Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260720_0600
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Mon 07/20 06Z 0.40 3119 77 20 9 0.00
Mon 07/20 07Z 0.39 3119 77 14 9 0.00
Mon 07/20 08Z 0.41 3119 77 18 9 0.00
Mon 07/20 09Z 0.40 3118 74 26 9 0.00
Mon 07/20 10Z 0.39 3118 71 36 9 0.00
Mon 07/20 11Z 0.39 3116 70 38 9 0.00
Mon 07/20 12Z 0.37 3115 69 44 9 0.00
Mon 07/20 13Z 0.35 3013 67 48 9 0.00
Mon 07/20 14Z 0.42 3010 66 50 9 0.00
Mon 07/20 15Z 1.17 2809 65 52 10 0.00
Mon 07/20 16Z 2.41 2607 63 49 10 0.00
Mon 07/20 17Z 4.01 2408 63 45 10 0.00
Mon 07/20 18Z 4.91 2408 63 41 10 0.00
Mon 07/20 19Z 4.84 2408 64 38 11 0.00
Mon 07/20 20Z 4.59 2309 67 35 11 0.00
Mon 07/20 21Z 3.11 2210 67 34 11 0.00
Mon 07/20 22Z 1.56 2112 64 36 11 0.00
Mon 07/20 23Z 0.76 2213 62 39 11 0.00
Tue 07/21 00Z 0.60 2116 63 32 12 0.00
Tue 07/21 01Z 0.55 2118 63 25 12 0.00
Tue 07/21 02Z 0.55 2119 62 19 12 0.00
Tue 07/21 03Z 0.58 2119 65 21 12 0.00
Tue 07/21 04Z 0.57 2120 70 22 12 0.00
Tue 07/21 05Z 0.61 2122 73 19 12 0.00
Tue 07/21 06Z 0.70 2125 78 16 11 0.00
Tue 07/21 07Z 0.71 2126 78 16 11 0.00
Tue 07/21 08Z 0.68 2127 80 13 11 0.00
Tue 07/21 09Z 0.65 2127 82 12 11 0.00
Tue 07/21 10Z 0.58 2127 87 14 12 0.00
Tue 07/21 11Z 0.52 2125 93 13 12 0.00
Tue 07/21 12Z 0.52 2127 93 9 12 0.00
Tue 07/21 13Z 0.49 2028 91 17 12 0.01
Tue 07/21 14Z 0.49 2028 92 60 12 0.00
Tue 07/21 15Z 0.40 1927 94 71 12 0.00
Tue 07/21 16Z 0.35 1927 96 80 13 0.01
Tue 07/21 17Z 0.31 1828 96 76 13 0.01
Tue 07/21 18Z 0.12 1730 97 76 13 0.04
Tue 07/21 19Z 0.08 1634 97 61 14 0.06
Tue 07/21 20Z 0.06 1637 97 86 15 0.03
Tue 07/21 21Z 0.06 1736 97 83 15 0.03
Tue 07/21 22Z 0.23 1833 97 89 16 0.02
Tue 07/21 23Z 0.37 1931 92 58 17 0.01
Wed 07/22 00Z 0.58 2031 94 76 16 0.00
Wed 07/22 01Z 0.57 2125 92 82 16 0.01
Wed 07/22 02Z 0.54 2126 87 65 16 0.00
Wed 07/22 03Z 0.71 2131 85 52 16 0.00
Wed 07/22 04Z 0.67 2131 84 63 16 0.00
Wed 07/22 05Z 0.73 2134 90 68 15 0.00
Wed 07/22 06Z 0.62 2030 92 60 15 0.00
Wed 07/22 07Z 0.70 2228 98 49 15 0.03
Wed 07/22 08Z 0.74 2326 96 58 15 0.02
Wed 07/22 09Z 0.71 2425 96 74 15 0.02
Wed 07/22 10Z 0.66 2422 96 74 14 0.03
Wed 07/22 11Z 0.56 2419 90 69 14 0.01
Wed 07/22 12Z 0.60 2419 90 57 14 0.01
Wed 07/22 13Z 0.62 2420 87 56 13 0.00
Wed 07/22 14Z 0.56 2318 83 30 13 0.00
Wed 07/22 15Z 0.65 2318 83 21 13 0.00
Wed 07/22 16Z 0.73 2216 85 34 13 0.00
Wed 07/22 17Z 1.59 2116 89 42 13 0.00
Run total areal avg QPF for the Central_Greens is: 0.35 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