Subject: NAM12 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM12_20260117_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)
=== ===== === ==== ==== === === === ====
Sat 01/17 18Z 0.24 2019 94 86 -7 0.00
Sat 01/17 21Z 0.46 2319 95 86 -7 0.02
Sun 01/18 00Z 0.60 2621 89 71 -7 0.01
Sun 01/18 03Z 0.64 2522 83 57 -6 0.00
Sun 01/18 06Z 0.82 2425 90 61 -7 0.00
Sun 01/18 09Z 0.84 2424 90 64 -8 0.00
Sun 01/18 12Z 0.81 2422 82 84 -9 0.00
Sun 01/18 15Z 1.41 2420 89 78 -11 0.00
Sun 01/18 18Z 1.30 2311 89 73 -11 0.00
Sun 01/18 21Z 0.24 2504 84 96 -11 0.00
Mon 01/19 00Z 0.09 0500 80 78 -10 0.00
Mon 01/19 03Z 0.06 0204 84 83 -10 0.00
Mon 01/19 06Z 0.03 0008 87 94 -11 0.00
Mon 01/19 09Z 0.03 3404 89 79 -11 0.01
Mon 01/19 12Z 0.10 2304 87 47 -11 0.00
Mon 01/19 15Z 0.27 2212 87 82 -12 0.00
Mon 01/19 18Z 3.71 2217 90 78 -14 0.01
Mon 01/19 21Z 2.81 2324 88 82 -14 0.00
Tue 01/20 00Z 1.75 2329 86 83 -14 0.00
Tue 01/20 03Z 4.59 2433 86 70 -15 0.00
Tue 01/20 06Z 1.65 2535 83 60 -16 0.00
Tue 01/20 09Z 3.01 2632 73 49 -19 0.00
Tue 01/20 12Z 1.82 2729 73 37 -21 0.00
Tue 01/20 15Z 1.85 2631 76 49 -18 0.00
Tue 01/20 18Z 11.55 2720 71 71 -22 0.00
Tue 01/20 21Z 6.44 2620 75 71 -21 0.00
Wed 01/21 00Z 2.22 2624 80 55 -21 0.00
Wed 01/21 03Z 1.25 2726 80 51 -21 0.00
Wed 01/21 06Z 1.02 2726 76 46 -21 0.00
Run total areal avg QPF for the greens is: 0.05 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