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Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260617_1200
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)
=== ===== === ==== ==== === === === ====
Wed 06/17 12Z 0.21 2010 72 77 9 0.00
Wed 06/17 13Z 0.26 2010 68 69 9 0.00
Wed 06/17 14Z 1.00 2010 65 60 9 0.00
Wed 06/17 15Z 2.15 2008 62 54 10 0.00
Wed 06/17 16Z 2.09 2008 58 42 10 0.01
Wed 06/17 17Z 0.88 1907 57 37 10 0.01
Wed 06/17 18Z 0.77 1808 56 40 11 0.00
Wed 06/17 19Z 0.92 1809 54 53 11 0.00
Wed 06/17 20Z 0.68 1808 55 69 11 0.00
Wed 06/17 21Z 0.40 1708 58 74 11 0.00
Wed 06/17 22Z 0.31 1710 61 77 11 0.00
Wed 06/17 23Z 0.12 1714 65 84 11 0.00
Thu 06/18 00Z 0.12 1816 68 72 11 0.00
Thu 06/18 01Z 0.13 1818 69 46 11 0.00
Thu 06/18 02Z 0.32 1922 73 48 11 0.00
Thu 06/18 03Z 0.38 1924 81 61 11 0.00
Thu 06/18 04Z 0.25 1924 84 63 11 0.01
Thu 06/18 05Z 0.27 1924 86 71 11 0.00
Thu 06/18 06Z 0.29 2023 87 52 11 0.00
Thu 06/18 07Z 0.29 2022 88 69 11 0.00
Thu 06/18 08Z 0.31 2021 89 90 11 0.03
Thu 06/18 09Z 0.11 1820 88 91 11 0.02
Thu 06/18 10Z 0.10 1725 85 96 11 0.01
Thu 06/18 11Z 0.12 1732 82 96 12 0.01
Thu 06/18 12Z 0.07 1737 87 91 13 0.01
Thu 06/18 13Z 0.18 1842 92 93 12 0.02
Thu 06/18 14Z 0.08 1841 86 90 13 0.05
Thu 06/18 15Z 0.12 1840 96 94 13 0.17
Thu 06/18 16Z 0.14 1836 98 80 13 0.18
Thu 06/18 17Z 0.26 1934 97 71 13 0.06
Thu 06/18 18Z 0.36 1932 96 55 13 0.02
Thu 06/18 19Z 0.56 2030 94 59 14 0.01
Thu 06/18 20Z 1.89 2126 91 65 13 0.01
Thu 06/18 21Z 2.16 2325 90 52 13 0.07
Thu 06/18 22Z 1.33 2424 95 57 13 0.03
Thu 06/18 23Z 1.61 2528 88 63 12 0.06
Fri 06/19 00Z 1.47 2527 84 73 11 0.02
Fri 06/19 01Z 1.44 2528 84 60 10 0.01
Fri 06/19 02Z 1.31 2529 86 63 9 0.00
Fri 06/19 03Z 1.12 2529 89 63 9 0.00
Fri 06/19 04Z 1.03 2629 88 63 9 0.00
Fri 06/19 05Z 1.11 2630 91 75 8 0.00
Fri 06/19 06Z 1.09 2630 93 68 8 0.01
Fri 06/19 07Z 1.06 2630 94 66 8 0.01
Fri 06/19 08Z 0.91 2629 94 67 8 0.01
Fri 06/19 09Z 0.89 2631 94 70 9 0.01
Fri 06/19 10Z 0.93 2633 94 62 9 0.01
Fri 06/19 11Z 0.92 2733 93 50 9 0.01
Fri 06/19 12Z 0.97 2733 92 45 9 0.01
Fri 06/19 13Z 1.04 2732 92 41 9 0.01
Fri 06/19 14Z 1.20 2731 92 42 9 0.01
Fri 06/19 15Z 1.50 2729 90 46 9 0.01
Fri 06/19 16Z 2.55 2727 89 52 9 0.00
Fri 06/19 17Z 7.29 2625 87 53 9 0.00
Fri 06/19 18Z 10.15 2623 87 52 9 0.00
Fri 06/19 19Z 11.81 2623 85 47 10 0.00
Fri 06/19 20Z 12.53 2624 83 40 10 0.00
Fri 06/19 21Z 13.23 2625 79 38 10 0.00
Fri 06/19 22Z 11.02 2627 70 35 10 0.03
Fri 06/19 23Z 6.11 2629 75 41 10 0.01
Run total areal avg QPF for the greens is: 0.96 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