Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260527_0000
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 05/27 00Z 1.47 2426 59 46 14 0.00
Wed 05/27 01Z 2.10 2431 59 55 14 0.00
Wed 05/27 02Z 1.87 2535 59 66 13 0.00
Wed 05/27 03Z 1.50 2537 55 66 14 0.00
Wed 05/27 04Z 1.44 2638 56 63 14 0.00
Wed 05/27 05Z 1.39 2637 61 61 14 0.00
Wed 05/27 06Z 1.25 2735 67 60 13 0.00
Wed 05/27 07Z 1.07 2833 70 53 13 0.01
Wed 05/27 08Z 0.98 2830 74 46 12 0.01
Wed 05/27 09Z 0.86 2926 83 41 12 0.00
Wed 05/27 10Z 0.74 2923 85 42 12 0.00
Wed 05/27 11Z 0.58 2920 84 43 12 0.00
Wed 05/27 12Z 0.50 2918 83 41 12 0.00
Wed 05/27 13Z 0.43 2916 79 40 11 0.00
Wed 05/27 14Z 0.43 2915 77 35 11 0.00
Wed 05/27 15Z 0.47 3014 78 35 11 0.00
Wed 05/27 16Z 0.69 3013 78 31 10 0.00
Wed 05/27 17Z 1.71 3012 80 27 10 0.00
Wed 05/27 18Z 2.22 3012 83 29 9 0.00
Wed 05/27 19Z 1.59 3013 86 28 9 0.01
Wed 05/27 20Z 1.14 3114 83 23 9 0.01
Wed 05/27 21Z 1.38 3215 81 22 9 0.00
Wed 05/27 22Z 1.06 3316 80 21 8 0.00
Wed 05/27 23Z 0.51 3317 82 26 8 0.00
Thu 05/28 00Z 0.30 3418 83 29 7 0.00
Thu 05/28 01Z 0.21 3420 86 35 7 0.00
Thu 05/28 02Z 0.12 3520 88 37 6 0.00
Thu 05/28 03Z 0.10 3520 90 46 6 0.00
Thu 05/28 04Z 0.08 0018 91 52 5 0.00
Thu 05/28 05Z 0.06 0018 90 50 5 0.00
Thu 05/28 06Z 0.05 0018 91 55 5 0.00
Thu 05/28 07Z 0.06 0018 92 57 5 0.00
Thu 05/28 08Z 0.05 0018 93 53 4 0.00
Thu 05/28 09Z 0.04 0019 93 56 4 0.00
Thu 05/28 10Z 0.03 0019 94 64 4 0.00
Thu 05/28 11Z 0.03 3519 95 72 4 0.00
Thu 05/28 12Z 0.04 3518 96 78 3 0.01
Thu 05/28 13Z 0.05 3517 96 78 3 0.01
Thu 05/28 14Z 0.06 3516 96 78 3 0.00
Thu 05/28 15Z 0.10 3516 96 76 3 0.00
Thu 05/28 16Z 0.20 3417 95 78 3 0.00
Thu 05/28 17Z 0.34 3419 94 73 3 0.00
Thu 05/28 18Z 0.53 3420 93 66 3 0.00
Thu 05/28 19Z 0.60 3420 92 56 2 0.00
Thu 05/28 20Z 0.48 3419 91 45 3 0.00
Thu 05/28 21Z 0.37 3419 90 43 3 0.00
Thu 05/28 22Z 0.42 3420 91 49 3 0.01
Thu 05/28 23Z 0.32 3422 94 57 3 0.01
Fri 05/29 00Z 0.30 3423 91 56 3 0.01
Fri 05/29 01Z 0.21 3423 85 41 3 0.00
Fri 05/29 02Z 0.24 3422 89 34 3 0.00
Fri 05/29 03Z 0.25 3421 93 33 3 0.01
Fri 05/29 04Z 0.25 3420 95 32 2 0.01
Fri 05/29 05Z 0.27 3318 96 34 2 0.01
Fri 05/29 06Z 0.29 3317 96 39 2 0.01
Fri 05/29 07Z 0.32 3316 94 44 2 0.00
Fri 05/29 08Z 0.35 3316 93 48 2 0.00
Fri 05/29 09Z 0.38 3215 91 56 2 0.00
Fri 05/29 10Z 0.41 3115 90 64 3 0.00
Fri 05/29 11Z 0.42 3115 90 68 3 0.00
Run total areal avg QPF for the greens is: 0.13 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