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Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260617_0600
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 06Z 0.36 2310 76 58 9 0.00
Wed 06/17 07Z 0.37 2210 76 59 9 0.00
Wed 06/17 08Z 0.31 2209 74 59 9 0.00
Wed 06/17 09Z 0.25 2109 71 57 9 0.00
Wed 06/17 10Z 0.23 2108 70 55 9 0.00
Wed 06/17 11Z 0.22 2109 70 53 9 0.00
Wed 06/17 12Z 0.18 2008 70 51 9 0.00
Wed 06/17 13Z 0.16 1908 70 58 9 0.00
Wed 06/17 14Z 0.16 1807 71 68 9 0.00
Wed 06/17 15Z 0.47 1707 71 75 10 0.00
Wed 06/17 16Z 0.51 1809 73 73 10 0.04
Wed 06/17 17Z 0.49 1809 72 66 10 0.04
Wed 06/17 18Z 0.34 1810 74 68 10 0.02
Wed 06/17 19Z 0.80 1911 73 73 10 0.02
Wed 06/17 20Z 0.33 1909 72 72 10 0.02
Wed 06/17 21Z 0.12 1710 71 67 11 0.00
Wed 06/17 22Z 0.22 1812 71 68 11 0.00
Wed 06/17 23Z 0.18 1814 71 65 11 0.00
Thu 06/18 00Z 0.15 1815 74 57 11 0.00
Thu 06/18 01Z 0.33 1917 77 50 11 0.00
Thu 06/18 02Z 0.34 1919 82 44 11 0.00
Thu 06/18 03Z 0.33 2021 85 42 11 0.00
Thu 06/18 04Z 0.29 2019 86 64 11 0.00
Thu 06/18 05Z 0.25 2018 83 58 11 0.00
Thu 06/18 06Z 0.23 1920 82 58 11 0.00
Thu 06/18 07Z 0.26 1923 86 70 11 0.00
Thu 06/18 08Z 0.18 1924 88 86 11 0.01
Thu 06/18 09Z 0.18 1927 89 81 11 0.02
Thu 06/18 10Z 0.10 1828 89 77 11 0.02
Thu 06/18 11Z 0.13 1830 91 89 12 0.02
Thu 06/18 12Z 0.08 1834 87 93 13 0.01
Thu 06/18 13Z 0.05 1838 86 81 13 0.02
Thu 06/18 14Z 0.07 1742 88 86 14 0.02
Thu 06/18 15Z 0.06 1844 95 96 13 0.04
Thu 06/18 16Z 0.09 1842 96 98 13 0.10
Thu 06/18 17Z 0.16 1840 98 90 13 0.22
Thu 06/18 18Z 0.22 1937 97 75 14 0.09
Thu 06/18 19Z 0.30 1933 96 71 14 0.05
Thu 06/18 20Z 0.51 2029 96 72 14 0.10
Thu 06/18 21Z 0.99 2326 93 82 14 0.16
Thu 06/18 22Z 1.10 2426 85 38 13 0.09
Thu 06/18 23Z 1.40 2425 91 41 12 0.00
Fri 06/19 00Z 1.55 2429 91 58 12 0.02
Fri 06/19 01Z 1.75 2533 92 72 10 0.06
Fri 06/19 02Z 1.60 2533 90 70 9 0.02
Fri 06/19 03Z 1.49 2533 94 69 8 0.01
Fri 06/19 04Z 1.34 2533 96 69 7 0.02
Fri 06/19 05Z 1.21 2632 97 67 7 0.02
Fri 06/19 06Z 1.15 2632 96 67 7 0.02
Fri 06/19 07Z 0.98 2632 95 69 8 0.01
Fri 06/19 08Z 0.94 2633 93 70 8 0.01
Fri 06/19 09Z 0.91 2634 92 70 8 0.01
Fri 06/19 10Z 0.92 2634 93 63 8 0.01
Fri 06/19 11Z 0.90 2633 93 64 9 0.01
Fri 06/19 12Z 0.92 2632 93 61 9 0.01
Fri 06/19 13Z 0.99 2632 93 60 9 0.01
Fri 06/19 14Z 1.10 2630 92 54 8 0.01
Fri 06/19 15Z 1.17 2629 89 49 9 0.01
Fri 06/19 16Z 1.76 2528 89 48 9 0.00
Fri 06/19 17Z 3.75 2528 89 51 8 0.00
Run total areal avg QPF for the greens is: 1.37 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