Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260507_1800
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Thu 05/07 18Z 7.76 2811 67 45 0 0.00
Thu 05/07 19Z 8.82 2713 65 32 0 0.00
Thu 05/07 20Z 9.22 2714 65 33 0 0.00
Thu 05/07 21Z 9.93 2715 63 34 0 0.00
Thu 05/07 22Z 8.83 2815 63 29 0 0.00
Thu 05/07 23Z 5.61 2815 62 25 0 0.00
Fri 05/08 00Z 2.31 2917 60 25 0 0.00
Fri 05/08 01Z 1.45 2917 60 28 -1 0.00
Fri 05/08 02Z 1.12 3017 63 31 -1 0.00
Fri 05/08 03Z 0.93 3016 65 34 -1 0.00
Fri 05/08 04Z 0.97 3016 69 50 -2 0.00
Fri 05/08 05Z 0.82 2916 72 47 -2 0.00
Fri 05/08 06Z 0.70 3017 73 53 -2 0.00
Fri 05/08 07Z 0.63 3016 74 40 -2 0.00
Fri 05/08 08Z 0.64 3015 75 33 -2 0.00
Fri 05/08 09Z 0.58 3015 71 34 -2 0.00
Fri 05/08 10Z 0.56 2915 70 37 -2 0.00
Fri 05/08 11Z 0.55 2914 69 43 -2 0.00
Fri 05/08 12Z 0.94 2813 67 36 -3 0.00
Fri 05/08 13Z 5.81 2813 66 32 -3 0.00
Fri 05/08 14Z 8.12 2712 63 39 -2 0.00
Fri 05/08 15Z 8.03 2711 63 55 -2 0.00
Fri 05/08 16Z 7.66 2711 63 70 -1 0.00
Fri 05/08 17Z 7.74 2711 61 81 -1 0.00
Fri 05/08 18Z 7.97 2711 61 85 0 0.00
Fri 05/08 19Z 6.14 2711 65 87 0 0.00
Fri 05/08 20Z 6.79 2711 63 84 0 0.00
Fri 05/08 21Z 5.86 2711 68 79 0 0.00
Fri 05/08 22Z 3.61 2710 69 64 0 0.00
Fri 05/08 23Z 1.67 2711 70 56 0 0.00
Sat 05/09 00Z 0.89 2713 69 47 0 0.00
Sat 05/09 01Z 1.36 2714 69 30 0 0.00
Sat 05/09 02Z 1.30 2814 67 21 -1 0.00
Sat 05/09 03Z 1.12 2813 68 28 -1 0.00
Sat 05/09 04Z 0.96 2713 68 37 -1 0.00
Sat 05/09 05Z 0.80 2712 68 36 -1 0.00
Sat 05/09 06Z 0.61 2611 65 34 -1 0.00
Sat 05/09 07Z 0.50 2511 61 44 -1 0.00
Sat 05/09 08Z 0.42 2510 55 34 -1 0.00
Sat 05/09 09Z 0.36 2508 51 18 0 0.00
Sat 05/09 10Z 0.33 2408 47 11 0 0.00
Sat 05/09 11Z 0.31 2209 44 7 0 0.00
Sat 05/09 12Z 0.30 2010 41 6 0 0.00
Sat 05/09 13Z 0.35 1911 46 6 0 0.00
Sat 05/09 14Z 1.38 1812 58 15 0 0.00
Sat 05/09 15Z 1.48 1813 75 38 0 0.00
Sat 05/09 16Z 0.58 1814 89 65 0 0.01
Sat 05/09 17Z 0.23 1714 92 90 0 0.02
Sat 05/09 18Z 0.05 1614 95 97 0 0.04
Sat 05/09 19Z 0.12 1517 96 93 0 0.05
Sat 05/09 20Z 0.17 1519 96 89 0 0.03
Sat 05/09 21Z 0.11 1518 96 82 1 0.02
Sat 05/09 22Z 0.06 1717 97 86 2 0.02
Sat 05/09 23Z 0.10 1817 98 80 3 0.01
Sun 05/10 00Z 0.18 1917 98 81 3 0.01
Sun 05/10 01Z 0.28 2018 98 62 3 0.01
Sun 05/10 02Z 0.39 2021 98 40 3 0.02
Sun 05/10 03Z 0.45 2119 98 42 3 0.01
Sun 05/10 04Z 0.55 2220 98 41 3 0.01
Sun 05/10 05Z 0.57 2221 96 44 3 0.01
Run total areal avg QPF for the Central_Greens is: 0.27 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