Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260420_1800
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 18Z 5.34 3010 83 58 -9 0.00
Mon 04/20 19Z 4.77 3112 77 54 -8 0.00
Mon 04/20 20Z 4.70 3113 74 56 -8 0.00
Mon 04/20 21Z 4.14 3113 74 51 -8 0.00
Mon 04/20 22Z 3.84 3213 72 41 -9 0.00
Mon 04/20 23Z 3.39 3114 67 31 -9 0.00
Tue 04/21 00Z 2.25 3214 63 23 -9 0.00
Tue 04/21 01Z 2.18 3214 60 18 -9 0.00
Tue 04/21 02Z 1.82 3114 58 16 -9 0.00
Tue 04/21 03Z 1.46 3114 56 16 -10 0.00
Tue 04/21 04Z 1.21 3213 55 14 -10 0.00
Tue 04/21 05Z 0.88 3212 54 10 -10 0.00
Tue 04/21 06Z 0.67 3111 53 8 -10 0.00
Tue 04/21 07Z 0.60 3110 53 8 -10 0.00
Tue 04/21 08Z 0.54 3008 53 7 -10 0.00
Tue 04/21 09Z 0.49 3007 54 7 -10 0.00
Tue 04/21 10Z 0.55 2907 55 7 -10 0.00
Tue 04/21 11Z 0.48 2806 57 8 -10 0.00
Tue 04/21 12Z 0.84 2606 57 9 -10 0.00
Tue 04/21 13Z 2.27 2405 57 9 -10 0.00
Tue 04/21 14Z 3.32 2306 56 10 -9 0.00
Tue 04/21 15Z 3.35 2306 54 10 -9 0.00
Tue 04/21 16Z 3.26 2306 51 14 -8 0.00
Tue 04/21 17Z 3.26 2206 48 25 -7 0.00
Tue 04/21 18Z 3.30 2207 46 64 -6 0.00
Tue 04/21 19Z 2.79 2206 43 83 -6 0.00
Tue 04/21 20Z 2.48 2306 42 84 -5 0.00
Tue 04/21 21Z 1.52 2206 40 84 -5 0.00
Tue 04/21 22Z 0.71 2206 39 84 -4 0.00
Tue 04/21 23Z 0.27 2107 38 79 -4 0.00
Wed 04/22 00Z 0.24 2108 38 79 -4 0.00
Wed 04/22 01Z 0.31 2110 41 84 -4 0.00
Wed 04/22 02Z 0.34 2112 44 85 -4 0.00
Wed 04/22 03Z 0.38 2113 46 84 -3 0.00
Wed 04/22 04Z 0.39 2115 48 79 -3 0.00
Wed 04/22 05Z 0.42 2117 50 81 -3 0.00
Wed 04/22 06Z 0.42 2117 52 84 -3 0.00
Wed 04/22 07Z 0.39 2117 56 87 -3 0.00
Wed 04/22 08Z 0.29 2116 61 82 -3 0.00
Wed 04/22 09Z 0.19 2015 65 76 -2 0.00
Wed 04/22 10Z 0.12 1914 71 67 -2 0.00
Wed 04/22 11Z 0.08 1914 79 57 -3 0.00
Wed 04/22 12Z 0.08 1914 87 49 -3 0.00
Wed 04/22 13Z 0.08 1914 90 33 -3 0.00
Wed 04/22 14Z 0.12 1913 91 21 -3 0.00
Wed 04/22 15Z 0.13 1913 92 14 -3 0.01
Wed 04/22 16Z 0.13 1911 94 13 -3 0.01
Wed 04/22 17Z 0.14 1910 95 10 -3 0.01
Wed 04/22 18Z 0.12 1909 97 7 -3 0.01
Wed 04/22 19Z 0.11 2007 98 5 -3 0.01
Wed 04/22 20Z 0.14 2106 98 5 -3 0.01
Wed 04/22 21Z 0.15 2205 98 7 -2 0.00
Wed 04/22 22Z 0.15 2404 98 7 -2 0.00
Wed 04/22 23Z 0.17 2704 97 9 -2 0.00
Thu 04/23 00Z 0.15 2904 97 12 -3 0.00
Thu 04/23 01Z 0.18 3005 97 12 -3 0.00
Thu 04/23 02Z 0.14 3105 96 13 -3 0.00
Thu 04/23 03Z 0.15 3105 95 17 -2 0.00
Thu 04/23 04Z 0.16 3105 95 23 -2 0.00
Thu 04/23 05Z 0.20 3006 95 28 -3 0.00
Run total areal avg QPF for the greens is: 0.06 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