Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260815_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 08/15 18Z 0.85 3208 87 28 9 0.00
Sat 08/15 19Z 0.43 3310 81 21 9 0.01
Sat 08/15 20Z 0.19 3411 75 19 10 0.01
Sat 08/15 21Z 0.16 3510 73 16 10 0.00
Sat 08/15 22Z 0.15 3509 76 12 9 0.00
Sat 08/15 23Z 0.15 3510 77 9 9 0.00
Sun 08/16 00Z 0.17 0010 76 9 9 0.00
Sun 08/16 01Z 0.16 0110 74 9 9 0.00
Sun 08/16 02Z 0.16 0208 70 9 10 0.00
Sun 08/16 03Z 0.12 0305 65 10 10 0.00
Sun 08/16 04Z 0.06 0502 63 12 10 0.00
Sun 08/16 05Z 0.03 1300 62 13 10 0.00
Sun 08/16 06Z 0.03 1901 61 14 10 0.00
Sun 08/16 07Z 0.04 2201 60 14 10 0.00
Sun 08/16 08Z 0.06 2302 60 13 10 0.00
Sun 08/16 09Z 0.06 2102 60 11 10 0.00
Sun 08/16 10Z 0.10 2104 62 10 10 0.00
Sun 08/16 11Z 0.10 2203 65 9 10 0.00
Sun 08/16 12Z 0.10 2005 69 7 9 0.00
Sun 08/16 13Z 0.13 2006 73 7 9 0.00
Sun 08/16 14Z 0.17 2007 77 6 9 0.00
Sun 08/16 15Z 0.27 2007 80 6 9 0.00
Sun 08/16 16Z 0.33 1907 82 6 10 0.00
Sun 08/16 17Z 0.30 1807 83 6 10 0.00
Sun 08/16 18Z 0.26 1809 84 6 11 0.00
Sun 08/16 19Z 0.20 1811 85 6 11 0.00
Sun 08/16 20Z 0.23 1812 86 5 11 0.00
Sun 08/16 21Z 0.25 1913 90 4 12 0.00
Sun 08/16 22Z 0.27 1914 98 21 12 0.01
Sun 08/16 23Z 0.31 2017 98 40 12 0.02
Mon 08/17 00Z 0.36 2019 97 50 12 0.01
Mon 08/17 01Z 0.36 2021 98 75 12 0.02
Mon 08/17 02Z 0.42 2024 98 82 12 0.03
Mon 08/17 03Z 0.45 2027 97 88 13 0.01
Mon 08/17 04Z 0.47 2027 97 94 13 0.01
Mon 08/17 05Z 0.45 2027 98 95 13 0.01
Mon 08/17 06Z 0.42 2025 98 95 13 0.01
Mon 08/17 07Z 0.41 2026 98 93 13 0.02
Mon 08/17 08Z 0.42 2026 99 94 12 0.02
Mon 08/17 09Z 0.45 2025 98 96 12 0.03
Mon 08/17 10Z 0.45 2026 98 89 12 0.02
Mon 08/17 11Z 0.41 2023 98 90 12 0.02
Mon 08/17 12Z 0.38 2021 99 87 13 0.02
Mon 08/17 13Z 0.36 2020 99 90 13 0.02
Mon 08/17 14Z 0.35 2119 99 91 13 0.02
Mon 08/17 15Z 0.32 2117 99 90 14 0.02
Mon 08/17 16Z 0.30 2116 99 93 14 0.01
Mon 08/17 17Z 0.27 2113 99 90 14 0.01
Mon 08/17 18Z 0.23 2210 99 87 14 0.01
Mon 08/17 19Z 0.20 2208 99 90 14 0.00
Mon 08/17 20Z 0.18 2406 99 88 14 0.00
Mon 08/17 21Z 0.16 2705 99 87 14 0.00
Mon 08/17 22Z 0.13 3005 99 88 14 0.01
Mon 08/17 23Z 0.12 3107 99 85 14 0.00
Tue 08/18 00Z 0.08 3308 99 61 14 0.00
Tue 08/18 01Z 0.08 3309 98 36 14 0.00
Tue 08/18 02Z 0.07 3310 96 34 13 0.00
Tue 08/18 03Z 0.03 3411 95 24 13 0.00
Tue 08/18 04Z 0.04 3412 96 12 13 0.01
Tue 08/18 05Z 0.03 3412 96 6 13 0.01
Run total areal avg QPF for the Central_Greens is: 0.40 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