Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260324_0600
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 03/24 06Z 0.29 3321 93 32 -10 0.00
Tue 03/24 07Z 0.24 3320 88 24 -10 0.00
Tue 03/24 08Z 0.21 3318 86 18 -10 0.00
Tue 03/24 09Z 0.20 3317 86 13 -10 0.00
Tue 03/24 10Z 0.19 3317 84 9 -10 0.00
Tue 03/24 11Z 0.16 3317 81 7 -11 0.00
Tue 03/24 12Z 0.17 3318 81 8 -11 0.00
Tue 03/24 13Z 0.20 3318 77 12 -11 0.00
Tue 03/24 14Z 0.32 3215 74 13 -12 0.00
Tue 03/24 15Z 1.26 3111 72 10 -12 0.00
Tue 03/24 16Z 1.50 2808 65 6 -11 0.00
Tue 03/24 17Z 1.40 2508 56 5 -10 0.00
Tue 03/24 18Z 2.20 2410 54 5 -9 0.00
Tue 03/24 19Z 2.66 2412 51 6 -8 0.00
Tue 03/24 20Z 1.91 2413 47 6 -8 0.00
Tue 03/24 21Z 1.37 2416 50 10 -7 0.00
Tue 03/24 22Z 1.04 2419 49 15 -7 0.00
Tue 03/24 23Z 1.02 2423 47 46 -6 0.00
Wed 03/25 00Z 1.57 2528 43 66 -7 0.00
Wed 03/25 01Z 2.89 2630 48 49 -7 0.00
Wed 03/25 02Z 3.06 2630 53 80 -8 0.00
Wed 03/25 03Z 1.33 2728 69 80 -8 0.00
Wed 03/25 04Z 0.87 2825 84 42 -8 0.00
Wed 03/25 05Z 0.78 2824 87 11 -8 0.00
Wed 03/25 06Z 0.73 2823 87 6 -8 0.00
Wed 03/25 07Z 0.62 2822 78 12 -8 0.00
Wed 03/25 08Z 0.47 2819 64 14 -7 0.00
Wed 03/25 09Z 0.45 2718 62 9 -7 0.00
Wed 03/25 10Z 0.46 2719 61 10 -6 0.00
Wed 03/25 11Z 0.46 2818 61 8 -7 0.00
Wed 03/25 12Z 0.44 2717 63 9 -7 0.00
Wed 03/25 13Z 0.41 2717 62 9 -7 0.00
Wed 03/25 14Z 0.38 2715 60 9 -6 0.00
Wed 03/25 15Z 0.39 2714 60 8 -6 0.00
Wed 03/25 16Z 0.44 2613 61 21 -6 0.00
Wed 03/25 17Z 0.50 2613 68 29 -6 0.00
Wed 03/25 18Z 0.53 2512 70 45 -5 0.00
Wed 03/25 19Z 0.62 2511 73 79 -5 0.00
Wed 03/25 20Z 0.60 2410 75 93 -4 0.00
Wed 03/25 21Z 0.71 2311 71 95 -4 0.00
Wed 03/25 22Z 1.39 2213 69 96 -4 0.00
Wed 03/25 23Z 0.75 2215 66 92 -4 0.00
Thu 03/26 00Z 0.66 2118 53 93 -3 0.00
Thu 03/26 01Z 0.67 2021 65 90 -3 0.00
Thu 03/26 02Z 0.68 2023 73 81 -2 0.00
Thu 03/26 03Z 0.75 2126 81 88 -2 0.00
Thu 03/26 04Z 1.06 2327 93 88 -3 0.02
Thu 03/26 05Z 0.83 2425 82 89 -2 0.00
Thu 03/26 06Z 0.76 2324 86 89 -1 0.00
Thu 03/26 07Z 0.60 2126 82 85 -1 0.00
Thu 03/26 08Z 0.56 2227 77 89 0 0.00
Thu 03/26 09Z 0.58 2228 84 89 0 0.00
Thu 03/26 10Z 0.62 2328 86 95 0 0.00
Thu 03/26 11Z 0.60 2327 88 95 0 0.01
Thu 03/26 12Z 0.58 2426 93 94 0 0.04
Thu 03/26 13Z 0.60 2329 96 93 1 0.05
Thu 03/26 14Z 0.64 2430 95 91 2 0.03
Thu 03/26 15Z 0.64 2430 95 85 3 0.02
Thu 03/26 16Z 0.72 2432 95 82 3 0.03
Thu 03/26 17Z 0.78 2431 91 45 4 0.01
Run total areal avg QPF for the Central_Greens is: 0.21 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