Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260509_1200
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)
=== ===== === ==== ==== === === === ====
Sat 05/09 12Z 0.17 1812 62 32 0 0.00
Sat 05/09 13Z 0.18 1813 65 34 0 0.00
Sat 05/09 14Z 0.20 1712 74 56 0 0.00
Sat 05/09 15Z 0.39 1612 84 71 0 0.01
Sat 05/09 16Z 0.26 1714 93 79 0 0.03
Sat 05/09 17Z 0.06 1614 95 89 0 0.05
Sat 05/09 18Z 0.06 1615 96 97 1 0.06
Sat 05/09 19Z 0.08 1617 97 96 1 0.07
Sat 05/09 20Z 0.10 1719 98 94 2 0.04
Sat 05/09 21Z 0.15 1817 97 92 2 0.02
Sat 05/09 22Z 0.07 1717 96 93 3 0.02
Sat 05/09 23Z 0.12 1817 97 80 3 0.04
Sun 05/10 00Z 0.18 1918 98 58 4 0.02
Sun 05/10 01Z 0.24 2016 98 46 4 0.01
Sun 05/10 02Z 0.27 2017 98 23 4 0.01
Sun 05/10 03Z 0.30 2117 96 20 4 0.01
Sun 05/10 04Z 0.37 2119 95 23 4 0.01
Sun 05/10 05Z 0.42 2122 91 42 5 0.01
Sun 05/10 06Z 0.34 2120 77 52 7 0.01
Sun 05/10 07Z 0.35 2121 71 63 7 0.01
Sun 05/10 08Z 0.39 2222 66 67 8 0.01
Sun 05/10 09Z 0.42 2223 69 73 7 0.01
Sun 05/10 10Z 0.54 2225 79 86 7 0.01
Sun 05/10 11Z 0.58 2322 89 91 6 0.01
Sun 05/10 12Z 0.71 2325 94 94 5 0.06
Sun 05/10 13Z 0.65 2421 92 94 4 0.04
Sun 05/10 14Z 0.69 2518 87 69 4 0.01
Sun 05/10 15Z 0.88 2518 83 60 3 0.00
Sun 05/10 16Z 3.75 2518 88 25 3 0.00
Sun 05/10 17Z 4.33 2417 89 11 3 0.01
Sun 05/10 18Z 5.90 2517 87 14 3 0.01
Sun 05/10 19Z 9.42 2516 71 18 3 0.00
Sun 05/10 20Z 12.15 2517 56 19 3 0.00
Sun 05/10 21Z 12.59 2617 47 19 3 0.00
Sun 05/10 22Z 11.92 2618 43 21 3 0.00
Sun 05/10 23Z 3.98 2719 43 22 2 0.00
Mon 05/11 00Z 1.99 2721 44 21 2 0.00
Mon 05/11 01Z 1.40 2822 42 21 1 0.00
Mon 05/11 02Z 1.01 2920 46 22 0 0.00
Mon 05/11 03Z 0.77 2919 55 25 0 0.00
Mon 05/11 04Z 0.60 3018 64 25 0 0.00
Mon 05/11 05Z 0.48 3017 75 23 -1 0.00
Mon 05/11 06Z 0.42 3116 83 21 -2 0.00
Mon 05/11 07Z 0.40 3115 84 20 -2 0.00
Mon 05/11 08Z 0.33 3114 85 17 -2 0.00
Mon 05/11 09Z 0.30 3113 84 15 -3 0.00
Mon 05/11 10Z 0.32 3113 84 17 -3 0.00
Mon 05/11 11Z 0.36 3112 86 20 -3 0.00
Mon 05/11 12Z 0.41 3011 88 24 -3 0.00
Mon 05/11 13Z 1.16 3010 86 26 -3 0.00
Mon 05/11 14Z 2.61 2909 79 27 -3 0.00
Mon 05/11 15Z 3.74 2909 70 27 -2 0.00
Mon 05/11 16Z 4.64 2908 72 31 -2 0.00
Mon 05/11 17Z 3.95 2809 79 40 -2 0.00
Mon 05/11 18Z 4.00 2809 77 44 -1 0.00
Mon 05/11 19Z 4.34 2909 71 47 -1 0.00
Mon 05/11 20Z 3.45 3009 69 45 -1 0.00
Mon 05/11 21Z 3.06 3109 69 43 -1 0.00
Mon 05/11 22Z 2.23 3111 72 48 -1 0.00
Mon 05/11 23Z 0.92 3212 76 52 -2 0.00
Run total areal avg QPF for the Central_Greens is: 0.60 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