Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260806_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)
=== ===== === ==== ==== === === === ====
Thu 08/06 12Z 0.24 2707 85 54 16 0.00
Thu 08/06 13Z 0.22 2706 85 66 16 0.00
Thu 08/06 14Z 0.18 2605 85 77 16 0.00
Thu 08/06 15Z 0.15 2503 86 88 16 0.00
Thu 08/06 16Z 0.13 2402 87 89 16 0.00
Thu 08/06 17Z 0.24 2303 85 86 16 0.01
Thu 08/06 18Z 0.31 2204 83 85 17 0.01
Thu 08/06 19Z 0.26 2202 83 86 17 0.00
Thu 08/06 20Z 0.31 2503 86 87 17 0.01
Thu 08/06 21Z 0.18 2602 85 81 17 0.02
Thu 08/06 22Z 0.10 2102 84 76 17 0.00
Thu 08/06 23Z 0.11 2202 84 73 17 0.00
Fri 08/07 00Z 0.17 2204 85 72 17 0.00
Fri 08/07 01Z 0.31 2307 86 77 17 0.00
Fri 08/07 02Z 0.25 2406 85 70 17 0.00
Fri 08/07 03Z 0.23 2306 86 74 17 0.00
Fri 08/07 04Z 0.29 2408 91 73 17 0.00
Fri 08/07 05Z 0.28 2408 93 71 17 0.00
Fri 08/07 06Z 0.28 2508 92 71 17 0.02
Fri 08/07 07Z 0.24 2707 92 73 17 0.00
Fri 08/07 08Z 0.27 2808 94 77 16 0.01
Fri 08/07 09Z 0.21 2908 92 62 17 0.01
Fri 08/07 10Z 0.16 3108 89 68 16 0.00
Fri 08/07 11Z 0.14 3208 89 75 16 0.00
Fri 08/07 12Z 0.09 3207 86 60 16 0.00
Fri 08/07 13Z 0.09 3105 84 58 16 0.00
Fri 08/07 14Z 0.13 3005 80 63 16 0.00
Fri 08/07 15Z 0.15 3005 75 50 16 0.00
Fri 08/07 16Z 0.19 2905 75 48 16 0.00
Fri 08/07 17Z 0.29 2906 76 42 16 0.00
Fri 08/07 18Z 0.35 2906 77 33 16 0.00
Fri 08/07 19Z 0.37 2906 78 26 16 0.00
Fri 08/07 20Z 0.33 2907 79 20 17 0.00
Fri 08/07 21Z 0.28 2906 81 20 17 0.00
Fri 08/07 22Z 0.24 2806 81 12 17 0.00
Fri 08/07 23Z 0.22 2805 82 18 17 0.00
Sat 08/08 00Z 0.21 2806 83 27 17 0.00
Sat 08/08 01Z 0.18 2705 84 30 17 0.00
Sat 08/08 02Z 0.24 2606 85 33 17 0.00
Sat 08/08 03Z 0.22 2606 83 33 17 0.00
Sat 08/08 04Z 0.18 2505 82 37 17 0.00
Sat 08/08 05Z 0.17 2405 80 54 17 0.00
Sat 08/08 06Z 0.14 2305 80 75 17 0.00
Sat 08/08 07Z 0.18 2206 82 81 17 0.00
Sat 08/08 08Z 0.20 2207 82 76 17 0.00
Sat 08/08 09Z 0.18 2107 82 74 17 0.00
Sat 08/08 10Z 0.18 2107 82 75 16 0.00
Sat 08/08 11Z 0.16 2007 82 76 16 0.00
Sat 08/08 12Z 0.17 2008 82 73 16 0.00
Sat 08/08 13Z 0.18 2008 85 72 16 0.00
Sat 08/08 14Z 0.23 2108 92 77 16 0.00
Sat 08/08 15Z 0.26 2109 91 86 16 0.10
Sat 08/08 16Z 0.12 1908 81 84 16 0.16
Sat 08/08 17Z 0.15 1910 79 79 17 0.01
Sat 08/08 18Z 0.36 2012 83 71 16 0.00
Sat 08/08 19Z 0.74 2112 85 70 16 0.00
Sat 08/08 20Z 1.29 2013 86 75 16 0.00
Sat 08/08 21Z 1.21 2214 84 80 17 0.00
Sat 08/08 22Z 0.84 2214 88 68 17 0.05
Sat 08/08 23Z 0.70 2316 94 72 17 0.03
Run total areal avg QPF for the Central_Greens is: 0.44 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