
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_1200
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 12Z 0.76 2429 57 53 3 0.00
Mon 03/09 13Z 0.77 2432 48 37 4 0.00
Mon 03/09 14Z 0.74 2433 39 34 5 0.00
Mon 03/09 15Z 0.72 2334 38 34 6 0.00
Mon 03/09 16Z 0.74 2335 35 34 6 0.00
Mon 03/09 17Z 0.78 2235 30 35 6 0.00
Mon 03/09 18Z 0.83 2236 27 34 6 0.00
Mon 03/09 19Z 0.83 2234 26 35 7 0.00
Mon 03/09 21Z 0.79 2333 32 34 7 0.00
Mon 03/09 23Z 0.88 2435 39 40 7 0.00
Tue 03/10 00Z 0.92 2436 41 43 7 0.00
Tue 03/10 01Z 0.95 2436 42 44 7 0.00
Tue 03/10 02Z 0.94 2436 43 44 8 0.00
Tue 03/10 04Z 1.02 2536 44 49 7 0.00
Tue 03/10 05Z 1.08 2635 46 49 7 0.00
Tue 03/10 06Z 1.14 2633 50 45 6 0.00
Tue 03/10 07Z 1.04 2731 56 44 6 0.00
Tue 03/10 09Z 0.75 2725 65 47 6 0.00
Tue 03/10 10Z 0.64 2722 68 53 6 0.00
Tue 03/10 11Z 0.54 2619 69 55 6 0.00
Tue 03/10 12Z 0.46 2617 69 50 7 0.00
Tue 03/10 13Z 0.46 2518 73 39 6 0.00
Tue 03/10 14Z 0.46 2419 76 43 6 0.00
Tue 03/10 15Z 0.47 2420 78 35 6 0.00
Tue 03/10 16Z 0.53 2421 82 38 6 0.00
Tue 03/10 17Z 0.57 2420 85 45 6 0.00
Tue 03/10 18Z 0.63 2420 89 48 6 0.00
Tue 03/10 19Z 0.60 2519 91 48 6 0.00
Tue 03/10 20Z 0.61 2518 93 48 6 0.00
Tue 03/10 21Z 0.64 2619 96 46 6 0.00
Tue 03/10 22Z 0.62 2719 97 46 6 0.00
Tue 03/10 23Z 0.53 2718 98 47 5 0.00
Wed 03/11 00Z 0.42 2916 98 48 5 0.00
Wed 03/11 01Z 0.28 3012 98 48 4 0.01
Wed 03/11 02Z 0.18 3109 97 45 4 0.02
Wed 03/11 03Z 0.13 3107 95 43 4 0.03
Wed 03/11 04Z 0.09 3105 94 47 4 0.02
Wed 03/11 05Z 0.09 3105 92 48 3 0.01
Wed 03/11 06Z 0.07 3003 90 54 4 0.01
Wed 03/11 07Z 0.05 2401 90 52 4 0.01
Wed 03/11 08Z 0.04 1603 90 56 4 0.01
Wed 03/11 09Z 0.07 1508 91 74 4 0.00
Wed 03/11 10Z 0.08 1613 93 82 5 0.00
Wed 03/11 11Z 0.12 1619 96 85 6 0.00
Wed 03/11 12Z 0.14 1624 97 82 6 0.00
Wed 03/11 13Z 0.14 1632 97 76 7 0.00
Wed 03/11 14Z 0.11 1636 96 62 7 0.01
Wed 03/11 15Z 0.06 1739 96 51 7 0.02
Wed 03/11 16Z 0.04 1741 96 48 8 0.03
Wed 03/11 17Z 0.06 1842 96 55 8 0.03
Wed 03/11 18Z 0.10 1841 97 67 10 0.02
Wed 03/11 19Z 0.15 1941 97 71 10 0.02
Wed 03/11 20Z 0.21 2041 97 71 10 0.02
Wed 03/11 21Z 0.21 2040 96 60 11 0.02
Wed 03/11 22Z 0.22 2042 95 84 11 0.02
Wed 03/11 23Z 0.25 2043 95 83 11 0.02
Run total areal avg QPF for the greens is: 0.33 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