Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260824_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)
=== ===== === ==== ==== === === === ====
Mon 08/24 00Z 0.40 2215 89 82 12 0.00
Mon 08/24 01Z 0.47 2315 87 83 12 0.00
Mon 08/24 02Z 0.57 2415 87 78 11 0.00
Mon 08/24 03Z 0.65 2515 86 78 11 0.00
Mon 08/24 04Z 0.56 2514 81 69 11 0.00
Mon 08/24 05Z 0.44 2512 78 68 11 0.00
Mon 08/24 06Z 0.35 2411 74 69 11 0.00
Mon 08/24 07Z 0.33 2312 74 69 10 0.00
Mon 08/24 08Z 0.33 2213 76 70 10 0.00
Mon 08/24 09Z 0.32 2214 77 67 10 0.00
Mon 08/24 10Z 0.33 2215 79 64 10 0.00
Mon 08/24 11Z 0.32 2116 80 64 10 0.00
Mon 08/24 12Z 0.29 2115 82 63 9 0.00
Mon 08/24 13Z 0.31 2115 84 55 9 0.00
Mon 08/24 14Z 0.30 2014 85 53 9 0.00
Mon 08/24 15Z 0.51 2113 84 47 9 0.00
Mon 08/24 16Z 1.23 2112 83 52 9 0.00
Mon 08/24 17Z 1.85 2011 81 55 9 0.00
Mon 08/24 18Z 1.84 1911 81 56 10 0.00
Mon 08/24 19Z 2.10 2014 80 69 10 0.05
Mon 08/24 20Z 1.08 2117 78 49 10 0.04
Mon 08/24 21Z 0.87 2116 73 40 10 0.00
Mon 08/24 22Z 0.65 2214 78 36 10 0.00
Mon 08/24 23Z 0.50 2213 79 45 10 0.00
Tue 08/25 00Z 0.55 2214 83 48 10 0.00
Tue 08/25 01Z 0.67 2215 83 56 9 0.00
Tue 08/25 02Z 0.71 2316 85 60 9 0.00
Tue 08/25 03Z 0.66 2315 89 65 9 0.01
Tue 08/25 04Z 0.56 2315 88 70 9 0.00
Tue 08/25 05Z 0.50 2316 89 83 9 0.00
Tue 08/25 06Z 0.45 2315 91 91 9 0.00
Tue 08/25 07Z 0.41 2315 93 92 9 0.01
Tue 08/25 08Z 0.38 2313 94 84 8 0.01
Tue 08/25 09Z 0.40 2413 96 81 8 0.00
Tue 08/25 10Z 0.40 2413 95 78 8 0.00
Tue 08/25 11Z 0.39 2412 94 78 8 0.00
Tue 08/25 12Z 0.36 2511 95 74 8 0.00
Tue 08/25 13Z 0.39 2511 96 75 8 0.00
Tue 08/25 14Z 0.39 2510 96 80 8 0.00
Tue 08/25 15Z 0.35 2608 96 79 8 0.00
Tue 08/25 16Z 0.32 2706 96 74 8 0.00
Tue 08/25 17Z 0.37 2706 95 70 8 0.00
Tue 08/25 18Z 0.41 2706 95 69 9 0.00
Tue 08/25 19Z 0.43 2707 95 72 9 0.01
Tue 08/25 20Z 0.37 2808 95 80 9 0.02
Tue 08/25 21Z 0.37 2910 93 73 9 0.02
Tue 08/25 22Z 0.37 3011 93 66 9 0.02
Tue 08/25 23Z 0.35 3011 92 59 9 0.01
Wed 08/26 00Z 0.33 3111 94 55 9 0.00
Wed 08/26 01Z 0.33 3112 95 54 9 0.02
Wed 08/26 02Z 0.31 3112 93 48 9 0.01
Wed 08/26 03Z 0.29 3112 93 48 9 0.01
Wed 08/26 04Z 0.29 3112 94 43 9 0.01
Wed 08/26 05Z 0.30 3111 94 39 9 0.01
Wed 08/26 06Z 0.30 3011 93 34 9 0.01
Wed 08/26 07Z 0.29 3112 92 34 9 0.01
Wed 08/26 08Z 0.28 3112 91 32 9 0.01
Wed 08/26 09Z 0.28 3111 92 34 9 0.01
Wed 08/26 10Z 0.26 3111 94 36 9 0.01
Wed 08/26 11Z 0.25 3110 93 41 9 0.01
Run total areal avg QPF for the greens is: 0.32 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