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Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260617_1200
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)
=== ===== === ==== ==== === === === ====
Wed 06/17 12Z 0.24 2009 70 71 9 0.00
Wed 06/17 13Z 0.35 2008 66 60 9 0.00
Wed 06/17 14Z 1.72 2008 62 51 9 0.00
Wed 06/17 15Z 2.93 2108 59 44 9 0.00
Wed 06/17 16Z 2.80 2007 57 30 10 0.00
Wed 06/17 17Z 1.77 1907 56 29 10 0.00
Wed 06/17 18Z 1.73 1808 54 35 11 0.00
Wed 06/17 19Z 1.98 1908 51 54 11 0.00
Wed 06/17 20Z 0.88 1707 52 71 11 0.00
Wed 06/17 21Z 0.29 1708 55 73 11 0.00
Wed 06/17 22Z 0.15 1711 60 82 11 0.00
Wed 06/17 23Z 0.30 1814 65 91 11 0.00
Thu 06/18 00Z 0.38 1816 70 70 11 0.00
Thu 06/18 01Z 0.32 1818 71 35 11 0.00
Thu 06/18 02Z 0.54 1922 76 41 11 0.00
Thu 06/18 03Z 0.55 2023 86 64 10 0.00
Thu 06/18 04Z 0.38 1923 86 64 11 0.01
Thu 06/18 05Z 0.40 2023 88 68 11 0.00
Thu 06/18 06Z 0.45 2122 93 42 11 0.00
Thu 06/18 07Z 0.43 2122 91 69 11 0.00
Thu 06/18 08Z 0.41 2118 90 90 10 0.04
Thu 06/18 09Z 0.14 1817 88 91 11 0.02
Thu 06/18 10Z 0.13 1825 87 95 12 0.00
Thu 06/18 11Z 0.16 1831 84 96 13 0.00
Thu 06/18 12Z 0.19 1836 87 87 14 0.01
Thu 06/18 13Z 0.45 1941 93 93 12 0.03
Thu 06/18 14Z 0.25 1840 81 88 14 0.03
Thu 06/18 15Z 0.33 1838 96 92 13 0.13
Thu 06/18 16Z 0.32 1833 98 78 13 0.23
Thu 06/18 17Z 0.47 1932 98 71 13 0.07
Thu 06/18 18Z 0.58 2030 96 60 14 0.02
Thu 06/18 19Z 0.87 2128 94 54 14 0.00
Thu 06/18 20Z 2.90 2224 88 61 14 0.01
Thu 06/18 21Z 2.93 2424 89 49 13 0.11
Thu 06/18 22Z 1.30 2422 94 55 13 0.01
Thu 06/18 23Z 1.60 2528 92 55 12 0.09
Fri 06/19 00Z 1.56 2527 88 76 11 0.03
Fri 06/19 01Z 1.23 2529 85 62 11 0.01
Fri 06/19 02Z 1.18 2529 85 65 10 0.00
Fri 06/19 03Z 1.01 2629 87 62 9 0.00
Fri 06/19 04Z 0.92 2629 86 63 10 0.00
Fri 06/19 05Z 0.99 2629 89 76 9 0.00
Fri 06/19 06Z 1.04 2630 91 66 8 0.01
Fri 06/19 07Z 1.05 2630 93 64 8 0.01
Fri 06/19 08Z 0.90 2630 93 64 8 0.01
Fri 06/19 09Z 0.86 2631 93 67 9 0.01
Fri 06/19 10Z 0.90 2633 92 62 9 0.01
Fri 06/19 11Z 0.87 2733 92 54 9 0.01
Fri 06/19 12Z 0.89 2733 91 49 9 0.01
Fri 06/19 13Z 0.95 2732 91 39 9 0.01
Fri 06/19 14Z 1.07 2731 90 36 9 0.01
Fri 06/19 15Z 1.44 2729 90 38 9 0.01
Fri 06/19 16Z 2.58 2727 90 45 9 0.00
Fri 06/19 17Z 8.08 2625 89 45 9 0.00
Fri 06/19 18Z 9.28 2623 88 47 10 0.00
Fri 06/19 19Z 10.14 2623 86 40 10 0.00
Fri 06/19 20Z 12.58 2624 84 29 10 0.00
Fri 06/19 21Z 13.72 2625 78 36 10 0.00
Fri 06/19 22Z 13.74 2627 62 25 10 0.00
Fri 06/19 23Z 7.50 2629 68 31 10 0.00
Run total areal avg QPF for the Central_Greens is: 0.95 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