Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260405_1200
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 04/05 12Z 0.30 2030 99 98 5 0.00
Sun 04/05 13Z 0.35 2128 98 96 6 0.06
Sun 04/05 14Z 0.41 2227 98 98 5 0.15
Sun 04/05 15Z 0.51 2327 98 97 5 0.16
Sun 04/05 16Z 0.51 2424 96 93 4 0.06
Sun 04/05 17Z 0.65 2525 95 84 2 0.02
Sun 04/05 18Z 0.72 2523 95 43 1 0.02
Sun 04/05 19Z 0.82 2623 96 30 0 0.01
Sun 04/05 20Z 1.10 2725 95 17 0 0.01
Sun 04/05 21Z 1.27 2724 95 14 -2 0.01
Sun 04/05 22Z 1.28 2724 94 10 -2 0.01
Sun 04/05 23Z 1.66 2626 92 9 -3 0.01
Mon 04/06 00Z 2.12 2728 86 10 -4 0.00
Mon 04/06 01Z 2.16 2728 86 16 -5 0.00
Mon 04/06 02Z 1.55 2729 86 25 -5 0.00
Mon 04/06 03Z 1.53 2730 89 30 -6 0.00
Mon 04/06 04Z 2.02 2732 93 32 -7 0.00
Mon 04/06 05Z 2.19 2732 94 32 -8 0.01
Mon 04/06 06Z 2.06 2732 92 35 -9 0.00
Mon 04/06 07Z 1.34 2831 92 42 -9 0.00
Mon 04/06 08Z 1.22 2832 94 51 -9 0.00
Mon 04/06 09Z 1.20 2831 93 54 -9 0.00
Mon 04/06 10Z 1.44 2831 94 55 -9 0.00
Mon 04/06 11Z 1.57 2929 96 56 -10 0.00
Mon 04/06 12Z 1.94 2926 96 59 -10 0.00
Mon 04/06 13Z 2.87 2925 95 67 -11 0.00
Mon 04/06 14Z 3.72 2824 95 71 -10 0.00
Mon 04/06 15Z 4.19 2823 93 73 -10 0.00
Mon 04/06 16Z 7.48 2822 90 72 -10 0.00
Mon 04/06 17Z 12.25 2822 84 72 -9 0.00
Mon 04/06 18Z 13.91 2821 77 72 -9 0.00
Mon 04/06 19Z 14.06 2721 74 73 -8 0.00
Mon 04/06 20Z 13.66 2720 73 81 -8 0.00
Mon 04/06 21Z 13.16 2820 72 80 -8 0.00
Mon 04/06 22Z 12.02 2821 73 79 -8 0.00
Mon 04/06 23Z 6.47 2821 74 75 -9 0.00
Tue 04/07 00Z 3.32 2821 76 74 -9 0.00
Tue 04/07 01Z 1.41 2819 82 76 -9 0.00
Tue 04/07 02Z 0.99 2818 89 79 -9 0.01
Tue 04/07 03Z 0.91 2919 90 80 -10 0.02
Tue 04/07 04Z 0.68 2917 90 79 -10 0.01
Tue 04/07 05Z 0.56 3015 91 83 -11 0.01
Tue 04/07 06Z 0.44 3113 90 87 -11 0.01
Tue 04/07 07Z 0.35 3112 85 85 -11 0.01
Tue 04/07 08Z 0.38 3112 84 88 -12 0.00
Tue 04/07 09Z 0.41 3013 86 87 -12 0.00
Tue 04/07 10Z 0.44 3013 90 75 -12 0.00
Tue 04/07 11Z 0.43 3013 92 75 -13 0.00
Tue 04/07 12Z 0.48 3013 94 75 -13 0.01
Tue 04/07 13Z 0.66 3013 91 71 -14 0.00
Tue 04/07 14Z 1.15 3013 85 61 -14 0.00
Tue 04/07 15Z 3.45 3013 81 47 -14 0.00
Tue 04/07 16Z 4.58 3013 77 28 -14 0.00
Tue 04/07 17Z 5.43 3013 74 21 -14 0.00
Tue 04/07 18Z 5.54 3013 71 10 -13 0.00
Tue 04/07 19Z 5.33 3013 66 9 -13 0.00
Tue 04/07 20Z 5.15 3013 60 12 -13 0.00
Tue 04/07 21Z 4.54 3013 55 19 -13 0.00
Tue 04/07 22Z 2.75 3013 52 27 -13 0.00
Tue 04/07 23Z 1.02 3014 48 32 -13 0.00
Run total areal avg QPF for the Central_Greens is: 0.61 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