Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260419_0000
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)
=== ===== === ==== ==== === === === ====
Sun 04/19 00Z 0.03 1623 80 7 8 0.00
Sun 04/19 01Z 0.06 1725 81 11 9 0.00
Sun 04/19 02Z 0.11 1827 78 11 10 0.00
Sun 04/19 03Z 0.20 1929 78 16 10 0.00
Sun 04/19 04Z 0.30 1931 77 44 10 0.00
Sun 04/19 05Z 0.42 2134 84 69 10 0.01
Sun 04/19 06Z 0.49 2134 94 88 9 0.05
Sun 04/19 07Z 0.52 2229 98 97 8 0.10
Sun 04/19 08Z 0.52 2325 98 95 7 0.05
Sun 04/19 09Z 0.45 2419 98 93 6 0.03
Sun 04/19 10Z 0.42 2416 98 91 6 0.03
Sun 04/19 11Z 0.50 2617 98 92 4 0.02
Sun 04/19 12Z 0.40 2813 98 89 3 0.03
Sun 04/19 13Z 0.32 3114 97 96 1 0.02
Sun 04/19 14Z 0.50 3120 98 99 0 0.05
Sun 04/19 15Z 0.30 3224 97 100 -1 0.11
Sun 04/19 16Z 0.34 3123 95 99 -2 0.13
Sun 04/19 17Z 0.35 3224 97 99 -4 0.07
Sun 04/19 18Z 0.41 3123 95 98 -5 0.07
Sun 04/19 19Z 0.51 3124 95 97 -6 0.04
Sun 04/19 20Z 0.56 3124 95 94 -6 0.03
Sun 04/19 21Z 0.47 3122 94 90 -6 0.03
Sun 04/19 22Z 0.34 3220 81 40 -6 0.02
Sun 04/19 23Z 0.43 3120 79 18 -5 0.00
Mon 04/20 00Z 0.54 3021 90 32 -5 0.00
Mon 04/20 01Z 0.69 2921 95 52 -5 0.02
Mon 04/20 02Z 0.91 2923 95 65 -6 0.02
Mon 04/20 03Z 0.87 3024 86 50 -6 0.01
Mon 04/20 04Z 0.80 3022 79 24 -6 0.00
Mon 04/20 05Z 0.73 2920 70 33 -6 0.00
Mon 04/20 06Z 0.84 2919 67 48 -7 0.00
Mon 04/20 07Z 0.82 2818 68 54 -7 0.00
Mon 04/20 08Z 0.85 2718 71 67 -7 0.00
Mon 04/20 09Z 0.76 2817 77 81 -7 0.00
Mon 04/20 10Z 0.63 2916 88 87 -8 0.00
Mon 04/20 11Z 0.47 3014 94 78 -8 0.02
Mon 04/20 12Z 0.36 3012 93 61 -9 0.01
Mon 04/20 13Z 0.38 3110 92 47 -9 0.00
Mon 04/20 14Z 0.89 3209 90 58 -9 0.00
Mon 04/20 15Z 0.86 3209 86 34 -9 0.00
Mon 04/20 16Z 1.38 3209 81 41 -9 0.00
Mon 04/20 17Z 2.22 3209 76 41 -9 0.00
Mon 04/20 18Z 2.93 3110 71 41 -9 0.00
Mon 04/20 19Z 3.90 3111 66 36 -9 0.00
Mon 04/20 20Z 4.24 3112 66 36 -9 0.00
Mon 04/20 21Z 3.51 3112 68 39 -9 0.00
Mon 04/20 22Z 2.35 3213 69 43 -9 0.00
Mon 04/20 23Z 1.06 3314 69 42 -10 0.00
Tue 04/21 00Z 0.57 3315 67 36 -10 0.00
Tue 04/21 01Z 0.70 3316 64 31 -11 0.00
Tue 04/21 02Z 0.93 3217 62 27 -11 0.00
Tue 04/21 03Z 0.92 3218 61 20 -12 0.00
Tue 04/21 04Z 0.72 3217 60 12 -12 0.00
Tue 04/21 05Z 0.62 3316 60 9 -12 0.00
Tue 04/21 06Z 0.46 3315 60 10 -12 0.00
Tue 04/21 07Z 0.30 3314 57 12 -12 0.00
Tue 04/21 08Z 0.19 3313 53 10 -12 0.00
Tue 04/21 09Z 0.10 3411 49 11 -12 0.00
Tue 04/21 10Z 0.12 3310 48 10 -12 0.00
Tue 04/21 11Z 0.14 3308 48 7 -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