Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260519_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)
=== ===== === ==== ==== === === === ====
Tue 05/19 00Z 0.60 2219 63 32 18 0.00
Tue 05/19 01Z 0.69 2319 61 28 18 0.00
Tue 05/19 02Z 0.74 2220 62 28 18 0.00
Tue 05/19 03Z 0.67 2222 64 27 18 0.00
Tue 05/19 04Z 0.69 2225 64 48 18 0.00
Tue 05/19 05Z 0.92 2331 63 41 18 0.00
Tue 05/19 06Z 1.48 2441 66 70 18 0.00
Tue 05/19 07Z 1.15 2635 73 59 16 0.09
Tue 05/19 08Z 1.15 2630 70 42 16 0.00
Tue 05/19 09Z 1.21 2630 71 47 16 0.00
Tue 05/19 10Z 1.27 2531 73 29 16 0.00
Tue 05/19 11Z 1.29 2533 77 31 15 0.00
Tue 05/19 12Z 1.24 2533 78 41 15 0.00
Tue 05/19 13Z 1.21 2632 81 56 15 0.00
Tue 05/19 14Z 1.06 2529 80 58 15 0.01
Tue 05/19 15Z 1.15 2526 81 54 15 0.00
Tue 05/19 16Z 2.42 2423 83 68 15 0.00
Tue 05/19 17Z 2.75 2425 87 80 15 0.01
Tue 05/19 18Z 7.15 2525 86 72 15 0.02
Tue 05/19 19Z 5.78 2525 84 79 15 0.01
Tue 05/19 20Z 6.16 2526 81 85 15 0.00
Tue 05/19 21Z 4.91 2624 80 72 15 0.00
Tue 05/19 22Z 3.37 2623 82 60 15 0.00
Tue 05/19 23Z 2.12 2523 83 59 15 0.00
Wed 05/20 00Z 1.16 2425 86 56 15 0.01
Wed 05/20 01Z 1.02 2527 77 51 16 0.00
Wed 05/20 02Z 0.97 2629 74 53 16 0.00
Wed 05/20 03Z 1.08 2532 73 62 16 0.00
Wed 05/20 04Z 1.43 2537 84 74 15 0.00
Wed 05/20 05Z 1.35 2538 88 71 15 0.00
Wed 05/20 06Z 1.24 2537 89 63 16 0.00
Wed 05/20 07Z 1.04 2535 84 54 16 0.00
Wed 05/20 08Z 1.19 2536 91 55 15 0.00
Wed 05/20 09Z 1.24 2635 95 58 14 0.01
Wed 05/20 10Z 1.18 2735 95 43 14 0.01
Wed 05/20 11Z 1.13 2734 95 40 13 0.02
Wed 05/20 12Z 1.11 2733 93 37 12 0.01
Wed 05/20 13Z 1.15 2731 89 30 12 0.01
Wed 05/20 14Z 1.48 2728 85 49 11 0.01
Wed 05/20 15Z 3.47 2726 80 54 10 0.01
Wed 05/20 16Z 7.33 2723 76 67 9 0.00
Wed 05/20 17Z 8.02 2822 72 42 9 0.00
Wed 05/20 18Z 10.72 2823 69 40 9 0.00
Wed 05/20 19Z 8.95 2823 71 24 8 0.00
Wed 05/20 20Z 7.01 2923 72 15 7 0.00
Wed 05/20 21Z 5.03 2923 75 18 6 0.00
Wed 05/20 22Z 1.95 3023 79 17 5 0.00
Wed 05/20 23Z 0.98 3024 82 16 4 0.00
Thu 05/21 00Z 0.89 3124 82 10 3 0.00
Thu 05/21 01Z 0.85 3125 79 5 2 0.00
Thu 05/21 02Z 0.89 3126 75 3 1 0.00
Thu 05/21 03Z 0.87 3127 73 2 0 0.00
Thu 05/21 04Z 0.69 3229 74 2 0 0.00
Thu 05/21 05Z 0.53 3228 75 2 0 0.00
Thu 05/21 06Z 0.41 3228 71 2 0 0.00
Thu 05/21 07Z 0.34 3328 65 2 0 0.00
Thu 05/21 08Z 0.31 3329 61 2 -1 0.00
Thu 05/21 09Z 0.24 3328 58 3 0 0.00
Thu 05/21 10Z 0.19 3327 55 4 0 0.00
Thu 05/21 11Z 0.14 3425 53 4 0 0.00
Run total areal avg QPF for the greens is: 0.23 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