Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260724_1200
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 07/24 12Z 0.28 2205 67 19 9 0.00
Fri 07/24 13Z 0.40 2306 67 19 9 0.00
Fri 07/24 14Z 0.93 2306 65 19 9 0.00
Fri 07/24 15Z 1.66 2406 62 20 9 0.00
Fri 07/24 16Z 2.29 2406 60 22 10 0.00
Fri 07/24 17Z 2.77 2505 59 24 10 0.00
Fri 07/24 18Z 2.04 2404 56 28 11 0.00
Fri 07/24 19Z 1.14 2402 55 33 11 0.00
Fri 07/24 20Z 0.70 2402 54 38 12 0.00
Fri 07/24 21Z 0.49 2202 54 42 12 0.00
Fri 07/24 22Z 0.22 2202 56 45 12 0.00
Fri 07/24 23Z 0.16 2202 57 47 12 0.00
Sat 07/25 00Z 0.18 2203 57 47 12 0.00
Sat 07/25 01Z 0.21 2303 57 43 12 0.00
Sat 07/25 02Z 0.20 2403 57 41 12 0.00
Sat 07/25 03Z 0.22 2403 59 42 12 0.00
Sat 07/25 04Z 0.19 2303 60 43 12 0.00
Sat 07/25 05Z 0.17 2402 60 45 12 0.00
Sat 07/25 06Z 0.12 2602 59 45 12 0.00
Sat 07/25 07Z 0.06 2200 59 43 12 0.00
Sat 07/25 08Z 0.04 1702 60 44 11 0.00
Sat 07/25 09Z 0.04 1703 59 42 11 0.00
Sat 07/25 10Z 0.10 1904 59 40 11 0.00
Sat 07/25 11Z 0.13 2004 60 38 11 0.00
Sat 07/25 12Z 0.19 2205 61 39 11 0.00
Sat 07/25 13Z 0.16 2204 64 38 11 0.00
Sat 07/25 14Z 0.14 2203 68 38 11 0.00
Sat 07/25 15Z 0.16 1902 71 37 11 0.00
Sat 07/25 16Z 0.25 1603 72 36 12 0.00
Sat 07/25 17Z 0.46 1503 72 33 12 0.00
Sat 07/25 18Z 0.61 1504 72 32 12 0.00
Sat 07/25 19Z 0.52 1604 72 30 13 0.00
Sat 07/25 20Z 0.87 1505 72 25 13 0.00
Sat 07/25 21Z 0.61 1506 72 23 13 0.00
Sat 07/25 22Z 0.13 1706 73 21 13 0.00
Sat 07/25 23Z 0.09 1708 75 18 13 0.00
Sun 07/26 00Z 0.09 1709 76 15 13 0.00
Sun 07/26 01Z 0.18 1810 77 12 12 0.00
Sun 07/26 02Z 0.26 1811 80 8 12 0.00
Sun 07/26 03Z 0.37 1910 83 8 12 0.00
Sun 07/26 04Z 0.39 2009 85 8 12 0.00
Sun 07/26 05Z 0.38 2108 85 10 11 0.00
Sun 07/26 06Z 0.43 2308 86 11 11 0.00
Sun 07/26 07Z 0.46 2308 85 12 11 0.00
Sun 07/26 08Z 0.43 2308 80 12 11 0.00
Sun 07/26 09Z 0.30 2306 76 13 11 0.00
Sun 07/26 10Z 0.30 2305 75 13 11 0.00
Sun 07/26 11Z 0.22 2204 76 14 11 0.00
Sun 07/26 12Z 0.14 2003 77 13 11 0.00
Sun 07/26 13Z 0.09 1804 78 12 11 0.00
Sun 07/26 14Z 0.13 1604 79 12 11 0.00
Sun 07/26 15Z 0.19 1704 81 12 11 0.00
Sun 07/26 16Z 0.25 1604 83 13 12 0.00
Sun 07/26 17Z 0.26 1803 84 15 12 0.00
Sun 07/26 18Z 0.53 1904 84 18 12 0.00
Sun 07/26 19Z 0.48 1804 83 23 12 0.00
Sun 07/26 20Z 0.26 1804 82 32 13 0.00
Sun 07/26 21Z 0.27 1804 81 41 13 0.00
Sun 07/26 22Z 0.08 1704 81 50 13 0.00
Sun 07/26 23Z 0.06 1704 83 55 13 0.00
Run total areal avg QPF for the Central_Greens is: 0.00 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