Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260712_1800
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)
=== ===== === ==== ==== === === === ====
Sun 07/12 18Z 0.90 3203 73 15 12 0.00
Sun 07/12 19Z 0.72 3203 72 18 12 0.00
Sun 07/12 20Z 0.29 3202 72 21 12 0.01
Sun 07/12 21Z 0.24 3102 70 22 12 0.00
Sun 07/12 22Z 0.16 3203 67 17 13 0.00
Sun 07/12 23Z 0.08 3202 66 10 13 0.00
Mon 07/13 00Z 0.09 2501 66 14 13 0.00
Mon 07/13 01Z 0.13 2003 65 13 12 0.00
Mon 07/13 02Z 0.22 2005 65 9 12 0.00
Mon 07/13 03Z 0.44 2107 66 7 12 0.00
Mon 07/13 04Z 0.68 2210 72 8 12 0.00
Mon 07/13 05Z 0.86 2312 76 7 12 0.00
Mon 07/13 06Z 0.90 2413 76 6 12 0.00
Mon 07/13 07Z 0.86 2414 77 8 11 0.00
Mon 07/13 08Z 0.83 2514 75 13 11 0.00
Mon 07/13 09Z 0.86 2514 73 16 11 0.00
Mon 07/13 10Z 0.82 2514 71 19 11 0.00
Mon 07/13 11Z 0.69 2414 76 22 11 0.00
Mon 07/13 12Z 0.66 2415 75 26 12 0.00
Mon 07/13 13Z 0.67 2415 81 27 12 0.00
Mon 07/13 14Z 0.73 2415 84 28 12 0.00
Mon 07/13 15Z 0.95 2316 85 31 12 0.00
Mon 07/13 16Z 1.39 2415 81 38 12 0.00
Mon 07/13 17Z 1.01 2413 80 40 13 0.00
Mon 07/13 18Z 0.62 2413 85 43 13 0.01
Mon 07/13 19Z 0.62 2412 84 48 14 0.00
Mon 07/13 20Z 0.58 2413 87 56 14 0.01
Mon 07/13 21Z 0.61 2415 86 66 15 0.00
Mon 07/13 22Z 0.66 2418 89 77 15 0.01
Mon 07/13 23Z 0.79 2621 90 87 15 0.01
Tue 07/14 00Z 0.70 2721 85 83 15 0.01
Tue 07/14 01Z 0.82 2723 86 67 14 0.00
Tue 07/14 02Z 0.87 2723 82 57 14 0.01
Tue 07/14 03Z 0.79 2822 72 44 15 0.00
Tue 07/14 04Z 0.72 2721 69 36 15 0.00
Tue 07/14 05Z 0.63 2720 74 27 15 0.00
Tue 07/14 06Z 0.73 2825 82 24 15 0.00
Tue 07/14 07Z 0.72 2926 84 24 15 0.00
Tue 07/14 08Z 0.66 2927 84 28 16 0.00
Tue 07/14 09Z 0.58 2927 82 36 17 0.00
Tue 07/14 10Z 0.56 2926 78 41 17 0.00
Tue 07/14 11Z 0.60 2927 78 35 18 0.00
Tue 07/14 12Z 0.61 2827 78 36 18 0.00
Tue 07/14 13Z 0.60 2826 73 35 19 0.00
Tue 07/14 14Z 0.61 2827 71 35 19 0.00
Tue 07/14 15Z 0.63 2727 76 33 20 0.00
Tue 07/14 16Z 0.65 2728 77 32 21 0.00
Tue 07/14 17Z 0.76 2728 83 21 20 0.00
Tue 07/14 18Z 0.92 2628 84 11 20 0.00
Tue 07/14 19Z 1.23 2629 83 11 20 0.00
Tue 07/14 20Z 1.76 2629 83 11 20 0.00
Tue 07/14 21Z 1.70 2628 82 11 20 0.00
Tue 07/14 22Z 1.90 2529 87 14 20 0.00
Tue 07/14 23Z 1.54 2630 90 17 20 0.01
Wed 07/15 00Z 1.43 2633 92 23 20 0.01
Wed 07/15 01Z 1.42 2636 92 27 19 0.01
Wed 07/15 02Z 1.40 2639 91 28 19 0.00
Wed 07/15 03Z 1.14 2735 88 35 19 0.00
Wed 07/15 04Z 1.04 2831 90 50 18 0.00
Wed 07/15 05Z 0.87 3029 94 68 17 0.05
Run total areal avg QPF for the Central_Greens is: 0.15 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