Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260718_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)
=== ===== === ==== ==== === === === ====
Sat 07/18 18Z 0.48 2027 91 94 14 0.00
Sat 07/18 19Z 0.59 2127 97 91 14 0.01
Sat 07/18 20Z 0.62 2126 99 91 15 0.04
Sat 07/18 21Z 0.71 2226 99 91 15 0.06
Sat 07/18 22Z 0.76 2326 98 86 15 0.10
Sat 07/18 23Z 0.80 2427 97 84 16 0.05
Sun 07/19 00Z 0.80 2328 97 71 16 0.03
Sun 07/19 01Z 0.91 2428 97 85 16 0.05
Sun 07/19 02Z 0.98 2429 96 77 15 0.18
Sun 07/19 03Z 1.03 2430 96 58 15 0.04
Sun 07/19 04Z 0.95 2629 97 44 15 0.03
Sun 07/19 05Z 0.87 2829 98 58 14 0.04
Sun 07/19 06Z 0.71 3028 98 75 12 0.06
Sun 07/19 07Z 0.49 3127 95 44 10 0.03
Sun 07/19 08Z 0.38 3228 90 12 9 0.01
Sun 07/19 09Z 0.33 3230 89 9 8 0.01
Sun 07/19 10Z 0.31 3231 92 9 8 0.01
Sun 07/19 11Z 0.30 3231 91 8 8 0.01
Sun 07/19 12Z 0.31 3229 90 7 8 0.01
Sun 07/19 13Z 0.31 3227 91 5 8 0.01
Sun 07/19 14Z 0.32 3224 91 3 7 0.01
Sun 07/19 15Z 0.31 3221 88 1 7 0.00
Sun 07/19 16Z 0.47 3219 85 4 7 0.00
Sun 07/19 17Z 5.19 3117 80 7 7 0.00
Sun 07/19 18Z 6.71 3017 72 10 7 0.00
Sun 07/19 19Z 7.36 3016 69 13 8 0.00
Sun 07/19 20Z 9.22 3018 67 12 8 0.00
Sun 07/19 21Z 9.84 3019 66 6 8 0.00
Sun 07/19 22Z 8.92 3019 67 6 9 0.00
Sun 07/19 23Z 3.70 3021 66 5 9 0.00
Mon 07/20 00Z 1.63 3122 62 4 8 0.00
Mon 07/20 01Z 1.50 3124 63 4 8 0.00
Mon 07/20 02Z 1.37 3125 69 4 8 0.00
Mon 07/20 03Z 1.14 3126 73 6 7 0.00
Mon 07/20 04Z 0.79 3125 71 7 7 0.00
Mon 07/20 05Z 0.65 3123 73 7 7 0.00
Mon 07/20 06Z 0.53 3221 76 8 7 0.00
Mon 07/20 07Z 0.40 3220 75 8 8 0.00
Mon 07/20 08Z 0.38 3219 75 11 8 0.00
Mon 07/20 09Z 0.39 3117 73 14 8 0.00
Mon 07/20 10Z 0.36 3115 72 15 8 0.00
Mon 07/20 11Z 0.35 3014 71 17 8 0.00
Mon 07/20 12Z 0.39 3013 72 20 8 0.00
Mon 07/20 13Z 0.45 2913 75 23 8 0.00
Mon 07/20 14Z 0.52 2811 74 25 8 0.00
Mon 07/20 15Z 1.03 2709 74 26 8 0.00
Mon 07/20 16Z 2.22 2608 73 25 8 0.00
Mon 07/20 17Z 2.71 2507 72 23 9 0.00
Mon 07/20 18Z 2.66 2407 72 21 10 0.00
Mon 07/20 19Z 2.63 2307 71 22 10 0.00
Mon 07/20 20Z 2.09 2308 71 24 11 0.00
Mon 07/20 21Z 1.25 2108 69 25 11 0.00
Mon 07/20 22Z 0.63 2110 66 21 11 0.00
Mon 07/20 23Z 0.48 2111 61 17 11 0.00
Tue 07/21 00Z 0.42 2013 55 12 12 0.00
Tue 07/21 01Z 0.42 2015 54 12 12 0.00
Tue 07/21 02Z 0.54 2117 58 15 12 0.00
Tue 07/21 03Z 0.58 2119 56 18 12 0.00
Tue 07/21 04Z 0.65 2121 58 18 12 0.00
Tue 07/21 05Z 0.73 2222 69 20 11 0.00
Run total areal avg QPF for the Central_Greens is: 0.79 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