Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260410_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 04/10 18Z 2.44 2218 59 70 8 0.00
Fri 04/10 19Z 2.08 2219 58 58 9 0.00
Fri 04/10 20Z 1.14 2221 56 59 10 0.00
Fri 04/10 21Z 0.88 2121 58 49 10 0.00
Fri 04/10 22Z 0.87 2124 64 41 10 0.00
Fri 04/10 23Z 0.80 2621 80 95 8 0.05
Sat 04/11 00Z 0.63 2720 91 88 6 0.04
Sat 04/11 01Z 0.60 2721 96 97 6 0.04
Sat 04/11 02Z 0.67 2622 98 95 5 0.04
Sat 04/11 03Z 0.54 2718 99 97 3 0.08
Sat 04/11 04Z 0.35 2915 98 97 3 0.08
Sat 04/11 05Z 0.35 3018 98 85 1 0.03
Sat 04/11 06Z 0.38 3121 98 73 0 0.01
Sat 04/11 07Z 0.39 3122 95 67 -1 0.01
Sat 04/11 08Z 0.44 3125 92 39 -2 0.01
Sat 04/11 09Z 0.46 3127 89 18 -3 0.01
Sat 04/11 10Z 0.49 3128 88 7 -4 0.00
Sat 04/11 11Z 0.47 3129 84 4 -4 0.00
Sat 04/11 12Z 0.47 3230 82 4 -5 0.00
Sat 04/11 13Z 0.49 3228 85 4 -5 0.00
Sat 04/11 14Z 0.58 3127 84 6 -6 0.00
Sat 04/11 15Z 0.85 3126 89 9 -6 0.00
Sat 04/11 16Z 3.93 3124 91 10 -6 0.00
Sat 04/11 17Z 7.30 3122 88 10 -6 0.00
Sat 04/11 18Z 6.92 3020 85 10 -5 0.00
Sat 04/11 19Z 6.03 3018 84 11 -5 0.00
Sat 04/11 20Z 5.60 3117 83 10 -5 0.00
Sat 04/11 21Z 4.43 3118 83 10 -5 0.00
Sat 04/11 22Z 3.03 3119 82 10 -5 0.00
Sat 04/11 23Z 1.43 3121 82 10 -5 0.00
Sun 04/12 00Z 1.52 3122 82 9 -5 0.00
Sun 04/12 01Z 1.24 3124 80 10 -5 0.00
Sun 04/12 02Z 0.72 3125 76 11 -5 0.00
Sun 04/12 03Z 0.57 3226 75 11 -5 0.00
Sun 04/12 04Z 0.50 3226 74 13 -6 0.00
Sun 04/12 05Z 0.35 3225 71 13 -6 0.00
Sun 04/12 06Z 0.26 3323 69 12 -5 0.00
Sun 04/12 07Z 0.20 3321 62 14 -5 0.00
Sun 04/12 08Z 0.18 3320 59 16 -5 0.00
Sun 04/12 09Z 0.16 3319 58 20 -5 0.00
Sun 04/12 10Z 0.13 3317 55 22 -4 0.00
Sun 04/12 11Z 0.09 3316 49 21 -3 0.00
Sun 04/12 12Z 0.05 3413 47 22 -3 0.00
Sun 04/12 13Z 0.05 3308 47 28 -3 0.00
Sun 04/12 14Z 0.07 3205 46 32 -2 0.00
Sun 04/12 15Z 0.14 2804 47 34 -2 0.00
Sun 04/12 16Z 0.20 2504 46 38 -2 0.00
Sun 04/12 17Z 0.40 2305 45 39 -1 0.00
Sun 04/12 18Z 0.47 2206 43 40 -1 0.00
Sun 04/12 19Z 0.65 2108 43 37 -1 0.00
Sun 04/12 20Z 0.46 2211 39 41 0 0.00
Sun 04/12 21Z 0.39 2114 32 61 0 0.00
Sun 04/12 22Z 0.46 2118 35 92 0 0.00
Sun 04/12 23Z 0.54 2119 66 96 0 0.00
Mon 04/13 00Z 0.45 2320 94 97 0 0.01
Mon 04/13 01Z 0.50 2224 91 98 0 0.02
Mon 04/13 02Z 0.52 2129 79 98 0 0.02
Mon 04/13 03Z 0.51 2129 81 97 1 0.01
Mon 04/13 04Z 0.51 2132 84 97 3 0.01
Mon 04/13 05Z 0.53 2235 88 94 5 0.03
Run total areal avg QPF for the Central_Greens is: 0.50 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