Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260406_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)
=== ===== === ==== ==== === === === ====
Mon 04/06 12Z 1.81 2923 94 82 -9 0.00
Mon 04/06 13Z 5.17 2924 94 78 -9 0.00
Mon 04/06 14Z 4.69 2924 94 76 -9 0.01
Mon 04/06 15Z 4.89 2923 92 75 -9 0.01
Mon 04/06 16Z 6.05 2922 89 75 -9 0.00
Mon 04/06 17Z 10.66 2921 86 77 -9 0.00
Mon 04/06 18Z 12.53 2820 80 76 -9 0.00
Mon 04/06 19Z 12.70 2819 76 72 -8 0.00
Mon 04/06 20Z 13.10 2820 74 70 -8 0.00
Mon 04/06 21Z 13.04 2821 73 71 -8 0.00
Mon 04/06 22Z 11.26 2821 73 70 -8 0.00
Mon 04/06 23Z 7.14 2821 74 68 -9 0.00
Tue 04/07 00Z 3.86 2921 77 64 -9 0.00
Tue 04/07 01Z 2.36 2920 78 62 -9 0.00
Tue 04/07 02Z 1.73 2918 78 60 -9 0.00
Tue 04/07 03Z 1.20 2916 78 56 -9 0.00
Tue 04/07 04Z 0.80 2914 79 54 -9 0.00
Tue 04/07 05Z 0.55 2911 78 52 -9 0.00
Tue 04/07 06Z 0.38 2909 78 49 -9 0.00
Tue 04/07 07Z 0.24 2906 78 51 -9 0.00
Tue 04/07 08Z 0.17 2904 78 48 -9 0.00
Tue 04/07 09Z 0.13 2803 79 51 -9 0.00
Tue 04/07 10Z 0.10 2502 81 57 -9 0.00
Tue 04/07 11Z 0.08 2302 82 62 -10 0.00
Tue 04/07 12Z 0.08 2001 83 67 -9 0.00
Tue 04/07 13Z 0.10 1901 85 72 -10 0.00
Tue 04/07 14Z 0.19 1200 86 78 -9 0.00
Tue 04/07 15Z 0.23 0700 86 86 -9 0.00
Tue 04/07 16Z 0.27 3502 87 88 -9 0.01
Tue 04/07 17Z 0.22 3405 89 87 -9 0.02
Tue 04/07 18Z 0.17 3408 90 87 -9 0.02
Tue 04/07 19Z 0.19 3308 88 87 -9 0.01
Tue 04/07 20Z 0.42 3309 86 83 -9 0.00
Tue 04/07 21Z 0.61 3212 85 73 -9 0.00
Tue 04/07 22Z 0.34 3214 83 76 -10 0.00
Tue 04/07 23Z 0.37 3217 78 78 -10 0.00
Wed 04/08 00Z 0.50 3219 79 56 -11 0.00
Wed 04/08 01Z 1.18 3221 81 28 -12 0.00
Wed 04/08 02Z 1.17 3121 76 23 -13 0.00
Wed 04/08 03Z 0.78 3120 62 25 -13 0.00
Wed 04/08 04Z 0.61 3120 46 22 -13 0.00
Wed 04/08 05Z 0.53 3120 39 20 -13 0.00
Wed 04/08 06Z 0.46 3119 38 21 -13 0.00
Wed 04/08 07Z 0.44 3118 38 21 -12 0.00
Wed 04/08 08Z 0.42 3119 40 18 -12 0.00
Wed 04/08 09Z 0.38 3119 41 17 -12 0.00
Wed 04/08 10Z 0.32 3117 40 17 -11 0.00
Wed 04/08 11Z 0.31 3016 40 13 -10 0.00
Wed 04/08 12Z 0.27 3014 38 9 -10 0.00
Wed 04/08 13Z 0.25 2912 37 7 -9 0.00
Wed 04/08 14Z 0.24 2910 35 6 -9 0.00
Wed 04/08 15Z 0.22 2808 32 5 -8 0.00
Wed 04/08 16Z 0.21 2706 29 4 -7 0.00
Wed 04/08 17Z 0.25 2506 26 3 -7 0.00
Wed 04/08 18Z 0.44 2406 24 3 -6 0.00
Wed 04/08 19Z 0.48 2307 23 3 -5 0.00
Wed 04/08 20Z 0.41 2208 22 3 -5 0.00
Wed 04/08 21Z 0.31 2110 24 4 -4 0.00
Wed 04/08 22Z 0.29 2113 24 4 -4 0.00
Wed 04/08 23Z 0.32 2116 22 4 -3 0.00
Run total areal avg QPF for the greens is: 0.08 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