Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260609_0000
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)
=== ===== === ==== ==== === === === ====
Tue 06/09 00Z 0.33 2506 66 3 12 0.00
Tue 06/09 01Z 0.32 2507 55 3 12 0.00
Tue 06/09 02Z 0.29 2607 48 3 12 0.00
Tue 06/09 03Z 0.31 2606 49 3 12 0.00
Tue 06/09 04Z 0.43 2709 57 2 12 0.00
Tue 06/09 05Z 0.58 2611 61 2 11 0.00
Tue 06/09 06Z 0.65 2613 62 2 11 0.00
Tue 06/09 07Z 0.65 2615 64 3 11 0.00
Tue 06/09 08Z 0.64 2615 66 3 11 0.00
Tue 06/09 09Z 0.61 2716 74 3 11 0.00
Tue 06/09 10Z 0.56 2717 86 3 11 0.00
Tue 06/09 11Z 0.47 2715 84 3 11 0.00
Tue 06/09 12Z 0.38 2712 83 3 11 0.00
Tue 06/09 13Z 0.32 2610 82 3 11 0.00
Tue 06/09 14Z 0.32 2509 81 3 11 0.00
Tue 06/09 15Z 0.41 2408 79 2 11 0.00
Tue 06/09 16Z 0.66 2406 74 2 11 0.00
Tue 06/09 17Z 1.33 2507 68 2 12 0.00
Tue 06/09 18Z 1.26 2607 65 1 12 0.00
Tue 06/09 19Z 0.98 2608 69 1 13 0.00
Tue 06/09 20Z 1.35 2610 77 1 13 0.00
Tue 06/09 21Z 1.15 2611 79 1 13 0.00
Tue 06/09 22Z 0.94 2513 85 1 13 0.00
Tue 06/09 23Z 0.76 2516 88 1 13 0.00
Wed 06/10 00Z 0.74 2618 89 1 14 0.00
Wed 06/10 01Z 0.75 2719 88 1 14 0.00
Wed 06/10 02Z 0.64 2818 82 0 14 0.00
Wed 06/10 03Z 0.58 2816 80 0 14 0.00
Wed 06/10 04Z 0.48 2814 80 0 14 0.00
Wed 06/10 05Z 0.44 2813 79 0 14 0.00
Wed 06/10 06Z 0.40 2712 78 0 14 0.00
Wed 06/10 07Z 0.37 2611 81 3 14 0.00
Wed 06/10 08Z 0.35 2511 86 48 14 0.01
Wed 06/10 09Z 0.36 2412 90 75 14 0.01
Wed 06/10 10Z 0.36 2313 90 76 14 0.00
Wed 06/10 11Z 0.35 2313 86 78 15 0.00
Wed 06/10 12Z 0.33 2212 85 81 15 0.00
Wed 06/10 13Z 0.28 2211 84 72 15 0.00
Wed 06/10 14Z 0.34 2111 83 78 15 0.00
Wed 06/10 15Z 0.37 2010 84 82 15 0.00
Wed 06/10 16Z 0.52 2010 84 81 15 0.00
Wed 06/10 17Z 0.37 1910 83 85 15 0.00
Wed 06/10 18Z 0.42 1911 83 90 16 0.00
Wed 06/10 19Z 0.37 1911 84 83 16 0.00
Wed 06/10 20Z 0.42 1912 83 78 16 0.00
Wed 06/10 21Z 0.36 1911 82 79 16 0.00
Wed 06/10 22Z 0.49 2013 86 88 16 0.00
Wed 06/10 23Z 0.39 2013 90 83 16 0.00
Thu 06/11 00Z 0.38 2113 96 90 16 0.01
Thu 06/11 01Z 0.41 2117 98 90 16 0.03
Thu 06/11 02Z 0.48 2219 96 79 16 0.23
Thu 06/11 03Z 0.54 2319 96 70 16 0.11
Thu 06/11 04Z 0.57 2418 97 81 15 0.02
Thu 06/11 05Z 0.62 2419 96 72 15 0.03
Thu 06/11 06Z 0.55 2517 96 65 15 0.03
Thu 06/11 07Z 0.45 2714 97 67 15 0.02
Thu 06/11 08Z 0.39 2914 96 77 15 0.01
Thu 06/11 09Z 0.45 2815 97 75 15 0.01
Thu 06/11 10Z 0.47 2816 96 72 15 0.01
Thu 06/11 11Z 0.46 2816 97 72 15 0.00
Run total areal avg QPF for the Central_Greens is: 0.53 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