Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260406_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)
=== ===== === ==== ==== === === === ====
Mon 04/06 00Z 1.15 2624 87 16 -3 0.00
Mon 04/06 01Z 2.21 2630 85 19 -4 0.00
Mon 04/06 02Z 2.69 2733 87 30 -5 0.00
Mon 04/06 03Z 2.14 2732 88 38 -6 0.00
Mon 04/06 04Z 2.25 2732 91 46 -7 0.00
Mon 04/06 05Z 1.89 2732 89 48 -7 0.00
Mon 04/06 06Z 1.59 2832 91 57 -8 0.00
Mon 04/06 07Z 1.37 2832 94 68 -8 0.01
Mon 04/06 08Z 1.29 2832 95 70 -8 0.01
Mon 04/06 09Z 1.42 2931 96 71 -9 0.01
Mon 04/06 10Z 1.76 2931 97 71 -9 0.01
Mon 04/06 11Z 1.89 2931 97 69 -10 0.01
Mon 04/06 12Z 1.82 2929 97 69 -10 0.01
Mon 04/06 13Z 2.23 2927 95 67 -11 0.01
Mon 04/06 14Z 3.92 2925 93 68 -11 0.01
Mon 04/06 15Z 6.45 2824 92 73 -10 0.00
Mon 04/06 16Z 8.81 2823 86 73 -10 0.00
Mon 04/06 17Z 13.14 2822 78 73 -10 0.00
Mon 04/06 18Z 13.99 2821 72 71 -9 0.00
Mon 04/06 19Z 14.16 2820 67 73 -8 0.00
Mon 04/06 20Z 13.97 2820 66 77 -8 0.00
Mon 04/06 21Z 13.77 2821 66 79 -8 0.00
Mon 04/06 22Z 12.33 2821 67 79 -8 0.00
Mon 04/06 23Z 8.59 2822 71 77 -9 0.00
Tue 04/07 00Z 4.16 2922 73 74 -9 0.00
Tue 04/07 01Z 2.62 2922 75 75 -9 0.00
Tue 04/07 02Z 1.88 3020 75 78 -10 0.00
Tue 04/07 03Z 1.16 3018 79 79 -10 0.00
Tue 04/07 04Z 0.90 3016 81 79 -10 0.00
Tue 04/07 05Z 0.61 3014 81 72 -10 0.00
Tue 04/07 06Z 0.47 3012 79 45 -10 0.00
Tue 04/07 07Z 0.46 2911 79 30 -11 0.00
Tue 04/07 08Z 0.42 3011 78 30 -11 0.00
Tue 04/07 09Z 0.41 3011 78 33 -11 0.00
Tue 04/07 10Z 0.35 3010 78 35 -11 0.00
Tue 04/07 11Z 0.33 3010 78 41 -11 0.00
Tue 04/07 12Z 0.36 3010 79 48 -12 0.00
Tue 04/07 13Z 0.54 3008 79 58 -12 0.00
Tue 04/07 14Z 1.03 3007 76 67 -12 0.00
Tue 04/07 15Z 1.31 3006 72 66 -11 0.00
Tue 04/07 16Z 1.74 3007 69 75 -11 0.00
Tue 04/07 17Z 2.06 3008 66 79 -11 0.00
Tue 04/07 18Z 2.17 3109 63 74 -11 0.00
Tue 04/07 19Z 2.66 3009 62 65 -10 0.00
Tue 04/07 20Z 3.19 3010 64 57 -11 0.00
Tue 04/07 21Z 2.78 3011 66 48 -11 0.00
Tue 04/07 22Z 1.79 3112 67 30 -11 0.00
Tue 04/07 23Z 0.82 3113 64 22 -11 0.00
Wed 04/08 00Z 0.62 3015 60 26 -11 0.00
Wed 04/08 01Z 0.63 3016 56 30 -12 0.00
Wed 04/08 02Z 0.71 3017 52 34 -12 0.00
Wed 04/08 03Z 0.74 3018 45 38 -13 0.00
Wed 04/08 04Z 0.72 3019 39 35 -13 0.00
Wed 04/08 05Z 0.64 3019 36 27 -13 0.00
Wed 04/08 06Z 0.63 3019 41 24 -13 0.00
Wed 04/08 07Z 0.61 3019 45 22 -13 0.00
Wed 04/08 08Z 0.55 3018 47 19 -12 0.00
Wed 04/08 09Z 0.47 3016 48 17 -12 0.00
Wed 04/08 10Z 0.40 3014 48 15 -11 0.00
Wed 04/08 11Z 0.34 2913 46 15 -11 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