Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260826_1200
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 08/26 12Z 0.04 3305 89 39 10 0.00
Wed 08/26 13Z 0.04 3304 89 38 10 0.00
Wed 08/26 14Z 0.03 3101 90 37 10 0.00
Wed 08/26 15Z 0.05 2301 90 37 10 0.00
Wed 08/26 16Z 0.06 2101 91 36 10 0.00
Wed 08/26 17Z 0.13 2302 91 34 10 0.00
Wed 08/26 18Z 0.23 2303 90 32 10 0.00
Wed 08/26 19Z 0.17 2103 87 29 11 0.00
Wed 08/26 20Z 0.14 1903 86 22 11 0.00
Wed 08/26 21Z 0.18 2004 87 18 11 0.00
Wed 08/26 22Z 0.16 1905 87 14 11 0.00
Wed 08/26 23Z 0.20 2006 88 14 11 0.00
Thu 08/27 00Z 0.22 2008 89 12 11 0.00
Thu 08/27 01Z 0.19 1908 88 9 11 0.00
Thu 08/27 02Z 0.18 2009 85 10 11 0.00
Thu 08/27 03Z 0.18 2009 83 11 11 0.00
Thu 08/27 04Z 0.22 2010 81 12 11 0.00
Thu 08/27 05Z 0.25 2111 78 15 12 0.00
Thu 08/27 06Z 0.27 2112 76 19 12 0.00
Thu 08/27 07Z 0.36 2114 79 18 11 0.00
Thu 08/27 08Z 0.42 2115 87 18 11 0.00
Thu 08/27 09Z 0.54 2117 89 16 11 0.00
Thu 08/27 10Z 0.56 2118 90 15 11 0.00
Thu 08/27 11Z 0.64 2120 89 26 11 0.00
Thu 08/27 12Z 0.66 2122 91 64 11 0.00
Thu 08/27 13Z 0.71 2123 90 66 11 0.00
Thu 08/27 14Z 0.68 2023 87 63 12 0.00
Thu 08/27 15Z 0.88 2022 88 53 12 0.00
Thu 08/27 16Z 0.74 2020 92 51 12 0.00
Thu 08/27 17Z 0.76 2022 94 74 13 0.01
Thu 08/27 18Z 0.48 2021 96 58 13 0.01
Thu 08/27 19Z 0.57 2022 96 65 13 0.02
Thu 08/27 20Z 0.54 1924 95 68 13 0.01
Thu 08/27 21Z 0.47 2021 87 49 14 0.02
Thu 08/27 22Z 0.44 1923 93 45 14 0.00
Thu 08/27 23Z 0.49 2026 93 58 14 0.00
Fri 08/28 00Z 0.50 2025 91 68 15 0.00
Fri 08/28 01Z 0.74 2131 96 75 14 0.01
Fri 08/28 02Z 0.69 2228 90 60 14 0.05
Fri 08/28 03Z 0.76 2228 95 63 14 0.08
Fri 08/28 04Z 0.76 2326 91 66 13 0.06
Fri 08/28 05Z 0.69 2323 94 61 13 0.01
Fri 08/28 06Z 0.64 2322 95 60 13 0.02
Fri 08/28 07Z 0.61 2419 95 62 13 0.01
Fri 08/28 08Z 0.52 2516 93 59 13 0.01
Fri 08/28 09Z 0.49 2515 93 56 12 0.01
Fri 08/28 10Z 0.43 2514 92 46 12 0.00
Fri 08/28 11Z 0.36 2512 92 49 12 0.00
Fri 08/28 12Z 0.35 2512 91 45 12 0.00
Fri 08/28 13Z 0.32 2510 90 46 12 0.00
Fri 08/28 14Z 0.29 2509 90 32 12 0.00
Fri 08/28 15Z 0.28 2507 92 30 12 0.00
Fri 08/28 16Z 0.30 2507 93 21 12 0.00
Fri 08/28 17Z 0.32 2607 92 21 12 0.00
Fri 08/28 18Z 0.37 2607 92 16 12 0.00
Fri 08/28 19Z 0.37 2708 94 11 12 0.00
Fri 08/28 20Z 0.34 2808 96 9 12 0.01
Fri 08/28 21Z 0.30 2809 95 12 12 0.01
Fri 08/28 22Z 0.25 2909 94 11 12 0.01
Fri 08/28 23Z 0.23 3009 94 14 11 0.01
Run total areal avg QPF for the Central_Greens is: 0.37 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