Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260519_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 05/19 18Z 1.87 2420 79 81 16 0.00
Tue 05/19 19Z 4.41 2520 84 86 16 0.01
Tue 05/19 20Z 3.82 2520 84 95 16 0.01
Tue 05/19 21Z 3.37 2626 77 71 16 0.04
Tue 05/19 22Z 2.86 2722 83 56 15 0.00
Tue 05/19 23Z 1.96 2722 85 40 15 0.00
Wed 05/20 00Z 1.41 2624 83 41 15 0.00
Wed 05/20 01Z 1.00 2625 78 41 16 0.00
Wed 05/20 02Z 1.04 2529 78 56 16 0.00
Wed 05/20 03Z 1.13 2531 81 63 16 0.00
Wed 05/20 04Z 1.17 2533 79 63 17 0.00
Wed 05/20 05Z 1.45 2438 78 63 17 0.00
Wed 05/20 06Z 1.36 2538 76 55 17 0.00
Wed 05/20 07Z 1.18 2535 83 52 17 0.00
Wed 05/20 08Z 1.22 2634 90 54 15 0.01
Wed 05/20 09Z 1.08 2631 90 50 14 0.01
Wed 05/20 10Z 0.93 2628 92 49 14 0.00
Wed 05/20 11Z 0.83 2729 90 58 14 0.00
Wed 05/20 12Z 0.83 2728 92 62 14 0.00
Wed 05/20 13Z 0.88 2726 94 66 13 0.00
Wed 05/20 14Z 0.96 2724 95 53 13 0.01
Wed 05/20 15Z 1.08 2624 96 60 12 0.02
Wed 05/20 16Z 1.23 2725 95 59 12 0.04
Wed 05/20 17Z 2.73 2724 92 49 11 0.02
Wed 05/20 18Z 7.55 2721 82 38 10 0.00
Wed 05/20 19Z 11.78 2820 74 36 10 0.00
Wed 05/20 20Z 9.74 2920 71 31 10 0.00
Wed 05/20 21Z 7.32 2920 71 29 9 0.00
Wed 05/20 22Z 3.20 3020 73 27 8 0.00
Wed 05/20 23Z 0.85 3022 78 24 7 0.00
Thu 05/21 00Z 0.67 3124 77 18 6 0.00
Thu 05/21 01Z 0.55 3124 80 16 5 0.00
Thu 05/21 02Z 0.40 3124 76 13 5 0.00
Thu 05/21 03Z 0.33 3225 70 9 4 0.00
Thu 05/21 04Z 0.28 3225 65 5 3 0.00
Thu 05/21 05Z 0.23 3225 63 4 3 0.00
Thu 05/21 06Z 0.21 3326 63 3 2 0.00
Thu 05/21 07Z 0.19 3328 64 2 1 0.00
Thu 05/21 08Z 0.14 3328 63 2 1 0.00
Thu 05/21 09Z 0.11 3327 58 2 1 0.00
Thu 05/21 10Z 0.08 3427 50 3 1 0.00
Thu 05/21 11Z 0.06 3425 46 3 1 0.00
Thu 05/21 12Z 0.05 3423 45 3 1 0.00
Thu 05/21 13Z 0.05 3421 44 2 1 0.00
Thu 05/21 14Z 0.04 3420 44 2 1 0.00
Thu 05/21 15Z 0.05 3418 45 2 0 0.00
Thu 05/21 16Z 0.08 3416 46 2 0 0.00
Thu 05/21 17Z 0.15 3415 47 3 0 0.00
Thu 05/21 18Z 0.16 3415 44 4 0 0.00
Thu 05/21 19Z 0.21 3415 40 5 1 0.00
Thu 05/21 20Z 0.28 3316 36 6 1 0.00
Thu 05/21 21Z 0.19 3317 32 8 1 0.00
Thu 05/21 22Z 0.17 3319 30 10 1 0.00
Thu 05/21 23Z 0.15 3320 29 7 2 0.00
Fri 05/22 00Z 0.11 3420 32 4 2 0.00
Fri 05/22 01Z 0.08 3419 36 3 2 0.00
Fri 05/22 02Z 0.02 3418 35 4 2 0.00
Fri 05/22 03Z 0.03 3516 35 5 2 0.00
Fri 05/22 04Z 0.08 3515 35 4 2 0.00
Fri 05/22 05Z 0.06 3513 34 5 2 0.00
Run total areal avg QPF for the Central_Greens is: 0.17 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