Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260507_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)
=== ===== === ==== ==== === === === ====
Thu 05/07 06Z 0.34 2912 86 81 0 0.00
Thu 05/07 07Z 0.44 2914 91 78 0 0.01
Thu 05/07 08Z 0.47 2814 94 60 0 0.01
Thu 05/07 09Z 0.61 2817 93 63 0 0.01
Thu 05/07 10Z 0.73 2820 96 60 -1 0.01
Thu 05/07 11Z 0.66 2720 82 53 -1 0.01
Thu 05/07 12Z 0.64 2821 63 32 -2 0.00
Thu 05/07 13Z 0.82 2821 66 19 -2 0.00
Thu 05/07 14Z 2.53 2818 76 26 -3 0.00
Thu 05/07 15Z 9.62 2816 82 31 -3 0.00
Thu 05/07 16Z 10.92 2816 77 40 -2 0.00
Thu 05/07 17Z 11.30 2817 68 35 -1 0.00
Thu 05/07 18Z 11.45 2817 62 38 -1 0.00
Thu 05/07 19Z 11.29 2816 55 34 0 0.00
Thu 05/07 20Z 11.08 2816 49 32 0 0.00
Thu 05/07 21Z 10.64 2816 47 32 0 0.00
Thu 05/07 22Z 9.36 2815 47 28 0 0.00
Thu 05/07 23Z 5.67 2816 50 22 0 0.00
Fri 05/08 00Z 1.63 2917 52 16 0 0.00
Fri 05/08 01Z 1.16 2918 56 15 0 0.00
Fri 05/08 02Z 1.00 2917 61 19 -1 0.00
Fri 05/08 03Z 1.03 2917 66 30 -1 0.00
Fri 05/08 04Z 1.13 2817 69 60 -2 0.00
Fri 05/08 05Z 1.02 2818 71 55 -2 0.00
Fri 05/08 06Z 0.93 2819 71 61 -2 0.00
Fri 05/08 07Z 0.90 2820 67 60 -2 0.00
Fri 05/08 08Z 0.82 2821 60 51 -2 0.00
Fri 05/08 09Z 0.77 2820 64 52 -2 0.00
Fri 05/08 10Z 0.71 2819 66 63 -2 0.00
Fri 05/08 11Z 0.69 2817 68 73 -2 0.00
Fri 05/08 12Z 0.84 2814 67 77 -2 0.00
Fri 05/08 13Z 3.80 2711 67 86 -2 0.00
Fri 05/08 14Z 5.83 2609 68 84 -2 0.00
Fri 05/08 15Z 4.79 2507 67 67 -1 0.00
Fri 05/08 16Z 5.11 2507 68 83 -1 0.00
Fri 05/08 17Z 5.94 2409 74 77 -1 0.00
Fri 05/08 18Z 5.03 2411 83 82 0 0.00
Fri 05/08 19Z 1.17 2515 92 77 -1 0.04
Fri 05/08 20Z 1.11 2613 90 68 -1 0.01
Fri 05/08 21Z 1.68 2812 86 51 0 0.00
Fri 05/08 22Z 1.64 2812 86 46 -1 0.00
Fri 05/08 23Z 0.90 2812 84 45 -1 0.01
Sat 05/09 00Z 0.74 2913 79 18 -1 0.00
Sat 05/09 01Z 0.93 2914 77 8 -1 0.00
Sat 05/09 02Z 1.06 2914 72 8 -1 0.00
Sat 05/09 03Z 1.14 2914 66 19 -2 0.00
Sat 05/09 04Z 1.01 2814 65 25 -2 0.00
Sat 05/09 05Z 0.78 2814 60 21 -2 0.00
Sat 05/09 06Z 0.59 2813 58 15 -2 0.00
Sat 05/09 07Z 0.53 2913 63 16 -2 0.00
Sat 05/09 08Z 0.48 2911 66 27 -2 0.00
Sat 05/09 09Z 0.44 2810 65 28 -2 0.00
Sat 05/09 10Z 0.42 2709 69 18 -2 0.00
Sat 05/09 11Z 0.43 2608 76 16 -2 0.00
Sat 05/09 12Z 0.53 2608 78 12 -2 0.00
Sat 05/09 13Z 1.91 2407 75 13 -2 0.00
Sat 05/09 14Z 3.05 2207 72 13 -1 0.00
Sat 05/09 15Z 4.06 2109 67 19 0 0.00
Sat 05/09 16Z 3.64 2010 63 19 0 0.00
Sat 05/09 17Z 3.07 1910 60 21 1 0.00
Run total areal avg QPF for the Central_Greens is: 0.11 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