Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260526_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)
=== ===== === ==== ==== === === === ====
Tue 05/26 06Z 0.45 3015 74 9 9 0.00
Tue 05/26 07Z 0.46 3015 75 14 9 0.00
Tue 05/26 08Z 0.37 3014 77 20 10 0.00
Tue 05/26 09Z 0.35 3115 70 25 10 0.00
Tue 05/26 10Z 0.39 3115 66 26 10 0.00
Tue 05/26 11Z 0.42 3014 65 33 10 0.00
Tue 05/26 12Z 0.46 2915 69 35 10 0.00
Tue 05/26 13Z 0.50 2915 79 34 10 0.00
Tue 05/26 14Z 0.54 2815 83 37 11 0.00
Tue 05/26 15Z 0.56 2814 79 41 11 0.00
Tue 05/26 16Z 0.73 2714 79 53 12 0.00
Tue 05/26 17Z 1.18 2615 75 60 12 0.00
Tue 05/26 18Z 1.98 2515 74 56 12 0.00
Tue 05/26 19Z 3.38 2417 76 60 12 0.00
Tue 05/26 20Z 4.70 2420 75 64 13 0.00
Tue 05/26 21Z 2.37 2422 73 62 13 0.00
Tue 05/26 22Z 2.28 2426 70 49 13 0.00
Tue 05/26 23Z 1.80 2429 65 45 13 0.00
Wed 05/27 00Z 1.72 2431 62 64 13 0.00
Wed 05/27 01Z 1.72 2534 64 71 13 0.00
Wed 05/27 02Z 1.53 2535 62 77 13 0.00
Wed 05/27 03Z 1.65 2636 59 78 13 0.00
Wed 05/27 04Z 1.56 2636 65 76 12 0.00
Wed 05/27 05Z 1.59 2735 70 70 12 0.00
Wed 05/27 06Z 1.28 2832 77 65 11 0.01
Wed 05/27 07Z 1.07 2828 81 61 11 0.00
Wed 05/27 08Z 0.90 2925 83 57 10 0.00
Wed 05/27 09Z 0.78 2923 84 46 10 0.00
Wed 05/27 10Z 0.69 2921 85 42 10 0.00
Wed 05/27 11Z 0.62 2919 83 39 9 0.00
Wed 05/27 12Z 0.54 3017 83 15 9 0.00
Wed 05/27 13Z 0.48 3016 82 15 9 0.00
Wed 05/27 14Z 0.47 3115 79 16 9 0.00
Wed 05/27 15Z 0.89 3114 74 15 9 0.00
Wed 05/27 16Z 1.98 3113 71 15 9 0.00
Wed 05/27 17Z 3.18 3113 74 16 9 0.00
Wed 05/27 18Z 3.21 3012 78 16 9 0.00
Wed 05/27 19Z 3.20 3011 78 19 9 0.00
Wed 05/27 20Z 3.02 3011 79 23 9 0.00
Wed 05/27 21Z 1.93 3112 80 24 9 0.00
Wed 05/27 22Z 1.29 3113 81 25 8 0.00
Wed 05/27 23Z 0.68 3214 83 28 8 0.00
Thu 05/28 00Z 0.49 3216 85 29 8 0.01
Thu 05/28 01Z 0.40 3317 87 32 7 0.00
Thu 05/28 02Z 0.33 3318 89 33 6 0.01
Thu 05/28 03Z 0.30 3419 88 33 6 0.00
Thu 05/28 04Z 0.20 3418 88 34 5 0.00
Thu 05/28 05Z 0.13 3417 89 37 5 0.00
Thu 05/28 06Z 0.08 3516 91 40 4 0.00
Thu 05/28 07Z 0.08 3514 91 40 4 0.00
Thu 05/28 08Z 0.10 3413 92 40 4 0.00
Thu 05/28 09Z 0.10 3414 94 40 3 0.00
Thu 05/28 10Z 0.10 3415 94 42 3 0.00
Thu 05/28 11Z 0.10 3415 95 44 2 0.00
Thu 05/28 12Z 0.10 3516 94 48 2 0.01
Thu 05/28 13Z 0.09 3516 94 50 2 0.01
Thu 05/28 14Z 0.09 3515 93 53 2 0.01
Thu 05/28 15Z 0.12 3515 94 60 2 0.00
Thu 05/28 16Z 0.15 3415 95 69 2 0.00
Thu 05/28 17Z 0.30 3417 94 76 2 0.01
Run total areal avg QPF for the greens is: 0.07 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