Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260420_1200
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)
=== ===== === ==== ==== === === === ====
Mon 04/20 12Z 0.86 2916 94 67 -9 0.00
Mon 04/20 13Z 1.09 3017 93 60 -10 0.01
Mon 04/20 14Z 1.38 3015 94 54 -10 0.00
Mon 04/20 15Z 3.29 3113 90 54 -10 0.00
Mon 04/20 16Z 4.70 3112 85 60 -10 0.00
Mon 04/20 17Z 5.35 3113 80 53 -10 0.01
Mon 04/20 18Z 5.91 3012 73 45 -10 0.00
Mon 04/20 19Z 6.36 3011 69 39 -9 0.00
Mon 04/20 20Z 6.16 3012 67 33 -9 0.00
Mon 04/20 21Z 5.40 3011 64 31 -9 0.00
Mon 04/20 22Z 4.59 3111 61 30 -9 0.00
Mon 04/20 23Z 2.64 3111 58 29 -9 0.00
Tue 04/21 00Z 1.47 3112 55 25 -9 0.00
Tue 04/21 01Z 1.31 3213 54 22 -9 0.00
Tue 04/21 02Z 1.53 3214 52 19 -10 0.00
Tue 04/21 03Z 1.39 3214 49 15 -10 0.00
Tue 04/21 04Z 1.03 3114 48 14 -10 0.00
Tue 04/21 05Z 0.86 3114 47 14 -11 0.00
Tue 04/21 06Z 0.70 3113 46 14 -11 0.00
Tue 04/21 07Z 0.64 3112 46 12 -11 0.00
Tue 04/21 08Z 0.56 3111 47 11 -11 0.00
Tue 04/21 09Z 0.49 3110 47 10 -11 0.00
Tue 04/21 10Z 0.51 3009 47 10 -11 0.00
Tue 04/21 11Z 0.39 3007 48 10 -11 0.00
Tue 04/21 12Z 0.36 2804 48 9 -10 0.00
Tue 04/21 13Z 1.49 2504 47 9 -10 0.00
Tue 04/21 14Z 2.50 2305 46 9 -10 0.00
Tue 04/21 15Z 3.44 2306 45 10 -9 0.00
Tue 04/21 16Z 2.79 2205 43 14 -8 0.00
Tue 04/21 17Z 2.53 2206 40 33 -7 0.00
Tue 04/21 18Z 2.67 2206 38 72 -6 0.00
Tue 04/21 19Z 2.65 2207 38 86 -6 0.00
Tue 04/21 20Z 2.27 2207 37 83 -5 0.00
Tue 04/21 21Z 1.65 2207 37 81 -5 0.00
Tue 04/21 22Z 0.54 2108 37 84 -4 0.00
Tue 04/21 23Z 0.24 2009 38 86 -4 0.00
Wed 04/22 00Z 0.33 2112 41 88 -4 0.00
Wed 04/22 01Z 0.44 2113 43 91 -4 0.00
Wed 04/22 02Z 0.48 2115 46 89 -4 0.00
Wed 04/22 03Z 0.55 2217 51 84 -4 0.00
Wed 04/22 04Z 0.62 2219 52 79 -3 0.00
Wed 04/22 05Z 0.64 2220 55 86 -4 0.00
Wed 04/22 06Z 0.51 2220 66 93 -4 0.00
Wed 04/22 07Z 0.31 2117 79 96 -3 0.00
Wed 04/22 08Z 0.20 2014 88 92 -3 0.00
Wed 04/22 09Z 0.15 2013 93 85 -3 0.01
Wed 04/22 10Z 0.16 2015 96 60 -3 0.01
Wed 04/22 11Z 0.16 2016 97 33 -3 0.01
Wed 04/22 12Z 0.19 2016 98 20 -3 0.01
Wed 04/22 13Z 0.20 2014 98 11 -3 0.01
Wed 04/22 14Z 0.18 2012 98 6 -3 0.01
Wed 04/22 15Z 0.15 2010 98 3 -3 0.01
Wed 04/22 16Z 0.12 2008 98 4 -3 0.01
Wed 04/22 17Z 0.11 2006 98 4 -3 0.00
Wed 04/22 18Z 0.12 2105 98 5 -3 0.00
Wed 04/22 19Z 0.12 2204 98 5 -3 0.00
Wed 04/22 20Z 0.15 2403 98 7 -3 0.00
Wed 04/22 21Z 0.17 2703 98 9 -3 0.00
Wed 04/22 22Z 0.22 2804 97 10 -3 0.00
Wed 04/22 23Z 0.24 3005 96 11 -3 0.00
Run total areal avg QPF for the greens is: 0.10 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