Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260608_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)
=== ===== === ==== ==== === === === ====
Mon 06/08 18Z 0.33 3101 72 7 10 0.00
Mon 06/08 19Z 0.78 2802 74 6 10 0.00
Mon 06/08 20Z 0.67 2803 77 5 10 0.00
Mon 06/08 21Z 0.65 2604 75 4 10 0.00
Mon 06/08 22Z 0.59 2505 69 4 11 0.00
Mon 06/08 23Z 0.37 2606 65 4 11 0.00
Tue 06/09 00Z 0.38 2508 63 4 11 0.00
Tue 06/09 01Z 0.38 2608 59 4 11 0.00
Tue 06/09 02Z 0.41 2609 57 4 11 0.00
Tue 06/09 03Z 0.44 2610 58 4 11 0.00
Tue 06/09 04Z 0.48 2612 59 4 11 0.00
Tue 06/09 05Z 0.52 2614 61 4 11 0.00
Tue 06/09 06Z 0.52 2714 65 4 11 0.00
Tue 06/09 07Z 0.56 2715 71 3 11 0.00
Tue 06/09 08Z 0.50 2714 77 3 11 0.00
Tue 06/09 09Z 0.37 2712 80 3 11 0.00
Tue 06/09 10Z 0.33 2611 81 3 11 0.00
Tue 06/09 11Z 0.30 2611 79 3 11 0.00
Tue 06/09 12Z 0.24 2409 77 3 11 0.00
Tue 06/09 13Z 0.21 2309 73 3 11 0.00
Tue 06/09 14Z 0.22 2308 71 3 11 0.00
Tue 06/09 15Z 0.23 2308 68 3 11 0.00
Tue 06/09 16Z 0.31 2308 69 3 11 0.00
Tue 06/09 17Z 0.43 2408 68 3 12 0.00
Tue 06/09 18Z 0.38 2507 65 2 12 0.00
Tue 06/09 19Z 0.43 2608 68 2 13 0.00
Tue 06/09 20Z 0.44 2610 74 2 13 0.00
Tue 06/09 21Z 0.46 2511 76 1 13 0.00
Tue 06/09 22Z 0.50 2514 79 1 14 0.00
Tue 06/09 23Z 0.44 2614 79 1 14 0.00
Wed 06/10 00Z 0.42 2615 77 0 15 0.00
Wed 06/10 01Z 0.39 2715 79 1 15 0.00
Wed 06/10 02Z 0.37 2714 82 1 15 0.00
Wed 06/10 03Z 0.32 2812 84 4 15 0.00
Wed 06/10 04Z 0.28 2710 86 21 15 0.00
Wed 06/10 05Z 0.29 2610 86 31 14 0.00
Wed 06/10 06Z 0.27 2509 85 48 15 0.00
Wed 06/10 07Z 0.29 2410 85 60 14 0.00
Wed 06/10 08Z 0.23 2408 84 54 15 0.00
Wed 06/10 09Z 0.22 2308 83 48 14 0.00
Wed 06/10 10Z 0.22 2209 81 59 15 0.00
Wed 06/10 11Z 0.21 2109 79 69 15 0.00
Wed 06/10 12Z 0.21 2110 76 76 15 0.00
Wed 06/10 13Z 0.16 2011 73 79 15 0.00
Wed 06/10 14Z 0.18 2011 72 78 15 0.00
Wed 06/10 15Z 0.17 2010 74 80 15 0.00
Wed 06/10 16Z 0.20 2011 75 67 15 0.00
Wed 06/10 17Z 0.25 2010 78 42 15 0.00
Wed 06/10 18Z 0.37 1910 82 55 15 0.00
Wed 06/10 19Z 0.32 1910 85 83 15 0.00
Wed 06/10 20Z 0.28 1911 89 86 15 0.00
Wed 06/10 21Z 0.23 1812 93 87 15 0.00
Wed 06/10 22Z 0.20 1814 95 92 15 0.01
Wed 06/10 23Z 0.12 1814 97 94 15 0.01
Thu 06/11 00Z 0.17 1913 98 93 15 0.02
Thu 06/11 01Z 0.23 2014 98 93 15 0.01
Thu 06/11 02Z 0.24 2014 99 96 15 0.13
Thu 06/11 03Z 0.25 2112 98 96 15 0.18
Thu 06/11 04Z 0.25 2310 98 91 15 0.03
Thu 06/11 05Z 0.25 2410 98 89 15 0.01
Run total areal avg QPF for the Central_Greens is: 0.40 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