Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260806_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 08/06 06Z 0.41 2413 77 43 16 0.00
Thu 08/06 07Z 0.42 2412 79 44 16 0.00
Thu 08/06 08Z 0.40 2512 80 49 16 0.00
Thu 08/06 09Z 0.39 2511 81 61 16 0.00
Thu 08/06 10Z 0.34 2609 81 67 16 0.00
Thu 08/06 11Z 0.26 2707 81 69 16 0.00
Thu 08/06 12Z 0.17 2504 82 73 16 0.00
Thu 08/06 13Z 0.14 2303 83 77 16 0.00
Thu 08/06 14Z 0.13 2104 84 78 16 0.00
Thu 08/06 15Z 0.20 2104 86 82 16 0.00
Thu 08/06 16Z 0.23 2005 87 81 16 0.00
Thu 08/06 17Z 0.37 2106 88 75 16 0.00
Thu 08/06 18Z 0.46 2107 89 72 16 0.00
Thu 08/06 19Z 0.58 2208 89 78 17 0.00
Thu 08/06 20Z 0.53 2108 88 77 17 0.00
Thu 08/06 21Z 0.55 2208 88 79 17 0.00
Thu 08/06 22Z 0.45 2308 91 70 17 0.04
Thu 08/06 23Z 0.38 2409 90 68 17 0.13
Fri 08/07 00Z 0.42 2511 91 68 17 0.05
Fri 08/07 01Z 0.43 2512 90 65 17 0.06
Fri 08/07 02Z 0.45 2513 91 65 17 0.01
Fri 08/07 03Z 0.41 2613 86 63 18 0.00
Fri 08/07 04Z 0.41 2714 84 68 18 0.00
Fri 08/07 05Z 0.41 2714 82 64 17 0.00
Fri 08/07 06Z 0.43 2814 77 71 17 0.00
Fri 08/07 07Z 0.39 2814 71 73 17 0.00
Fri 08/07 08Z 0.32 2913 67 61 17 0.00
Fri 08/07 09Z 0.24 3010 64 62 17 0.00
Fri 08/07 10Z 0.24 2909 64 57 17 0.00
Fri 08/07 11Z 0.22 2908 67 58 16 0.00
Fri 08/07 12Z 0.21 2908 69 49 16 0.00
Fri 08/07 13Z 0.20 2908 74 36 16 0.00
Fri 08/07 14Z 0.21 2808 81 40 16 0.00
Fri 08/07 15Z 0.22 2807 85 43 16 0.00
Fri 08/07 16Z 0.25 2807 87 51 15 0.00
Fri 08/07 17Z 0.27 2806 87 49 16 0.00
Fri 08/07 18Z 0.24 2804 84 51 16 0.00
Fri 08/07 19Z 0.38 2804 83 56 16 0.00
Fri 08/07 20Z 0.47 2804 82 55 16 0.00
Fri 08/07 21Z 0.31 2805 81 53 16 0.00
Fri 08/07 22Z 0.21 2804 82 56 16 0.00
Fri 08/07 23Z 0.19 2805 82 57 17 0.00
Sat 08/08 00Z 0.20 2805 82 46 17 0.00
Sat 08/08 01Z 0.22 2706 86 34 17 0.00
Sat 08/08 02Z 0.18 2705 87 28 16 0.00
Sat 08/08 03Z 0.17 2704 85 22 17 0.00
Sat 08/08 04Z 0.19 2605 86 19 16 0.00
Sat 08/08 05Z 0.19 2605 88 21 16 0.00
Sat 08/08 06Z 0.18 2705 89 26 16 0.00
Sat 08/08 07Z 0.14 2704 88 33 16 0.00
Sat 08/08 08Z 0.13 2604 88 41 16 0.00
Sat 08/08 09Z 0.12 2603 86 48 16 0.00
Sat 08/08 10Z 0.12 2603 85 51 16 0.00
Sat 08/08 11Z 0.10 2403 84 52 16 0.00
Sat 08/08 12Z 0.09 2303 83 50 16 0.00
Sat 08/08 13Z 0.09 2203 81 45 17 0.00
Sat 08/08 14Z 0.09 2104 81 39 17 0.00
Sat 08/08 15Z 0.13 2105 81 32 17 0.00
Sat 08/08 16Z 0.25 2106 83 33 17 0.00
Sat 08/08 17Z 0.32 2206 84 40 16 0.00
Run total areal avg QPF for the Central_Greens is: 0.29 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