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Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260130_0600
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)
=== ===== === ==== ==== === === === ====
Fri 01/30 06Z 0.75 2927 81 45 -24 0.00
Fri 01/30 07Z 0.76 2931 82 46 -24 0.00
Fri 01/30 08Z 0.66 3031 80 50 -24 0.00
Fri 01/30 09Z 0.58 3031 80 55 -23 0.00
Fri 01/30 10Z 0.52 3030 82 60 -23 0.00
Fri 01/30 11Z 0.45 3029 82 67 -22 0.00
Fri 01/30 12Z 0.43 3029 81 72 -22 0.00
Fri 01/30 13Z 0.40 3029 81 76 -21 0.00
Fri 01/30 14Z 0.36 3027 82 77 -21 0.00
Fri 01/30 15Z 0.33 3025 83 76 -20 0.00
Fri 01/30 17Z 0.30 3021 83 72 -18 0.00
Fri 01/30 18Z 0.31 3021 83 69 -18 0.00
Fri 01/30 19Z 0.35 3022 84 67 -18 0.00
Fri 01/30 20Z 0.36 3022 84 66 -18 0.00
Fri 01/30 21Z 0.36 3022 84 64 -17 0.00
Fri 01/30 22Z 0.34 3022 85 63 -17 0.00
Fri 01/30 23Z 0.31 3022 85 64 -16 0.00
Sat 01/31 00Z 0.28 3123 86 63 -16 0.00
Sat 01/31 01Z 0.25 3223 87 62 -16 0.00
Sat 01/31 02Z 0.22 3222 86 59 -16 0.00
Sat 01/31 03Z 0.20 3220 86 55 -15 0.00
Sat 01/31 04Z 0.19 3219 85 51 -15 0.00
Sat 01/31 05Z 0.18 3218 84 47 -14 0.00
Sat 01/31 06Z 0.18 3117 83 45 -14 0.00
Sat 01/31 07Z 0.18 3117 83 44 -14 0.00
Sat 01/31 09Z 0.19 3117 84 44 -15 0.00
Sat 01/31 10Z 0.19 3117 84 43 -15 0.00
Sat 01/31 12Z 0.17 3116 84 42 -15 0.00
Sat 01/31 13Z 0.16 3115 84 41 -15 0.00
Sat 01/31 14Z 0.15 3114 84 40 -15 0.00
Sat 01/31 15Z 0.15 3113 84 39 -15 0.00
Sat 01/31 16Z 0.15 3113 84 38 -15 0.00
Sat 01/31 17Z 0.15 3112 84 38 -15 0.00
Sat 01/31 18Z 0.14 3212 84 38 -15 0.00
Sat 01/31 19Z 0.13 3212 83 36 -14 0.00
Sat 01/31 20Z 0.12 3312 84 36 -14 0.00
Sat 01/31 21Z 0.10 3311 84 38 -14 0.00
Sat 01/31 22Z 0.10 3313 83 38 -14 0.00
Sat 01/31 23Z 0.09 3315 83 38 -14 0.00
Sun 02/01 00Z 0.04 3514 83 37 -13 0.00
Sun 02/01 01Z 0.03 3512 84 39 -14 0.00
Sun 02/01 02Z 0.03 3511 82 38 -13 0.00
Sun 02/01 03Z 0.03 0011 77 36 -12 0.00
Sun 02/01 04Z 0.03 0011 75 35 -12 0.00
Sun 02/01 05Z 0.05 0112 73 31 -11 0.00
Sun 02/01 06Z 0.05 0114 69 29 -10 0.00
Sun 02/01 07Z 0.06 0114 66 28 -10 0.00
Sun 02/01 08Z 0.10 0214 64 29 -11 0.00
Sun 02/01 09Z 0.10 0215 61 29 -10 0.00
Sun 02/01 10Z 0.07 0116 58 27 -10 0.00
Sun 02/01 11Z 0.08 0117 56 23 -9 0.00
Sun 02/01 12Z 0.11 0219 58 22 -10 0.00
Sun 02/01 13Z 0.13 0219 58 21 -10 0.00
Sun 02/01 14Z 0.12 0218 56 18 -9 0.00
Sun 02/01 15Z 0.11 0218 53 16 -9 0.00
Sun 02/01 16Z 0.12 0219 51 15 -8 0.00
Sun 02/01 17Z 0.10 0219 52 13 -8 0.00
Run total areal avg QPF for the greens is: 0.00 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