Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260912_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)
=== ===== === ==== ==== === === === ====
Sat 09/12 12Z 0.05 1807 57 21 11 0.00
Sat 09/12 13Z 0.11 1909 55 19 11 0.00
Sat 09/12 14Z 0.15 1912 54 18 11 0.00
Sat 09/12 15Z 0.18 2013 54 18 11 0.00
Sat 09/12 16Z 0.24 2013 54 18 11 0.00
Sat 09/12 17Z 0.27 2012 55 15 12 0.00
Sat 09/12 18Z 0.32 2012 60 11 12 0.00
Sat 09/12 19Z 0.42 2012 63 7 11 0.00
Sat 09/12 20Z 0.36 1913 66 4 11 0.00
Sat 09/12 21Z 0.36 1914 69 4 12 0.00
Sat 09/12 22Z 0.33 1916 69 4 12 0.00
Sat 09/12 23Z 0.35 2018 69 5 12 0.00
Sun 09/13 00Z 0.37 2019 68 4 13 0.00
Sun 09/13 01Z 0.44 2022 70 5 13 0.00
Sun 09/13 02Z 0.47 2123 75 15 13 0.00
Sun 09/13 03Z 0.45 2124 80 45 13 0.00
Sun 09/13 04Z 0.44 2123 84 79 13 0.00
Sun 09/13 05Z 0.47 2223 93 91 13 0.00
Sun 09/13 06Z 0.45 2223 97 92 13 0.08
Sun 09/13 07Z 0.41 2222 95 88 14 0.06
Sun 09/13 08Z 0.35 2219 95 95 14 0.09
Sun 09/13 09Z 0.38 2123 96 97 13 0.12
Sun 09/13 10Z 0.37 2222 96 91 14 0.37
Sun 09/13 11Z 0.51 2228 98 93 14 0.20
Sun 09/13 12Z 0.54 2327 98 84 14 0.07
Sun 09/13 13Z 0.54 2325 98 78 14 0.03
Sun 09/13 14Z 0.55 2323 98 75 14 0.04
Sun 09/13 15Z 0.50 2420 97 71 14 0.04
Sun 09/13 16Z 0.45 2417 97 46 14 0.02
Sun 09/13 17Z 0.40 2414 95 40 14 0.01
Sun 09/13 18Z 0.41 2313 95 44 14 0.01
Sun 09/13 19Z 0.45 2413 94 43 14 0.00
Sun 09/13 20Z 0.41 2410 92 42 14 0.00
Sun 09/13 21Z 0.40 2510 92 42 14 0.00
Sun 09/13 22Z 0.37 2410 92 44 14 0.00
Sun 09/13 23Z 0.45 2413 94 40 14 0.00
Mon 09/14 00Z 0.52 2415 95 45 14 0.01
Mon 09/14 01Z 0.54 2517 91 46 14 0.01
Mon 09/14 02Z 0.63 2519 93 60 14 0.01
Mon 09/14 03Z 0.68 2520 95 59 14 0.01
Mon 09/14 04Z 0.76 2522 97 67 14 0.03
Mon 09/14 05Z 0.86 2824 95 82 12 0.08
Mon 09/14 06Z 0.50 3021 83 83 11 0.06
Mon 09/14 07Z 0.35 3017 81 70 11 0.07
Mon 09/14 08Z 0.32 3117 88 66 10 0.01
Mon 09/14 09Z 0.31 3117 88 62 10 0.01
Mon 09/14 10Z 0.40 3119 93 60 8 0.01
Mon 09/14 11Z 0.48 3122 95 42 7 0.01
Mon 09/14 12Z 0.46 3125 95 27 7 0.02
Mon 09/14 13Z 0.45 3225 93 18 6 0.02
Mon 09/14 14Z 0.36 3223 89 20 5 0.01
Mon 09/14 15Z 0.33 3323 90 24 5 0.01
Mon 09/14 16Z 0.37 3321 91 29 4 0.00
Mon 09/14 17Z 0.58 3319 88 33 4 0.00
Mon 09/14 18Z 0.63 3319 87 35 4 0.00
Mon 09/14 19Z 0.60 3319 79 24 4 0.00
Mon 09/14 20Z 1.19 3319 80 9 4 0.00
Mon 09/14 21Z 1.12 3219 84 8 4 0.00
Mon 09/14 22Z 0.37 3220 82 17 4 0.00
Mon 09/14 23Z 0.34 3222 79 23 4 0.00
Run total areal avg QPF for the Central_Greens is: 1.52 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