Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260214_0600
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)
=== ===== === ==== ==== === === === ====
Sat 02/14 06Z 0.42 2616 74 62 -10 0.00
Sat 02/14 07Z 0.54 2719 79 62 -11 0.00
Sat 02/14 08Z 0.53 2819 83 63 -11 0.00
Sat 02/14 09Z 0.53 2817 87 69 -11 0.00
Sat 02/14 10Z 0.55 2917 88 77 -11 0.00
Sat 02/14 11Z 0.52 2816 90 79 -11 0.00
Sat 02/14 12Z 0.51 2817 93 79 -11 0.00
Sat 02/14 13Z 0.52 2817 93 74 -11 0.01
Sat 02/14 14Z 0.55 2818 94 69 -11 0.01
Sat 02/14 15Z 0.58 2818 95 61 -11 0.00
Sat 02/14 16Z 0.60 2917 96 49 -11 0.00
Sat 02/14 17Z 0.66 2916 95 38 -11 0.00
Sat 02/14 18Z 0.77 2916 94 29 -10 0.00
Sat 02/14 19Z 0.78 2817 94 24 -10 0.00
Sat 02/14 20Z 0.82 2818 95 23 -10 0.00
Sat 02/14 21Z 0.93 2819 95 22 -10 0.00
Sat 02/14 22Z 0.94 2820 93 21 -10 0.01
Sat 02/14 23Z 0.88 2921 89 18 -10 0.01
Sun 02/15 00Z 0.68 3022 82 17 -10 0.01
Sun 02/15 01Z 0.64 3022 77 16 -10 0.00
Sun 02/15 02Z 0.69 3023 75 16 -11 0.00
Sun 02/15 03Z 0.64 3023 71 15 -11 0.00
Sun 02/15 04Z 0.60 3023 70 15 -11 0.00
Sun 02/15 05Z 0.56 3023 73 15 -11 0.00
Sun 02/15 06Z 0.51 3023 74 15 -12 0.00
Sun 02/15 07Z 0.47 3023 73 16 -12 0.00
Sun 02/15 08Z 0.41 3123 70 17 -11 0.00
Sun 02/15 09Z 0.35 3122 68 18 -11 0.00
Sun 02/15 10Z 0.30 3121 61 18 -11 0.00
Sun 02/15 11Z 0.23 3220 50 18 -11 0.00
Sun 02/15 12Z 0.16 3319 41 17 -10 0.00
Sun 02/15 13Z 0.11 3417 31 17 -9 0.00
Sun 02/15 14Z 0.08 0013 23 17 -8 0.00
Sun 02/15 15Z 0.09 0210 22 19 -8 0.00
Sun 02/15 16Z 0.11 0308 23 24 -7 0.00
Sun 02/15 17Z 0.13 0607 25 30 -7 0.00
Sun 02/15 18Z 0.14 0806 27 37 -7 0.00
Sun 02/15 19Z 0.14 1006 29 41 -7 0.00
Sun 02/15 20Z 0.12 1206 29 43 -7 0.00
Sun 02/15 21Z 0.09 1406 28 45 -6 0.00
Sun 02/15 22Z 0.08 1508 25 46 -6 0.00
Sun 02/15 23Z 0.06 1610 23 40 -5 0.00
Mon 02/16 00Z 0.04 1711 23 37 -5 0.00
Mon 02/16 01Z 0.03 1711 25 42 -5 0.00
Mon 02/16 02Z 0.02 1712 29 51 -5 0.00
Mon 02/16 03Z 0.03 1812 35 52 -5 0.00
Mon 02/16 04Z 0.05 1813 44 56 -6 0.00
Mon 02/16 05Z 0.05 1813 58 72 -6 0.00
Mon 02/16 06Z 0.05 1912 71 80 -5 0.00
Mon 02/16 08Z 0.05 1911 84 91 -5 0.00
Mon 02/16 09Z 0.06 1910 86 93 -5 0.00
Mon 02/16 10Z 0.05 1909 87 90 -5 0.00
Mon 02/16 11Z 0.05 1908 86 88 -5 0.00
Mon 02/16 12Z 0.04 1809 85 84 -5 0.00
Mon 02/16 13Z 0.04 1809 84 84 -5 0.00
Mon 02/16 14Z 0.04 1809 84 82 -5 0.00
Mon 02/16 15Z 0.06 1909 84 82 -5 0.00
Mon 02/16 16Z 0.05 1909 84 79 -5 0.00
Mon 02/16 17Z 0.07 1909 83 67 -5 0.00
Run total areal avg QPF for the greens is: 0.05 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