Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260823_0600
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)
=== ===== === ==== ==== === === === ====
Sun 08/23 06Z 0.10 1514 95 51 11 0.00
Sun 08/23 07Z 0.10 1515 94 62 12 0.00
Sun 08/23 08Z 0.08 1616 93 61 11 0.01
Sun 08/23 09Z 0.06 1616 93 54 11 0.01
Sun 08/23 10Z 0.09 1516 94 42 12 0.01
Sun 08/23 11Z 0.11 1517 94 47 11 0.01
Sun 08/23 12Z 0.09 1619 93 54 12 0.01
Sun 08/23 13Z 0.11 1519 93 59 12 0.01
Sun 08/23 14Z 0.05 1618 94 60 12 0.01
Sun 08/23 15Z 0.05 1718 95 56 12 0.01
Sun 08/23 16Z 0.07 1716 96 71 12 0.01
Sun 08/23 17Z 0.03 1614 95 65 12 0.00
Sun 08/23 18Z 0.03 1713 95 71 12 0.00
Sun 08/23 19Z 0.03 1614 96 77 12 0.00
Sun 08/23 20Z 0.08 1615 96 73 12 0.00
Sun 08/23 21Z 0.10 1616 96 67 13 0.01
Sun 08/23 22Z 0.10 1618 96 60 13 0.01
Sun 08/23 23Z 0.13 1720 98 34 12 0.01
Mon 08/24 00Z 0.38 1921 99 12 12 0.02
Mon 08/24 01Z 0.50 2020 98 19 12 0.02
Mon 08/24 02Z 0.68 2319 95 64 11 0.12
Mon 08/24 03Z 0.52 2417 77 66 12 0.05
Mon 08/24 04Z 0.50 2517 77 61 11 0.00
Mon 08/24 05Z 0.43 2416 75 58 12 0.00
Mon 08/24 06Z 0.37 2415 75 44 12 0.00
Mon 08/24 07Z 0.36 2415 75 42 11 0.00
Mon 08/24 08Z 0.38 2316 73 26 11 0.00
Mon 08/24 09Z 0.40 2317 76 14 11 0.00
Mon 08/24 10Z 0.42 2317 78 20 10 0.00
Mon 08/24 11Z 0.40 2316 75 22 10 0.00
Mon 08/24 12Z 0.33 2314 77 27 10 0.00
Mon 08/24 13Z 0.25 2112 79 33 10 0.00
Mon 08/24 14Z 0.27 2013 83 41 9 0.00
Mon 08/24 15Z 0.31 2014 86 47 9 0.00
Mon 08/24 16Z 0.49 2014 89 63 9 0.00
Mon 08/24 17Z 0.55 2012 90 73 9 0.00
Mon 08/24 18Z 0.91 2012 88 58 9 0.02
Mon 08/24 19Z 1.54 2012 83 44 10 0.02
Mon 08/24 20Z 1.15 2112 87 65 10 0.02
Mon 08/24 21Z 0.54 2215 82 66 9 0.09
Mon 08/24 22Z 0.53 2214 73 47 10 0.01
Mon 08/24 23Z 0.57 2315 75 65 10 0.00
Tue 08/25 00Z 0.57 2314 86 63 9 0.00
Tue 08/25 01Z 0.54 2413 87 71 9 0.00
Tue 08/25 02Z 0.52 2413 84 81 9 0.01
Tue 08/25 03Z 0.54 2413 89 82 9 0.00
Tue 08/25 04Z 0.40 2411 86 90 9 0.01
Tue 08/25 05Z 0.32 2509 89 93 9 0.02
Tue 08/25 06Z 0.31 2609 89 97 9 0.01
Tue 08/25 07Z 0.32 2610 90 98 8 0.01
Tue 08/25 08Z 0.27 2508 91 99 8 0.02
Tue 08/25 09Z 0.26 2508 93 99 8 0.02
Tue 08/25 10Z 0.26 2508 93 99 8 0.01
Tue 08/25 11Z 0.27 2508 93 97 8 0.00
Tue 08/25 12Z 0.30 2609 95 93 8 0.00
Tue 08/25 13Z 0.35 2610 96 89 7 0.01
Tue 08/25 14Z 0.33 2708 96 82 7 0.01
Tue 08/25 15Z 0.33 2708 96 79 7 0.00
Tue 08/25 16Z 0.31 2807 95 78 7 0.00
Tue 08/25 17Z 0.35 2907 95 77 8 0.00
Run total areal avg QPF for the Central_Greens is: 0.62 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