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Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260418_1800
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sat 04/18 18Z 0.34 1518 81 5 7 0.00
Sat 04/18 19Z 0.21 1522 80 18 7 0.00
Sat 04/18 20Z 0.22 1525 78 11 8 0.00
Sat 04/18 21Z 0.23 1526 77 4 7 0.00
Sat 04/18 22Z 0.19 1527 74 6 8 0.00
Sat 04/18 23Z 0.10 1628 71 7 9 0.00
Sun 04/19 00Z 0.03 1629 68 6 10 0.00
Sun 04/19 01Z 0.12 1830 67 19 10 0.00
Sun 04/19 02Z 0.18 1831 67 31 10 0.00
Sun 04/19 03Z 0.25 1931 68 51 11 0.00
Sun 04/19 04Z 0.33 2032 68 68 11 0.00
Sun 04/19 05Z 0.37 2033 69 90 11 0.00
Sun 04/19 06Z 0.51 2134 88 84 8 0.01
Sun 04/19 07Z 0.56 2233 97 91 8 0.04
Sun 04/19 08Z 0.55 2325 98 89 6 0.03
Sun 04/19 09Z 0.42 2417 98 90 6 0.03
Sun 04/19 10Z 0.31 2412 99 94 5 0.04
Sun 04/19 11Z 0.45 2515 99 99 4 0.03
Sun 04/19 12Z 0.61 2717 99 99 2 0.07
Sun 04/19 13Z 0.47 3019 98 99 0 0.05
Sun 04/19 14Z 0.42 3122 97 99 0 0.07
Sun 04/19 15Z 0.53 3124 97 99 -2 0.03
Sun 04/19 16Z 0.61 3125 97 99 -4 0.10
Sun 04/19 17Z 0.60 3124 96 98 -5 0.12
Sun 04/19 18Z 0.61 3022 96 95 -6 0.11
Sun 04/19 19Z 0.62 3122 95 91 -6 0.12
Sun 04/19 20Z 0.50 3121 93 88 -6 0.06
Sun 04/19 21Z 0.55 3120 82 58 -7 0.01
Sun 04/19 22Z 0.68 3020 81 16 -6 0.00
Sun 04/19 23Z 0.63 3022 74 18 -6 0.00
Mon 04/20 00Z 0.65 3024 69 25 -6 0.00
Mon 04/20 01Z 0.73 3024 67 24 -6 0.00
Mon 04/20 02Z 0.86 2924 71 26 -6 0.00
Mon 04/20 03Z 1.06 2922 74 34 -6 0.00
Mon 04/20 04Z 1.22 2921 75 36 -7 0.00
Mon 04/20 05Z 1.37 2821 74 41 -7 0.00
Mon 04/20 06Z 1.04 2821 75 43 -7 0.00
Mon 04/20 07Z 0.90 2720 78 48 -7 0.00
Mon 04/20 08Z 0.78 2619 84 63 -7 0.00
Mon 04/20 09Z 0.86 2622 87 68 -7 0.00
Mon 04/20 10Z 0.91 2722 90 64 -8 0.00
Mon 04/20 11Z 0.88 2821 92 70 -8 0.01
Mon 04/20 12Z 0.74 2919 93 63 -9 0.01
Mon 04/20 13Z 0.64 3116 95 54 -10 0.01
Mon 04/20 14Z 0.46 3215 88 45 -10 0.01
Mon 04/20 15Z 1.78 3213 81 38 -10 0.01
Mon 04/20 16Z 3.06 3212 75 39 -10 0.00
Mon 04/20 17Z 3.65 3111 68 39 -9 0.00
Mon 04/20 18Z 4.12 3110 70 45 -9 0.00
Mon 04/20 19Z 3.75 3110 70 52 -9 0.00
Mon 04/20 20Z 3.27 3110 69 55 -9 0.00
Mon 04/20 21Z 3.28 3111 70 58 -9 0.00
Mon 04/20 22Z 2.52 3212 72 56 -9 0.00
Mon 04/20 23Z 1.34 3213 71 47 -10 0.00
Tue 04/21 00Z 0.59 3213 70 30 -10 0.00
Tue 04/21 01Z 0.61 3213 66 18 -11 0.00
Tue 04/21 02Z 0.70 3213 62 13 -11 0.00
Tue 04/21 03Z 0.84 3214 60 11 -11 0.00
Tue 04/21 04Z 0.89 3214 60 11 -11 0.00
Tue 04/21 05Z 0.80 3114 57 11 -11 0.00
Run total areal avg QPF for the Central_Greens is: 0.97 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