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Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260313_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 03/13 00Z 6.41 3120 81 51 -12 0.00
Fri 03/13 01Z 6.19 3028 86 56 -13 0.00
Fri 03/13 02Z 3.44 3127 87 60 -13 0.00
Fri 03/13 03Z 3.31 3127 89 51 -14 0.00
Fri 03/13 04Z 2.74 3126 90 48 -14 0.00
Fri 03/13 05Z 2.50 3126 92 46 -14 0.00
Fri 03/13 06Z 1.93 3124 93 50 -14 0.00
Fri 03/13 07Z 1.38 3021 92 54 -14 0.00
Fri 03/13 08Z 0.86 3021 89 55 -14 0.00
Fri 03/13 09Z 0.66 3020 87 50 -13 0.00
Fri 03/13 10Z 0.58 2920 85 40 -13 0.00
Fri 03/13 11Z 0.60 2920 85 30 -13 0.00
Fri 03/13 12Z 0.53 2918 83 17 -13 0.00
Fri 03/13 13Z 0.53 2815 81 11 -13 0.00
Fri 03/13 14Z 0.56 2813 78 6 -13 0.00
Fri 03/13 15Z 0.74 2609 73 3 -12 0.00
Fri 03/13 16Z 1.36 2307 69 2 -12 0.00
Fri 03/13 17Z 1.56 2207 63 3 -11 0.00
Fri 03/13 18Z 1.82 2108 58 6 -11 0.00
Fri 03/13 19Z 1.16 2011 57 51 -10 0.00
Fri 03/13 20Z 0.24 1913 52 79 -9 0.00
Fri 03/13 21Z 0.71 1815 61 85 -10 0.00
Fri 03/13 22Z 0.17 1717 78 87 -10 0.00
Fri 03/13 23Z 0.17 1720 85 91 -9 0.01
Sat 03/14 00Z 0.14 1723 89 90 -9 0.01
Sat 03/14 01Z 0.18 1626 90 92 -9 0.02
Sat 03/14 02Z 0.19 1627 87 93 -9 0.02
Sat 03/14 03Z 0.20 1629 90 91 -9 0.01
Sat 03/14 04Z 0.15 1728 93 92 -8 0.06
Sat 03/14 05Z 0.13 1726 95 80 -8 0.04
Sat 03/14 06Z 0.18 1823 96 84 -7 0.02
Sat 03/14 07Z 0.24 1919 96 87 -7 0.02
Sat 03/14 08Z 0.30 2019 97 88 -6 0.02
Sat 03/14 09Z 0.46 2119 96 87 -6 0.03
Sat 03/14 10Z 0.60 2220 96 85 -7 0.03
Sat 03/14 11Z 0.75 2321 96 84 -7 0.04
Sat 03/14 12Z 0.93 2421 96 84 -8 0.03
Sat 03/14 13Z 1.07 2521 95 83 -8 0.02
Sat 03/14 14Z 1.16 2620 94 84 -8 0.02
Sat 03/14 15Z 1.73 2620 94 83 -8 0.02
Sat 03/14 16Z 1.17 2619 94 86 -7 0.02
Sat 03/14 17Z 1.21 2520 95 85 -7 0.02
Sat 03/14 18Z 2.63 2622 94 86 -7 0.02
Sat 03/14 19Z 2.78 2726 93 85 -7 0.03
Sat 03/14 20Z 3.71 2829 91 83 -8 0.03
Sat 03/14 21Z 2.92 2931 91 82 -9 0.03
Sat 03/14 22Z 2.52 2931 92 79 -10 0.02
Sat 03/14 23Z 1.75 2932 94 77 -10 0.02
Sun 03/15 00Z 1.54 2933 96 72 -10 0.02
Sun 03/15 01Z 1.35 2932 96 73 -10 0.02
Sun 03/15 02Z 1.33 2931 96 57 -10 0.02
Sun 03/15 03Z 1.37 2930 96 31 -11 0.02
Sun 03/15 04Z 1.28 3029 96 14 -12 0.02
Sun 03/15 05Z 1.13 3027 90 12 -12 0.01
Sun 03/15 06Z 0.78 3026 81 11 -12 0.00
Sun 03/15 07Z 0.59 3125 70 11 -11 0.00
Sun 03/15 08Z 0.50 3023 60 9 -11 0.00
Sun 03/15 09Z 0.41 3121 52 9 -10 0.00
Sun 03/15 10Z 0.33 3119 44 13 -10 0.00
Sun 03/15 11Z 0.24 3116 34 19 -9 0.00
Run total areal avg QPF for the greens is: 0.72 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