Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260512_0000
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)
=== ===== === ==== ==== === === === ====
Tue 05/12 00Z 0.25 3311 64 80 0 0.00
Tue 05/12 01Z 0.17 3312 65 77 -1 0.00
Tue 05/12 02Z 0.15 3414 64 71 -1 0.00
Tue 05/12 03Z 0.15 3415 66 69 -1 0.00
Tue 05/12 04Z 0.15 3415 68 70 -2 0.00
Tue 05/12 05Z 0.19 3416 68 63 -2 0.00
Tue 05/12 06Z 0.24 3316 67 59 -2 0.00
Tue 05/12 07Z 0.26 3316 65 58 -2 0.00
Tue 05/12 08Z 0.25 3316 65 51 -2 0.00
Tue 05/12 09Z 0.26 3316 65 56 -3 0.00
Tue 05/12 10Z 0.27 3316 65 57 -3 0.00
Tue 05/12 11Z 0.29 3215 63 49 -3 0.00
Tue 05/12 12Z 0.39 3215 63 37 -3 0.00
Tue 05/12 13Z 2.34 3214 65 33 -3 0.00
Tue 05/12 14Z 4.66 3114 64 36 -3 0.00
Tue 05/12 15Z 5.50 3114 63 40 -3 0.00
Tue 05/12 16Z 5.30 3113 62 40 -2 0.00
Tue 05/12 17Z 5.13 3011 62 40 -2 0.00
Tue 05/12 18Z 5.41 3010 62 39 -1 0.00
Tue 05/12 19Z 5.68 3011 63 41 -1 0.00
Tue 05/12 20Z 6.41 2912 64 45 0 0.00
Tue 05/12 21Z 4.86 2910 64 35 0 0.00
Tue 05/12 22Z 2.19 3008 61 29 0 0.00
Tue 05/12 23Z 0.60 3007 59 25 0 0.00
Wed 05/13 00Z 0.54 2808 58 28 0 0.00
Wed 05/13 01Z 0.49 2607 58 27 0 0.00
Wed 05/13 02Z 0.46 2507 58 27 0 0.00
Wed 05/13 03Z 0.49 2508 58 25 0 0.00
Wed 05/13 04Z 0.50 2408 59 17 0 0.00
Wed 05/13 05Z 0.55 2309 59 9 0 0.00
Wed 05/13 06Z 0.55 2310 59 8 0 0.00
Wed 05/13 07Z 0.60 2213 60 46 1 0.00
Wed 05/13 08Z 0.62 2213 63 85 1 0.00
Wed 05/13 09Z 0.61 2214 68 98 1 0.00
Wed 05/13 10Z 0.47 2113 74 96 1 0.00
Wed 05/13 11Z 0.36 2015 83 97 1 0.00
Wed 05/13 12Z 0.26 1916 86 97 2 0.00
Wed 05/13 13Z 0.24 1918 94 91 3 0.01
Wed 05/13 14Z 0.25 1919 96 97 3 0.03
Wed 05/13 15Z 0.27 2020 97 95 4 0.06
Wed 05/13 16Z 0.22 1919 94 90 4 0.02
Wed 05/13 17Z 0.19 1822 96 91 4 0.04
Wed 05/13 18Z 0.23 1924 94 85 5 0.03
Wed 05/13 19Z 0.35 1924 93 92 5 0.01
Wed 05/13 20Z 0.36 1924 96 94 5 0.01
Wed 05/13 21Z 0.32 1925 91 97 5 0.02
Wed 05/13 22Z 0.35 1927 92 93 6 0.01
Wed 05/13 23Z 0.38 1929 95 91 5 0.01
Thu 05/14 00Z 0.43 1931 95 90 5 0.02
Thu 05/14 01Z 0.46 1932 95 80 5 0.01
Thu 05/14 02Z 0.49 2032 95 82 5 0.01
Thu 05/14 03Z 0.48 2033 94 86 5 0.02
Thu 05/14 04Z 0.46 1932 92 83 5 0.02
Thu 05/14 05Z 0.36 1930 93 89 5 0.02
Thu 05/14 06Z 0.26 1929 95 97 5 0.05
Thu 05/14 07Z 0.24 1830 96 99 5 0.07
Thu 05/14 08Z 0.21 1828 96 97 5 0.06
Thu 05/14 09Z 0.15 1827 98 98 5 0.08
Thu 05/14 10Z 0.09 1725 97 97 5 0.05
Thu 05/14 11Z 0.05 1725 96 98 5 0.06
Run total areal avg QPF for the Central_Greens is: 0.72 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