
Wind gusts in the 40-50 mph range are expected across the St. Lawrence Valley today. Isolated power outages are possible. Elsewhere, gusts in the 20-40 mph range are expected. Read More >
Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260309_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)
=== ===== === ==== ==== === === === ====
Mon 03/09 06Z 0.98 2733 61 25 1 0.00
Mon 03/09 07Z 0.97 2733 55 30 1 0.00
Mon 03/09 08Z 0.94 2633 52 37 2 0.00
Mon 03/09 09Z 0.95 2631 53 39 2 0.00
Mon 03/09 10Z 0.91 2630 54 77 2 0.00
Mon 03/09 11Z 0.86 2531 53 62 3 0.00
Mon 03/09 12Z 0.85 2532 49 43 3 0.00
Mon 03/09 13Z 0.88 2434 44 51 4 0.00
Mon 03/09 14Z 0.88 2437 34 44 6 0.00
Mon 03/09 15Z 0.84 2437 29 40 7 0.00
Mon 03/09 16Z 0.80 2336 28 37 7 0.00
Mon 03/09 17Z 0.80 2336 27 33 7 0.00
Mon 03/09 18Z 0.80 2236 27 30 7 0.00
Mon 03/09 19Z 0.80 2235 28 27 7 0.00
Mon 03/09 20Z 0.83 2235 31 30 7 0.00
Mon 03/09 21Z 0.88 2335 36 33 7 0.00
Mon 03/09 22Z 0.92 2336 41 33 7 0.00
Mon 03/09 23Z 0.95 2337 44 39 7 0.00
Tue 03/10 00Z 1.01 2437 44 44 7 0.00
Tue 03/10 01Z 1.08 2438 44 45 7 0.00
Tue 03/10 02Z 1.05 2438 44 54 7 0.00
Tue 03/10 03Z 1.08 2538 45 56 7 0.00
Tue 03/10 04Z 1.14 2539 49 55 7 0.00
Tue 03/10 05Z 1.25 2638 54 57 6 0.00
Tue 03/10 06Z 1.28 2735 60 56 6 0.00
Tue 03/10 07Z 1.12 2732 68 57 5 0.00
Tue 03/10 08Z 0.95 2729 73 58 5 0.00
Tue 03/10 09Z 0.79 2826 77 55 5 0.00
Tue 03/10 10Z 0.59 2822 79 57 5 0.00
Tue 03/10 11Z 0.45 2817 80 59 6 0.00
Tue 03/10 12Z 0.37 2615 78 56 7 0.00
Tue 03/10 13Z 0.35 2516 75 54 7 0.00
Tue 03/10 14Z 0.36 2417 74 46 8 0.00
Tue 03/10 15Z 0.40 2419 76 59 7 0.00
Tue 03/10 16Z 0.46 2420 80 57 7 0.00
Tue 03/10 17Z 0.52 2419 84 45 6 0.00
Tue 03/10 18Z 0.56 2418 88 41 6 0.00
Tue 03/10 19Z 0.56 2418 91 38 5 0.00
Tue 03/10 20Z 0.56 2417 93 39 5 0.00
Tue 03/10 21Z 0.57 2417 94 42 5 0.00
Tue 03/10 22Z 0.57 2417 96 43 6 0.01
Tue 03/10 23Z 0.54 2517 96 41 6 0.01
Wed 03/11 00Z 0.51 2616 96 40 6 0.01
Wed 03/11 01Z 0.44 2615 97 41 6 0.01
Wed 03/11 02Z 0.38 2613 97 44 6 0.01
Wed 03/11 03Z 0.33 2612 97 46 6 0.01
Wed 03/11 04Z 0.24 2509 98 53 6 0.01
Wed 03/11 05Z 0.19 2409 99 66 7 0.02
Wed 03/11 06Z 0.15 2407 99 76 7 0.01
Wed 03/11 07Z 0.11 2107 99 71 7 0.01
Wed 03/11 08Z 0.06 1908 99 73 7 0.01
Wed 03/11 09Z 0.04 1812 99 79 8 0.01
Wed 03/11 10Z 0.03 1717 99 73 8 0.02
Wed 03/11 11Z 0.03 1723 98 69 8 0.03
Wed 03/11 12Z 0.03 1727 98 58 8 0.03
Wed 03/11 13Z 0.03 1829 98 44 8 0.04
Wed 03/11 14Z 0.06 1833 98 37 8 0.02
Wed 03/11 15Z 0.10 1835 97 33 9 0.02
Wed 03/11 16Z 0.16 1936 98 49 9 0.03
Wed 03/11 17Z 0.19 1937 96 56 10 0.03
Run total areal avg QPF for the greens is: 0.35 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