Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260502_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)
=== ===== === ==== ==== === === === ====
Sat 05/02 12Z 0.12 1806 99 72 -1 0.00
Sat 05/02 13Z 0.11 2005 99 80 -1 0.03
Sat 05/02 14Z 0.23 2505 99 80 -2 0.03
Sat 05/02 15Z 0.32 2606 99 85 -2 0.01
Sat 05/02 16Z 0.38 2808 97 86 -2 0.01
Sat 05/02 17Z 0.57 2907 92 83 -2 0.00
Sat 05/02 18Z 1.40 2806 83 81 -2 0.00
Sat 05/02 19Z 3.74 2706 76 65 -1 0.00
Sat 05/02 20Z 3.11 2709 87 60 -1 0.00
Sat 05/02 21Z 0.88 2709 91 51 -1 0.02
Sat 05/02 22Z 0.50 2810 88 50 -2 0.01
Sat 05/02 23Z 0.55 2810 89 50 -2 0.00
Sun 05/03 00Z 0.64 2911 90 53 -2 0.00
Sun 05/03 01Z 0.58 2912 90 42 -3 0.01
Sun 05/03 02Z 0.49 3012 90 34 -3 0.00
Sun 05/03 03Z 0.38 3112 88 29 -4 0.00
Sun 05/03 04Z 0.32 3112 86 28 -4 0.00
Sun 05/03 05Z 0.27 3112 86 30 -4 0.00
Sun 05/03 06Z 0.22 3212 87 36 -4 0.00
Sun 05/03 07Z 0.16 3212 87 44 -4 0.00
Sun 05/03 08Z 0.14 3313 87 40 -4 0.00
Sun 05/03 09Z 0.14 3315 87 36 -5 0.00
Sun 05/03 10Z 0.16 3317 88 36 -5 0.00
Sun 05/03 11Z 0.17 3317 88 39 -5 0.00
Sun 05/03 12Z 0.23 3316 86 47 -5 0.00
Sun 05/03 13Z 1.16 3215 84 46 -5 0.00
Sun 05/03 14Z 3.07 3215 83 47 -5 0.00
Sun 05/03 15Z 4.30 3214 80 47 -4 0.00
Sun 05/03 16Z 5.05 3214 75 43 -4 0.00
Sun 05/03 17Z 5.50 3114 75 45 -3 0.00
Sun 05/03 18Z 5.26 3114 77 45 -3 0.00
Sun 05/03 19Z 5.83 3014 73 44 -3 0.00
Sun 05/03 20Z 6.67 3014 70 51 -3 0.00
Sun 05/03 21Z 7.82 2914 70 50 -2 0.00
Sun 05/03 22Z 7.27 2915 69 50 -2 0.00
Sun 05/03 23Z 3.88 2916 67 50 -2 0.00
Mon 05/04 00Z 1.96 2818 67 30 -2 0.00
Mon 05/04 01Z 1.78 2820 65 15 -2 0.00
Mon 05/04 02Z 1.49 2821 61 5 -2 0.00
Mon 05/04 03Z 1.13 2823 68 85 -2 0.00
Mon 05/04 04Z 0.88 2722 66 91 -1 0.00
Mon 05/04 05Z 0.75 2724 90 95 -1 0.02
Mon 05/04 06Z 0.83 2628 94 92 0 0.07
Mon 05/04 07Z 0.92 2531 90 92 0 0.04
Mon 05/04 08Z 0.96 2532 88 90 0 0.03
Mon 05/04 09Z 0.93 2632 87 83 1 0.01
Mon 05/04 10Z 0.94 2632 85 70 1 0.00
Mon 05/04 11Z 1.01 2532 85 26 0 0.00
Mon 05/04 12Z 1.09 2531 87 36 0 0.00
Mon 05/04 13Z 1.03 2530 90 85 1 0.00
Mon 05/04 14Z 0.89 2527 90 88 1 0.00
Mon 05/04 15Z 0.92 2523 91 85 1 0.00
Mon 05/04 16Z 1.09 2522 92 73 1 0.01
Mon 05/04 17Z 1.66 2522 91 44 1 0.00
Mon 05/04 18Z 3.60 2421 91 28 2 0.00
Mon 05/04 19Z 4.57 2421 90 29 2 0.00
Mon 05/04 20Z 5.48 2421 88 34 3 0.00
Mon 05/04 21Z 4.64 2421 88 26 3 0.01
Mon 05/04 22Z 2.59 2521 88 31 3 0.00
Mon 05/04 23Z 1.31 2421 89 34 4 0.00
Run total areal avg QPF for the Central_Greens is: 0.31 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