Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260508_0000
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)
=== ===== === ==== ==== === === === ====
Fri 05/08 00Z 0.60 2913 61 36 0 0.00
Fri 05/08 01Z 0.79 2915 59 43 0 0.00
Fri 05/08 02Z 1.01 2916 58 33 -1 0.00
Fri 05/08 03Z 1.21 2917 58 35 -1 0.00
Fri 05/08 04Z 1.14 2918 63 45 -1 0.00
Fri 05/08 05Z 0.94 2919 66 51 -2 0.00
Fri 05/08 06Z 0.85 2920 67 45 -2 0.00
Fri 05/08 07Z 0.79 2921 66 41 -2 0.00
Fri 05/08 08Z 0.74 2921 69 49 -2 0.00
Fri 05/08 09Z 0.67 3020 70 57 -3 0.00
Fri 05/08 10Z 0.61 3019 68 63 -3 0.00
Fri 05/08 11Z 0.61 2917 69 66 -3 0.00
Fri 05/08 12Z 0.92 2915 68 71 -3 0.00
Fri 05/08 13Z 4.26 2812 66 77 -3 0.00
Fri 05/08 14Z 6.95 2811 64 74 -3 0.00
Fri 05/08 15Z 7.06 2710 64 69 -2 0.00
Fri 05/08 16Z 7.25 2610 64 64 -1 0.00
Fri 05/08 17Z 7.49 2510 63 71 -1 0.00
Fri 05/08 18Z 6.78 2511 68 82 -1 0.00
Fri 05/08 19Z 5.86 2613 74 87 -1 0.00
Fri 05/08 20Z 5.22 2613 77 83 -1 0.01
Fri 05/08 21Z 5.95 2712 72 74 -1 0.00
Fri 05/08 22Z 5.12 2812 69 64 0 0.00
Fri 05/08 23Z 2.84 2812 69 59 -1 0.00
Sat 05/09 00Z 1.11 2812 69 39 -1 0.00
Sat 05/09 01Z 1.28 2814 69 33 -1 0.00
Sat 05/09 02Z 1.22 2914 70 34 -1 0.00
Sat 05/09 03Z 1.24 2814 67 23 -2 0.00
Sat 05/09 04Z 0.92 2814 66 20 -2 0.00
Sat 05/09 05Z 0.66 2813 63 24 -2 0.00
Sat 05/09 06Z 0.56 2812 63 21 -2 0.00
Sat 05/09 07Z 0.51 2811 63 14 -2 0.00
Sat 05/09 08Z 0.45 2809 62 12 -2 0.00
Sat 05/09 09Z 0.42 2708 60 9 -1 0.00
Sat 05/09 10Z 0.34 2506 60 6 -1 0.00
Sat 05/09 11Z 0.26 2206 58 6 -1 0.00
Sat 05/09 12Z 0.27 2008 55 9 -1 0.00
Sat 05/09 13Z 0.37 1811 53 12 -1 0.00
Sat 05/09 14Z 0.49 1712 51 27 0 0.00
Sat 05/09 15Z 0.74 1714 55 52 -1 0.00
Sat 05/09 16Z 0.28 1714 72 71 -1 0.00
Sat 05/09 17Z 0.08 1716 90 94 0 0.04
Sat 05/09 18Z 0.03 1719 96 95 0 0.05
Sat 05/09 19Z 0.06 1722 97 96 0 0.04
Sat 05/09 20Z 0.10 1822 97 95 1 0.03
Sat 05/09 21Z 0.14 1821 98 91 1 0.02
Sat 05/09 22Z 0.17 1822 98 76 2 0.02
Sat 05/09 23Z 0.24 1922 98 66 2 0.02
Sun 05/10 00Z 0.30 2023 98 36 3 0.02
Sun 05/10 01Z 0.36 2121 98 39 3 0.02
Sun 05/10 02Z 0.43 2121 98 59 3 0.01
Sun 05/10 03Z 0.50 2123 97 74 4 0.01
Sun 05/10 04Z 0.56 2225 94 72 5 0.01
Sun 05/10 05Z 0.58 2227 88 74 5 0.01
Sun 05/10 06Z 0.81 2330 95 90 5 0.01
Sun 05/10 07Z 0.90 2329 95 91 4 0.02
Sun 05/10 08Z 0.96 2427 94 81 3 0.05
Sun 05/10 09Z 0.89 2525 92 72 3 0.02
Sun 05/10 10Z 0.79 2524 77 68 3 0.01
Sun 05/10 11Z 0.68 2623 56 42 3 0.00
Run total areal avg QPF for the Central_Greens is: 0.42 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