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Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260505_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)
=== ===== === ==== ==== === === === ====
Tue 05/05 06Z 0.73 2136 61 75 9 0.00
Tue 05/05 07Z 0.77 2238 60 83 9 0.00
Tue 05/05 08Z 0.77 2236 61 60 9 0.00
Tue 05/05 09Z 0.80 2236 68 46 9 0.00
Tue 05/05 10Z 0.73 2232 73 70 9 0.00
Tue 05/05 11Z 0.73 2332 76 77 9 0.00
Tue 05/05 12Z 0.81 2333 83 91 9 0.01
Tue 05/05 13Z 0.79 2333 79 75 9 0.01
Tue 05/05 14Z 0.87 2331 75 75 10 0.00
Tue 05/05 15Z 1.24 2232 75 85 10 0.00
Tue 05/05 16Z 4.07 2230 72 74 10 0.00
Tue 05/05 17Z 9.10 2228 72 65 10 0.00
Tue 05/05 18Z 9.07 2127 73 63 11 0.01
Tue 05/05 19Z 8.68 2127 70 72 11 0.00
Tue 05/05 20Z 4.55 2228 77 73 11 0.12
Tue 05/05 21Z 2.97 2228 79 74 11 0.05
Tue 05/05 22Z 2.47 2329 81 87 10 0.08
Tue 05/05 23Z 1.20 2232 81 89 10 0.04
Wed 05/06 00Z 0.88 2333 82 68 10 0.09
Wed 05/06 01Z 0.94 2334 81 81 10 0.00
Wed 05/06 02Z 0.94 2429 86 96 9 0.10
Wed 05/06 03Z 0.88 2624 95 96 7 0.12
Wed 05/06 04Z 0.66 2521 96 99 7 0.11
Wed 05/06 05Z 0.59 2520 89 97 6 0.06
Wed 05/06 06Z 0.49 2517 87 93 5 0.03
Wed 05/06 07Z 0.33 2513 94 85 5 0.04
Wed 05/06 08Z 0.22 2311 94 84 5 0.02
Wed 05/06 09Z 0.17 2113 95 83 6 0.01
Wed 05/06 10Z 0.10 1916 95 69 7 0.01
Wed 05/06 11Z 0.08 1919 97 73 7 0.01
Wed 05/06 12Z 0.11 1922 98 65 7 0.02
Wed 05/06 13Z 0.17 1923 99 72 7 0.04
Wed 05/06 14Z 0.19 1924 98 86 8 0.05
Wed 05/06 15Z 0.19 1922 99 84 8 0.06
Wed 05/06 16Z 0.18 1920 99 92 8 0.07
Wed 05/06 17Z 0.25 2020 99 97 7 0.14
Wed 05/06 18Z 0.21 2016 99 99 6 0.16
Wed 05/06 19Z 0.20 2410 99 99 5 0.16
Wed 05/06 20Z 0.19 2810 96 97 4 0.14
Wed 05/06 21Z 0.22 3013 96 94 3 0.03
Wed 05/06 22Z 0.23 3114 93 81 2 0.01
Wed 05/06 23Z 0.21 3215 86 42 1 0.00
Thu 05/07 00Z 0.22 3216 79 22 1 0.00
Thu 05/07 01Z 0.23 3216 64 12 1 0.00
Thu 05/07 02Z 0.27 3116 49 7 0 0.00
Thu 05/07 03Z 0.35 3117 54 5 0 0.00
Thu 05/07 04Z 0.37 3118 69 5 0 0.00
Thu 05/07 05Z 0.45 3118 79 16 0 0.00
Thu 05/07 06Z 0.48 3017 81 23 0 0.00
Thu 05/07 07Z 0.52 2919 79 19 0 0.00
Thu 05/07 08Z 0.50 2919 68 28 0 0.00
Thu 05/07 09Z 0.55 2920 57 29 0 0.00
Thu 05/07 10Z 0.63 2821 56 45 0 0.00
Thu 05/07 11Z 0.66 2823 53 45 -1 0.00
Thu 05/07 12Z 0.65 2822 49 32 -1 0.00
Thu 05/07 13Z 0.66 2821 51 25 -1 0.00
Thu 05/07 14Z 0.80 2820 55 21 -2 0.00
Thu 05/07 15Z 2.89 2717 61 22 -2 0.00
Thu 05/07 16Z 11.25 2716 68 19 -2 0.00
Thu 05/07 17Z 11.90 2716 64 21 -1 0.00
Run total areal avg QPF for the greens is: 1.80 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