Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260507_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)
=== ===== === ==== ==== === === === ====
Thu 05/07 12Z 0.90 2717 96 26 -2 0.00
Thu 05/07 13Z 0.98 2817 84 27 -2 0.00
Thu 05/07 14Z 2.90 2818 82 36 -3 0.00
Thu 05/07 15Z 9.10 2817 79 38 -3 0.00
Thu 05/07 16Z 11.90 2716 74 36 -2 0.00
Thu 05/07 17Z 12.27 2817 67 39 -1 0.00
Thu 05/07 18Z 12.55 2817 60 40 -1 0.00
Thu 05/07 19Z 12.74 2818 55 38 0 0.00
Thu 05/07 20Z 12.99 2818 54 39 0 0.00
Thu 05/07 21Z 12.41 2818 54 39 0 0.00
Thu 05/07 22Z 11.09 2817 55 34 0 0.00
Thu 05/07 23Z 6.75 2916 55 30 0 0.00
Fri 05/08 00Z 1.91 2916 56 30 0 0.00
Fri 05/08 01Z 1.90 2917 58 35 0 0.00
Fri 05/08 02Z 1.35 2918 61 33 -1 0.00
Fri 05/08 03Z 1.19 2917 66 40 -1 0.00
Fri 05/08 04Z 1.35 2917 69 66 -2 0.00
Fri 05/08 05Z 1.16 2817 71 69 -2 0.00
Fri 05/08 06Z 1.01 2917 73 55 -2 0.00
Fri 05/08 07Z 0.99 2818 75 44 -2 0.00
Fri 05/08 08Z 0.98 2919 72 49 -2 0.00
Fri 05/08 09Z 0.87 2918 69 58 -2 0.00
Fri 05/08 10Z 0.78 2918 69 63 -3 0.00
Fri 05/08 11Z 0.75 2916 72 67 -3 0.00
Fri 05/08 12Z 1.38 2913 73 65 -3 0.00
Fri 05/08 13Z 4.80 2811 71 63 -3 0.00
Fri 05/08 14Z 6.85 2710 67 62 -3 0.00
Fri 05/08 15Z 6.94 2710 66 61 -2 0.00
Fri 05/08 16Z 7.06 2710 66 62 -2 0.00
Fri 05/08 17Z 7.14 2710 65 69 -1 0.00
Fri 05/08 18Z 7.36 2710 64 78 -1 0.00
Fri 05/08 19Z 7.41 2711 64 83 -1 0.00
Fri 05/08 20Z 6.41 2812 67 83 -1 0.00
Fri 05/08 21Z 6.29 2812 69 77 -1 0.00
Fri 05/08 22Z 3.35 2812 70 59 -1 0.00
Fri 05/08 23Z 1.31 2812 66 35 -1 0.00
Sat 05/09 00Z 1.16 2813 65 33 -1 0.00
Sat 05/09 01Z 1.08 2813 62 36 -1 0.00
Sat 05/09 02Z 1.41 2813 62 41 -1 0.00
Sat 05/09 03Z 1.10 2714 62 40 -1 0.00
Sat 05/09 04Z 1.02 2715 61 43 -1 0.00
Sat 05/09 05Z 0.81 2715 54 55 -1 0.00
Sat 05/09 06Z 0.72 2715 55 57 -1 0.00
Sat 05/09 07Z 0.66 2714 65 44 -1 0.00
Sat 05/09 08Z 0.59 2712 63 22 -1 0.00
Sat 05/09 09Z 0.50 2610 61 18 -1 0.00
Sat 05/09 10Z 0.45 2509 60 16 -1 0.00
Sat 05/09 11Z 0.40 2309 60 12 -1 0.00
Sat 05/09 12Z 0.37 2109 57 7 -1 0.00
Sat 05/09 13Z 0.76 1910 55 11 -1 0.00
Sat 05/09 14Z 0.85 1810 52 14 0 0.00
Sat 05/09 15Z 0.74 1811 50 18 0 0.00
Sat 05/09 16Z 0.98 1711 51 31 0 0.00
Sat 05/09 17Z 1.07 1711 56 51 0 0.00
Sat 05/09 18Z 1.28 1613 62 64 1 0.00
Sat 05/09 19Z 1.34 1614 68 71 1 0.00
Sat 05/09 20Z 1.03 1615 76 80 1 0.00
Sat 05/09 21Z 0.37 1717 82 79 1 0.01
Sat 05/09 22Z 0.19 1718 90 77 1 0.01
Sat 05/09 23Z 0.08 1720 94 78 2 0.01
Run total areal avg QPF for the greens is: 0.03 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