Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260526_0000
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 05/26 00Z 0.50 2914 77 2 9 0.00
Tue 05/26 01Z 0.76 2917 72 2 9 0.00
Tue 05/26 02Z 0.67 3018 70 4 9 0.00
Tue 05/26 03Z 0.53 3017 67 6 9 0.00
Tue 05/26 04Z 0.41 3118 66 7 9 0.00
Tue 05/26 05Z 0.42 3119 65 8 9 0.00
Tue 05/26 06Z 0.55 3019 65 9 9 0.00
Tue 05/26 07Z 0.60 3019 68 9 9 0.00
Tue 05/26 08Z 0.55 3020 74 9 9 0.00
Tue 05/26 09Z 0.46 3019 78 11 10 0.00
Tue 05/26 10Z 0.38 3017 79 12 10 0.00
Tue 05/26 11Z 0.35 3015 76 13 10 0.00
Tue 05/26 12Z 0.33 3015 75 19 10 0.00
Tue 05/26 13Z 0.31 3012 73 17 11 0.00
Tue 05/26 14Z 0.35 2911 76 39 11 0.00
Tue 05/26 15Z 0.48 2812 78 60 11 0.00
Tue 05/26 16Z 0.65 2812 76 58 11 0.00
Tue 05/26 17Z 1.47 2712 74 49 12 0.00
Tue 05/26 18Z 1.47 2711 77 33 12 0.00
Tue 05/26 19Z 3.01 2512 79 34 12 0.00
Tue 05/26 20Z 4.41 2415 81 34 12 0.00
Tue 05/26 21Z 3.59 2318 83 32 12 0.00
Tue 05/26 22Z 2.69 2422 80 23 12 0.01
Tue 05/26 23Z 1.56 2425 72 26 13 0.00
Wed 05/27 00Z 1.56 2428 71 31 13 0.00
Wed 05/27 01Z 1.67 2431 72 38 12 0.00
Wed 05/27 02Z 1.33 2532 67 41 13 0.00
Wed 05/27 03Z 1.26 2532 63 48 13 0.00
Wed 05/27 04Z 1.19 2631 60 58 13 0.00
Wed 05/27 05Z 1.20 2630 61 58 12 0.00
Wed 05/27 06Z 1.17 2729 62 53 12 0.00
Wed 05/27 07Z 1.09 2828 65 46 12 0.00
Wed 05/27 08Z 0.91 2926 74 55 11 0.00
Wed 05/27 09Z 0.73 2923 84 54 11 0.00
Wed 05/27 10Z 0.66 2922 87 54 11 0.00
Wed 05/27 11Z 0.60 2920 88 60 11 0.00
Wed 05/27 12Z 0.54 2817 88 58 11 0.00
Wed 05/27 13Z 0.53 2815 90 58 11 0.00
Wed 05/27 14Z 0.54 2813 92 45 11 0.00
Wed 05/27 15Z 0.68 2812 93 35 11 0.00
Wed 05/27 16Z 0.83 2910 94 31 10 0.00
Wed 05/27 17Z 1.19 3012 94 32 10 0.01
Wed 05/27 18Z 0.34 3115 92 30 10 0.04
Wed 05/27 19Z 0.69 3215 85 30 10 0.00
Wed 05/27 20Z 1.75 3215 79 26 10 0.00
Wed 05/27 21Z 2.38 3215 77 23 9 0.00
Wed 05/27 22Z 1.46 3316 76 18 9 0.00
Wed 05/27 23Z 0.68 3318 74 14 8 0.00
Thu 05/28 00Z 0.42 3320 74 13 7 0.00
Thu 05/28 01Z 0.31 3321 77 9 7 0.00
Thu 05/28 02Z 0.21 3321 81 9 6 0.00
Thu 05/28 03Z 0.12 3420 85 7 6 0.00
Thu 05/28 04Z 0.05 3420 90 8 6 0.00
Thu 05/28 05Z 0.04 3518 93 18 5 0.00
Thu 05/28 06Z 0.03 3517 94 21 5 0.00
Thu 05/28 07Z 0.04 3416 93 25 5 0.00
Thu 05/28 08Z 0.05 3416 92 27 5 0.00
Thu 05/28 09Z 0.06 3416 91 31 5 0.00
Thu 05/28 10Z 0.05 3417 91 36 5 0.00
Thu 05/28 11Z 0.03 3417 93 42 4 0.00
Run total areal avg QPF for the Central_Greens is: 0.06 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