Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260723_0000
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)
=== ===== === ==== ==== === === === ====
Thu 07/23 00Z 0.73 2720 87 28 9 0.00
Thu 07/23 01Z 0.85 2721 89 28 8 0.00
Thu 07/23 02Z 1.00 2824 91 35 7 0.00
Thu 07/23 03Z 1.18 2928 92 39 7 0.01
Thu 07/23 04Z 1.15 3029 91 33 6 0.01
Thu 07/23 05Z 0.94 3028 90 28 5 0.00
Thu 07/23 06Z 0.63 3125 83 27 5 0.00
Thu 07/23 07Z 0.48 3224 76 33 5 0.00
Thu 07/23 08Z 0.52 3224 72 35 5 0.00
Thu 07/23 09Z 0.58 3222 69 33 5 0.00
Thu 07/23 10Z 0.75 3121 69 37 5 0.00
Thu 07/23 11Z 0.76 3020 69 41 6 0.00
Thu 07/23 12Z 0.77 2919 69 38 6 0.00
Thu 07/23 13Z 0.82 2919 66 35 6 0.00
Thu 07/23 14Z 0.98 2917 62 30 6 0.00
Thu 07/23 15Z 2.67 2915 62 28 7 0.00
Thu 07/23 16Z 6.71 2813 66 26 7 0.00
Thu 07/23 17Z 9.12 2713 69 22 7 0.00
Thu 07/23 18Z 9.53 2713 67 22 8 0.00
Thu 07/23 19Z 9.04 2713 67 17 8 0.00
Thu 07/23 20Z 8.64 2713 66 11 9 0.00
Thu 07/23 21Z 6.89 2612 66 9 9 0.00
Thu 07/23 22Z 4.01 2612 66 8 9 0.00
Thu 07/23 23Z 1.96 2712 67 9 9 0.00
Fri 07/24 00Z 1.51 2712 67 10 9 0.00
Fri 07/24 01Z 1.57 2712 69 13 9 0.00
Fri 07/24 02Z 1.12 2711 69 14 9 0.00
Fri 07/24 03Z 0.91 2711 70 15 9 0.00
Fri 07/24 04Z 0.68 2810 68 15 9 0.00
Fri 07/24 05Z 0.57 2810 67 17 9 0.00
Fri 07/24 06Z 0.53 2909 68 18 9 0.00
Fri 07/24 07Z 0.42 2907 67 17 9 0.00
Fri 07/24 08Z 0.33 2906 67 17 9 0.00
Fri 07/24 09Z 0.26 2804 68 17 9 0.00
Fri 07/24 10Z 0.23 2504 68 20 9 0.00
Fri 07/24 11Z 0.19 2304 68 22 9 0.00
Fri 07/24 12Z 0.18 2204 68 22 9 0.00
Fri 07/24 13Z 0.28 2205 70 20 8 0.00
Fri 07/24 14Z 0.63 2206 72 21 8 0.00
Fri 07/24 15Z 1.13 2205 72 21 9 0.00
Fri 07/24 16Z 1.50 2205 71 21 9 0.00
Fri 07/24 17Z 1.83 2406 69 22 10 0.00
Fri 07/24 18Z 1.78 2405 65 25 10 0.00
Fri 07/24 19Z 1.33 2404 62 24 11 0.00
Fri 07/24 20Z 1.12 2504 62 23 11 0.00
Fri 07/24 21Z 0.70 2503 62 23 11 0.00
Fri 07/24 22Z 0.35 2603 61 24 12 0.00
Fri 07/24 23Z 0.20 2602 61 25 12 0.00
Sat 07/25 00Z 0.13 2402 60 25 12 0.00
Sat 07/25 01Z 0.11 2302 61 25 12 0.00
Sat 07/25 02Z 0.08 2201 61 25 12 0.00
Sat 07/25 03Z 0.09 1901 62 26 11 0.00
Sat 07/25 04Z 0.07 1802 62 25 11 0.00
Sat 07/25 05Z 0.06 1703 63 24 11 0.00
Sat 07/25 06Z 0.05 1903 63 24 11 0.00
Sat 07/25 07Z 0.09 2003 63 24 11 0.00
Sat 07/25 08Z 0.03 1901 62 23 11 0.00
Sat 07/25 09Z 0.03 1901 62 22 11 0.00
Sat 07/25 10Z 0.06 1201 62 19 11 0.00
Sat 07/25 11Z 0.12 1203 63 17 11 0.00
Run total areal avg QPF for the greens is: 0.02 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