Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260507_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)
=== ===== === ==== ==== === === === ====
Thu 05/07 00Z 0.21 3112 95 98 3 0.00
Thu 05/07 01Z 0.28 3014 90 95 2 0.01
Thu 05/07 02Z 0.27 3114 82 90 2 0.01
Thu 05/07 03Z 0.33 3117 78 92 1 0.00
Thu 05/07 04Z 0.44 3017 85 92 0 0.01
Thu 05/07 05Z 0.52 3017 86 91 0 0.00
Thu 05/07 06Z 0.46 2915 84 83 0 0.00
Thu 05/07 07Z 0.53 2916 87 70 0 0.00
Thu 05/07 08Z 0.61 2817 91 55 0 0.00
Thu 05/07 09Z 0.66 2819 93 48 -1 0.01
Thu 05/07 10Z 0.57 2718 86 52 -1 0.01
Thu 05/07 11Z 0.68 2721 74 38 -2 0.00
Thu 05/07 12Z 0.57 2819 64 21 -2 0.00
Thu 05/07 13Z 0.70 2820 70 22 -3 0.00
Thu 05/07 14Z 0.93 2919 75 25 -3 0.00
Thu 05/07 15Z 5.71 2817 79 35 -3 0.00
Thu 05/07 16Z 10.26 2815 78 43 -2 0.00
Thu 05/07 17Z 10.46 2714 72 49 -1 0.00
Thu 05/07 18Z 10.81 2715 65 39 -1 0.00
Thu 05/07 19Z 11.83 2716 58 32 0 0.00
Thu 05/07 20Z 12.26 2717 54 28 0 0.00
Thu 05/07 21Z 11.83 2817 53 29 0 0.00
Thu 05/07 22Z 10.77 2817 55 28 0 0.00
Thu 05/07 23Z 7.33 2917 56 28 0 0.00
Fri 05/08 00Z 2.19 2919 58 25 -1 0.00
Fri 05/08 01Z 2.00 2919 63 27 -1 0.00
Fri 05/08 02Z 1.95 2919 65 27 -2 0.00
Fri 05/08 03Z 1.72 2919 69 27 -2 0.00
Fri 05/08 04Z 1.36 2919 72 30 -2 0.00
Fri 05/08 05Z 1.08 2919 72 37 -2 0.00
Fri 05/08 06Z 0.89 2918 72 45 -2 0.00
Fri 05/08 07Z 0.81 2918 71 42 -2 0.00
Fri 05/08 08Z 0.79 2918 70 57 -2 0.00
Fri 05/08 09Z 0.76 2917 69 56 -3 0.00
Fri 05/08 10Z 0.74 2916 68 55 -3 0.00
Fri 05/08 11Z 0.74 2915 71 58 -3 0.00
Fri 05/08 12Z 1.05 2814 76 60 -3 0.00
Fri 05/08 13Z 2.72 2813 78 56 -3 0.00
Fri 05/08 14Z 6.32 2711 73 54 -3 0.00
Fri 05/08 15Z 8.18 2711 72 56 -3 0.00
Fri 05/08 16Z 8.33 2712 73 52 -2 0.00
Fri 05/08 17Z 8.20 2812 68 53 -2 0.00
Fri 05/08 18Z 8.19 2812 68 57 -2 0.00
Fri 05/08 19Z 8.06 2812 70 52 -2 0.00
Fri 05/08 20Z 8.32 2812 68 54 -2 0.00
Fri 05/08 21Z 6.51 2711 69 34 -2 0.00
Fri 05/08 22Z 6.98 2711 67 27 -1 0.00
Fri 05/08 23Z 4.85 2712 66 23 -1 0.00
Sat 05/09 00Z 2.52 2714 66 19 -2 0.00
Sat 05/09 01Z 1.90 2714 66 13 -2 0.00
Sat 05/09 02Z 1.68 2715 65 12 -2 0.00
Sat 05/09 03Z 1.28 2714 64 15 -2 0.00
Sat 05/09 04Z 1.04 2713 60 19 -2 0.00
Sat 05/09 05Z 0.75 2712 57 19 -2 0.00
Sat 05/09 06Z 0.62 2611 56 19 -2 0.00
Sat 05/09 07Z 0.52 2610 55 23 -2 0.00
Sat 05/09 08Z 0.43 2609 54 21 -1 0.00
Sat 05/09 09Z 0.35 2507 54 18 -1 0.00
Sat 05/09 10Z 0.29 2406 54 19 -1 0.00
Sat 05/09 11Z 0.19 2106 53 17 -1 0.00
Run total areal avg QPF for the greens is: 0.05 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