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Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260623_1800
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)
=== ===== === ==== ==== === === === ====
Tue 06/23 18Z 0.05 3509 94 29 10 0.00
Tue 06/23 19Z 0.05 3409 91 26 11 0.00
Tue 06/23 20Z 0.08 3508 90 33 11 0.01
Tue 06/23 21Z 0.06 3508 88 40 11 0.02
Tue 06/23 22Z 0.04 3408 87 39 11 0.00
Tue 06/23 23Z 0.08 3410 88 28 11 0.00
Wed 06/24 00Z 0.10 3412 90 32 11 0.00
Wed 06/24 01Z 0.16 3313 89 40 10 0.01
Wed 06/24 02Z 0.22 3316 90 42 10 0.01
Wed 06/24 03Z 0.22 3318 92 41 10 0.01
Wed 06/24 04Z 0.21 3319 90 36 9 0.00
Wed 06/24 05Z 0.17 3317 87 31 9 0.00
Wed 06/24 06Z 0.15 3317 86 33 9 0.00
Wed 06/24 07Z 0.11 3315 84 36 9 0.00
Wed 06/24 08Z 0.11 3314 84 28 9 0.00
Wed 06/24 09Z 0.13 3314 84 25 9 0.00
Wed 06/24 10Z 0.16 3314 85 19 9 0.00
Wed 06/24 11Z 0.22 3215 87 21 8 0.00
Wed 06/24 12Z 0.27 3215 88 26 8 0.00
Wed 06/24 13Z 0.37 3115 90 30 7 0.00
Wed 06/24 14Z 0.61 3115 90 35 7 0.00
Wed 06/24 15Z 1.51 3114 88 37 7 0.00
Wed 06/24 16Z 2.52 3014 90 29 7 0.00
Wed 06/24 17Z 1.91 3014 89 32 8 0.00
Wed 06/24 18Z 4.08 3013 86 33 8 0.01
Wed 06/24 19Z 6.37 2914 85 38 9 0.00
Wed 06/24 20Z 6.04 2913 83 38 9 0.00
Wed 06/24 21Z 5.27 2915 80 36 9 0.00
Wed 06/24 22Z 2.30 2914 75 24 10 0.00
Wed 06/24 23Z 2.28 2917 76 23 10 0.00
Thu 06/25 00Z 1.71 2919 77 23 10 0.00
Thu 06/25 01Z 1.11 2920 83 20 9 0.00
Thu 06/25 02Z 0.83 3021 82 21 9 0.00
Thu 06/25 03Z 0.65 3019 81 16 9 0.00
Thu 06/25 04Z 0.55 3018 77 15 9 0.00
Thu 06/25 05Z 0.53 3016 77 11 9 0.00
Thu 06/25 06Z 0.47 3015 76 8 9 0.00
Thu 06/25 07Z 0.45 3013 75 8 9 0.00
Thu 06/25 08Z 0.47 2912 76 9 9 0.00
Thu 06/25 09Z 0.43 2910 75 14 9 0.00
Thu 06/25 10Z 0.43 2909 75 17 9 0.00
Thu 06/25 11Z 0.43 2808 76 18 9 0.00
Thu 06/25 12Z 0.41 2708 76 25 9 0.00
Thu 06/25 13Z 0.43 2706 76 39 9 0.00
Thu 06/25 14Z 0.66 2505 76 43 9 0.00
Thu 06/25 15Z 1.13 2406 76 60 9 0.00
Thu 06/25 16Z 1.62 2406 75 66 10 0.00
Thu 06/25 17Z 1.40 2406 71 71 10 0.00
Thu 06/25 18Z 1.21 2305 66 57 11 0.00
Thu 06/25 19Z 0.81 2003 64 24 11 0.00
Thu 06/25 20Z 0.57 1904 64 17 11 0.00
Thu 06/25 21Z 0.27 2003 66 25 11 0.00
Thu 06/25 22Z 0.10 1605 69 51 12 0.00
Thu 06/25 23Z 0.13 1608 71 75 11 0.00
Fri 06/26 00Z 0.20 1610 73 93 11 0.00
Fri 06/26 01Z 0.22 1712 80 90 11 0.00
Fri 06/26 02Z 0.23 1814 83 86 11 0.01
Fri 06/26 03Z 0.31 1918 84 85 11 0.01
Fri 06/26 04Z 0.43 1920 88 90 11 0.04
Fri 06/26 05Z 0.36 1921 90 94 11 0.05
Run total areal avg QPF for the Central_Greens is: 0.18 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