NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20240630_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)
=== ===== === ==== ==== === === === ====
Sun 06/30 06Z 0.71 2329  98  89  16 0.00
Sun 06/30 07Z 0.85 2331  97  77  16 0.13
Sun 06/30 08Z 0.92 2431  98  73  16 0.07
Sun 06/30 09Z 0.91 2530  96  61  16 0.04
Sun 06/30 10Z 0.81 2528  89  58  16 0.05
Sun 06/30 11Z 0.83 2528  91  42  16 0.01
Sun 06/30 12Z 0.80 2526  91  40  16 0.02
Sun 06/30 13Z 0.77 2524  91  38  16 0.01
Sun 06/30 14Z 0.76 2522  90  44  16 0.01
Sun 06/30 15Z 0.81 2422  89  53  16 0.00
Sun 06/30 16Z 1.12 2525  93  60  15 0.12
Sun 06/30 17Z 1.36 2527  92  47  15 0.07
Sun 06/30 18Z 2.00 2623  86  41  15 0.06
Sun 06/30 19Z 2.46 2622  86  28  15 0.04
Sun 06/30 20Z 2.94 2721  88  38  14 0.02
Sun 06/30 21Z 4.10 2820  81  34  13 0.03
Sun 06/30 22Z 3.82 2920  81  35  13 0.01
Sun 06/30 23Z 1.71 2916  82  44  12 0.02
Mon 07/01 00Z 0.86 3116  86  52  11 0.01
Mon 07/01 01Z 0.46 3218  93  62  11 0.03
Mon 07/01 02Z 0.26 3320  95  66  10 0.02
Mon 07/01 03Z 0.21 3421  97  77  10 0.02
Mon 07/01 04Z 0.18 3422  97  69   9 0.02
Mon 07/01 05Z 0.18 3421  97  65   8 0.02
Mon 07/01 06Z 0.18 3421  97  63   8 0.01
Mon 07/01 07Z 0.16 3422  96  60   7 0.01
Mon 07/01 08Z 0.13 3524  96  48   7 0.01
Mon 07/01 09Z 0.09 3524  96  51   6 0.01
Mon 07/01 10Z 0.10 0023  94  60   6 0.01
Mon 07/01 11Z 0.13 0022  94  67   6 0.01
Mon 07/01 12Z 0.12 0121  92  71   7 0.00
Mon 07/01 13Z 0.11 0118  94  72   7 0.00
Mon 07/01 14Z 0.09 0016  94  76   7 0.00
Mon 07/01 15Z 0.04 3515  91  74   7 0.00
Mon 07/01 16Z 0.37 3415  90  71   7 0.00
Mon 07/01 17Z 1.06 3416  89  62   7 0.00
Mon 07/01 18Z 1.58 3416  85  52   7 0.00
Mon 07/01 19Z 1.50 3417  81  41   7 0.00
Mon 07/01 20Z 1.06 3418  79  29   8 0.00
Mon 07/01 21Z 0.50 3518  76  25   8 0.00
Mon 07/01 22Z 0.19 3517  74  23   8 0.00
Mon 07/01 23Z 0.09 3517  72  23   8 0.00
Tue 07/02 00Z 0.05 0018  68  21   9 0.00
Tue 07/02 01Z 0.11 0018  64  22   9 0.00
Tue 07/02 02Z 0.19 0118  62  23   9 0.00
Tue 07/02 03Z 0.26 0117  60  22   9 0.00
Tue 07/02 04Z 0.30 0216  59  20   9 0.00
Tue 07/02 05Z 0.32 0214  58  19   9 0.00
Tue 07/02 06Z 0.32 0313  57  20   9 0.00
Tue 07/02 07Z 0.33 0312  57  22   9 0.00
Tue 07/02 08Z 0.41 0313  56  22   9 0.00
Tue 07/02 09Z 0.44 0413  55  21   9 0.00
Tue 07/02 10Z 0.47 0412  55  20   9 0.00
Tue 07/02 11Z 0.46 0511  52  15  10 0.00
Tue 07/02 12Z 0.44 0610  51  14  10 0.00
Tue 07/02 13Z 0.47 0708  51  13  10 0.00
Tue 07/02 14Z 0.72 0805  55  14  10 0.00
Tue 07/02 15Z 1.21 1003  57  14  10 0.00
Tue 07/02 16Z 1.24 1103  57  13  10 0.00
Tue 07/02 17Z 0.92 1202  56  12  11 0.00

Run total areal avg QPF for the greens is: 0.89 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