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Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260619_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)
=== ===== === ==== ==== === === === ====
Fri 06/19 18Z 2.58 2617 84 57 9 0.00
Fri 06/19 19Z 11.53 2619 80 47 9 0.00
Fri 06/19 20Z 11.06 2622 78 50 10 0.00
Fri 06/19 21Z 12.42 2624 67 36 10 0.01
Fri 06/19 22Z 14.28 2627 69 52 10 0.00
Fri 06/19 23Z 9.08 2629 78 61 9 0.00
Sat 06/20 00Z 2.27 2729 85 59 8 0.00
Sat 06/20 01Z 1.74 2730 87 64 8 0.00
Sat 06/20 02Z 1.57 2730 89 67 8 0.01
Sat 06/20 03Z 1.46 2732 91 76 8 0.02
Sat 06/20 04Z 1.21 2731 91 79 8 0.03
Sat 06/20 05Z 1.05 2730 94 86 8 0.05
Sat 06/20 06Z 0.96 2730 96 93 8 0.07
Sat 06/20 07Z 0.89 2830 97 94 8 0.09
Sat 06/20 08Z 0.79 2828 97 93 8 0.09
Sat 06/20 09Z 0.66 2925 97 87 8 0.05
Sat 06/20 10Z 0.67 2926 97 81 7 0.04
Sat 06/20 11Z 0.67 2925 97 67 7 0.02
Sat 06/20 12Z 0.63 3024 95 66 7 0.01
Sat 06/20 13Z 0.70 3025 95 69 7 0.01
Sat 06/20 14Z 0.86 2924 94 69 8 0.01
Sat 06/20 15Z 1.20 2922 95 68 8 0.01
Sat 06/20 16Z 1.13 2921 96 77 8 0.03
Sat 06/20 17Z 1.11 3021 96 74 8 0.03
Sat 06/20 18Z 0.82 3021 95 66 8 0.03
Sat 06/20 19Z 0.79 3021 95 68 9 0.03
Sat 06/20 20Z 0.73 3020 92 72 9 0.01
Sat 06/20 21Z 0.68 3120 92 70 9 0.02
Sat 06/20 22Z 0.67 3018 93 69 9 0.01
Sat 06/20 23Z 0.52 3017 91 71 9 0.01
Sun 06/21 00Z 0.57 3017 89 65 9 0.01
Sun 06/21 01Z 0.44 3016 90 60 9 0.00
Sun 06/21 02Z 0.35 3015 89 58 9 0.00
Sun 06/21 03Z 0.31 3014 86 57 10 0.00
Sun 06/21 04Z 0.28 3014 86 59 10 0.00
Sun 06/21 05Z 0.27 3013 87 63 9 0.00
Sun 06/21 06Z 0.25 3012 88 67 9 0.00
Sun 06/21 07Z 0.20 3111 88 70 9 0.00
Sun 06/21 08Z 0.20 3111 88 69 10 0.00
Sun 06/21 09Z 0.21 3010 88 65 10 0.00
Sun 06/21 10Z 0.23 2809 89 61 9 0.00
Sun 06/21 11Z 0.22 2708 88 61 10 0.00
Sun 06/21 12Z 0.22 2607 86 67 10 0.00
Sun 06/21 13Z 0.23 2607 85 68 10 0.00
Sun 06/21 14Z 0.28 2608 86 72 9 0.00
Sun 06/21 15Z 0.35 2507 87 70 9 0.00
Sun 06/21 16Z 0.73 2508 88 69 9 0.00
Sun 06/21 17Z 2.69 2709 88 69 9 0.00
Sun 06/21 18Z 2.76 2708 87 72 10 0.02
Sun 06/21 19Z 0.99 2710 82 57 10 0.06
Sun 06/21 20Z 0.54 2808 81 42 10 0.01
Sun 06/21 21Z 0.51 2711 87 43 10 0.01
Sun 06/21 22Z 0.34 2811 77 49 10 0.01
Sun 06/21 23Z 0.36 2912 75 37 10 0.00
Mon 06/22 00Z 0.40 2913 81 41 10 0.00
Mon 06/22 01Z 0.43 2812 81 46 10 0.00
Mon 06/22 02Z 0.48 2813 85 49 10 0.00
Mon 06/22 03Z 0.43 2813 85 37 10 0.00
Mon 06/22 04Z 0.30 2911 79 30 10 0.00
Mon 06/22 05Z 0.25 2910 77 32 10 0.00
Run total areal avg QPF for the Central_Greens is: 0.81 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