Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260815_1800
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 18Z 0.89 3209 87 27 9 0.00
Sat 08/15 19Z 0.57 3310 80 21 9 0.01
Sat 08/15 20Z 0.39 3311 75 19 9 0.00
Sat 08/15 21Z 0.21 3411 74 17 9 0.00
Sat 08/15 22Z 0.12 3410 76 14 9 0.00
Sat 08/15 23Z 0.07 3511 77 12 9 0.00
Sun 08/16 00Z 0.06 0010 76 12 9 0.00
Sun 08/16 01Z 0.07 0110 75 12 9 0.00
Sun 08/16 02Z 0.11 0209 71 12 10 0.00
Sun 08/16 03Z 0.11 0306 67 12 10 0.00
Sun 08/16 04Z 0.06 0403 67 14 10 0.00
Sun 08/16 05Z 0.04 0400 66 14 10 0.00
Sun 08/16 06Z 0.03 2100 66 15 10 0.00
Sun 08/16 07Z 0.03 2100 64 16 10 0.00
Sun 08/16 08Z 0.04 2301 63 15 10 0.00
Sun 08/16 09Z 0.04 2002 62 14 10 0.00
Sun 08/16 10Z 0.06 2103 62 12 10 0.00
Sun 08/16 11Z 0.07 2103 64 11 10 0.00
Sun 08/16 12Z 0.06 2004 65 9 10 0.00
Sun 08/16 13Z 0.07 1906 68 8 10 0.00
Sun 08/16 14Z 0.10 2007 71 7 9 0.00
Sun 08/16 15Z 0.16 2007 75 6 10 0.00
Sun 08/16 16Z 0.19 1907 78 6 10 0.00
Sun 08/16 17Z 0.12 1807 80 5 10 0.00
Sun 08/16 18Z 0.08 1809 80 4 11 0.00
Sun 08/16 19Z 0.09 1810 83 4 11 0.00
Sun 08/16 20Z 0.08 1812 85 4 11 0.00
Sun 08/16 21Z 0.14 1814 88 5 11 0.00
Sun 08/16 22Z 0.16 1915 92 15 12 0.01
Sun 08/16 23Z 0.20 1917 94 27 12 0.01
Mon 08/17 00Z 0.23 2019 96 39 12 0.01
Mon 08/17 01Z 0.25 2021 98 56 12 0.02
Mon 08/17 02Z 0.30 2024 98 74 12 0.03
Mon 08/17 03Z 0.32 2027 97 83 13 0.02
Mon 08/17 04Z 0.35 2028 97 87 13 0.01
Mon 08/17 05Z 0.35 2027 98 93 13 0.01
Mon 08/17 06Z 0.33 2026 98 93 13 0.01
Mon 08/17 07Z 0.32 2027 98 94 13 0.02
Mon 08/17 08Z 0.33 2027 98 94 13 0.02
Mon 08/17 09Z 0.35 2026 98 95 12 0.03
Mon 08/17 10Z 0.37 2026 98 90 12 0.02
Mon 08/17 11Z 0.34 2124 98 90 13 0.02
Mon 08/17 12Z 0.32 2122 98 87 13 0.02
Mon 08/17 13Z 0.30 2121 98 90 13 0.02
Mon 08/17 14Z 0.29 2119 98 91 13 0.02
Mon 08/17 15Z 0.26 2117 98 92 14 0.01
Mon 08/17 16Z 0.27 2115 99 94 14 0.01
Mon 08/17 17Z 0.25 2213 99 91 14 0.01
Mon 08/17 18Z 0.22 2210 99 88 14 0.01
Mon 08/17 19Z 0.21 2308 99 91 14 0.01
Mon 08/17 20Z 0.20 2407 99 88 14 0.01
Mon 08/17 21Z 0.20 2606 99 89 14 0.02
Mon 08/17 22Z 0.19 2806 99 90 14 0.01
Mon 08/17 23Z 0.19 3007 99 77 14 0.01
Tue 08/18 00Z 0.17 3108 97 51 14 0.01
Tue 08/18 01Z 0.16 3209 95 29 13 0.00
Tue 08/18 02Z 0.18 3210 96 28 13 0.01
Tue 08/18 03Z 0.15 3311 95 19 13 0.01
Tue 08/18 04Z 0.14 3411 96 13 13 0.02
Tue 08/18 05Z 0.09 3412 96 6 12 0.02
Run total areal avg QPF for the greens is: 0.48 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