NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260412_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 04/12 06Z 0.36 3319  70  15  -5 0.00
Sun 04/12 07Z 0.39 3319  69  20  -5 0.00
Sun 04/12 08Z 0.34 3317  67  23  -5 0.00
Sun 04/12 09Z 0.26 3315  64  21  -5 0.00
Sun 04/12 10Z 0.20 3312  62  24  -4 0.00
Sun 04/12 11Z 0.16 3309  60  24  -4 0.00
Sun 04/12 12Z 0.13 3206  58  25  -3 0.00
Sun 04/12 13Z 0.12 2903  57  24  -3 0.00
Sun 04/12 14Z 0.12 2403  56  25  -3 0.00
Sun 04/12 15Z 0.17 2105  56  27  -3 0.00
Sun 04/12 16Z 0.41 2005  56  31  -2 0.00
Sun 04/12 17Z 0.61 2007  56  35  -2 0.00
Sun 04/12 18Z 0.48 1909  53  45  -1 0.00
Sun 04/12 19Z 0.34 1911  52  89   0 0.00
Sun 04/12 20Z 0.28 1913  52  93   0 0.00
Sun 04/12 21Z 0.32 1915  60  95   0 0.00
Sun 04/12 22Z 0.33 1918  65  98   0 0.00
Sun 04/12 23Z 0.33 2021  85  98   0 0.02
Mon 04/13 00Z 0.30 2023  93  98   0 0.03
Mon 04/13 01Z 0.30 2027  94  99   1 0.04
Mon 04/13 02Z 0.37 2130  96  99   2 0.05
Mon 04/13 03Z 0.44 2132  96  99   3 0.07
Mon 04/13 04Z 0.43 2233  97  99   5 0.09
Mon 04/13 06Z 0.50 2237  94  97   8 0.09
Mon 04/13 07Z 0.54 2339  89  95   9 0.09
Mon 04/13 08Z 0.57 2339  85  88  10 0.03
Mon 04/13 09Z 0.60 2440  84  68  10 0.01
Mon 04/13 10Z 0.66 2441  89  90  10 0.01
Mon 04/13 11Z 0.68 2439  93  84   9 0.02
Mon 04/13 12Z 0.74 2540  93  77   9 0.06
Mon 04/13 13Z 0.83 2542  94  75   8 0.02
Mon 04/13 14Z 0.78 2537  88  76   9 0.02
Mon 04/13 15Z 0.77 2436  90  92   8 0.01
Mon 04/13 16Z 0.76 2335  96  96   8 0.01
Mon 04/13 17Z 0.88 2338  97  97   8 0.05
Mon 04/13 18Z 0.89 2340  97  98   9 0.09
Mon 04/13 19Z 0.98 2440  98  98   8 0.12
Mon 04/13 20Z 1.03 2539  98  97   8 0.11
Mon 04/13 21Z 1.03 2637  98  90   8 0.09
Mon 04/13 22Z 1.03 2635  98  70   8 0.05
Mon 04/13 23Z 1.05 2735  98  62   8 0.03
Tue 04/14 00Z 1.15 2737  98  66   8 0.03
Tue 04/14 01Z 1.17 2738  98  74   9 0.06
Tue 04/14 02Z 1.22 2837  98  77   8 0.06
Tue 04/14 03Z 1.24 2836  97  58   7 0.03
Tue 04/14 04Z 1.17 2834  98  45   7 0.03
Tue 04/14 05Z 1.10 2932  98  47   6 0.03
Tue 04/14 06Z 0.93 2929  97  41   6 0.04
Tue 04/14 07Z 0.75 3026  96  41   6 0.04
Tue 04/14 08Z 0.57 3023  95  37   6 0.03
Tue 04/14 09Z 0.46 3021  93  34   7 0.02
Tue 04/14 10Z 0.38 2918  90  22   7 0.02
Tue 04/14 11Z 0.32 2916  86  22   8 0.01
Tue 04/14 12Z 0.32 2815  85  31   8 0.01
Tue 04/14 13Z 0.27 2713  82  46   9 0.01
Tue 04/14 14Z 0.26 2612  81  54   9 0.01
Tue 04/14 15Z 0.25 2512  79  55   9 0.01
Tue 04/14 16Z 0.26 2413  77  56  10 0.00
Tue 04/14 17Z 0.30 2315  73  46  11 0.00

Run total areal avg QPF for the greens is: 1.65 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