Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260815_1200
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 12Z 0.11 3310 85 8 8 0.00
Sat 08/15 13Z 0.04 3410 85 5 8 0.00
Sat 08/15 14Z 0.09 3309 84 5 8 0.00
Sat 08/15 15Z 0.08 3410 83 9 8 0.00
Sat 08/15 16Z 0.09 3307 83 15 8 0.00
Sat 08/15 17Z 0.31 3207 81 16 8 0.00
Sat 08/15 18Z 0.63 3109 79 15 8 0.00
Sat 08/15 19Z 0.79 3210 77 18 8 0.00
Sat 08/15 20Z 0.68 3311 77 22 8 0.00
Sat 08/15 21Z 0.37 3311 78 17 8 0.00
Sat 08/15 22Z 0.12 3410 75 13 8 0.00
Sat 08/15 23Z 0.07 3409 72 11 8 0.00
Sun 08/16 00Z 0.04 3509 71 10 8 0.00
Sun 08/16 01Z 0.04 3410 67 9 8 0.00
Sun 08/16 02Z 0.05 3509 60 8 9 0.00
Sun 08/16 03Z 0.05 0008 59 8 9 0.00
Sun 08/16 04Z 0.06 0005 54 8 9 0.00
Sun 08/16 05Z 0.05 3504 52 8 9 0.00
Sun 08/16 06Z 0.05 0003 49 8 10 0.00
Sun 08/16 07Z 0.04 3502 48 8 10 0.00
Sun 08/16 08Z 0.04 3502 46 7 10 0.00
Sun 08/16 09Z 0.03 0101 48 7 10 0.00
Sun 08/16 10Z 0.02 3401 48 8 10 0.00
Sun 08/16 11Z 0.04 2201 46 7 11 0.00
Sun 08/16 12Z 0.09 2204 47 7 10 0.00
Sun 08/16 13Z 0.12 2106 49 7 10 0.00
Sun 08/16 14Z 0.14 2106 54 6 10 0.00
Sun 08/16 15Z 0.20 2107 63 5 10 0.00
Sun 08/16 16Z 0.34 2107 72 5 9 0.00
Sun 08/16 17Z 0.50 2007 76 6 10 0.00
Sun 08/16 18Z 0.60 1908 79 7 10 0.00
Sun 08/16 19Z 0.52 1910 78 6 11 0.00
Sun 08/16 20Z 0.36 1810 77 7 11 0.00
Sun 08/16 21Z 0.38 1912 86 12 11 0.00
Sun 08/16 22Z 0.34 1914 92 27 11 0.00
Sun 08/16 23Z 0.32 2016 95 34 12 0.00
Mon 08/17 00Z 0.31 1918 96 70 12 0.01
Mon 08/17 01Z 0.30 1922 97 79 12 0.01
Mon 08/17 02Z 0.35 1924 98 72 12 0.01
Mon 08/17 03Z 0.45 2027 97 85 13 0.02
Mon 08/17 04Z 0.43 2027 96 96 13 0.01
Mon 08/17 05Z 0.43 2028 95 97 12 0.02
Mon 08/17 06Z 0.47 2030 95 96 12 0.02
Mon 08/17 07Z 0.43 1929 98 94 12 0.01
Mon 08/17 08Z 0.42 1926 99 95 11 0.04
Mon 08/17 09Z 0.40 2024 99 96 12 0.09
Mon 08/17 10Z 0.35 1924 99 95 12 0.08
Mon 08/17 11Z 0.31 1924 99 95 12 0.09
Mon 08/17 12Z 0.33 2023 99 94 12 0.07
Mon 08/17 13Z 0.33 2022 99 95 12 0.04
Mon 08/17 14Z 0.30 2019 99 96 12 0.03
Mon 08/17 15Z 0.26 2016 99 94 12 0.02
Mon 08/17 16Z 0.22 2013 99 92 12 0.02
Mon 08/17 17Z 0.18 2109 99 85 13 0.01
Mon 08/17 18Z 0.13 2206 99 72 13 0.01
Mon 08/17 19Z 0.12 2604 97 64 14 0.00
Mon 08/17 20Z 0.10 3004 96 55 15 0.00
Mon 08/17 21Z 0.08 3205 95 51 15 0.00
Mon 08/17 22Z 0.06 3306 95 43 15 0.00
Mon 08/17 23Z 0.05 3307 95 34 14 0.00
Run total areal avg QPF for the Central_Greens is: 0.61 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