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Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260629_0000
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)
=== ===== === ==== ==== === === === ====
Mon 06/29 00Z 0.17 3411 60 42 14 0.00
Mon 06/29 01Z 0.04 3513 54 42 14 0.00
Mon 06/29 02Z 0.11 0015 52 46 14 0.00
Mon 06/29 03Z 0.21 0115 55 49 13 0.00
Mon 06/29 04Z 0.27 0212 58 55 13 0.00
Mon 06/29 05Z 0.24 0309 61 60 13 0.00
Mon 06/29 06Z 0.20 0207 60 63 13 0.00
Mon 06/29 07Z 0.16 0106 60 57 13 0.00
Mon 06/29 08Z 0.14 3506 60 52 13 0.00
Mon 06/29 09Z 0.14 3506 60 46 13 0.00
Mon 06/29 10Z 0.12 0007 60 41 13 0.00
Mon 06/29 11Z 0.10 3508 60 35 13 0.00
Mon 06/29 12Z 0.11 3408 61 27 13 0.00
Mon 06/29 13Z 0.12 3407 65 20 13 0.00
Mon 06/29 14Z 0.14 3406 67 18 13 0.00
Mon 06/29 15Z 0.23 3304 67 19 13 0.00
Mon 06/29 16Z 0.31 3305 65 24 13 0.00
Mon 06/29 17Z 0.52 3205 63 33 13 0.01
Mon 06/29 18Z 0.99 3106 60 28 13 0.01
Mon 06/29 19Z 1.30 3105 56 22 14 0.00
Mon 06/29 20Z 1.30 3105 53 19 14 0.00
Mon 06/29 21Z 0.81 3105 51 24 14 0.00
Mon 06/29 22Z 0.44 3105 49 24 14 0.00
Mon 06/29 23Z 0.36 3005 48 21 14 0.00
Tue 06/30 00Z 0.41 3006 49 15 14 0.00
Tue 06/30 01Z 0.45 3005 52 12 14 0.00
Tue 06/30 02Z 0.52 2705 55 11 14 0.00
Tue 06/30 03Z 0.47 2505 57 9 14 0.00
Tue 06/30 04Z 0.57 2407 58 10 14 0.00
Tue 06/30 05Z 0.62 2409 60 13 14 0.00
Tue 06/30 06Z 0.71 2311 61 18 14 0.00
Tue 06/30 07Z 0.77 2413 61 22 14 0.00
Tue 06/30 08Z 0.74 2415 60 28 14 0.00
Tue 06/30 09Z 0.80 2416 60 40 14 0.00
Tue 06/30 10Z 0.79 2416 64 46 14 0.00
Tue 06/30 11Z 0.79 2517 69 51 14 0.00
Tue 06/30 12Z 0.79 2518 73 48 14 0.00
Tue 06/30 13Z 0.75 2418 77 40 14 0.00
Tue 06/30 14Z 0.83 2519 83 47 14 0.00
Tue 06/30 15Z 0.69 2517 90 91 13 0.02
Tue 06/30 16Z 0.35 2312 81 95 14 0.07
Tue 06/30 17Z 0.36 2313 83 95 14 0.01
Tue 06/30 18Z 0.39 2315 92 85 14 0.02
Tue 06/30 19Z 0.41 2216 91 75 15 0.00
Tue 06/30 20Z 0.51 2218 91 83 16 0.01
Tue 06/30 21Z 0.60 2221 95 84 16 0.01
Tue 06/30 22Z 0.62 2223 95 83 16 0.01
Tue 06/30 23Z 0.71 2325 94 91 16 0.01
Wed 07/01 00Z 0.68 2325 95 89 17 0.07
Wed 07/01 01Z 0.72 2327 95 79 17 0.14
Wed 07/01 02Z 0.73 2428 97 75 18 0.17
Wed 07/01 03Z 0.82 2529 98 69 18 0.08
Wed 07/01 04Z 0.84 2628 97 52 18 0.09
Wed 07/01 05Z 0.76 2826 97 39 18 0.07
Wed 07/01 06Z 0.69 2823 95 48 18 0.08
Wed 07/01 07Z 0.71 2724 89 67 18 0.20
Wed 07/01 08Z 0.65 2824 86 43 18 0.09
Wed 07/01 09Z 0.61 2823 91 26 18 0.01
Wed 07/01 10Z 0.65 2824 95 21 18 0.06
Wed 07/01 11Z 0.63 2924 96 9 18 0.04
Run total areal avg QPF for the greens is: 1.28 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