
A coastal low will bring strong winds and snow to southern Vermont tonight into Monday. For Rutland and Windsor counties, snowfall amounts of 3 to 7 inches are expected, along with wind gusts to 35 mph, which could result in poor visibility and blowing snow. Very difficult travel is expected across southern Vermont due to the combination of wind and snow, especially between mountain passes. Read More >
Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260223_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)
=== ===== === ==== ==== === === === ====
Mon 02/23 00Z 0.46 1013 86 74 -8 0.00
Mon 02/23 01Z 0.59 0916 86 72 -8 0.00
Mon 02/23 02Z 0.64 0919 85 75 -8 0.00
Mon 02/23 03Z 0.63 0920 84 74 -8 0.00
Mon 02/23 05Z 0.61 0821 78 54 -8 0.00
Mon 02/23 06Z 0.68 0822 77 32 -9 0.00
Mon 02/23 07Z 0.67 0822 76 47 -9 0.00
Mon 02/23 08Z 0.63 0822 73 67 -8 0.00
Mon 02/23 09Z 0.56 0721 72 77 -8 0.00
Mon 02/23 12Z 0.46 0525 69 76 -8 0.00
Mon 02/23 13Z 0.50 0526 61 75 -8 0.00
Mon 02/23 15Z 0.45 0426 47 69 -8 0.00
Mon 02/23 16Z 0.37 0323 49 63 -9 0.01
Mon 02/23 17Z 0.33 0222 56 63 -9 0.00
Mon 02/23 18Z 0.26 0222 61 67 -10 0.00
Mon 02/23 19Z 0.17 0122 64 75 -10 0.00
Mon 02/23 20Z 0.10 0023 70 81 -10 0.00
Mon 02/23 21Z 0.09 3525 71 71 -10 0.00
Mon 02/23 22Z 0.12 3528 74 56 -10 0.00
Mon 02/23 23Z 0.13 3531 73 45 -11 0.00
Tue 02/24 00Z 0.12 3534 76 32 -12 0.00
Tue 02/24 01Z 0.17 3533 87 23 -13 0.00
Tue 02/24 02Z 0.31 3433 92 17 -13 0.00
Tue 02/24 04Z 0.28 3428 92 19 -13 0.00
Tue 02/24 05Z 0.36 3427 95 18 -14 0.00
Tue 02/24 06Z 0.41 3328 95 20 -14 0.00
Tue 02/24 07Z 0.52 3328 95 23 -15 0.00
Tue 02/24 08Z 0.61 3326 96 29 -16 0.00
Tue 02/24 09Z 0.55 3224 93 30 -16 0.00
Tue 02/24 10Z 0.44 3224 90 44 -16 0.01
Tue 02/24 11Z 0.41 3123 89 56 -16 0.01
Tue 02/24 12Z 0.37 3123 89 58 -16 0.01
Tue 02/24 13Z 0.32 3122 88 60 -16 0.01
Tue 02/24 14Z 0.31 3121 89 62 -16 0.01
Tue 02/24 15Z 0.31 3120 89 64 -16 0.01
Tue 02/24 16Z 0.31 3118 88 62 -16 0.01
Tue 02/24 17Z 0.34 3017 89 61 -16 0.01
Tue 02/24 18Z 0.38 3015 88 62 -15 0.00
Tue 02/24 19Z 0.42 2915 88 62 -15 0.00
Tue 02/24 20Z 0.44 2914 87 53 -15 0.00
Tue 02/24 21Z 0.46 2814 86 36 -14 0.00
Tue 02/24 22Z 0.63 2815 88 20 -15 0.00
Tue 02/24 23Z 0.51 2715 86 7 -14 0.00
Wed 02/25 00Z 0.38 2714 83 3 -14 0.00
Wed 02/25 01Z 0.30 2713 79 3 -13 0.00
Wed 02/25 02Z 0.26 2612 73 4 -13 0.00
Wed 02/25 03Z 0.22 2412 63 10 -12 0.00
Wed 02/25 04Z 0.21 2313 55 36 -12 0.00
Wed 02/25 05Z 0.21 2214 48 64 -11 0.00
Wed 02/25 06Z 0.22 2216 39 84 -11 0.00
Wed 02/25 07Z 0.27 2218 45 87 -12 0.00
Wed 02/25 09Z 0.21 2022 86 86 -11 0.00
Wed 02/25 10Z 0.17 1925 90 84 -10 0.00
Wed 02/25 11Z 0.21 2026 92 87 -10 0.00
Run total areal avg QPF for the greens is: 0.09 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