Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260807_0000
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 08/07 00Z 0.24 2206 87 86 17 0.00
Fri 08/07 01Z 0.35 2508 92 85 17 0.03
Fri 08/07 02Z 0.36 2510 92 83 17 0.25
Fri 08/07 03Z 0.32 2609 90 88 17 0.08
Fri 08/07 04Z 0.34 2611 88 85 17 0.01
Fri 08/07 05Z 0.34 2812 88 88 17 0.01
Fri 08/07 06Z 0.28 2911 86 89 17 0.00
Fri 08/07 07Z 0.24 3012 86 87 17 0.00
Fri 08/07 08Z 0.21 3111 85 83 16 0.00
Fri 08/07 09Z 0.17 3109 81 72 16 0.00
Fri 08/07 10Z 0.19 3009 78 64 16 0.00
Fri 08/07 11Z 0.17 3108 74 59 16 0.00
Fri 08/07 12Z 0.16 3108 73 61 16 0.00
Fri 08/07 13Z 0.14 3107 76 66 16 0.00
Fri 08/07 14Z 0.10 3206 79 77 15 0.00
Fri 08/07 15Z 0.11 3205 81 72 15 0.00
Fri 08/07 16Z 0.07 3304 82 63 15 0.00
Fri 08/07 17Z 0.08 3203 82 58 16 0.00
Fri 08/07 18Z 0.14 2903 82 51 16 0.00
Fri 08/07 19Z 0.17 2803 80 48 16 0.01
Fri 08/07 20Z 0.34 2804 79 46 16 0.00
Fri 08/07 21Z 0.32 2703 79 49 17 0.00
Fri 08/07 22Z 0.20 2603 78 47 17 0.00
Fri 08/07 23Z 0.16 2703 77 34 17 0.00
Sat 08/08 00Z 0.17 2504 75 39 17 0.00
Sat 08/08 01Z 0.20 2404 75 41 17 0.00
Sat 08/08 02Z 0.21 2405 76 40 17 0.00
Sat 08/08 03Z 0.24 2306 79 39 17 0.00
Sat 08/08 04Z 0.21 2206 81 38 16 0.00
Sat 08/08 05Z 0.16 2304 82 37 17 0.00
Sat 08/08 06Z 0.14 2503 82 44 16 0.00
Sat 08/08 07Z 0.14 2303 84 56 16 0.00
Sat 08/08 08Z 0.12 2103 85 65 16 0.00
Sat 08/08 09Z 0.02 1703 82 82 16 0.00
Sat 08/08 10Z 0.05 1902 83 89 16 0.00
Sat 08/08 11Z 0.02 1602 81 86 16 0.00
Sat 08/08 12Z 0.02 1704 82 84 16 0.00
Sat 08/08 13Z 0.03 1705 84 87 16 0.00
Sat 08/08 14Z 0.04 1706 86 84 16 0.00
Sat 08/08 15Z 0.19 1807 89 88 16 0.00
Sat 08/08 16Z 0.34 1908 89 83 16 0.02
Sat 08/08 17Z 0.44 2110 89 71 16 0.03
Sat 08/08 18Z 0.81 2110 89 66 16 0.00
Sat 08/08 19Z 1.02 2111 89 63 17 0.00
Sat 08/08 20Z 1.00 2214 88 73 17 0.00
Sat 08/08 21Z 0.68 2314 88 64 17 0.00
Sat 08/08 22Z 0.61 2314 89 77 17 0.05
Sat 08/08 23Z 0.61 2416 92 77 16 0.05
Sun 08/09 00Z 0.53 2515 91 74 17 0.03
Sun 08/09 01Z 0.50 2614 90 67 17 0.13
Sun 08/09 02Z 0.51 2715 87 67 17 0.01
Sun 08/09 03Z 0.45 2713 91 70 16 0.00
Sun 08/09 04Z 0.37 2811 91 71 16 0.00
Sun 08/09 05Z 0.41 2612 91 69 16 0.00
Sun 08/09 06Z 0.45 2614 92 53 16 0.00
Sun 08/09 07Z 0.49 2515 91 34 16 0.00
Sun 08/09 08Z 0.59 2618 94 41 16 0.01
Sun 08/09 09Z 0.62 2620 94 34 16 0.01
Sun 08/09 10Z 0.58 2620 90 45 16 0.01
Sun 08/09 11Z 0.53 2619 90 60 16 0.00
Run total areal avg QPF for the Central_Greens is: 0.74 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