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Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260320_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)
=== ===== === ==== ==== === === === ====
Fri 03/20 12Z 0.37 2712 80 21 -5 0.00
Fri 03/20 13Z 0.25 2509 72 22 -4 0.00
Fri 03/20 14Z 0.28 2310 74 8 -4 0.00
Fri 03/20 15Z 0.28 2112 71 39 -4 0.00
Fri 03/20 16Z 0.30 2015 70 86 -3 0.00
Fri 03/20 17Z 0.14 1818 67 94 -2 0.00
Fri 03/20 18Z 0.11 1820 77 89 -1 0.00
Fri 03/20 19Z 0.16 1820 88 96 -1 0.04
Fri 03/20 20Z 0.21 1921 98 97 -1 0.17
Fri 03/20 21Z 0.40 2024 99 95 0 0.17
Fri 03/20 22Z 0.55 2227 99 94 0 0.09
Fri 03/20 23Z 0.61 2326 99 95 1 0.07
Sat 03/21 00Z 0.60 2424 99 84 1 0.08
Sat 03/21 01Z 0.55 2521 99 31 0 0.03
Sat 03/21 02Z 0.50 2519 98 7 0 0.02
Sat 03/21 03Z 0.49 2518 98 6 0 0.02
Sat 03/21 04Z 0.40 2716 98 8 0 0.02
Sat 03/21 05Z 0.27 2913 99 8 0 0.01
Sat 03/21 06Z 0.17 3113 99 7 -1 0.01
Sat 03/21 07Z 0.11 3213 98 6 -2 0.01
Sat 03/21 08Z 0.08 3315 97 8 -2 0.01
Sat 03/21 09Z 0.07 3316 96 36 -3 0.00
Sat 03/21 10Z 0.09 3318 95 53 -4 0.00
Sat 03/21 11Z 0.09 3320 94 68 -5 0.00
Sat 03/21 12Z 0.09 3421 91 55 -6 0.00
Sat 03/21 13Z 0.08 3421 86 50 -6 0.00
Sat 03/21 14Z 0.09 3421 82 29 -6 0.00
Sat 03/21 15Z 0.10 3320 80 21 -6 0.00
Sat 03/21 16Z 0.12 3319 78 18 -6 0.00
Sat 03/21 17Z 0.19 3319 78 18 -7 0.00
Sat 03/21 18Z 0.28 3218 75 20 -7 0.00
Sat 03/21 19Z 0.31 3217 70 20 -7 0.00
Sat 03/21 20Z 0.26 3316 67 18 -6 0.00
Sat 03/21 21Z 0.23 3214 65 14 -6 0.00
Sat 03/21 22Z 0.18 3211 62 18 -6 0.00
Sat 03/21 23Z 0.16 3109 62 35 -6 0.00
Sun 03/22 00Z 0.22 3010 67 63 -6 0.00
Sun 03/22 01Z 0.22 2908 71 89 -5 0.00
Sun 03/22 02Z 0.19 2706 72 93 -5 0.00
Sun 03/22 03Z 0.24 2507 76 95 -5 0.00
Sun 03/22 04Z 0.35 2409 86 94 -6 0.00
Sun 03/22 05Z 0.31 2310 89 92 -6 0.01
Sun 03/22 06Z 0.36 2213 90 92 -5 0.01
Sun 03/22 07Z 0.40 2215 88 92 -5 0.01
Sun 03/22 08Z 0.51 2218 94 91 -6 0.02
Sun 03/22 09Z 0.44 2120 97 93 -4 0.04
Sun 03/22 10Z 0.43 2121 98 92 -3 0.06
Sun 03/22 11Z 0.40 2021 98 93 -3 0.08
Sun 03/22 12Z 0.34 2022 98 95 -3 0.10
Sun 03/22 13Z 0.31 2022 98 98 -1 0.07
Sun 03/22 14Z 0.28 2021 98 99 0 0.05
Sun 03/22 15Z 0.27 2019 99 99 0 0.09
Sun 03/22 16Z 0.30 2117 99 99 0 0.11
Sun 03/22 17Z 0.27 2214 99 98 0 0.09
Sun 03/22 18Z 0.26 2212 99 98 0 0.08
Sun 03/22 19Z 0.27 2311 99 97 0 0.09
Sun 03/22 20Z 0.26 2410 99 97 0 0.07
Sun 03/22 21Z 0.28 2510 99 94 0 0.07
Sun 03/22 22Z 0.27 2710 99 72 0 0.05
Sun 03/22 23Z 0.22 2910 99 52 -1 0.03
Run total areal avg QPF for the Central_Greens is: 1.88 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