Subject: NAM12 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM12_20260113_0000
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)
=== ===== === ==== ==== === === === ====
Tue 01/13 00Z 1.40 2425 92 82 -10 0.00
Tue 01/13 03Z 1.24 2630 88 78 -9 0.00
Tue 01/13 06Z 0.97 2627 94 83 -9 0.01
Tue 01/13 09Z 0.72 2623 92 87 -7 0.03
Tue 01/13 12Z 0.59 2622 92 38 -6 0.02
Tue 01/13 15Z 0.51 2618 90 19 -6 0.00
Tue 01/13 18Z 0.31 2316 79 16 -3 0.00
Tue 01/13 21Z 0.21 2021 79 47 0 0.00
Wed 01/14 00Z 0.37 2132 72 78 0 0.00
Wed 01/14 03Z 0.37 2134 85 87 0 0.01
Wed 01/14 06Z 0.61 2136 97 91 -3 0.08
Wed 01/14 09Z 0.61 2334 85 78 -1 0.02
Wed 01/14 12Z 0.58 2331 81 56 0 0.00
Wed 01/14 15Z 0.59 2327 87 47 -1 0.00
Wed 01/14 18Z 0.47 2319 89 82 -2 0.00
Wed 01/14 21Z 0.25 2114 95 93 -2 0.00
Thu 01/15 00Z 0.08 1912 97 92 -2 0.05
Thu 01/15 03Z 0.16 2012 97 90 -3 0.09
Thu 01/15 06Z 0.22 2111 97 89 -3 0.06
Thu 01/15 09Z 0.50 2714 95 88 -6 0.07
Thu 01/15 12Z 0.87 2822 89 81 -13 0.04
Thu 01/15 15Z 7.52 2719 89 57 -17 0.02
Thu 01/15 18Z 11.73 2621 84 83 -19 0.01
Thu 01/15 21Z 2.14 2720 87 74 -16 0.01
Fri 01/16 00Z 9.02 2725 79 80 -24 0.01
Fri 01/16 03Z 1.46 2724 81 53 -25 0.00
Fri 01/16 06Z 0.69 2724 65 49 -23 0.00
Fri 01/16 09Z 0.55 2724 65 37 -19 0.00
Fri 01/16 12Z 0.66 2527 82 17 -17 0.00
Run total areal avg QPF for the 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