Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260508_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 05/08 18Z 4.95 2807 65 80 -2 0.00
Fri 05/08 19Z 6.02 2608 63 86 -1 0.00
Fri 05/08 20Z 5.24 2608 68 90 -1 0.00
Fri 05/08 21Z 3.38 2610 76 87 -1 0.00
Fri 05/08 22Z 1.66 2610 76 74 -1 0.00
Fri 05/08 23Z 0.83 2611 78 68 -1 0.00
Sat 05/09 00Z 0.67 2612 78 44 -1 0.00
Sat 05/09 01Z 0.65 2712 77 29 -1 0.00
Sat 05/09 02Z 0.72 2713 77 19 -1 0.00
Sat 05/09 03Z 0.80 2713 70 15 -2 0.00
Sat 05/09 04Z 0.70 2711 64 19 -2 0.00
Sat 05/09 05Z 0.53 2710 57 31 -1 0.00
Sat 05/09 06Z 0.45 2610 49 30 -1 0.00
Sat 05/09 07Z 0.41 2510 46 19 -1 0.00
Sat 05/09 08Z 0.39 2510 45 17 0 0.00
Sat 05/09 09Z 0.33 2408 43 14 0 0.00
Sat 05/09 10Z 0.29 2207 42 26 0 0.00
Sat 05/09 11Z 0.20 2007 42 31 0 0.00
Sat 05/09 12Z 0.13 1809 44 36 0 0.00
Sat 05/09 13Z 0.08 1711 50 43 0 0.00
Sat 05/09 14Z 0.12 1712 58 63 0 0.00
Sat 05/09 15Z 0.30 1613 73 68 0 0.00
Sat 05/09 16Z 0.45 1714 87 89 0 0.02
Sat 05/09 17Z 0.14 1616 94 94 0 0.02
Sat 05/09 18Z 0.06 1615 96 93 1 0.02
Sat 05/09 19Z 0.07 1616 97 92 1 0.03
Sat 05/09 20Z 0.08 1717 97 90 2 0.03
Sat 05/09 21Z 0.07 1718 98 70 2 0.02
Sat 05/09 22Z 0.08 1717 98 69 3 0.02
Sat 05/09 23Z 0.09 1815 97 73 3 0.01
Sun 05/10 00Z 0.18 1916 98 73 3 0.01
Sun 05/10 01Z 0.27 2017 98 77 3 0.01
Sun 05/10 02Z 0.36 2119 98 56 4 0.01
Sun 05/10 03Z 0.40 2119 98 47 4 0.01
Sun 05/10 04Z 0.44 2120 98 29 4 0.01
Sun 05/10 05Z 0.49 2120 98 36 4 0.01
Sun 05/10 06Z 0.52 2221 97 38 4 0.01
Sun 05/10 07Z 0.51 2221 94 40 5 0.01
Sun 05/10 08Z 0.51 2222 93 61 5 0.01
Sun 05/10 09Z 0.50 2221 92 76 5 0.01
Sun 05/10 10Z 0.58 2322 96 89 5 0.01
Sun 05/10 11Z 0.64 2422 96 87 5 0.02
Sun 05/10 12Z 0.67 2422 96 84 4 0.01
Sun 05/10 13Z 0.76 2521 94 84 4 0.02
Sun 05/10 14Z 0.84 2519 89 53 3 0.01
Sun 05/10 15Z 1.07 2518 87 33 3 0.00
Sun 05/10 16Z 4.23 2416 93 23 3 0.01
Sun 05/10 17Z 3.04 2516 93 16 3 0.02
Sun 05/10 18Z 4.89 2515 83 18 3 0.02
Sun 05/10 19Z 9.74 2516 71 15 3 0.00
Sun 05/10 20Z 10.94 2515 67 14 4 0.00
Sun 05/10 21Z 11.20 2516 65 15 4 0.00
Sun 05/10 22Z 10.86 2518 63 13 3 0.00
Sun 05/10 23Z 5.60 2619 62 14 3 0.00
Mon 05/11 00Z 2.62 2720 59 22 2 0.00
Mon 05/11 01Z 1.58 2718 52 21 2 0.00
Mon 05/11 02Z 1.11 2818 44 20 1 0.00
Mon 05/11 03Z 0.75 2817 41 18 1 0.00
Mon 05/11 04Z 0.55 2916 51 19 0 0.00
Mon 05/11 05Z 0.43 3016 61 23 0 0.00
Run total areal avg QPF for the Central_Greens is: 0.39 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