Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260411_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)
=== ===== === ==== ==== === === === ====
Sat 04/11 18Z 6.52 3016 85 15 -4 0.00
Sat 04/11 19Z 6.71 3018 81 13 -4 0.00
Sat 04/11 20Z 6.02 3118 79 13 -4 0.00
Sat 04/11 21Z 4.98 3119 76 13 -4 0.00
Sat 04/11 22Z 4.74 3120 74 10 -4 0.00
Sat 04/11 23Z 3.13 3222 75 8 -5 0.00
Sun 04/12 00Z 1.81 3224 78 7 -5 0.00
Sun 04/12 01Z 1.12 3225 80 8 -5 0.00
Sun 04/12 02Z 0.85 3226 78 9 -6 0.00
Sun 04/12 03Z 0.61 3227 75 10 -6 0.00
Sun 04/12 04Z 0.44 3326 71 11 -6 0.00
Sun 04/12 05Z 0.28 3324 67 10 -5 0.00
Sun 04/12 06Z 0.18 3322 64 10 -5 0.00
Sun 04/12 07Z 0.13 3420 64 11 -5 0.00
Sun 04/12 08Z 0.13 3317 65 14 -5 0.00
Sun 04/12 09Z 0.16 3316 65 18 -5 0.00
Sun 04/12 10Z 0.12 3314 62 19 -4 0.00
Sun 04/12 11Z 0.07 3312 57 23 -3 0.00
Sun 04/12 12Z 0.06 3310 52 27 -2 0.00
Sun 04/12 13Z 0.06 3207 47 32 -1 0.00
Sun 04/12 14Z 0.09 2904 45 31 -1 0.00
Sun 04/12 15Z 0.17 2504 47 25 -1 0.00
Sun 04/12 16Z 0.26 2305 47 24 -1 0.00
Sun 04/12 17Z 0.35 2105 46 36 -1 0.00
Sun 04/12 18Z 0.54 2006 45 34 -1 0.00
Sun 04/12 19Z 0.83 2008 44 29 0 0.00
Sun 04/12 20Z 0.45 1911 40 63 0 0.00
Sun 04/12 21Z 0.33 1912 40 93 0 0.00
Sun 04/12 22Z 0.16 1815 43 80 0 0.00
Sun 04/12 23Z 0.32 1920 49 92 0 0.00
Mon 04/13 00Z 0.39 1923 57 98 0 0.00
Mon 04/13 01Z 0.51 2026 66 98 1 0.01
Mon 04/13 02Z 0.49 2029 81 98 2 0.03
Mon 04/13 03Z 0.53 2132 82 98 3 0.02
Mon 04/13 04Z 0.51 2134 80 87 6 0.01
Mon 04/13 05Z 0.56 2237 86 86 7 0.00
Mon 04/13 06Z 0.59 2240 86 84 9 0.01
Mon 04/13 07Z 0.67 2343 88 70 9 0.00
Mon 04/13 08Z 0.75 2447 92 62 10 0.00
Mon 04/13 09Z 0.79 2447 92 50 9 0.01
Mon 04/13 10Z 0.81 2546 91 53 9 0.00
Mon 04/13 11Z 0.82 2546 91 67 10 0.01
Mon 04/13 12Z 0.83 2545 91 75 9 0.01
Mon 04/13 13Z 0.83 2542 93 74 9 0.01
Mon 04/13 14Z 0.83 2542 88 93 9 0.02
Mon 04/13 15Z 0.88 2443 90 95 9 0.02
Mon 04/13 16Z 0.99 2446 94 95 9 0.06
Mon 04/13 17Z 1.05 2445 96 94 9 0.08
Mon 04/13 18Z 1.07 2545 97 94 9 0.13
Mon 04/13 19Z 1.04 2542 97 91 9 0.11
Mon 04/13 20Z 1.02 2640 97 82 9 0.06
Mon 04/13 21Z 1.00 2639 97 61 10 0.04
Mon 04/13 22Z 1.00 2636 97 53 9 0.03
Mon 04/13 23Z 1.03 2735 98 46 9 0.03
Tue 04/14 00Z 1.10 2735 98 39 9 0.03
Tue 04/14 01Z 1.22 2737 97 31 9 0.02
Tue 04/14 02Z 1.27 2737 97 30 8 0.02
Tue 04/14 03Z 1.13 2836 96 29 8 0.02
Tue 04/14 04Z 0.99 2832 95 32 8 0.01
Tue 04/14 05Z 0.89 2930 96 33 8 0.01
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