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Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260625_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)
=== ===== === ==== ==== === === === ====
Thu 06/25 12Z 0.17 2904 76 56 10 0.00
Thu 06/25 13Z 0.18 2703 75 54 10 0.00
Thu 06/25 14Z 0.41 2604 75 55 10 0.00
Thu 06/25 15Z 0.84 2404 73 54 10 0.00
Thu 06/25 16Z 1.79 2305 71 52 11 0.00
Thu 06/25 17Z 2.66 2306 70 57 11 0.00
Thu 06/25 18Z 3.29 2206 70 68 11 0.00
Thu 06/25 19Z 2.40 2106 70 77 11 0.00
Thu 06/25 20Z 2.03 2107 70 82 12 0.00
Thu 06/25 21Z 1.59 2107 68 79 12 0.00
Thu 06/25 22Z 0.99 2107 66 80 12 0.00
Thu 06/25 23Z 0.60 2208 69 85 12 0.00
Fri 06/26 00Z 0.40 2212 78 93 11 0.01
Fri 06/26 01Z 0.18 1912 76 92 11 0.02
Fri 06/26 02Z 0.17 1814 75 93 11 0.01
Fri 06/26 03Z 0.26 1917 78 91 11 0.00
Fri 06/26 04Z 0.34 1918 87 96 11 0.02
Fri 06/26 05Z 0.25 1917 92 97 10 0.09
Fri 06/26 06Z 0.21 1917 93 95 10 0.13
Fri 06/26 07Z 0.25 1919 95 92 11 0.16
Fri 06/26 08Z 0.31 2019 96 92 10 0.03
Fri 06/26 09Z 0.32 2018 93 86 11 0.01
Fri 06/26 10Z 0.28 2017 94 86 11 0.01
Fri 06/26 11Z 0.36 2018 96 91 10 0.14
Fri 06/26 12Z 0.36 2215 96 67 11 0.02
Fri 06/26 13Z 0.40 2315 95 75 11 0.01
Fri 06/26 14Z 0.38 2413 94 81 11 0.01
Fri 06/26 15Z 0.36 2411 93 62 11 0.00
Fri 06/26 16Z 0.38 2310 94 39 11 0.00
Fri 06/26 17Z 0.50 2311 94 33 11 0.00
Fri 06/26 18Z 0.71 2410 92 48 11 0.00
Fri 06/26 19Z 1.02 2412 89 51 11 0.00
Fri 06/26 20Z 0.81 2411 91 60 12 0.07
Fri 06/26 21Z 0.69 2512 93 64 12 0.16
Fri 06/26 22Z 0.61 2916 90 63 11 0.31
Fri 06/26 23Z 0.39 3015 85 54 12 0.05
Sat 06/27 00Z 0.34 3013 87 30 11 0.02
Sat 06/27 01Z 0.31 3012 90 30 11 0.00
Sat 06/27 02Z 0.29 2910 92 35 11 0.00
Sat 06/27 03Z 0.27 2810 93 34 11 0.01
Sat 06/27 04Z 0.28 2810 92 37 11 0.01
Sat 06/27 05Z 0.25 2910 91 34 11 0.01
Sat 06/27 06Z 0.22 3010 91 35 11 0.01
Sat 06/27 07Z 0.21 3010 92 39 11 0.01
Sat 06/27 08Z 0.15 3109 91 40 11 0.01
Sat 06/27 09Z 0.11 3208 89 41 11 0.01
Sat 06/27 10Z 0.11 3207 89 41 11 0.00
Sat 06/27 11Z 0.08 3206 88 46 11 0.00
Sat 06/27 12Z 0.09 3104 90 48 10 0.00
Sat 06/27 13Z 0.12 2904 92 51 10 0.00
Sat 06/27 14Z 0.10 2703 94 50 10 0.00
Sat 06/27 15Z 0.08 2502 96 48 10 0.00
Sat 06/27 16Z 0.08 2501 96 47 10 0.01
Sat 06/27 17Z 0.08 2601 94 46 10 0.02
Sat 06/27 18Z 0.05 2601 93 46 11 0.02
Sat 06/27 19Z 0.04 2601 92 43 11 0.01
Sat 06/27 20Z 0.05 2401 91 43 11 0.01
Sat 06/27 21Z 0.08 2302 92 44 11 0.01
Sat 06/27 22Z 0.05 2200 90 48 11 0.01
Sat 06/27 23Z 0.04 0101 91 60 11 0.03
Run total areal avg QPF for the Central_Greens is: 1.47 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