Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260608_1800
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)
=== ===== === ==== ==== === === === ====
Mon 06/08 18Z 0.61 3002 75 7 9 0.00
Mon 06/08 19Z 1.04 2803 76 6 10 0.00
Mon 06/08 20Z 0.92 2804 77 5 10 0.00
Mon 06/08 21Z 0.65 2604 72 5 10 0.00
Mon 06/08 22Z 0.54 2606 65 4 11 0.00
Mon 06/08 23Z 0.35 2606 61 4 11 0.00
Tue 06/09 00Z 0.38 2608 62 4 11 0.00
Tue 06/09 01Z 0.38 2608 60 4 11 0.00
Tue 06/09 02Z 0.41 2609 61 4 11 0.00
Tue 06/09 03Z 0.44 2610 62 4 11 0.00
Tue 06/09 04Z 0.50 2612 62 4 11 0.00
Tue 06/09 05Z 0.56 2613 63 4 11 0.00
Tue 06/09 06Z 0.60 2713 68 4 11 0.00
Tue 06/09 07Z 0.65 2714 72 3 11 0.00
Tue 06/09 08Z 0.62 2714 78 3 11 0.00
Tue 06/09 09Z 0.48 2813 81 3 11 0.00
Tue 06/09 10Z 0.41 2712 82 3 11 0.00
Tue 06/09 11Z 0.36 2711 83 3 11 0.00
Tue 06/09 12Z 0.26 2609 81 3 11 0.00
Tue 06/09 13Z 0.20 2408 78 3 11 0.00
Tue 06/09 14Z 0.19 2307 75 3 11 0.00
Tue 06/09 15Z 0.21 2307 72 3 11 0.00
Tue 06/09 16Z 0.30 2307 71 2 11 0.00
Tue 06/09 17Z 0.55 2407 69 2 12 0.00
Tue 06/09 18Z 0.60 2507 66 2 12 0.00
Tue 06/09 19Z 0.70 2508 68 2 12 0.00
Tue 06/09 20Z 0.53 2610 74 2 13 0.00
Tue 06/09 21Z 0.50 2511 77 1 13 0.00
Tue 06/09 22Z 0.50 2513 79 1 13 0.00
Tue 06/09 23Z 0.47 2614 82 0 14 0.00
Wed 06/10 00Z 0.46 2614 82 0 14 0.00
Wed 06/10 01Z 0.45 2714 84 1 14 0.00
Wed 06/10 02Z 0.43 2714 85 1 14 0.00
Wed 06/10 03Z 0.37 2813 85 3 14 0.00
Wed 06/10 04Z 0.31 2710 88 14 14 0.00
Wed 06/10 05Z 0.31 2710 88 22 14 0.00
Wed 06/10 06Z 0.28 2609 88 36 14 0.00
Wed 06/10 07Z 0.28 2409 89 50 14 0.00
Wed 06/10 08Z 0.25 2409 88 55 14 0.00
Wed 06/10 09Z 0.22 2308 86 53 14 0.00
Wed 06/10 10Z 0.21 2209 85 59 14 0.00
Wed 06/10 11Z 0.19 2109 82 67 14 0.00
Wed 06/10 12Z 0.20 2110 80 73 15 0.00
Wed 06/10 13Z 0.15 2011 77 77 15 0.00
Wed 06/10 14Z 0.15 2011 76 80 15 0.00
Wed 06/10 15Z 0.14 2010 76 84 15 0.00
Wed 06/10 16Z 0.15 2011 77 76 15 0.00
Wed 06/10 17Z 0.17 2011 80 61 15 0.00
Wed 06/10 18Z 0.20 1910 82 67 15 0.00
Wed 06/10 19Z 0.13 1910 83 81 15 0.00
Wed 06/10 20Z 0.11 1911 85 83 15 0.00
Wed 06/10 21Z 0.09 1812 88 85 15 0.00
Wed 06/10 22Z 0.08 1814 92 91 15 0.00
Wed 06/10 23Z 0.06 1815 94 92 15 0.01
Thu 06/11 00Z 0.09 1813 96 93 15 0.02
Thu 06/11 01Z 0.14 1913 98 94 15 0.04
Thu 06/11 02Z 0.15 1913 99 97 15 0.17
Thu 06/11 03Z 0.17 2012 98 97 15 0.20
Thu 06/11 04Z 0.18 2110 98 92 15 0.08
Thu 06/11 05Z 0.19 2209 98 91 15 0.02
Run total areal avg QPF for the greens is: 0.54 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