Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260615_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)
=== ===== === ==== ==== === === === ====
Mon 06/15 06Z 0.28 2310 96 95 12 0.00
Mon 06/15 07Z 0.35 2811 99 98 11 0.27
Mon 06/15 08Z 0.38 3117 97 98 10 0.14
Mon 06/15 09Z 0.41 3119 95 97 9 0.08
Mon 06/15 10Z 0.51 3022 93 88 9 0.02
Mon 06/15 11Z 0.56 3122 92 74 8 0.00
Mon 06/15 12Z 0.55 3122 88 64 8 0.01
Mon 06/15 13Z 0.62 3123 86 36 7 0.00
Mon 06/15 14Z 0.73 3020 90 22 7 0.00
Mon 06/15 15Z 1.46 3017 94 25 7 0.00
Mon 06/15 16Z 1.16 3016 95 26 7 0.01
Mon 06/15 17Z 1.21 3014 93 21 7 0.01
Mon 06/15 18Z 2.09 3013 93 14 7 0.00
Mon 06/15 19Z 1.64 3012 90 14 7 0.00
Mon 06/15 20Z 1.99 2912 92 13 7 0.00
Mon 06/15 21Z 1.21 2912 92 10 7 0.01
Mon 06/15 22Z 1.26 3014 91 7 6 0.00
Mon 06/15 23Z 0.71 3016 92 6 6 0.00
Tue 06/16 00Z 0.65 3018 90 7 6 0.00
Tue 06/16 01Z 0.66 3019 94 7 6 0.00
Tue 06/16 02Z 0.58 3019 93 6 6 0.00
Tue 06/16 03Z 0.50 3020 93 8 5 0.00
Tue 06/16 04Z 0.45 3120 93 7 5 0.00
Tue 06/16 05Z 0.46 3122 95 5 5 0.00
Tue 06/16 06Z 0.39 3121 93 2 5 0.00
Tue 06/16 07Z 0.30 3221 85 3 5 0.00
Tue 06/16 08Z 0.24 3222 80 4 5 0.00
Tue 06/16 09Z 0.19 3321 78 7 5 0.00
Tue 06/16 10Z 0.20 3321 77 11 5 0.00
Tue 06/16 11Z 0.20 3219 71 12 6 0.00
Tue 06/16 12Z 0.18 3216 64 14 6 0.00
Tue 06/16 13Z 0.17 3314 58 17 6 0.00
Tue 06/16 14Z 0.23 3212 56 16 6 0.00
Tue 06/16 15Z 0.89 3109 53 14 7 0.00
Tue 06/16 16Z 2.27 3008 50 14 7 0.00
Tue 06/16 17Z 3.37 2907 49 17 8 0.00
Tue 06/16 18Z 4.07 2706 52 20 8 0.00
Tue 06/16 19Z 4.56 2506 55 15 8 0.00
Tue 06/16 20Z 5.39 2408 57 16 9 0.00
Tue 06/16 21Z 5.00 2408 60 13 9 0.00
Tue 06/16 22Z 3.44 2309 61 12 9 0.00
Tue 06/16 23Z 0.86 2309 60 14 9 0.00
Wed 06/17 00Z 0.57 2210 55 14 9 0.00
Wed 06/17 01Z 0.59 2311 50 14 9 0.00
Wed 06/17 02Z 0.64 2312 53 16 9 0.00
Wed 06/17 03Z 0.67 2313 58 18 9 0.00
Wed 06/17 04Z 0.62 2313 61 15 8 0.00
Wed 06/17 05Z 0.56 2312 62 16 8 0.00
Wed 06/17 06Z 0.46 2211 62 16 8 0.00
Wed 06/17 07Z 0.44 2211 62 13 8 0.00
Wed 06/17 08Z 0.41 2111 64 13 8 0.00
Wed 06/17 09Z 0.36 2011 66 12 8 0.00
Wed 06/17 10Z 0.29 1912 67 11 8 0.00
Wed 06/17 11Z 0.28 1913 68 14 8 0.00
Wed 06/17 12Z 0.30 1913 68 14 7 0.00
Wed 06/17 13Z 1.01 1813 69 13 7 0.00
Wed 06/17 14Z 2.33 1813 71 8 8 0.00
Wed 06/17 15Z 2.00 1812 68 7 8 0.00
Wed 06/17 16Z 1.04 1712 66 8 9 0.00
Wed 06/17 17Z 1.05 1713 67 43 9 0.00
Run total areal avg QPF for the Central_Greens is: 0.55 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