Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260815_0600
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)
=== ===== === ==== ==== === === === ====
Sat 08/15 06Z 0.04 3508 81 16 10 0.00
Sat 08/15 07Z 0.06 3408 83 17 9 0.00
Sat 08/15 08Z 0.10 3308 83 17 9 0.00
Sat 08/15 09Z 0.10 3306 82 16 9 0.00
Sat 08/15 10Z 0.17 3208 81 17 9 0.00
Sat 08/15 11Z 0.21 3210 80 17 9 0.00
Sat 08/15 12Z 0.20 3211 80 16 9 0.00
Sat 08/15 13Z 0.20 3313 79 14 9 0.00
Sat 08/15 14Z 0.20 3313 79 14 9 0.00
Sat 08/15 15Z 0.24 3311 81 16 8 0.00
Sat 08/15 16Z 0.34 3210 81 19 8 0.00
Sat 08/15 17Z 0.77 3210 80 26 8 0.00
Sat 08/15 18Z 0.85 3211 77 30 8 0.00
Sat 08/15 19Z 0.90 3212 77 25 8 0.00
Sat 08/15 20Z 0.83 3212 79 26 8 0.00
Sat 08/15 21Z 0.45 3212 78 17 8 0.00
Sat 08/15 22Z 0.37 3212 79 10 8 0.00
Sat 08/15 23Z 0.27 3311 80 10 8 0.00
Sun 08/16 00Z 0.19 3310 79 10 8 0.00
Sun 08/16 01Z 0.20 3310 79 11 8 0.00
Sun 08/16 02Z 0.13 3308 75 10 8 0.00
Sun 08/16 03Z 0.18 3208 76 10 8 0.00
Sun 08/16 04Z 0.17 3207 76 10 8 0.00
Sun 08/16 05Z 0.13 3206 75 10 8 0.00
Sun 08/16 06Z 0.09 3305 74 10 9 0.00
Sun 08/16 07Z 0.08 3204 72 10 9 0.00
Sun 08/16 08Z 0.07 3102 72 9 9 0.00
Sun 08/16 09Z 0.08 2701 72 8 9 0.00
Sun 08/16 10Z 0.12 2403 73 8 8 0.00
Sun 08/16 11Z 0.10 2303 71 8 9 0.00
Sun 08/16 12Z 0.10 2104 70 8 9 0.00
Sun 08/16 13Z 0.09 2005 71 8 9 0.00
Sun 08/16 14Z 0.13 2007 73 7 9 0.00
Sun 08/16 15Z 0.24 2108 79 6 9 0.00
Sun 08/16 16Z 0.28 2009 85 6 9 0.00
Sun 08/16 17Z 0.24 2009 87 9 10 0.00
Sun 08/16 18Z 0.20 2009 86 8 10 0.00
Sun 08/16 19Z 0.14 1909 87 10 11 0.00
Sun 08/16 20Z 0.06 1811 86 14 11 0.00
Sun 08/16 21Z 0.06 1812 87 20 11 0.00
Sun 08/16 22Z 0.06 1815 89 34 12 0.00
Sun 08/16 23Z 0.07 1818 90 63 12 0.00
Mon 08/17 00Z 0.08 1820 93 78 12 0.00
Mon 08/17 01Z 0.10 1822 95 87 12 0.01
Mon 08/17 02Z 0.12 1822 95 95 12 0.01
Mon 08/17 03Z 0.14 1923 96 99 12 0.02
Mon 08/17 04Z 0.12 1824 96 96 13 0.02
Mon 08/17 05Z 0.15 1927 97 94 13 0.03
Mon 08/17 06Z 0.17 1929 97 89 13 0.03
Mon 08/17 07Z 0.17 1929 98 94 13 0.02
Mon 08/17 08Z 0.18 1928 98 98 13 0.02
Mon 08/17 09Z 0.18 1927 98 97 13 0.02
Mon 08/17 10Z 0.21 1925 98 95 13 0.03
Mon 08/17 11Z 0.22 2023 98 92 13 0.02
Mon 08/17 12Z 0.22 2020 99 92 13 0.03
Mon 08/17 13Z 0.18 2017 99 89 13 0.03
Mon 08/17 14Z 0.18 2114 99 85 14 0.02
Mon 08/17 15Z 0.16 2111 99 80 14 0.01
Mon 08/17 16Z 0.14 2208 98 83 15 0.01
Mon 08/17 17Z 0.15 2406 98 87 15 0.00
Run total areal avg QPF for the greens is: 0.33 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