Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260814_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)
=== ===== === ==== ==== === === === ====
Fri 08/14 18Z 1.32 3310 82 63 10 0.00
Fri 08/14 19Z 1.13 3311 75 70 10 0.00
Fri 08/14 20Z 0.66 3310 74 71 10 0.00
Fri 08/14 21Z 0.88 3212 76 66 10 0.00
Fri 08/14 22Z 0.32 3212 76 57 10 0.00
Fri 08/14 23Z 0.23 3313 76 54 10 0.00
Sat 08/15 00Z 0.30 3315 78 58 10 0.00
Sat 08/15 01Z 0.16 3417 78 51 10 0.00
Sat 08/15 02Z 0.13 3417 81 39 9 0.00
Sat 08/15 03Z 0.10 3416 82 32 9 0.00
Sat 08/15 04Z 0.08 3415 84 26 8 0.00
Sat 08/15 05Z 0.03 3413 83 22 8 0.00
Sat 08/15 06Z 0.03 3411 82 17 8 0.00
Sat 08/15 07Z 0.09 3310 80 15 8 0.00
Sat 08/15 08Z 0.13 3310 77 11 9 0.00
Sat 08/15 09Z 0.21 3212 76 9 8 0.00
Sat 08/15 10Z 0.26 3214 78 9 8 0.00
Sat 08/15 11Z 0.27 3215 79 9 8 0.00
Sat 08/15 12Z 0.22 3215 81 9 8 0.00
Sat 08/15 13Z 0.17 3314 82 10 8 0.00
Sat 08/15 14Z 0.12 3312 79 11 8 0.00
Sat 08/15 15Z 0.15 3309 79 11 8 0.00
Sat 08/15 16Z 0.18 3209 80 12 8 0.00
Sat 08/15 17Z 0.24 3209 80 10 8 0.00
Sat 08/15 18Z 0.34 3210 77 8 8 0.00
Sat 08/15 19Z 0.56 3211 73 6 8 0.00
Sat 08/15 20Z 0.78 3211 73 6 8 0.00
Sat 08/15 21Z 0.34 3210 72 5 9 0.00
Sat 08/15 22Z 0.16 3210 67 6 9 0.00
Sat 08/15 23Z 0.07 3310 62 9 9 0.00
Sun 08/16 00Z 0.07 3309 60 8 9 0.00
Sun 08/16 01Z 0.05 3409 56 7 9 0.00
Sun 08/16 02Z 0.07 3309 56 7 9 0.00
Sun 08/16 03Z 0.05 3409 58 8 9 0.00
Sun 08/16 04Z 0.03 3407 56 9 10 0.00
Sun 08/16 05Z 0.02 3405 53 8 10 0.00
Sun 08/16 06Z 0.04 3304 52 7 10 0.00
Sun 08/16 07Z 0.02 3302 51 6 11 0.00
Sun 08/16 08Z 0.02 2800 51 9 11 0.00
Sun 08/16 09Z 0.05 2003 55 10 10 0.00
Sun 08/16 10Z 0.11 2205 60 12 10 0.00
Sun 08/16 11Z 0.10 2006 64 12 10 0.00
Sun 08/16 12Z 0.20 2109 74 11 9 0.00
Sun 08/16 13Z 0.25 2111 81 11 9 0.00
Sun 08/16 14Z 0.28 2212 82 9 9 0.00
Sun 08/16 15Z 0.31 2211 80 5 10 0.00
Sun 08/16 16Z 0.34 2210 83 3 10 0.00
Sun 08/16 17Z 0.33 2109 84 4 10 0.00
Sun 08/16 18Z 0.32 2009 86 6 10 0.00
Sun 08/16 19Z 0.24 1910 89 6 11 0.00
Sun 08/16 20Z 0.27 1911 91 21 11 0.00
Sun 08/16 21Z 0.26 1912 92 24 11 0.00
Sun 08/16 22Z 0.24 1914 96 31 11 0.00
Sun 08/16 23Z 0.34 2017 93 46 11 0.00
Mon 08/17 00Z 0.43 2019 93 54 12 0.00
Mon 08/17 01Z 0.40 2021 95 87 12 0.01
Mon 08/17 02Z 0.43 2025 97 76 12 0.01
Mon 08/17 03Z 0.52 2126 98 79 12 0.03
Mon 08/17 04Z 0.59 2126 97 91 12 0.03
Mon 08/17 05Z 0.56 2128 97 93 13 0.03
Run total areal avg QPF for the Central_Greens is: 0.11 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