Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260909_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 09/09 06Z 0.13 2205 89 15 11 0.00
Wed 09/09 07Z 0.19 2207 92 15 10 0.00
Wed 09/09 08Z 0.16 2008 93 37 10 0.00
Wed 09/09 09Z 0.20 2010 94 73 10 0.00
Wed 09/09 10Z 0.25 2013 94 70 11 0.00
Wed 09/09 11Z 0.28 2016 91 64 12 0.00
Wed 09/09 12Z 0.31 2020 90 63 12 0.00
Wed 09/09 13Z 0.39 2024 91 51 12 0.00
Wed 09/09 14Z 0.43 2124 93 47 12 0.00
Wed 09/09 15Z 0.47 2123 91 54 12 0.00
Wed 09/09 16Z 0.49 2123 86 43 13 0.00
Wed 09/09 17Z 0.51 2221 89 12 13 0.00
Wed 09/09 18Z 0.51 2121 93 30 12 0.00
Wed 09/09 19Z 0.52 2124 96 81 12 0.02
Wed 09/09 20Z 0.49 2024 96 97 13 0.04
Wed 09/09 21Z 0.48 2026 96 98 13 0.03
Wed 09/09 22Z 0.51 2029 99 98 14 0.17
Wed 09/09 23Z 0.78 2133 99 99 14 0.15
Thu 09/10 00Z 0.91 2234 99 98 14 0.15
Thu 09/10 01Z 1.02 2333 98 92 15 0.08
Thu 09/10 02Z 1.01 2435 97 94 15 0.07
Thu 09/10 03Z 1.00 2436 96 94 16 0.03
Thu 09/10 04Z 0.99 2338 97 91 16 0.03
Thu 09/10 05Z 1.09 2340 97 95 16 0.13
Thu 09/10 06Z 1.22 2443 97 95 15 0.24
Thu 09/10 07Z 1.17 2538 97 89 15 0.17
Thu 09/10 08Z 1.10 2534 98 89 15 0.20
Thu 09/10 09Z 0.97 2630 98 72 15 0.13
Thu 09/10 10Z 0.93 2627 97 35 14 0.07
Thu 09/10 11Z 0.97 2727 95 35 14 0.04
Thu 09/10 12Z 1.01 2827 93 42 12 0.02
Thu 09/10 13Z 1.07 2827 89 26 12 0.01
Thu 09/10 14Z 1.06 2727 83 9 12 0.00
Thu 09/10 15Z 1.54 2727 81 5 12 0.00
Thu 09/10 16Z 7.00 2725 77 5 11 0.00
Thu 09/10 17Z 15.60 2724 71 5 11 0.00
Thu 09/10 18Z 17.11 2725 63 7 11 0.00
Thu 09/10 19Z 17.76 2726 58 8 11 0.00
Thu 09/10 20Z 16.08 2725 57 5 11 0.00
Thu 09/10 21Z 11.58 2825 63 6 10 0.00
Thu 09/10 22Z 4.28 2925 76 9 9 0.00
Thu 09/10 23Z 1.52 2926 87 5 8 0.00
Fri 09/11 00Z 1.08 3026 94 6 7 0.01
Fri 09/11 01Z 0.79 3026 96 11 6 0.01
Fri 09/11 02Z 0.66 3025 96 12 6 0.01
Fri 09/11 03Z 0.66 3025 94 14 5 0.01
Fri 09/11 04Z 0.62 3124 92 15 4 0.00
Fri 09/11 05Z 0.61 3024 91 16 3 0.00
Fri 09/11 06Z 0.53 3024 90 15 3 0.00
Fri 09/11 07Z 0.40 3123 86 11 4 0.00
Fri 09/11 08Z 0.36 3123 81 6 4 0.00
Fri 09/11 09Z 0.31 3123 78 2 5 0.00
Fri 09/11 10Z 0.26 3123 73 1 5 0.00
Fri 09/11 11Z 0.25 3122 68 2 6 0.00
Fri 09/11 12Z 0.25 3122 66 3 6 0.00
Fri 09/11 13Z 0.24 3121 62 3 6 0.00
Fri 09/11 14Z 0.27 3120 59 2 5 0.00
Fri 09/11 15Z 0.30 3120 56 2 5 0.00
Fri 09/11 16Z 0.33 3120 53 1 5 0.00
Fri 09/11 17Z 0.35 3119 51 2 5 0.00
Run total areal avg QPF for the Central_Greens is: 1.82 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