Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260128_0000
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Wed 01/28 00Z 0.82 2514 83 75 -19 0.00
Wed 01/28 01Z 1.10 2719 86 75 -20 0.00
Wed 01/28 02Z 1.09 2720 77 72 -20 0.00
Wed 01/28 03Z 0.95 2721 80 70 -20 0.00
Wed 01/28 04Z 0.86 2722 85 69 -20 0.01
Wed 01/28 05Z 0.83 2821 87 69 -20 0.01
Wed 01/28 06Z 0.71 2920 87 67 -20 0.01
Wed 01/28 07Z 0.62 2919 88 64 -20 0.01
Wed 01/28 08Z 0.60 2919 90 62 -20 0.00
Wed 01/28 09Z 0.62 2920 89 59 -20 0.00
Wed 01/28 10Z 0.58 2920 87 49 -20 0.00
Wed 01/28 11Z 0.59 2920 90 41 -20 0.00
Wed 01/28 12Z 0.56 2919 89 32 -20 0.00
Wed 01/28 13Z 0.48 3017 87 27 -20 0.00
Wed 01/28 14Z 0.40 3015 84 25 -20 0.00
Wed 01/28 15Z 0.40 2914 82 28 -19 0.00
Wed 01/28 16Z 0.44 2813 79 38 -19 0.00
Wed 01/28 17Z 0.49 2812 76 48 -19 0.00
Wed 01/28 18Z 0.59 2810 72 54 -19 0.00
Wed 01/28 19Z 0.86 2809 69 56 -19 0.00
Wed 01/28 20Z 1.04 2809 72 57 -19 0.00
Wed 01/28 21Z 0.64 2809 80 60 -19 0.00
Wed 01/28 22Z 0.53 2809 86 62 -19 0.00
Wed 01/28 23Z 0.57 2810 86 67 -19 0.00
Thu 01/29 00Z 0.64 2811 84 72 -19 0.00
Thu 01/29 01Z 0.65 2811 83 78 -19 0.00
Thu 01/29 02Z 0.55 2911 83 80 -19 0.00
Thu 01/29 03Z 0.44 3011 85 79 -18 0.01
Thu 01/29 04Z 0.41 3012 86 79 -18 0.01
Thu 01/29 05Z 0.45 3013 88 79 -18 0.01
Thu 01/29 06Z 0.47 3113 89 78 -19 0.01
Thu 01/29 07Z 0.48 3114 91 78 -19 0.01
Thu 01/29 08Z 0.52 3115 92 77 -19 0.01
Thu 01/29 09Z 0.51 3115 93 75 -19 0.01
Thu 01/29 10Z 0.46 3115 93 72 -19 0.00
Thu 01/29 11Z 0.43 3115 92 69 -19 0.00
Thu 01/29 12Z 0.41 3114 90 67 -19 0.00
Thu 01/29 13Z 0.40 3014 89 66 -19 0.00
Thu 01/29 14Z 0.40 2914 87 65 -19 0.00
Thu 01/29 15Z 0.45 2914 86 63 -19 0.00
Thu 01/29 16Z 0.58 2915 87 60 -19 0.00
Thu 01/29 17Z 0.83 3016 89 56 -19 0.00
Thu 01/29 18Z 1.47 3017 90 54 -19 0.00
Thu 01/29 19Z 3.11 3017 90 52 -19 0.00
Thu 01/29 20Z 3.36 2918 89 50 -19 0.00
Thu 01/29 21Z 2.69 2920 87 49 -19 0.00
Thu 01/29 22Z 2.64 2923 84 47 -20 0.00
Thu 01/29 23Z 1.56 2925 84 43 -20 0.00
Fri 01/30 00Z 1.34 2926 84 39 -21 0.00
Fri 01/30 01Z 1.15 2927 83 36 -21 0.00
Fri 01/30 02Z 1.03 3027 82 34 -22 0.00
Fri 01/30 03Z 1.04 3027 85 30 -22 0.00
Fri 01/30 04Z 0.95 3026 84 28 -23 0.00
Fri 01/30 05Z 0.82 3027 82 27 -23 0.00
Fri 01/30 06Z 0.75 2927 80 27 -23 0.00
Fri 01/30 07Z 0.69 2927 77 29 -23 0.00
Fri 01/30 08Z 0.64 2927 75 34 -22 0.00
Fri 01/30 09Z 0.59 2927 74 38 -22 0.00
Fri 01/30 10Z 0.53 2927 72 42 -22 0.00
Fri 01/30 11Z 0.46 3026 69 46 -21 0.00
Run total areal avg QPF for the greens is: 0.11 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