Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260810_0600
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)
=== ===== === ==== ==== === === === ====
Mon 08/10 06Z 0.17 3212 72 36 14 0.00
Mon 08/10 07Z 0.17 3213 72 38 14 0.00
Mon 08/10 08Z 0.16 3213 73 37 13 0.00
Mon 08/10 09Z 0.14 3312 74 40 13 0.00
Mon 08/10 10Z 0.05 3410 76 39 13 0.00
Mon 08/10 11Z 0.07 0006 75 37 13 0.00
Mon 08/10 12Z 0.12 0703 73 33 13 0.00
Mon 08/10 13Z 0.09 1304 72 33 13 0.00
Mon 08/10 14Z 0.03 1607 74 34 13 0.00
Mon 08/10 15Z 0.14 1809 75 35 13 0.00
Mon 08/10 16Z 0.43 1910 77 38 13 0.00
Mon 08/10 17Z 1.37 2011 77 42 13 0.00
Mon 08/10 18Z 1.40 2112 76 50 14 0.00
Mon 08/10 19Z 1.65 2212 74 57 14 0.00
Mon 08/10 20Z 1.78 2112 74 58 14 0.00
Mon 08/10 21Z 1.54 2114 80 82 14 0.00
Mon 08/10 22Z 0.82 2016 82 87 14 0.00
Mon 08/10 23Z 0.78 2118 89 94 14 0.01
Tue 08/11 00Z 0.58 2217 88 80 14 0.01
Tue 08/11 01Z 0.69 2220 92 66 15 0.00
Tue 08/11 02Z 0.65 2421 89 69 15 0.09
Tue 08/11 03Z 0.62 2521 86 68 15 0.03
Tue 08/11 04Z 0.65 2623 89 71 15 0.00
Tue 08/11 05Z 0.66 2723 91 63 15 0.00
Tue 08/11 06Z 0.69 2723 92 57 14 0.01
Tue 08/11 07Z 0.77 2724 95 34 14 0.01
Tue 08/11 08Z 0.76 2825 95 29 13 0.02
Tue 08/11 09Z 0.64 2925 93 22 12 0.01
Tue 08/11 10Z 0.57 3025 91 23 12 0.01
Tue 08/11 11Z 0.50 3025 88 32 12 0.01
Tue 08/11 12Z 0.47 3123 86 40 12 0.01
Tue 08/11 13Z 0.47 3124 81 28 12 0.01
Tue 08/11 14Z 0.51 3024 79 22 11 0.00
Tue 08/11 15Z 0.61 3022 84 21 11 0.00
Tue 08/11 16Z 1.10 3019 86 23 11 0.00
Tue 08/11 17Z 5.48 3018 83 22 11 0.00
Tue 08/11 18Z 8.70 2917 78 19 12 0.00
Tue 08/11 19Z 8.12 2917 80 24 12 0.00
Tue 08/11 20Z 2.87 2919 78 19 12 0.02
Tue 08/11 21Z 1.81 2917 75 23 12 0.00
Tue 08/11 22Z 1.09 2916 73 34 13 0.01
Tue 08/11 23Z 1.07 2917 68 42 13 0.00
Wed 08/12 00Z 1.03 3019 70 26 12 0.00
Wed 08/12 01Z 0.86 3020 78 30 12 0.00
Wed 08/12 02Z 0.57 3018 85 32 12 0.00
Wed 08/12 03Z 0.52 3119 86 24 11 0.00
Wed 08/12 04Z 0.39 3119 84 24 11 0.00
Wed 08/12 05Z 0.35 3117 83 22 11 0.00
Wed 08/12 06Z 0.30 3116 84 23 11 0.00
Wed 08/12 07Z 0.30 3115 81 23 11 0.00
Wed 08/12 08Z 0.28 3115 79 22 11 0.00
Wed 08/12 09Z 0.31 3115 78 26 11 0.00
Wed 08/12 10Z 0.28 3114 79 33 11 0.00
Wed 08/12 11Z 0.25 3113 76 43 11 0.00
Wed 08/12 12Z 0.22 3112 72 75 11 0.00
Wed 08/12 13Z 0.23 3111 72 76 11 0.00
Wed 08/12 14Z 0.23 3110 71 73 11 0.00
Wed 08/12 15Z 0.26 3109 70 62 11 0.00
Wed 08/12 16Z 0.71 3108 69 52 11 0.00
Wed 08/12 17Z 1.02 3105 66 45 11 0.00
Run total areal avg QPF for the Central_Greens is: 0.26 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