Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260520_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)
=== ===== === ==== ==== === === === ====
Wed 05/20 06Z 1.18 2532 78 83 16 0.00
Wed 05/20 07Z 1.42 2637 83 74 16 0.00
Wed 05/20 08Z 1.36 2637 89 66 15 0.00
Wed 05/20 09Z 1.20 2634 92 54 14 0.00
Wed 05/20 10Z 1.05 2731 95 75 14 0.01
Wed 05/20 11Z 0.94 2728 95 70 14 0.02
Wed 05/20 12Z 0.91 2726 95 77 14 0.01
Wed 05/20 13Z 1.03 2727 97 86 13 0.01
Wed 05/20 14Z 1.02 2726 97 82 13 0.05
Wed 05/20 15Z 1.11 2725 96 78 12 0.04
Wed 05/20 16Z 1.30 2724 95 79 12 0.04
Wed 05/20 17Z 1.81 2724 91 62 11 0.04
Wed 05/20 18Z 2.22 2823 92 55 11 0.01
Wed 05/20 19Z 3.98 2823 84 48 10 0.01
Wed 05/20 20Z 5.86 2922 82 40 9 0.01
Wed 05/20 21Z 4.81 2922 82 33 9 0.00
Wed 05/20 22Z 2.14 3022 84 25 8 0.00
Wed 05/20 23Z 0.82 3122 85 18 7 0.00
Thu 05/21 00Z 0.66 3124 80 16 6 0.00
Thu 05/21 01Z 0.56 3124 74 13 5 0.00
Thu 05/21 02Z 0.48 3223 72 8 4 0.00
Thu 05/21 03Z 0.43 3223 68 7 4 0.00
Thu 05/21 04Z 0.40 3224 67 6 3 0.00
Thu 05/21 05Z 0.34 3225 64 5 2 0.00
Thu 05/21 06Z 0.32 3226 60 5 2 0.00
Thu 05/21 07Z 0.28 3327 59 4 1 0.00
Thu 05/21 08Z 0.24 3326 58 4 1 0.00
Thu 05/21 09Z 0.19 3325 55 3 0 0.00
Thu 05/21 10Z 0.17 3324 53 3 0 0.00
Thu 05/21 11Z 0.16 3323 52 3 0 0.00
Thu 05/21 12Z 0.14 3321 52 3 0 0.00
Thu 05/21 13Z 0.14 3319 49 4 0 0.00
Thu 05/21 14Z 0.14 3317 47 4 0 0.00
Thu 05/21 15Z 0.16 3317 47 4 0 0.00
Thu 05/21 16Z 0.19 3316 47 4 0 0.00
Thu 05/21 17Z 0.23 3316 46 4 0 0.00
Thu 05/21 18Z 0.34 3316 44 4 0 0.00
Thu 05/21 19Z 0.40 3317 43 3 0 0.00
Thu 05/21 20Z 0.35 3318 43 4 0 0.00
Thu 05/21 21Z 0.33 3317 44 3 0 0.00
Thu 05/21 22Z 0.26 3318 42 3 0 0.00
Thu 05/21 23Z 0.25 3319 40 4 1 0.00
Fri 05/22 00Z 0.21 3420 37 3 1 0.00
Fri 05/22 01Z 0.16 3419 34 3 1 0.00
Fri 05/22 02Z 0.12 3418 32 3 1 0.00
Fri 05/22 03Z 0.10 3516 33 4 1 0.00
Fri 05/22 04Z 0.09 3516 34 5 1 0.00
Fri 05/22 05Z 0.09 3516 35 6 1 0.00
Fri 05/22 06Z 0.08 0016 36 6 1 0.00
Fri 05/22 07Z 0.10 0016 36 5 1 0.00
Fri 05/22 08Z 0.13 0115 37 4 1 0.00
Fri 05/22 09Z 0.17 0214 37 5 1 0.00
Fri 05/22 10Z 0.19 0212 38 6 1 0.00
Fri 05/22 11Z 0.19 0311 40 7 1 0.00
Fri 05/22 12Z 0.20 0309 42 7 1 0.00
Fri 05/22 13Z 0.21 0306 46 8 1 0.00
Fri 05/22 14Z 0.29 0204 49 10 1 0.00
Fri 05/22 15Z 0.46 3503 52 9 1 0.00
Fri 05/22 16Z 0.80 3502 53 10 1 0.00
Fri 05/22 17Z 0.71 3302 53 13 2 0.00
Run total areal avg QPF for the greens is: 0.25 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