Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260606_1800
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)
=== ===== === ==== ==== === === === ====
Sat 06/06 18Z 0.73 2222 83 97 13 0.00
Sat 06/06 19Z 0.98 2223 81 90 14 0.03
Sat 06/06 20Z 2.73 2122 81 97 14 0.02
Sat 06/06 21Z 2.81 2021 81 66 14 0.02
Sat 06/06 22Z 0.97 1922 80 75 15 0.01
Sat 06/06 23Z 0.67 2225 90 83 14 0.36
Sun 06/07 00Z 0.87 2428 93 67 14 0.28
Sun 06/07 01Z 1.19 2432 94 59 12 0.07
Sun 06/07 04Z 0.91 2729 94 82 11 0.04
Sun 06/07 05Z 0.95 2730 96 79 11 0.02
Sun 06/07 06Z 0.98 2731 96 80 11 0.01
Sun 06/07 07Z 0.97 2731 97 78 11 0.02
Sun 06/07 08Z 0.97 2830 96 61 10 0.03
Sun 06/07 09Z 0.97 2830 96 64 10 0.02
Sun 06/07 10Z 0.96 2831 95 58 10 0.02
Sun 06/07 11Z 0.86 2831 93 50 10 0.01
Sun 06/07 12Z 0.79 2929 94 49 10 0.01
Sun 06/07 13Z 0.82 2927 96 54 10 0.01
Sun 06/07 14Z 0.87 2826 97 63 9 0.01
Sun 06/07 15Z 0.81 2925 98 76 9 0.01
Sun 06/07 16Z 0.65 3024 98 90 9 0.03
Sun 06/07 17Z 0.47 3225 98 95 8 0.04
Sun 06/07 18Z 0.25 3325 98 86 8 0.04
Sun 06/07 19Z 0.19 3427 97 89 8 0.04
Sun 06/07 20Z 0.17 3529 96 92 8 0.04
Sun 06/07 21Z 0.22 0026 94 78 8 0.02
Sun 06/07 22Z 0.22 0027 92 60 8 0.01
Sun 06/07 23Z 0.22 0028 82 22 9 0.00
Mon 06/08 00Z 0.35 0128 81 1 8 0.00
Mon 06/08 01Z 0.48 0129 88 1 6 0.00
Mon 06/08 02Z 0.60 0231 83 1 6 0.00
Mon 06/08 03Z 0.79 0432 67 0 7 0.00
Mon 06/08 04Z 0.93 0434 61 1 7 0.00
Mon 06/08 05Z 0.93 0433 60 0 7 0.00
Mon 06/08 06Z 0.84 0430 57 1 7 0.00
Mon 06/08 07Z 0.79 0329 54 1 8 0.00
Mon 06/08 08Z 0.69 0327 50 2 8 0.00
Mon 06/08 09Z 0.66 0328 51 3 8 0.00
Mon 06/08 10Z 0.62 0327 44 4 8 0.00
Mon 06/08 11Z 0.60 0427 38 6 9 0.00
Mon 06/08 12Z 0.59 0426 40 10 9 0.00
Mon 06/08 13Z 0.57 0422 44 10 8 0.00
Mon 06/08 14Z 0.55 0517 49 11 8 0.00
Mon 06/08 15Z 0.48 0412 47 12 8 0.00
Mon 06/08 16Z 0.57 0509 48 12 9 0.00
Mon 06/08 17Z 0.93 0403 52 9 9 0.00
Mon 06/08 18Z 0.29 0002 56 7 9 0.00
Mon 06/08 19Z 0.17 3501 59 6 10 0.00
Mon 06/08 20Z 0.54 3103 65 6 10 0.00
Mon 06/08 21Z 0.41 3003 68 6 10 0.00
Mon 06/08 22Z 0.22 3003 65 6 10 0.00
Mon 06/08 23Z 0.08 3103 58 4 11 0.00
Tue 06/09 00Z 0.13 3004 53 3 11 0.00
Tue 06/09 01Z 0.22 3006 50 1 11 0.00
Tue 06/09 02Z 0.20 3006 57 1 10 0.00
Tue 06/09 03Z 0.20 3006 62 1 10 0.00
Tue 06/09 04Z 0.19 2905 62 2 11 0.00
Tue 06/09 05Z 0.24 2606 61 4 11 0.00
Run total areal avg QPF for the Central_Greens is: 1.22 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