Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260709_0600
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 07/09 06Z 0.58 2715 83 14 16 0.00
Thu 07/09 07Z 0.58 2716 84 8 16 0.00
Thu 07/09 08Z 0.50 2815 80 12 16 0.00
Thu 07/09 09Z 0.43 2814 77 23 16 0.00
Thu 07/09 10Z 0.44 2913 78 25 15 0.00
Thu 07/09 11Z 0.36 2910 82 34 15 0.00
Thu 07/09 12Z 0.31 2908 88 53 14 0.00
Thu 07/09 13Z 0.27 2707 91 52 14 0.01
Thu 07/09 14Z 0.27 2506 92 51 15 0.00
Thu 07/09 15Z 0.29 2406 90 34 15 0.00
Thu 07/09 16Z 0.43 2407 87 22 15 0.00
Thu 07/09 17Z 0.66 2407 83 37 16 0.00
Thu 07/09 18Z 1.41 2308 83 45 16 0.00
Thu 07/09 19Z 1.57 2308 81 56 16 0.00
Thu 07/09 20Z 1.95 2311 82 68 16 0.01
Thu 07/09 21Z 1.81 2312 81 68 16 0.00
Thu 07/09 22Z 0.91 2314 86 73 16 0.01
Thu 07/09 23Z 0.80 2417 90 72 16 0.05
Fri 07/10 00Z 0.68 2616 93 72 16 0.05
Fri 07/10 01Z 0.52 2614 92 68 16 0.07
Fri 07/10 02Z 0.44 2512 94 61 16 0.01
Fri 07/10 03Z 0.43 2512 96 67 16 0.01
Fri 07/10 04Z 0.44 2513 96 75 15 0.01
Fri 07/10 05Z 0.48 2514 97 70 15 0.01
Fri 07/10 06Z 0.48 2715 97 67 15 0.04
Fri 07/10 07Z 0.39 2916 98 64 14 0.03
Fri 07/10 08Z 0.25 3116 97 65 14 0.02
Fri 07/10 09Z 0.18 3216 96 63 14 0.01
Fri 07/10 10Z 0.17 3216 91 69 14 0.01
Fri 07/10 11Z 0.10 3316 86 69 13 0.00
Fri 07/10 12Z 0.06 3415 84 73 13 0.00
Fri 07/10 13Z 0.05 3415 84 70 13 0.00
Fri 07/10 14Z 0.04 3413 85 67 12 0.00
Fri 07/10 15Z 0.05 3511 87 69 12 0.00
Fri 07/10 16Z 0.09 3410 88 64 12 0.00
Fri 07/10 17Z 0.13 3411 86 52 12 0.00
Fri 07/10 18Z 0.16 3411 83 49 12 0.00
Fri 07/10 19Z 0.38 3410 79 33 13 0.00
Fri 07/10 20Z 0.53 3309 74 26 13 0.00
Fri 07/10 21Z 0.74 3309 72 21 13 0.00
Fri 07/10 22Z 0.28 3309 73 33 13 0.00
Fri 07/10 23Z 0.13 3310 74 30 13 0.00
Sat 07/11 00Z 0.17 3311 77 44 12 0.00
Sat 07/11 01Z 0.14 3312 81 33 12 0.00
Sat 07/11 02Z 0.11 3413 83 30 11 0.00
Sat 07/11 03Z 0.11 3415 82 37 11 0.00
Sat 07/11 04Z 0.04 3414 80 35 11 0.00
Sat 07/11 05Z 0.03 3413 77 34 10 0.00
Sat 07/11 06Z 0.08 3511 78 39 10 0.00
Sat 07/11 07Z 0.14 0009 79 25 10 0.00
Sat 07/11 08Z 0.20 0108 81 25 10 0.00
Sat 07/11 09Z 0.21 0208 82 27 9 0.00
Sat 07/11 10Z 0.22 0208 82 16 9 0.00
Sat 07/11 11Z 0.19 0207 82 8 9 0.00
Sat 07/11 12Z 0.16 0106 81 11 9 0.00
Sat 07/11 13Z 0.23 0006 82 14 9 0.00
Sat 07/11 14Z 0.25 3506 83 17 9 0.00
Sat 07/11 15Z 0.17 3507 83 19 9 0.00
Sat 07/11 16Z 0.19 3508 82 20 9 0.00
Sat 07/11 17Z 0.34 3509 79 25 9 0.00
Run total areal avg QPF for the Central_Greens is: 0.35 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