 90 30 14 0.00
Sun 09/13 23Z 0.64 2718 94 28 13 0.01
Mon 09/14 00Z 0.64 2719 87 33 13 0.01
Mon 09/14 01Z 0.75 2722 90 35 13 0.02
Mon 09/14 02Z 0.61 2822 77 45 13 0.02
Mon 09/14 03Z 0.73 2824 71 35 11 0.00
Mon 09/14 04Z 0.67 2923 70 47 11 0.00
Mon 09/14 05Z 0.70 2924 78 49 10 0.00
Run total areal avg QPF for the Central_Greens is: 0.91 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