Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260919_0000
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sat 09/19 00Z 0.33 3420 70 5 5 0.00
Sat 09/19 01Z 0.25 3422 68 6 5 0.00
Sat 09/19 02Z 0.15 3522 70 6 5 0.00
Sat 09/19 03Z 0.05 3522 69 5 4 0.00
Sat 09/19 04Z 0.04 0021 67 5 4 0.00
Sat 09/19 05Z 0.03 0019 63 5 4 0.00
Sat 09/19 06Z 0.03 0017 59 5 5 0.00
Sat 09/19 07Z 0.02 0016 53 5 5 0.00
Sat 09/19 08Z 0.02 0014 49 5 6 0.00
Sat 09/19 09Z 0.02 0014 44 5 6 0.00
Sat 09/19 10Z 0.02 0013 40 5 6 0.00
Sat 09/19 11Z 0.03 0013 38 5 6 0.00
Sat 09/19 12Z 0.05 0112 36 5 6 0.00
Sat 09/19 13Z 0.05 0110 36 6 6 0.00
Sat 09/19 14Z 0.05 0108 37 5 6 0.00
Sat 09/19 15Z 0.05 0206 41 5 5 0.00
Sat 09/19 16Z 0.05 0204 46 6 5 0.00
Sat 09/19 17Z 0.05 0202 51 6 4 0.00
Sat 09/19 18Z 0.06 0200 55 6 4 0.00
Sat 09/19 19Z 0.06 1800 58 5 5 0.00
Sat 09/19 20Z 0.05 2300 60 6 5 0.00
Sat 09/19 21Z 0.04 1400 61 6 5 0.00
Sat 09/19 22Z 0.04 1602 59 6 5 0.00
Sat 09/19 23Z 0.03 1604 54 6 6 0.00
Sun 09/20 00Z 0.02 1705 49 6 7 0.00
Sun 09/20 01Z 0.03 1706 46 6 7 0.00
Sun 09/20 02Z 0.02 1807 46 6 7 0.00
Sun 09/20 03Z 0.03 1810 45 6 7 0.00
Sun 09/20 04Z 0.09 1912 48 6 7 0.00
Sun 09/20 05Z 0.15 2014 53 6 6 0.00
Sun 09/20 06Z 0.18 2016 59 6 6 0.00
Sun 09/20 07Z 0.24 2018 68 7 5 0.00
Sun 09/20 08Z 0.23 2018 75 9 6 0.00
Sun 09/20 09Z 0.24 2019 81 12 6 0.00
Sun 09/20 10Z 0.26 2018 88 16 5 0.00
Sun 09/20 11Z 0.25 2018 91 23 5 0.00
Sun 09/20 12Z 0.20 2017 90 33 6 0.00
Sun 09/20 13Z 0.18 2016 88 44 6 0.00
Sun 09/20 14Z 0.16 2016 88 62 6 0.00
Sun 09/20 15Z 0.13 1915 88 76 6 0.00
Sun 09/20 16Z 0.11 1915 89 87 6 0.00
Sun 09/20 17Z 0.08 1914 90 95 6 0.01
Sun 09/20 18Z 0.07 1914 94 98 7 0.02
Sun 09/20 19Z 0.06 1813 95 99 7 0.03
Sun 09/20 20Z 0.06 1812 96 99 7 0.04
Sun 09/20 21Z 0.07 1912 97 98 7 0.06
Sun 09/20 22Z 0.09 1911 98 99 7 0.05
Sun 09/20 23Z 0.13 2110 98 96 7 0.05
Mon 09/21 00Z 0.15 2210 98 91 7 0.04
Mon 09/21 01Z 0.17 2209 99 82 7 0.04
Mon 09/21 02Z 0.16 2407 99 64 7 0.03
Mon 09/21 03Z 0.13 2605 99 59 6 0.02
Mon 09/21 04Z 0.09 3004 98 54 6 0.01
Mon 09/21 05Z 0.07 3205 96 40 6 0.00
Mon 09/21 06Z 0.04 3407 93 22 6 0.00
Mon 09/21 07Z 0.02 3509 89 17 6 0.00
Mon 09/21 08Z 0.02 0011 83 11 5 0.00
Mon 09/21 09Z 0.03 0013 80 7 5 0.00
Mon 09/21 10Z 0.05 0013 79 5 5 0.00
Mon 09/21 11Z 0.07 0114 77 3 5 0.00
Run total areal avg QPF for the greens is: 0.40 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