Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260904_0000
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 09/04 00Z 0.73 3019 80 42 14 0.00
Fri 09/04 01Z 0.80 3020 82 34 13 0.00
Fri 09/04 02Z 0.76 3020 83 39 13 0.00
Fri 09/04 03Z 0.56 3116 78 41 13 0.00
Fri 09/04 04Z 0.54 3016 76 45 13 0.00
Fri 09/04 05Z 0.47 3015 77 48 13 0.00
Fri 09/04 06Z 0.36 3013 79 46 13 0.00
Fri 09/04 07Z 0.31 3012 84 46 12 0.00
Fri 09/04 08Z 0.33 3012 89 41 12 0.01
Fri 09/04 09Z 0.25 3111 93 38 12 0.01
Fri 09/04 10Z 0.18 3210 94 39 11 0.01
Fri 09/04 11Z 0.12 3310 91 42 11 0.01
Fri 09/04 12Z 0.15 3311 89 47 11 0.00
Fri 09/04 13Z 0.17 3312 83 37 11 0.01
Fri 09/04 14Z 0.20 3212 78 24 11 0.00
Fri 09/04 15Z 0.60 3212 79 22 10 0.00
Fri 09/04 16Z 1.93 3112 81 26 10 0.00
Fri 09/04 17Z 2.39 3112 84 35 11 0.00
Fri 09/04 18Z 1.38 3112 87 47 11 0.01
Fri 09/04 19Z 1.10 3014 88 45 11 0.01
Fri 09/04 20Z 0.71 3114 87 46 11 0.00
Fri 09/04 21Z 0.64 3114 89 42 11 0.00
Fri 09/04 22Z 0.37 3216 89 35 10 0.00
Fri 09/04 23Z 0.35 3216 90 39 10 0.00
Sat 09/05 00Z 0.25 3316 91 38 10 0.00
Sat 09/05 01Z 0.16 3316 92 39 10 0.00
Sat 09/05 02Z 0.17 3316 92 43 10 0.00
Sat 09/05 03Z 0.14 3317 92 45 10 0.01
Sat 09/05 04Z 0.07 3417 92 46 10 0.00
Sat 09/05 05Z 0.04 3417 93 48 10 0.01
Sat 09/05 06Z 0.02 3515 92 48 10 0.00
Sat 09/05 07Z 0.04 3514 91 52 10 0.00
Sat 09/05 08Z 0.05 3514 92 56 10 0.01
Sat 09/05 09Z 0.08 3515 94 57 10 0.01
Sat 09/05 10Z 0.13 0016 96 63 9 0.01
Sat 09/05 11Z 0.20 0017 96 70 9 0.01
Sat 09/05 12Z 0.23 0117 94 72 9 0.00
Sat 09/05 13Z 0.22 0117 93 69 9 0.00
Sat 09/05 14Z 0.23 0116 94 68 9 0.00
Sat 09/05 15Z 0.25 0116 94 66 9 0.00
Sat 09/05 16Z 0.27 0114 95 66 9 0.00
Sat 09/05 17Z 0.26 0112 95 66 8 0.00
Sat 09/05 18Z 0.30 0111 96 65 8 0.00
Sat 09/05 19Z 0.27 0111 97 65 8 0.01
Sat 09/05 20Z 0.27 0111 97 64 9 0.01
Sat 09/05 21Z 0.31 0211 97 65 8 0.02
Sat 09/05 22Z 0.35 0311 96 66 8 0.01
Sat 09/05 23Z 0.32 0311 97 70 9 0.01
Sun 09/06 00Z 0.38 0412 98 75 8 0.03
Sun 09/06 01Z 0.48 0613 98 78 8 0.04
Sun 09/06 02Z 0.56 0715 95 75 7 0.03
Sun 09/06 03Z 0.52 0716 91 77 7 0.01
Sun 09/06 04Z 0.48 0615 90 80 7 0.00
Sun 09/06 05Z 0.46 0714 85 79 7 0.00
Sun 09/06 06Z 0.42 0713 84 74 6 0.00
Sun 09/06 07Z 0.38 0612 85 64 6 0.00
Sun 09/06 08Z 0.31 0510 86 60 6 0.00
Sun 09/06 09Z 0.28 0411 86 54 6 0.00
Sun 09/06 10Z 0.26 0410 86 50 6 0.00
Sun 09/06 11Z 0.27 0311 85 49 6 0.00
Run total areal avg QPF for the Central_Greens is: 0.30 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