Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260819_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)
=== ===== === ==== ==== === === === ====
Wed 08/19 06Z 0.07 3002 85 10 12 0.00
Wed 08/19 07Z 0.11 2803 83 11 12 0.00
Wed 08/19 08Z 0.18 2804 83 12 12 0.00
Wed 08/19 09Z 0.19 2604 83 13 12 0.00
Wed 08/19 10Z 0.16 2504 83 17 12 0.00
Wed 08/19 11Z 0.18 2405 84 24 12 0.00
Wed 08/19 12Z 0.18 2206 86 38 12 0.00
Wed 08/19 13Z 0.22 2208 86 47 12 0.00
Wed 08/19 14Z 0.26 2208 86 56 12 0.00
Wed 08/19 15Z 0.32 2209 81 57 12 0.00
Wed 08/19 16Z 0.50 2310 76 60 12 0.00
Wed 08/19 17Z 1.45 2311 77 70 12 0.00
Wed 08/19 18Z 1.71 2311 73 73 13 0.00
Wed 08/19 19Z 1.34 2312 75 70 13 0.00
Wed 08/19 20Z 1.38 2313 80 78 13 0.00
Wed 08/19 21Z 0.86 2313 82 94 13 0.00
Wed 08/19 22Z 0.72 2314 85 90 13 0.00
Wed 08/19 23Z 0.88 2318 92 88 13 0.00
Thu 08/20 00Z 0.76 2420 95 73 13 0.03
Thu 08/20 01Z 0.79 2620 93 50 13 0.02
Thu 08/20 02Z 0.76 2720 96 34 13 0.02
Thu 08/20 03Z 0.56 2919 91 21 13 0.03
Thu 08/20 04Z 0.43 3018 80 10 12 0.01
Thu 08/20 05Z 0.44 3018 71 10 12 0.01
Thu 08/20 06Z 0.39 3017 75 8 11 0.00
Thu 08/20 07Z 0.42 3017 78 6 11 0.00
Thu 08/20 08Z 0.36 3117 74 11 10 0.00
Thu 08/20 09Z 0.29 3115 72 6 10 0.00
Thu 08/20 10Z 0.30 3114 71 8 10 0.00
Thu 08/20 11Z 0.24 3112 70 4 10 0.00
Thu 08/20 12Z 0.26 3111 70 6 9 0.00
Thu 08/20 13Z 0.22 3110 72 8 9 0.00
Thu 08/20 14Z 0.22 3109 75 8 9 0.00
Thu 08/20 15Z 0.22 3106 78 6 9 0.00
Thu 08/20 16Z 0.66 3005 80 9 9 0.00
Thu 08/20 17Z 0.94 2905 78 12 9 0.00
Thu 08/20 18Z 0.68 2805 74 9 10 0.00
Thu 08/20 19Z 0.47 2806 75 10 10 0.00
Thu 08/20 20Z 0.49 2708 81 11 10 0.00
Thu 08/20 21Z 0.39 2608 81 12 10 0.00
Thu 08/20 22Z 0.39 2708 83 11 10 0.00
Thu 08/20 23Z 0.41 2709 87 12 9 0.00
Fri 08/21 00Z 0.37 2908 85 14 9 0.00
Fri 08/21 01Z 0.27 3108 88 12 9 0.00
Fri 08/21 02Z 0.16 3208 89 15 9 0.00
Fri 08/21 03Z 0.04 3408 88 16 8 0.00
Fri 08/21 04Z 0.06 3507 86 17 8 0.00
Fri 08/21 05Z 0.05 3505 84 19 8 0.00
Fri 08/21 06Z 0.04 3506 81 18 9 0.00
Fri 08/21 07Z 0.07 0006 79 18 8 0.00
Fri 08/21 08Z 0.07 0005 79 19 8 0.00
Fri 08/21 09Z 0.14 0305 77 18 8 0.00
Fri 08/21 10Z 0.12 0404 76 20 8 0.00
Fri 08/21 11Z 0.12 0503 75 19 8 0.00
Fri 08/21 12Z 0.11 0603 74 19 8 0.00
Fri 08/21 13Z 0.13 0803 75 15 8 0.00
Fri 08/21 14Z 0.16 1003 78 13 8 0.00
Fri 08/21 15Z 0.33 1204 83 11 8 0.00
Fri 08/21 16Z 0.33 1402 86 10 8 0.00
Fri 08/21 17Z 0.45 1202 87 8 9 0.00
Run total areal avg QPF for the Central_Greens is: 0.12 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