Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260301_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)
=== ===== === ==== ==== === === === ====
Sun 03/01 00Z 1.01 2720 74 20 -3 0.00
Sun 03/01 01Z 0.81 2820 72 27 -3 0.00
Sun 03/01 04Z 0.31 3014 58 51 -5 0.00
Sun 03/01 05Z 0.24 3012 60 77 -6 0.00
Sun 03/01 06Z 0.24 3012 63 81 -7 0.00
Sun 03/01 07Z 0.30 3015 67 89 -8 0.00
Sun 03/01 08Z 0.25 3014 63 92 -8 0.00
Sun 03/01 09Z 0.23 3113 70 84 -9 0.00
Sun 03/01 10Z 0.21 3114 79 86 -11 0.00
Sun 03/01 11Z 0.19 3214 84 88 -12 0.00
Sun 03/01 12Z 0.21 3215 85 86 -14 0.00
Sun 03/01 13Z 0.23 3216 82 83 -14 0.00
Sun 03/01 14Z 0.29 3216 80 73 -15 0.01
Sun 03/01 15Z 0.31 3116 73 63 -15 0.00
Sun 03/01 16Z 0.36 3117 63 41 -16 0.00
Sun 03/01 17Z 0.42 3117 58 33 -17 0.00
Sun 03/01 18Z 0.45 3117 57 35 -17 0.00
Sun 03/01 19Z 0.62 3118 65 36 -18 0.00
Sun 03/01 20Z 0.66 3119 70 34 -18 0.00
Sun 03/01 21Z 0.69 3119 73 29 -19 0.00
Sun 03/01 22Z 0.68 3120 77 27 -19 0.00
Sun 03/01 23Z 0.64 3121 72 23 -20 0.00
Mon 03/02 00Z 0.55 3121 66 20 -20 0.00
Mon 03/02 02Z 0.40 3122 55 16 -20 0.00
Mon 03/02 03Z 0.37 3121 51 15 -20 0.00
Mon 03/02 04Z 0.35 3121 50 13 -20 0.00
Mon 03/02 05Z 0.34 3120 48 12 -20 0.00
Mon 03/02 06Z 0.32 3119 46 11 -20 0.00
Mon 03/02 07Z 0.31 3119 45 12 -20 0.00
Mon 03/02 08Z 0.30 3119 44 13 -20 0.00
Mon 03/02 09Z 0.31 3118 45 15 -20 0.00
Mon 03/02 10Z 0.31 3118 43 16 -20 0.00
Mon 03/02 11Z 0.34 3119 42 18 -20 0.00
Mon 03/02 12Z 0.33 3018 40 14 -20 0.00
Mon 03/02 13Z 0.35 3018 40 14 -20 0.00
Mon 03/02 14Z 0.34 3017 41 15 -20 0.00
Mon 03/02 15Z 0.37 2916 43 16 -20 0.00
Mon 03/02 16Z 0.34 2913 42 14 -19 0.00
Mon 03/02 17Z 0.35 2912 40 14 -18 0.00
Mon 03/02 18Z 0.36 2812 39 19 -18 0.00
Mon 03/02 19Z 0.39 2712 44 19 -17 0.00
Mon 03/02 20Z 0.39 2612 49 24 -16 0.00
Mon 03/02 21Z 0.38 2513 49 27 -15 0.00
Mon 03/02 22Z 0.36 2514 43 34 -14 0.00
Mon 03/02 23Z 0.38 2416 36 43 -12 0.00
Tue 03/03 00Z 0.38 2418 30 52 -11 0.00
Tue 03/03 01Z 0.40 2321 28 50 -10 0.00
Tue 03/03 02Z 0.45 2324 29 54 -10 0.00
Tue 03/03 03Z 0.50 2327 30 54 -9 0.00
Tue 03/03 04Z 0.53 2429 31 49 -8 0.00
Tue 03/03 05Z 0.55 2431 31 45 -7 0.00
Tue 03/03 06Z 0.57 2432 32 41 -6 0.00
Tue 03/03 07Z 0.58 2431 28 41 -6 0.00
Tue 03/03 08Z 0.57 2431 28 37 -5 0.00
Tue 03/03 09Z 0.55 2529 35 34 -5 0.00
Tue 03/03 10Z 0.52 2528 41 29 -4 0.00
Tue 03/03 11Z 0.50 2527 43 26 -4 0.00
Run total areal avg QPF for the greens is: 0.01 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