Subject: NAM12 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM12_20260118_0600
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)
=== ===== === ==== ==== === === === ====
Sun 01/18 06Z 0.75 2423 90 67 -7 0.00
Sun 01/18 09Z 0.72 2419 88 53 -8 0.00
Sun 01/18 12Z 0.71 2421 79 78 -9 0.00
Sun 01/18 15Z 1.08 2420 74 84 -11 0.00
Sun 01/18 18Z 1.87 2514 78 87 -12 0.00
Sun 01/18 21Z 0.44 2805 75 45 -12 0.00
Mon 01/19 00Z 0.09 0103 69 22 -11 0.00
Mon 01/19 03Z 0.04 3504 74 34 -11 0.00
Mon 01/19 06Z 0.12 3411 82 45 -12 0.00
Mon 01/19 09Z 0.18 3207 85 58 -13 0.00
Mon 01/19 12Z 0.36 2710 82 25 -14 0.00
Mon 01/19 15Z 0.45 2312 86 58 -14 0.00
Mon 01/19 18Z 2.15 2116 88 82 -14 0.00
Mon 01/19 21Z 1.43 2223 90 88 -13 0.01
Tue 01/20 00Z 2.15 2328 84 77 -14 0.01
Tue 01/20 03Z 2.38 2432 86 67 -15 0.00
Tue 01/20 06Z 1.42 2432 81 61 -16 0.00
Tue 01/20 09Z 2.19 2629 78 37 -18 0.00
Tue 01/20 12Z 1.34 2624 80 24 -19 0.00
Tue 01/20 15Z 1.15 2618 82 46 -19 0.00
Tue 01/20 18Z 2.46 2517 84 75 -20 0.00
Tue 01/20 21Z 3.42 2621 82 72 -20 0.01
Wed 01/21 00Z 1.68 2725 84 64 -21 0.01
Wed 01/21 03Z 1.79 2621 83 70 -20 0.01
Wed 01/21 06Z 1.16 2726 77 48 -21 0.01
Wed 01/21 09Z 0.84 2724 75 21 -20 0.00
Wed 01/21 12Z 0.71 2623 78 48 -19 0.00
Wed 01/21 15Z 0.38 2319 68 42 -16 0.00
Wed 01/21 18Z 0.30 2027 45 85 -14 0.00
Run total areal avg QPF for the greens is: 0.06 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