Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260913_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)
=== ===== === ==== ==== === === === ====
Sun 09/13 18Z 0.26 2210 98 35 13 0.00
Sun 09/13 19Z 0.25 2211 95 36 13 0.00
Sun 09/13 20Z 0.23 2111 92 33 14 0.00
Sun 09/13 21Z 0.31 2313 86 30 15 0.00
Sun 09/13 22Z 0.38 2415 81 35 15 0.00
Sun 09/13 23Z 0.48 2518 81 42 15 0.00
Mon 09/14 00Z 0.64 2521 86 42 15 0.00
Mon 09/14 01Z 0.74 2523 90 60 14 0.00
Mon 09/14 02Z 0.81 2525 95 67 14 0.04
Mon 09/14 03Z 0.80 2624 90 71 14 0.04
Mon 09/14 04Z 0.87 2824 90 71 13 0.04
Mon 09/14 05Z 1.00 2926 91 79 12 0.03
Mon 09/14 06Z 0.91 2925 90 83 10 0.03
Mon 09/14 07Z 0.81 2923 77 84 10 0.01
Mon 09/14 08Z 0.98 2826 85 62 9 0.01
Mon 09/14 09Z 0.88 2928 86 40 8 0.00
Mon 09/14 10Z 0.71 3029 85 21 7 0.02
Mon 09/14 11Z 0.55 3229 84 11 6 0.01
Mon 09/14 12Z 0.45 3228 84 10 5 0.01
Mon 09/14 13Z 0.38 3327 86 11 4 0.01
Mon 09/14 14Z 0.33 3324 87 10 4 0.01
Mon 09/14 15Z 0.32 3322 85 9 4 0.01
Mon 09/14 16Z 0.35 3320 83 10 4 0.01
Mon 09/14 17Z 0.44 3219 80 7 4 0.01
Mon 09/14 18Z 0.51 3218 76 7 4 0.00
Mon 09/14 19Z 1.14 3218 80 9 3 0.00
Mon 09/14 20Z 1.92 3217 84 14 3 0.00
Mon 09/14 21Z 1.18 3218 85 18 3 0.00
Mon 09/14 22Z 0.80 3218 85 20 3 0.00
Mon 09/14 23Z 0.72 3221 85 20 3 0.00
Tue 09/15 00Z 0.61 3221 84 19 3 0.00
Tue 09/15 01Z 0.40 3220 80 17 4 0.00
Tue 09/15 02Z 0.26 3320 76 14 5 0.00
Tue 09/15 03Z 0.10 3417 68 9 7 0.00
Tue 09/15 04Z 0.07 3517 69 9 6 0.00
Tue 09/15 05Z 0.06 3515 66 8 6 0.00
Tue 09/15 06Z 0.06 0112 58 6 7 0.00
Tue 09/15 07Z 0.06 0108 55 5 8 0.00
Tue 09/15 08Z 0.05 0205 52 5 8 0.00
Tue 09/15 09Z 0.04 3401 48 5 8 0.00
Tue 09/15 10Z 0.03 2801 43 5 8 0.00
Tue 09/15 11Z 0.03 2101 42 5 8 0.00
Tue 09/15 12Z 0.04 2003 43 5 8 0.00
Tue 09/15 13Z 0.05 2005 43 6 8 0.00
Tue 09/15 14Z 0.06 2006 44 6 8 0.00
Tue 09/15 15Z 0.09 2006 46 7 8 0.00
Tue 09/15 16Z 0.06 2007 47 7 9 0.00
Tue 09/15 17Z 0.07 1908 49 9 10 0.00
Tue 09/15 18Z 0.06 1909 51 10 10 0.00
Tue 09/15 19Z 0.04 1811 50 12 11 0.00
Tue 09/15 20Z 0.09 1912 51 13 11 0.00
Tue 09/15 21Z 0.11 1915 51 15 12 0.00
Tue 09/15 22Z 0.15 1917 48 16 12 0.00
Tue 09/15 23Z 0.18 2020 40 21 13 0.00
Wed 09/16 00Z 0.22 2022 35 29 14 0.00
Wed 09/16 01Z 0.26 2123 31 43 14 0.00
Wed 09/16 02Z 0.31 2124 30 60 14 0.00
Wed 09/16 03Z 0.37 2225 32 73 14 0.00
Wed 09/16 04Z 0.40 2324 34 77 14 0.00
Wed 09/16 05Z 0.42 2323 38 86 14 0.00
Run total areal avg QPF for the greens is: 0.29 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