Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260615_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 06/15 18Z 2.48 2911 93 18 7 0.00
Mon 06/15 19Z 2.42 2912 91 16 7 0.00
Mon 06/15 20Z 3.22 2913 89 19 7 0.00
Mon 06/15 21Z 2.27 2916 90 25 7 0.01
Mon 06/15 22Z 1.05 2918 93 25 7 0.01
Mon 06/15 23Z 0.83 3021 95 28 6 0.01
Tue 06/16 00Z 0.81 3022 95 22 6 0.01
Tue 06/16 01Z 0.72 3021 93 23 6 0.01
Tue 06/16 02Z 0.70 3021 94 24 5 0.01
Tue 06/16 03Z 0.59 3121 92 25 5 0.00
Tue 06/16 04Z 0.61 3123 90 26 5 0.00
Tue 06/16 05Z 0.63 3123 95 31 5 0.00
Tue 06/16 06Z 0.65 3122 95 25 4 0.01
Tue 06/16 07Z 0.59 3222 95 8 4 0.00
Tue 06/16 08Z 0.60 3120 96 4 4 0.01
Tue 06/16 09Z 0.47 3218 93 7 4 0.01
Tue 06/16 10Z 0.37 3218 87 12 5 0.00
Tue 06/16 11Z 0.31 3216 82 18 5 0.00
Tue 06/16 12Z 0.29 3113 82 21 5 0.00
Tue 06/16 13Z 0.33 3112 84 30 6 0.00
Tue 06/16 14Z 0.44 3012 84 37 6 0.00
Tue 06/16 15Z 1.66 3011 81 37 6 0.00
Tue 06/16 16Z 3.14 2910 77 42 7 0.00
Tue 06/16 17Z 4.47 2809 73 44 7 0.00
Tue 06/16 18Z 5.43 2709 72 45 8 0.00
Tue 06/16 19Z 5.95 2609 73 44 8 0.00
Tue 06/16 20Z 5.57 2509 73 41 9 0.00
Tue 06/16 21Z 4.76 2509 73 41 9 0.00
Tue 06/16 22Z 2.91 2409 73 39 9 0.00
Tue 06/16 23Z 1.08 2309 71 31 9 0.00
Wed 06/17 00Z 0.63 2310 66 31 9 0.00
Wed 06/17 01Z 0.67 2312 64 29 9 0.00
Wed 06/17 02Z 0.75 2414 65 27 9 0.00
Wed 06/17 03Z 0.77 2514 67 32 9 0.00
Wed 06/17 04Z 0.75 2614 68 31 9 0.00
Wed 06/17 05Z 0.66 2613 70 24 9 0.00
Wed 06/17 06Z 0.62 2611 70 25 8 0.00
Wed 06/17 07Z 0.51 2509 71 26 8 0.00
Wed 06/17 08Z 0.43 2408 71 23 8 0.00
Wed 06/17 09Z 0.35 2308 72 26 8 0.00
Wed 06/17 10Z 0.30 2207 72 26 8 0.00
Wed 06/17 11Z 0.31 2108 72 26 8 0.00
Wed 06/17 12Z 0.34 2108 73 27 8 0.00
Wed 06/17 13Z 0.68 2006 75 25 8 0.00
Wed 06/17 14Z 0.77 1905 76 22 8 0.00
Wed 06/17 15Z 0.42 1705 75 18 9 0.00
Wed 06/17 16Z 0.46 1705 76 15 9 0.00
Wed 06/17 17Z 0.30 1706 77 16 9 0.00
Wed 06/17 18Z 0.34 1707 76 12 9 0.00
Wed 06/17 19Z 0.49 1708 75 10 10 0.00
Wed 06/17 20Z 0.29 1808 73 11 10 0.00
Wed 06/17 21Z 0.35 1808 72 14 10 0.00
Wed 06/17 22Z 0.26 1809 71 11 11 0.00
Wed 06/17 23Z 0.07 1810 71 13 11 0.00
Thu 06/18 00Z 0.06 1711 71 20 11 0.00
Thu 06/18 01Z 0.17 1913 72 23 11 0.00
Thu 06/18 02Z 0.24 1915 72 26 11 0.00
Thu 06/18 03Z 0.24 1916 75 31 10 0.00
Thu 06/18 04Z 0.50 2020 79 32 10 0.00
Thu 06/18 05Z 0.43 2021 82 39 11 0.00
Run total areal avg QPF for the greens is: 0.09 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