Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260412_1200
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sun 04/12 12Z 0.05 3505 66 20 -4 0.00
Sun 04/12 13Z 0.06 3101 64 22 -4 0.00
Sun 04/12 14Z 0.06 2101 61 24 -3 0.00
Sun 04/12 15Z 0.07 1903 60 25 -2 0.00
Sun 04/12 16Z 0.14 1905 60 27 -2 0.00
Sun 04/12 17Z 0.35 1906 61 29 -2 0.00
Sun 04/12 18Z 0.59 2009 59 73 -2 0.00
Sun 04/12 19Z 0.21 1911 54 89 -1 0.00
Sun 04/12 20Z 0.21 1913 52 97 -1 0.00
Sun 04/12 21Z 0.08 1813 68 95 -2 0.00
Sun 04/12 22Z 0.08 1816 72 91 -1 0.02
Sun 04/12 23Z 0.18 1921 74 98 -1 0.01
Mon 04/13 00Z 0.21 1924 88 97 -1 0.01
Mon 04/13 01Z 0.26 2026 88 99 0 0.01
Mon 04/13 02Z 0.32 2028 90 99 1 0.02
Mon 04/13 03Z 0.35 2129 93 99 3 0.03
Mon 04/13 04Z 0.35 2130 95 97 5 0.03
Mon 04/13 05Z 0.39 2232 94 97 6 0.08
Mon 04/13 06Z 0.39 2232 92 97 8 0.09
Mon 04/13 07Z 0.43 2234 90 88 9 0.05
Mon 04/13 08Z 0.47 2336 87 39 10 0.02
Mon 04/13 09Z 0.56 2337 89 61 9 0.01
Mon 04/13 10Z 0.62 2340 92 87 9 0.02
Mon 04/13 11Z 0.67 2439 90 80 10 0.02
Mon 04/13 12Z 0.71 2440 92 72 9 0.01
Mon 04/13 13Z 0.76 2440 87 80 9 0.01
Mon 04/13 14Z 0.72 2437 92 90 9 0.04
Mon 04/13 15Z 0.77 2341 89 95 9 0.05
Mon 04/13 16Z 0.84 2246 97 97 8 0.12
Mon 04/13 17Z 0.99 2345 98 96 8 0.12
Mon 04/13 18Z 1.11 2445 98 96 8 0.12
Mon 04/13 19Z 1.12 2641 98 71 8 0.05
Mon 04/13 20Z 1.07 2638 97 62 9 0.02
Mon 04/13 21Z 1.12 2637 98 62 9 0.02
Mon 04/13 22Z 1.22 2737 98 58 9 0.05
Mon 04/13 23Z 1.36 2737 98 60 9 0.05
Tue 04/14 00Z 1.41 2738 98 42 9 0.03
Tue 04/14 01Z 1.45 2839 99 39 8 0.06
Tue 04/14 02Z 1.27 2935 98 26 7 0.05
Tue 04/14 03Z 1.05 2932 98 32 7 0.04
Tue 04/14 04Z 0.87 3028 97 35 6 0.03
Tue 04/14 05Z 0.65 3025 94 38 6 0.02
Tue 04/14 07Z 0.38 3020 83 44 8 0.02
Tue 04/14 08Z 0.31 3018 76 42 9 0.01
Tue 04/14 09Z 0.27 2915 70 42 9 0.01
Tue 04/14 10Z 0.25 2813 67 34 9 0.01
Tue 04/14 11Z 0.25 2712 64 36 10 0.01
Tue 04/14 12Z 0.24 2612 61 38 10 0.00
Tue 04/14 13Z 0.24 2513 59 47 10 0.00
Tue 04/14 14Z 0.22 2313 58 45 10 0.00
Tue 04/14 15Z 0.30 2218 61 54 10 0.00
Tue 04/14 16Z 0.40 2321 76 58 10 0.00
Tue 04/14 17Z 0.46 2222 85 56 11 0.00
Tue 04/14 18Z 0.56 2324 89 84 11 0.00
Tue 04/14 19Z 0.62 2229 86 78 11 0.02
Tue 04/14 20Z 0.68 2232 82 73 12 0.01
Tue 04/14 21Z 0.69 2329 76 61 13 0.01
Tue 04/14 22Z 0.66 2326 79 70 12 0.01
Tue 04/14 23Z 0.69 2228 88 73 12 0.00
Run total areal avg QPF for the greens is: 1.42 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