NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260601_1800
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 06/01 18Z 0.74 0105  75  67   3 0.00
Mon 06/01 19Z 0.54 0005  75  63   4 0.01
Mon 06/01 20Z 0.36 0005  75  60   4 0.01
Mon 06/01 21Z 0.33 3504  75  60   4 0.01
Mon 06/01 22Z 0.25 3504  75  58   4 0.01
Mon 06/01 23Z 0.21 3404  75  56   4 0.01
Tue 06/02 00Z 0.18 3305  74  53   4 0.00
Tue 06/02 01Z 0.20 3407  73  51   4 0.00
Tue 06/02 02Z 0.28 3409  71  49   4 0.00
Tue 06/02 03Z 0.26 3410  70  45   4 0.00
Tue 06/02 04Z 0.25 3411  69  41   4 0.00
Tue 06/02 05Z 0.27 3311  69  39   4 0.00
Tue 06/02 06Z 0.27 3311  69  37   4 0.00
Tue 06/02 07Z 0.30 3211  67  41   5 0.00
Tue 06/02 08Z 0.33 3211  68  43   5 0.00
Tue 06/02 09Z 0.37 3112  66  45   5 0.00
Tue 06/02 10Z 0.39 3113  64  45   5 0.00
Tue 06/02 11Z 0.38 3215  62  41   5 0.00
Tue 06/02 12Z 0.35 3216  59  28   5 0.00
Tue 06/02 13Z 0.32 3216  55  20   6 0.00
Tue 06/02 14Z 0.36 3317  51  14   6 0.00
Tue 06/02 15Z 0.45 3317  50  10   6 0.00
Tue 06/02 16Z 1.94 3318  50   8   6 0.00
Tue 06/02 17Z 3.57 3318  51  12   6 0.00
Tue 06/02 18Z 4.69 3319  49  22   6 0.00
Tue 06/02 19Z 4.82 3318  52  34   6 0.00
Tue 06/02 20Z 4.41 3318  53  53   6 0.00
Tue 06/02 21Z 3.30 3318  52  67   6 0.00
Tue 06/02 22Z 1.83 3319  54  76   7 0.00
Tue 06/02 23Z 0.64 3421  52  68   7 0.00
Wed 06/03 00Z 0.52 3422  51  56   7 0.00
Wed 06/03 01Z 0.46 3422  49  39   7 0.00
Wed 06/03 02Z 0.23 3520  49  34   7 0.00
Wed 06/03 03Z 0.08 3518  47  27   8 0.00
Wed 06/03 04Z 0.08 3517  45  21   8 0.00
Wed 06/03 05Z 0.12 0015  44  12   8 0.00
Wed 06/03 06Z 0.13 3514  43  13   8 0.00
Wed 06/03 07Z 0.11 3514  44  17   8 0.00
Wed 06/03 08Z 0.09 3514  44  24   8 0.00
Wed 06/03 09Z 0.10 3513  44  34   8 0.00
Wed 06/03 10Z 0.12 3413  44  44   8 0.00
Wed 06/03 11Z 0.10 3512  44  53   8 0.00
Wed 06/03 12Z 0.12 3411  44  54   8 0.00
Wed 06/03 13Z 0.21 3310  45  65   8 0.00
Wed 06/03 14Z 0.34 3210  46  72   8 0.00
Wed 06/03 15Z 0.47 3210  47  76   9 0.00
Wed 06/03 16Z 1.02 3110  48  76   9 0.00
Wed 06/03 17Z 1.66 3111  47  74   9 0.00
Wed 06/03 18Z 1.56 3210  46  71  10 0.00
Wed 06/03 19Z 1.53 3110  48  66  10 0.00
Wed 06/03 20Z 1.46 3010  49  62  10 0.00
Wed 06/03 21Z 0.92 3011  51  59  11 0.00
Wed 06/03 22Z 0.61 3010  52  52  11 0.00
Wed 06/03 23Z 0.58 2911  54  44  11 0.00
Thu 06/04 00Z 0.57 2811  55  41  11 0.00
Thu 06/04 01Z 0.62 2811  56  36  11 0.00
Thu 06/04 02Z 0.67 2812  57  33  11 0.00
Thu 06/04 03Z 0.61 2912  57  34  11 0.00
Thu 06/04 04Z 0.49 3012  58  33  11 0.00
Thu 06/04 05Z 0.40 2911  55  33  11 0.00

Run total areal avg QPF for the greens is: 0.05 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