Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260128_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)
=== ===== === ==== ==== === === === ====
Wed 01/28 12Z 0.42 3017 80 32 -19 0.00
Wed 01/28 13Z 0.46 2918 80 28 -19 0.00
Wed 01/28 14Z 0.44 2916 80 28 -19 0.00
Wed 01/28 15Z 0.45 2815 78 35 -19 0.00
Wed 01/28 16Z 0.45 2813 72 43 -19 0.00
Wed 01/28 17Z 0.50 2812 69 52 -18 0.00
Wed 01/28 18Z 0.56 2912 69 61 -18 0.00
Wed 01/28 19Z 0.61 2811 70 63 -18 0.00
Wed 01/28 20Z 0.63 2810 75 56 -18 0.00
Wed 01/28 21Z 0.73 2711 83 52 -18 0.00
Wed 01/28 22Z 0.67 2811 83 49 -18 0.00
Wed 01/28 23Z 0.71 2912 79 48 -18 0.00
Thu 01/29 00Z 0.59 2912 77 48 -18 0.00
Thu 01/29 01Z 0.45 2910 80 52 -18 0.00
Thu 01/29 02Z 0.41 2909 84 55 -18 0.00
Thu 01/29 03Z 0.42 2809 87 57 -18 0.00
Thu 01/29 04Z 0.39 2809 91 62 -18 0.00
Thu 01/29 05Z 0.35 2909 90 65 -18 0.00
Thu 01/29 06Z 0.33 2910 87 65 -18 0.00
Thu 01/29 07Z 0.34 2911 83 64 -18 0.00
Thu 01/29 08Z 0.34 2911 83 62 -19 0.00
Thu 01/29 09Z 0.35 2911 84 56 -19 0.00
Thu 01/29 10Z 0.40 2812 85 52 -19 0.00
Thu 01/29 11Z 0.43 2814 85 50 -19 0.00
Thu 01/29 12Z 0.41 2814 82 51 -19 0.00
Thu 01/29 13Z 0.37 2914 83 59 -19 0.00
Thu 01/29 14Z 0.31 3012 83 64 -19 0.00
Thu 01/29 15Z 0.32 3011 85 68 -19 0.00
Thu 01/29 16Z 0.37 3011 87 68 -19 0.00
Thu 01/29 17Z 0.57 3011 87 66 -19 0.00
Thu 01/29 18Z 1.37 3014 88 62 -19 0.00
Thu 01/29 19Z 2.26 3015 90 59 -19 0.00
Thu 01/29 20Z 1.73 3014 92 60 -19 0.00
Thu 01/29 21Z 1.45 3015 92 59 -19 0.01
Thu 01/29 22Z 1.43 3018 93 54 -19 0.01
Thu 01/29 23Z 0.92 3121 92 48 -20 0.01
Fri 01/30 00Z 0.75 3121 92 44 -20 0.00
Fri 01/30 01Z 0.69 3123 89 39 -21 0.00
Fri 01/30 02Z 0.75 3024 86 38 -22 0.00
Fri 01/30 03Z 0.78 3025 86 37 -23 0.00
Fri 01/30 04Z 0.74 3025 86 35 -23 0.00
Fri 01/30 05Z 0.73 3025 86 34 -24 0.00
Fri 01/30 06Z 0.71 2926 83 32 -24 0.00
Fri 01/30 07Z 0.63 2928 75 28 -23 0.00
Fri 01/30 08Z 0.56 3030 67 27 -23 0.00
Fri 01/30 09Z 0.49 3029 65 28 -23 0.00
Fri 01/30 10Z 0.41 3028 63 30 -22 0.00
Fri 01/30 11Z 0.35 3028 62 37 -22 0.00
Fri 01/30 12Z 0.32 3127 62 49 -22 0.00
Fri 01/30 13Z 0.31 3026 65 61 -21 0.00
Fri 01/30 14Z 0.29 3025 69 72 -20 0.00
Fri 01/30 15Z 0.28 3024 72 79 -20 0.00
Fri 01/30 16Z 0.28 3022 75 83 -20 0.00
Fri 01/30 17Z 0.29 3021 77 81 -20 0.00
Fri 01/30 18Z 0.30 3020 76 80 -19 0.00
Fri 01/30 19Z 0.31 3019 77 77 -19 0.00
Fri 01/30 20Z 0.35 2919 79 74 -19 0.00
Fri 01/30 21Z 0.38 2919 80 67 -19 0.00
Fri 01/30 22Z 0.37 2920 81 63 -19 0.00
Fri 01/30 23Z 0.32 3021 83 60 -18 0.00
Run total areal avg QPF for the Central_Greens is: 0.03 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