Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260530_1200
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)
=== ===== === ==== ==== === === === ====
Sat 05/30 12Z 0.55 0323 96 65 -1 0.00
Sat 05/30 13Z 0.54 0322 93 52 -1 0.05
Sat 05/30 14Z 0.43 0319 90 46 0 0.02
Sat 05/30 15Z 0.45 0318 89 43 0 0.01
Sat 05/30 16Z 0.67 0216 89 43 0 0.00
Sat 05/30 17Z 0.98 0114 87 47 0 0.00
Sat 05/30 18Z 1.16 0115 83 46 0 0.00
Sat 05/30 19Z 1.42 0016 80 47 0 0.00
Sat 05/30 20Z 1.91 0116 76 47 0 0.00
Sat 05/30 21Z 1.81 0116 73 50 1 0.00
Sat 05/30 22Z 1.44 0116 70 50 1 0.00
Sat 05/30 23Z 0.85 0116 69 48 1 0.00
Sun 05/31 00Z 0.50 0117 67 41 1 0.00
Sun 05/31 01Z 0.39 0219 65 36 1 0.00
Sun 05/31 02Z 0.32 0119 62 26 2 0.00
Sun 05/31 03Z 0.28 0119 60 18 2 0.00
Sun 05/31 04Z 0.18 0118 63 13 2 0.00
Sun 05/31 05Z 0.14 0016 67 12 2 0.00
Sun 05/31 06Z 0.13 3516 69 13 2 0.00
Sun 05/31 07Z 0.15 3516 72 14 3 0.00
Sun 05/31 08Z 0.19 3415 71 16 3 0.00
Sun 05/31 09Z 0.24 3314 68 18 3 0.00
Sun 05/31 10Z 0.30 3214 68 22 3 0.00
Sun 05/31 11Z 0.44 3115 68 30 4 0.00
Sun 05/31 12Z 0.53 3116 67 31 4 0.00
Sun 05/31 13Z 0.53 3115 67 48 4 0.00
Sun 05/31 14Z 0.62 3115 68 72 4 0.00
Sun 05/31 15Z 1.19 3116 69 83 4 0.00
Sun 05/31 16Z 3.02 3117 75 87 4 0.00
Sun 05/31 17Z 2.31 3115 77 85 4 0.01
Sun 05/31 18Z 0.96 3014 82 89 4 0.01
Sun 05/31 19Z 0.91 2914 85 93 4 0.01
Sun 05/31 20Z 0.93 2915 81 87 4 0.01
Sun 05/31 21Z 1.11 2915 81 79 4 0.01
Sun 05/31 22Z 1.15 2919 83 83 4 0.04
Sun 05/31 23Z 1.08 3021 80 86 4 0.02
Mon 06/01 00Z 0.73 3122 85 86 4 0.03
Mon 06/01 01Z 0.67 3121 82 84 4 0.02
Mon 06/01 02Z 0.65 3220 80 77 4 0.04
Mon 06/01 03Z 0.49 3219 79 67 3 0.06
Mon 06/01 04Z 0.31 3416 79 56 3 0.00
Mon 06/01 05Z 0.17 3413 80 51 3 0.00
Mon 06/01 06Z 0.17 3412 82 62 3 0.00
Mon 06/01 07Z 0.09 3511 83 66 3 0.00
Mon 06/01 08Z 0.09 0109 86 75 2 0.00
Mon 06/01 09Z 0.10 0108 87 73 2 0.00
Mon 06/01 10Z 0.13 0208 87 69 2 0.00
Mon 06/01 11Z 0.19 0408 90 73 1 0.00
Mon 06/01 12Z 0.26 0608 94 76 1 0.00
Mon 06/01 13Z 0.31 0708 95 77 1 0.00
Mon 06/01 14Z 0.35 0809 94 72 1 0.00
Mon 06/01 15Z 0.43 0909 92 64 1 0.00
Mon 06/01 16Z 0.64 0808 91 58 1 0.00
Mon 06/01 17Z 0.99 0706 87 58 1 0.00
Mon 06/01 18Z 1.10 0405 82 55 1 0.00
Mon 06/01 19Z 1.05 0205 79 52 2 0.00
Mon 06/01 20Z 0.89 0106 79 48 3 0.00
Mon 06/01 21Z 0.66 0106 80 51 3 0.00
Mon 06/01 22Z 0.29 0106 79 57 3 0.00
Mon 06/01 23Z 0.08 0007 79 54 3 0.00
Run total areal avg QPF for the greens is: 0.34 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