Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260718_0000
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 07/18 00Z 0.46 2705 55 13 12 0.00
Sat 07/18 01Z 0.56 2706 50 12 12 0.00
Sat 07/18 02Z 0.49 2606 47 11 12 0.00
Sat 07/18 03Z 0.46 2406 47 9 12 0.00
Sat 07/18 04Z 0.50 2308 49 10 12 0.00
Sat 07/18 05Z 0.51 2310 51 12 12 0.00
Sat 07/18 06Z 0.52 2311 53 22 12 0.00
Sat 07/18 07Z 0.47 2311 51 65 12 0.00
Sat 07/18 08Z 0.50 2312 48 83 12 0.00
Sat 07/18 09Z 0.48 2312 46 90 13 0.00
Sat 07/18 10Z 0.59 2414 44 97 12 0.00
Sat 07/18 11Z 0.46 2314 46 94 13 0.00
Sat 07/18 12Z 0.57 2119 53 85 13 0.00
Sat 07/18 13Z 0.69 2125 66 80 13 0.00
Sat 07/18 14Z 0.84 2128 73 70 14 0.00
Sat 07/18 15Z 0.90 2129 75 71 15 0.00
Sat 07/18 16Z 0.96 2128 66 66 16 0.00
Sat 07/18 17Z 1.92 2232 87 82 14 0.01
Sat 07/18 18Z 0.89 2132 95 91 14 0.01
Sat 07/18 19Z 0.85 2232 98 68 15 0.02
Sat 07/18 20Z 0.78 2230 98 71 16 0.03
Sat 07/18 21Z 0.73 2228 98 71 16 0.02
Sat 07/18 22Z 0.72 2227 97 65 16 0.01
Sat 07/18 23Z 0.65 2228 94 66 17 0.02
Sun 07/19 00Z 0.96 2336 91 63 17 0.02
Sun 07/19 01Z 0.67 2232 74 51 17 0.07
Sun 07/19 02Z 0.74 2232 87 40 16 0.00
Sun 07/19 03Z 0.85 2429 92 46 15 0.01
Sun 07/19 04Z 0.94 2629 94 52 14 0.04
Sun 07/19 05Z 0.95 2728 98 62 13 0.07
Sun 07/19 06Z 0.75 3027 97 43 11 0.04
Sun 07/19 07Z 0.53 3129 95 14 10 0.02
Sun 07/19 08Z 0.45 3231 93 9 9 0.01
Sun 07/19 09Z 0.35 3230 92 9 9 0.01
Sun 07/19 10Z 0.27 3230 90 10 9 0.01
Sun 07/19 11Z 0.23 3328 87 14 8 0.01
Sun 07/19 12Z 0.21 3327 89 18 8 0.00
Sun 07/19 13Z 0.28 3225 90 16 8 0.00
Sun 07/19 14Z 0.40 3224 90 9 7 0.00
Sun 07/19 15Z 0.68 3121 91 5 7 0.00
Sun 07/19 16Z 0.71 3119 89 8 7 0.00
Sun 07/19 17Z 2.20 3118 82 20 7 0.00
Sun 07/19 18Z 6.13 3117 73 27 8 0.00
Sun 07/19 19Z 8.69 3018 68 11 8 0.00
Sun 07/19 20Z 8.25 3019 68 3 8 0.00
Sun 07/19 21Z 8.87 3020 70 2 8 0.00
Sun 07/19 22Z 8.16 3020 73 6 8 0.00
Sun 07/19 23Z 3.34 3120 71 9 8 0.00
Mon 07/20 00Z 1.19 3121 66 8 8 0.00
Mon 07/20 01Z 0.95 3121 62 10 8 0.00
Mon 07/20 02Z 0.91 3122 60 12 8 0.00
Mon 07/20 03Z 0.78 3222 61 14 8 0.00
Mon 07/20 04Z 0.61 3221 64 16 8 0.00
Mon 07/20 05Z 0.53 3221 66 16 8 0.00
Mon 07/20 06Z 0.46 3219 65 19 8 0.00
Mon 07/20 07Z 0.40 3216 64 21 8 0.00
Mon 07/20 08Z 0.39 3214 65 26 8 0.00
Mon 07/20 09Z 0.36 3213 64 29 8 0.00
Mon 07/20 10Z 0.33 3113 63 32 8 0.00
Mon 07/20 11Z 0.30 3112 62 37 8 0.00
Run total areal avg QPF for the Central_Greens is: 0.43 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