NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20250602_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)
=== ===== === ==== ==== === === === ====
Mon 06/02 06Z 0.72 2717  96  61   0 0.00
Mon 06/02 07Z 0.71 2718  95  72   0 0.01
Mon 06/02 08Z 0.71 2720  96  80   0 0.02
Mon 06/02 09Z 0.72 2820  96  91   0 0.02
Mon 06/02 10Z 0.67 2919  93  93   0 0.01
Mon 06/02 11Z 0.66 2919  92  82   1 0.00
Mon 06/02 12Z 0.68 2819  92  61   1 0.00
Mon 06/02 13Z 0.69 2819  90  38   2 0.00
Mon 06/02 14Z 0.73 2818  84  16   2 0.00
Mon 06/02 15Z 1.23 2717  85   5   2 0.00
Mon 06/02 16Z 7.61 2716  85   2   2 0.00
Mon 06/02 17Z 9.90 2716  76   6   3 0.00
Mon 06/02 18Z 9.20 2715  71  10   3 0.00
Mon 06/02 19Z 9.30 2714  66  11   4 0.00
Mon 06/02 20Z 7.97 2713  65  11   4 0.00
Mon 06/02 21Z 5.60 2712  66  12   4 0.00
Mon 06/02 22Z 2.22 2712  66  16   5 0.00
Mon 06/02 23Z 1.06 2712  65  23   5 0.00
Tue 06/03 00Z 1.02 2814  64  19   5 0.00
Tue 06/03 01Z 1.50 2915  60  22   5 0.00
Tue 06/03 02Z 1.03 3015  60  20   5 0.00
Tue 06/03 03Z 0.94 3014  60  18   5 0.00
Tue 06/03 04Z 0.97 2913  62  15   5 0.00
Tue 06/03 05Z 0.70 2910  58  14   5 0.00
Tue 06/03 06Z 0.69 2910  55  12   5 0.00
Tue 06/03 07Z 0.65 2909  54  11   5 0.00
Tue 06/03 08Z 0.52 2908  53   9   5 0.00
Tue 06/03 09Z 0.38 3007  50   9   6 0.00
Tue 06/03 10Z 0.32 3007  48   9   6 0.00
Tue 06/03 11Z 0.23 3005  45   9   6 0.00
Tue 06/03 12Z 0.21 3004  45   8   6 0.00
Tue 06/03 13Z 0.33 2604  47   6   6 0.00
Tue 06/03 14Z 0.61 2505  49   4   7 0.00
Tue 06/03 15Z 1.18 2405  49   4   7 0.00
Tue 06/03 16Z 2.34 2506  48   7   7 0.00
Tue 06/03 17Z 2.46 2506  46  27   8 0.00
Tue 06/03 18Z 2.16 2506  43  63   9 0.00
Tue 06/03 19Z 1.51 2507  45  80   9 0.00
Tue 06/03 20Z 0.93 2507  51  91   9 0.00
Tue 06/03 21Z 0.44 2507  53  84  10 0.00
Tue 06/03 22Z 0.33 2407  56  70  11 0.00
Tue 06/03 23Z 0.28 2307  61  54  11 0.00
Wed 06/04 00Z 0.24 2307  63  42  12 0.00
Wed 06/04 01Z 0.26 2309  60  35  12 0.00
Wed 06/04 02Z 0.29 2310  57  35  13 0.00
Wed 06/04 03Z 0.30 2311  57  31  13 0.00
Wed 06/04 04Z 0.27 2311  56  29  13 0.00
Wed 06/04 05Z 0.24 2310  55  25  14 0.00
Wed 06/04 06Z 0.25 2211  54  22  14 0.00
Wed 06/04 07Z 0.29 2312  53  16  14 0.00
Wed 06/04 08Z 0.32 2313  54  16  14 0.00
Wed 06/04 09Z 0.41 2315  56  16  14 0.00
Wed 06/04 10Z 0.46 2416  56  18  14 0.00
Wed 06/04 11Z 0.53 2417  56  18  13 0.00
Wed 06/04 12Z 0.55 2416  57  18  13 0.00
Wed 06/04 13Z 0.49 2315  56  15  13 0.00
Wed 06/04 14Z 0.41 2213  55  14  14 0.00
Wed 06/04 15Z 0.34 2112  55  12  14 0.00
Wed 06/04 16Z 0.34 2011  57  14  14 0.00
Wed 06/04 17Z 0.37 1911  59  14  14 0.00

Run total areal avg QPF for the greens is: 0.06 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