Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260510_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)
=== ===== === ==== ==== === === === ====
Sun 05/10 00Z 0.14 1815 97 53 2 0.00
Sun 05/10 01Z 0.19 1918 96 39 3 0.01
Sun 05/10 02Z 0.25 1919 96 35 3 0.01
Sun 05/10 03Z 0.27 1920 96 33 3 0.01
Sun 05/10 04Z 0.38 2021 97 33 3 0.01
Sun 05/10 05Z 0.44 2122 96 35 3 0.00
Sun 05/10 06Z 0.50 2123 94 46 4 0.00
Sun 05/10 07Z 0.52 2223 92 49 4 0.01
Sun 05/10 08Z 0.56 2323 93 64 5 0.01
Sun 05/10 09Z 0.61 2322 94 82 5 0.02
Sun 05/10 10Z 0.61 2422 96 81 5 0.01
Sun 05/10 11Z 0.58 2421 94 59 5 0.01
Sun 05/10 12Z 0.55 2321 91 53 5 0.01
Sun 05/10 13Z 0.55 2421 88 69 5 0.01
Sun 05/10 14Z 0.59 2421 86 73 5 0.00
Sun 05/10 15Z 0.66 2420 87 81 5 0.00
Sun 05/10 16Z 0.96 2419 92 92 4 0.00
Sun 05/10 17Z 0.76 2417 88 73 4 0.02
Sun 05/10 18Z 1.75 2414 88 28 4 0.00
Sun 05/10 19Z 3.58 2514 91 23 4 0.00
Sun 05/10 20Z 4.14 2515 81 14 4 0.01
Sun 05/10 21Z 7.22 2617 68 16 4 0.00
Sun 05/10 22Z 10.23 2719 46 17 4 0.00
Sun 05/10 23Z 5.18 2720 43 19 3 0.00
Mon 05/11 00Z 2.08 2721 39 25 2 0.00
Mon 05/11 01Z 1.50 2822 42 26 1 0.00
Mon 05/11 02Z 1.11 2921 52 24 0 0.00
Mon 05/11 03Z 0.99 2920 64 29 0 0.00
Mon 05/11 04Z 1.00 3020 74 22 -1 0.00
Mon 05/11 05Z 0.87 3020 76 19 -1 0.00
Mon 05/11 06Z 0.63 3119 80 17 -2 0.00
Mon 05/11 07Z 0.52 3117 81 16 -2 0.00
Mon 05/11 08Z 0.41 3114 82 17 -2 0.00
Mon 05/11 09Z 0.35 3113 84 17 -2 0.00
Mon 05/11 10Z 0.31 3111 85 19 -3 0.00
Mon 05/11 11Z 0.30 3009 85 20 -3 0.00
Mon 05/11 12Z 0.34 2908 85 21 -3 0.00
Mon 05/11 13Z 0.47 2908 84 26 -3 0.00
Mon 05/11 14Z 1.83 2908 79 29 -3 0.00
Mon 05/11 15Z 3.63 2808 68 32 -2 0.00
Mon 05/11 16Z 5.15 2809 69 38 -2 0.00
Mon 05/11 17Z 5.46 2909 69 45 -1 0.00
Mon 05/11 18Z 5.61 2810 67 66 -1 0.00
Mon 05/11 19Z 4.94 2910 63 65 -1 0.00
Mon 05/11 20Z 5.67 2911 62 84 -1 0.00
Mon 05/11 21Z 4.41 2911 68 82 -1 0.00
Mon 05/11 22Z 2.71 3012 73 77 -1 0.00
Mon 05/11 23Z 0.86 3113 77 65 -2 0.00
Tue 05/12 00Z 0.41 3216 72 69 -2 0.00
Tue 05/12 01Z 0.40 3217 74 64 -2 0.00
Tue 05/12 02Z 0.41 3217 77 60 -3 0.00
Tue 05/12 03Z 0.56 3218 79 50 -3 0.00
Tue 05/12 04Z 0.57 3219 80 44 -4 0.00
Tue 05/12 05Z 0.51 3220 75 46 -4 0.00
Tue 05/12 06Z 0.46 3220 73 35 -4 0.00
Tue 05/12 07Z 0.40 3320 74 25 -4 0.00
Tue 05/12 08Z 0.35 3318 74 31 -5 0.00
Tue 05/12 09Z 0.32 3317 74 45 -5 0.00
Tue 05/12 10Z 0.31 3216 72 48 -5 0.00
Tue 05/12 11Z 0.36 3216 72 33 -5 0.00
Run total areal avg QPF for the Central_Greens is: 0.15 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