Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260609_1200
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Tue 06/09 12Z 0.28 2810 72 2 12 0.00
Tue 06/09 13Z 0.27 2809 73 2 11 0.00
Tue 06/09 14Z 0.26 2807 74 1 11 0.00
Tue 06/09 15Z 0.30 2805 72 1 11 0.00
Tue 06/09 16Z 0.51 2604 69 0 12 0.00
Tue 06/09 17Z 0.87 2505 64 0 12 0.00
Tue 06/09 18Z 1.08 2606 64 0 13 0.00
Tue 06/09 19Z 1.20 2607 74 0 13 0.00
Tue 06/09 20Z 1.05 2508 80 0 13 0.00
Tue 06/09 21Z 0.82 2508 82 1 13 0.00
Tue 06/09 22Z 0.76 2511 84 1 13 0.00
Tue 06/09 23Z 0.61 2513 87 1 13 0.00
Wed 06/10 00Z 0.55 2514 89 1 14 0.00
Wed 06/10 01Z 0.52 2615 89 2 14 0.00
Wed 06/10 02Z 0.49 2715 87 2 14 0.01
Wed 06/10 03Z 0.45 2714 85 3 14 0.01
Wed 06/10 04Z 0.40 2812 84 4 14 0.01
Wed 06/10 05Z 0.41 2813 83 5 14 0.01
Wed 06/10 06Z 0.38 2812 84 6 14 0.01
Wed 06/10 07Z 0.27 2809 79 7 15 0.01
Wed 06/10 08Z 0.25 2808 75 14 15 0.01
Wed 06/10 09Z 0.24 2808 70 22 15 0.01
Wed 06/10 10Z 0.25 2808 72 42 15 0.00
Wed 06/10 11Z 0.26 2708 73 55 15 0.00
Wed 06/10 12Z 0.25 2607 76 67 15 0.00
Wed 06/10 13Z 0.22 2407 77 81 15 0.00
Wed 06/10 14Z 0.22 2407 80 84 15 0.00
Wed 06/10 15Z 0.20 2307 82 86 15 0.01
Wed 06/10 16Z 0.21 2208 88 90 15 0.01
Wed 06/10 17Z 0.17 2108 89 88 15 0.01
Wed 06/10 18Z 0.18 2108 90 92 15 0.01
Wed 06/10 19Z 0.15 2008 89 93 15 0.01
Wed 06/10 20Z 0.13 2007 89 91 15 0.00
Wed 06/10 21Z 0.08 1907 90 93 15 0.01
Wed 06/10 22Z 0.05 1707 91 92 16 0.01
Wed 06/10 23Z 0.06 1708 92 91 16 0.00
Thu 06/11 00Z 0.05 1709 92 94 15 0.00
Thu 06/11 01Z 0.05 1711 92 94 15 0.00
Thu 06/11 02Z 0.08 1812 92 93 15 0.01
Thu 06/11 03Z 0.09 1813 92 90 15 0.05
Thu 06/11 04Z 0.10 1912 92 91 15 0.12
Thu 06/11 05Z 0.12 2011 93 89 15 0.09
Thu 06/11 06Z 0.13 2009 90 87 15 0.08
Thu 06/11 07Z 0.10 2007 89 89 15 0.02
Thu 06/11 08Z 0.07 2005 92 88 15 0.01
Thu 06/11 09Z 0.03 1804 95 89 15 0.01
Thu 06/11 10Z 0.03 1603 95 89 15 0.01
Thu 06/11 11Z 0.06 1403 95 84 15 0.00
Thu 06/11 12Z 0.07 1403 95 79 15 0.00
Thu 06/11 13Z 0.04 1802 96 84 15 0.00
Thu 06/11 14Z 0.04 1602 96 83 15 0.00
Thu 06/11 15Z 0.06 1403 95 79 15 0.00
Thu 06/11 16Z 0.10 1202 94 75 15 0.00
Thu 06/11 17Z 0.09 1503 93 71 15 0.00
Thu 06/11 18Z 0.05 1601 93 72 15 0.00
Thu 06/11 19Z 0.09 1402 92 69 16 0.02
Thu 06/11 20Z 0.15 1302 91 67 16 0.04
Thu 06/11 21Z 0.05 1702 92 70 16 0.03
Thu 06/11 22Z 0.06 1802 93 75 16 0.06
Thu 06/11 23Z 0.05 1902 93 76 16 0.09
Run total areal avg QPF for the greens is: 0.79 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