Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260218_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 02/18 06Z 0.55 2821 81 20 -2 0.00
Wed 02/18 07Z 0.54 2823 76 17 -2 0.01
Wed 02/18 08Z 0.51 2924 73 19 -3 0.01
Wed 02/18 09Z 0.44 3023 72 21 -3 0.00
Wed 02/18 10Z 0.39 3023 69 32 -3 0.00
Wed 02/18 11Z 0.35 3023 64 29 -3 0.01
Wed 02/18 12Z 0.32 3023 58 31 -3 0.01
Wed 02/18 13Z 0.25 3121 53 32 -3 0.00
Wed 02/18 14Z 0.21 3118 52 31 -4 0.00
Wed 02/18 15Z 0.19 3116 47 28 -4 0.00
Wed 02/18 16Z 0.17 3115 41 27 -3 0.00
Wed 02/18 17Z 0.15 3214 35 23 -3 0.00
Wed 02/18 18Z 0.10 3212 32 19 -3 0.00
Wed 02/18 19Z 0.06 3310 32 18 -3 0.00
Wed 02/18 20Z 0.04 3409 34 17 -4 0.00
Wed 02/18 21Z 0.04 3509 37 15 -4 0.00
Wed 02/18 22Z 0.07 0009 36 17 -4 0.00
Wed 02/18 23Z 0.15 0211 32 16 -4 0.00
Thu 02/19 00Z 0.18 0312 31 9 -4 0.00
Thu 02/19 01Z 0.15 0210 31 12 -5 0.00
Thu 02/19 02Z 0.18 0311 30 16 -5 0.00
Thu 02/19 03Z 0.21 0314 29 20 -5 0.00
Thu 02/19 04Z 0.21 0314 28 29 -5 0.00
Thu 02/19 05Z 0.14 0211 27 31 -5 0.00
Thu 02/19 06Z 0.15 0310 26 34 -5 0.00
Thu 02/19 07Z 0.12 0208 27 24 -5 0.00
Thu 02/19 08Z 0.13 0308 27 18 -5 0.00
Thu 02/19 09Z 0.10 0307 27 17 -6 0.00
Thu 02/19 10Z 0.10 0306 26 24 -5 0.00
Thu 02/19 11Z 0.05 0303 25 18 -5 0.00
Thu 02/19 12Z 0.02 0101 24 14 -5 0.00
Thu 02/19 13Z 0.02 0301 22 8 -4 0.00
Thu 02/19 14Z 0.02 0800 22 8 -4 0.00
Thu 02/19 15Z 0.01 1501 24 12 -4 0.00
Thu 02/19 16Z 0.01 1703 26 25 -4 0.00
Thu 02/19 17Z 0.05 1904 29 32 -3 0.00
Thu 02/19 18Z 0.10 2105 33 43 -3 0.00
Thu 02/19 19Z 0.15 2207 37 35 -3 0.00
Thu 02/19 20Z 0.19 2307 46 27 -3 0.00
Thu 02/19 21Z 0.19 2308 61 21 -3 0.00
Thu 02/19 22Z 0.22 2309 79 13 -3 0.00
Thu 02/19 23Z 0.23 2310 88 11 -3 0.00
Fri 02/20 00Z 0.24 2410 91 11 -2 0.00
Fri 02/20 01Z 0.19 2608 89 19 -1 0.00
Fri 02/20 02Z 0.12 2706 84 40 0 0.00
Fri 02/20 03Z 0.08 2704 82 52 0 0.00
Fri 02/20 04Z 0.10 2205 87 50 0 0.00
Fri 02/20 05Z 0.16 2111 89 48 -1 0.00
Fri 02/20 06Z 0.11 2108 80 44 0 0.00
Fri 02/20 07Z 0.11 2109 78 35 0 0.00
Fri 02/20 08Z 0.12 2010 76 28 0 0.00
Fri 02/20 09Z 0.11 2010 73 17 0 0.00
Fri 02/20 10Z 0.10 2011 71 5 1 0.00
Fri 02/20 11Z 0.10 2011 68 7 1 0.00
Fri 02/20 12Z 0.10 2010 65 12 1 0.00
Fri 02/20 13Z 0.08 1910 70 16 1 0.00
Fri 02/20 14Z 0.09 1911 74 15 1 0.00
Fri 02/20 15Z 0.08 1813 76 25 0 0.00
Fri 02/20 16Z 0.05 1715 84 63 0 0.00
Fri 02/20 17Z 0.02 1717 94 95 0 0.02
Run total areal avg QPF for the Central_Greens is: 0.06 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