Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260214_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)
=== ===== === ==== ==== === === === ====
Sat 02/14 00Z 0.45 2615 72 35 -10 0.00
Sat 02/14 01Z 0.57 2618 72 36 -10 0.00
Sat 02/14 02Z 0.60 2620 74 47 -10 0.00
Sat 02/14 03Z 0.58 2621 74 56 -10 0.00
Sat 02/14 04Z 0.48 2719 67 45 -10 0.00
Sat 02/14 05Z 0.42 2718 67 46 -10 0.00
Sat 02/14 06Z 0.43 2819 74 63 -10 0.00
Sat 02/14 07Z 0.47 2819 80 75 -11 0.00
Sat 02/14 08Z 0.45 2818 87 75 -11 0.00
Sat 02/14 09Z 0.41 2816 89 72 -10 0.00
Sat 02/14 10Z 0.45 2816 93 76 -11 0.00
Sat 02/14 11Z 0.46 2816 93 79 -11 0.00
Sat 02/14 12Z 0.46 2816 93 80 -10 0.00
Sat 02/14 13Z 0.46 2816 93 79 -10 0.00
Sat 02/14 14Z 0.51 2817 94 70 -10 0.00
Sat 02/14 15Z 0.53 2817 96 54 -10 0.01
Sat 02/14 16Z 0.56 2817 96 38 -10 0.01
Sat 02/14 17Z 0.59 2917 95 29 -10 0.00
Sat 02/14 18Z 0.66 2916 95 23 -10 0.00
Sat 02/14 19Z 0.71 2816 95 19 -10 0.00
Sat 02/14 20Z 0.79 2816 96 18 -10 0.00
Sat 02/14 21Z 0.85 2718 95 19 -10 0.00
Sat 02/14 22Z 0.88 2820 92 20 -10 0.01
Sat 02/14 23Z 0.82 2821 88 21 -10 0.01
Sun 02/15 00Z 0.79 2923 84 22 -10 0.01
Sun 02/15 01Z 0.72 2924 80 21 -10 0.01
Sun 02/15 02Z 0.69 3025 77 20 -10 0.01
Sun 02/15 03Z 0.75 3026 77 18 -11 0.01
Sun 02/15 04Z 0.67 3126 78 17 -11 0.00
Sun 02/15 05Z 0.51 3125 78 17 -12 0.00
Sun 02/15 06Z 0.41 3224 74 16 -11 0.00
Sun 02/15 07Z 0.31 3224 63 16 -11 0.00
Sun 02/15 08Z 0.25 3223 53 16 -11 0.00
Sun 02/15 09Z 0.19 3322 41 17 -10 0.00
Sun 02/15 10Z 0.12 3422 31 20 -9 0.00
Sun 02/15 11Z 0.09 3420 25 21 -9 0.00
Sun 02/15 12Z 0.06 3517 23 22 -9 0.00
Sun 02/15 13Z 0.04 3514 21 21 -9 0.00
Sun 02/15 14Z 0.03 0010 21 23 -8 0.00
Sun 02/15 15Z 0.02 0006 22 25 -8 0.00
Sun 02/15 16Z 0.02 0104 23 30 -8 0.00
Sun 02/15 17Z 0.04 0402 24 40 -7 0.00
Sun 02/15 18Z 0.04 0801 25 42 -7 0.00
Sun 02/15 19Z 0.03 1402 26 41 -6 0.00
Sun 02/15 20Z 0.03 1503 26 34 -6 0.00
Sun 02/15 21Z 0.02 1705 26 35 -6 0.00
Sun 02/15 22Z 0.02 1807 25 45 -6 0.00
Sun 02/15 23Z 0.03 1809 25 53 -6 0.00
Mon 02/16 00Z 0.03 1810 25 54 -5 0.00
Mon 02/16 01Z 0.06 1911 27 54 -6 0.00
Mon 02/16 02Z 0.07 1911 32 63 -6 0.00
Mon 02/16 03Z 0.07 1911 39 70 -6 0.00
Mon 02/16 04Z 0.08 1912 46 80 -6 0.00
Mon 02/16 07Z 0.04 1910 72 87 -6 0.00
Mon 02/16 08Z 0.03 1810 79 89 -6 0.00
Mon 02/16 09Z 0.03 1809 83 91 -6 0.00
Mon 02/16 10Z 0.02 1809 85 92 -5 0.00
Mon 02/16 11Z 0.02 1809 86 92 -5 0.00
Run total areal avg QPF for the greens is: 0.08 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