Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260724_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)
=== ===== === ==== ==== === === === ====
Fri 07/24 00Z 1.28 2812 72 28 10 0.00
Fri 07/24 01Z 1.12 2912 72 24 9 0.00
Fri 07/24 02Z 0.73 2910 72 29 9 0.00
Fri 07/24 03Z 0.55 2909 74 25 9 0.00
Fri 07/24 04Z 0.51 2809 75 17 9 0.00
Fri 07/24 05Z 0.55 2810 72 12 9 0.00
Fri 07/24 06Z 0.52 2809 72 12 9 0.00
Fri 07/24 07Z 0.50 2708 72 15 9 0.00
Fri 07/24 08Z 0.53 2608 72 21 9 0.00
Fri 07/24 09Z 0.51 2508 72 24 9 0.00
Fri 07/24 10Z 0.52 2509 72 27 9 0.00
Fri 07/24 11Z 0.47 2408 73 30 9 0.00
Fri 07/24 12Z 0.48 2409 74 33 9 0.00
Fri 07/24 13Z 0.57 2408 77 33 8 0.00
Fri 07/24 14Z 1.21 2408 79 31 8 0.00
Fri 07/24 15Z 1.83 2408 79 31 9 0.00
Fri 07/24 16Z 2.21 2407 75 33 9 0.00
Fri 07/24 17Z 2.05 2406 71 36 10 0.00
Fri 07/24 18Z 1.88 2505 69 39 10 0.00
Fri 07/24 19Z 1.73 2504 69 41 11 0.00
Fri 07/24 20Z 1.33 2503 69 41 11 0.00
Fri 07/24 21Z 0.90 2603 70 41 11 0.00
Fri 07/24 22Z 0.50 2603 71 42 11 0.00
Fri 07/24 23Z 0.16 2302 71 44 12 0.00
Sat 07/25 00Z 0.15 2303 70 45 12 0.00
Sat 07/25 01Z 0.09 2003 69 43 12 0.00
Sat 07/25 02Z 0.07 1804 68 40 12 0.00
Sat 07/25 03Z 0.08 1906 67 40 12 0.00
Sat 07/25 04Z 0.11 1906 67 40 12 0.00
Sat 07/25 05Z 0.18 2007 68 42 12 0.00
Sat 07/25 06Z 0.22 2107 69 41 12 0.00
Sat 07/25 07Z 0.15 2106 67 38 12 0.00
Sat 07/25 08Z 0.15 2205 65 36 12 0.00
Sat 07/25 09Z 0.13 2403 64 34 12 0.00
Sat 07/25 10Z 0.06 2401 63 32 12 0.00
Sat 07/25 11Z 0.05 1800 63 32 12 0.00
Sat 07/25 12Z 0.07 1402 64 32 11 0.00
Sat 07/25 13Z 0.14 1405 67 32 11 0.00
Sat 07/25 14Z 0.29 1507 70 31 11 0.00
Sat 07/25 15Z 0.58 1607 74 30 11 0.00
Sat 07/25 16Z 0.51 1706 75 29 11 0.00
Sat 07/25 17Z 0.64 1605 75 29 12 0.00
Sat 07/25 18Z 0.90 1505 75 28 12 0.00
Sat 07/25 19Z 1.50 1405 73 25 13 0.00
Sat 07/25 20Z 1.62 1406 74 23 13 0.00
Sat 07/25 21Z 0.85 1506 77 21 13 0.00
Sat 07/25 22Z 0.45 1607 79 22 13 0.00
Sat 07/25 23Z 0.34 1508 81 20 13 0.00
Sun 07/26 00Z 0.24 1610 84 19 12 0.00
Sun 07/26 01Z 0.17 1610 84 18 12 0.00
Sun 07/26 02Z 0.08 1710 84 18 12 0.00
Sun 07/26 03Z 0.06 1808 81 17 12 0.00
Sun 07/26 04Z 0.07 1907 79 16 12 0.00
Sun 07/26 05Z 0.09 2004 80 16 12 0.00
Sun 07/26 06Z 0.10 2103 82 17 12 0.00
Sun 07/26 07Z 0.11 2203 84 17 12 0.00
Sun 07/26 08Z 0.10 2302 87 17 11 0.00
Sun 07/26 09Z 0.10 2602 89 17 11 0.00
Sun 07/26 10Z 0.08 2801 90 18 11 0.00
Sun 07/26 11Z 0.04 0001 89 18 11 0.00
Run total areal avg QPF for the greens is: 0.00 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