Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260818_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)
=== ===== === ==== ==== === === === ====
Tue 08/18 18Z 1.07 2804 86 12 13 0.00
Tue 08/18 19Z 1.45 2806 85 26 13 0.01
Tue 08/18 20Z 1.16 2908 85 41 13 0.01
Tue 08/18 21Z 0.33 3108 83 41 13 0.00
Tue 08/18 22Z 0.15 3308 85 42 12 0.00
Tue 08/18 23Z 0.04 3507 86 46 12 0.00
Wed 08/19 00Z 0.04 3505 85 40 12 0.00
Wed 08/19 01Z 0.02 3405 85 35 12 0.00
Wed 08/19 02Z 0.07 3204 84 23 12 0.00
Wed 08/19 03Z 0.08 3204 84 13 12 0.00
Wed 08/19 04Z 0.07 3203 83 11 12 0.00
Wed 08/19 05Z 0.10 3003 84 26 12 0.00
Wed 08/19 06Z 0.16 2803 85 26 11 0.00
Wed 08/19 07Z 0.20 2604 85 25 11 0.00
Wed 08/19 08Z 0.27 2606 88 14 11 0.00
Wed 08/19 09Z 0.31 2507 86 10 11 0.00
Wed 08/19 10Z 0.34 2508 84 12 11 0.00
Wed 08/19 11Z 0.46 2512 85 17 11 0.00
Wed 08/19 12Z 0.43 2513 83 18 11 0.00
Wed 08/19 13Z 0.47 2414 80 29 11 0.00
Wed 08/19 14Z 0.45 2513 74 53 12 0.00
Wed 08/19 15Z 0.52 2513 80 63 12 0.00
Wed 08/19 16Z 0.52 2412 79 64 13 0.00
Wed 08/19 17Z 0.68 2413 81 72 13 0.00
Wed 08/19 18Z 0.63 2413 80 72 13 0.00
Wed 08/19 19Z 0.82 2414 85 70 13 0.00
Wed 08/19 20Z 1.39 2415 90 73 13 0.00
Wed 08/19 21Z 1.27 2415 91 76 13 0.00
Wed 08/19 22Z 0.86 2416 88 77 14 0.00
Wed 08/19 23Z 0.91 2417 88 81 14 0.00
Thu 08/20 00Z 0.81 2417 86 87 14 0.00
Thu 08/20 01Z 0.86 2419 88 75 13 0.01
Thu 08/20 02Z 0.70 2518 91 51 13 0.01
Thu 08/20 03Z 0.57 2617 91 49 13 0.01
Thu 08/20 04Z 0.46 2714 92 46 13 0.01
Thu 08/20 05Z 0.40 2814 93 33 12 0.01
Thu 08/20 06Z 0.33 2913 93 34 12 0.01
Thu 08/20 07Z 0.26 3011 90 22 12 0.01
Thu 08/20 08Z 0.24 3011 86 15 11 0.01
Thu 08/20 09Z 0.24 3012 82 11 11 0.00
Thu 08/20 10Z 0.24 3012 81 6 11 0.00
Thu 08/20 11Z 0.22 3112 80 6 10 0.00
Thu 08/20 12Z 0.17 3111 74 6 11 0.00
Thu 08/20 13Z 0.18 3110 77 4 10 0.00
Thu 08/20 14Z 0.11 3208 78 4 10 0.00
Thu 08/20 15Z 0.17 3107 81 6 10 0.00
Thu 08/20 16Z 0.21 3105 81 6 10 0.00
Thu 08/20 17Z 0.40 3004 80 5 10 0.00
Thu 08/20 18Z 0.42 3004 75 6 10 0.00
Thu 08/20 19Z 0.49 2904 73 6 10 0.00
Thu 08/20 20Z 0.35 2906 71 5 10 0.00
Thu 08/20 21Z 0.21 2905 72 13 10 0.00
Thu 08/20 22Z 0.15 2905 72 10 10 0.00
Thu 08/20 23Z 0.11 3104 72 10 10 0.00
Fri 08/21 00Z 0.04 3405 73 9 10 0.00
Fri 08/21 01Z 0.03 3405 75 9 10 0.00
Fri 08/21 02Z 0.02 3505 75 11 9 0.00
Fri 08/21 03Z 0.03 3506 76 12 9 0.00
Fri 08/21 04Z 0.06 0007 77 12 9 0.00
Fri 08/21 05Z 0.08 0008 77 13 9 0.00
Run total areal avg QPF for the Central_Greens is: 0.10 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