NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260525_1200
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 05/25 12Z 0.29 2414  99  93   8 0.00
Mon 05/25 13Z 0.37 2615  98  92   8 0.03
Mon 05/25 14Z 0.40 2717  98  88   8 0.02
Mon 05/25 15Z 0.36 2916  97  77   8 0.01
Mon 05/25 16Z 0.43 2918  97  71   8 0.01
Mon 05/25 17Z 0.49 3020  95  66   8 0.01
Mon 05/25 18Z 0.56 3020  93  50   8 0.00
Mon 05/25 19Z 0.64 2918  94  31   8 0.00
Mon 05/25 20Z 0.74 2918  96  19   8 0.01
Mon 05/25 21Z 0.68 2918  94  11   8 0.01
Mon 05/25 22Z 0.63 2918  89   7   9 0.01
Mon 05/25 23Z 0.57 2918  80   6   9 0.01
Tue 05/26 00Z 0.55 2919  71   5   9 0.00
Tue 05/26 01Z 0.57 2920  65   7   9 0.00
Tue 05/26 02Z 0.59 3021  63   9   9 0.00
Tue 05/26 03Z 0.63 3022  61  10   9 0.00
Tue 05/26 04Z 0.70 3123  65  13   9 0.00
Tue 05/26 05Z 0.81 3023  71  15   9 0.00
Tue 05/26 06Z 0.87 3023  71  18   9 0.00
Tue 05/26 07Z 0.76 3023  70  18   9 0.00
Tue 05/26 08Z 0.62 3023  72  19  10 0.00
Tue 05/26 09Z 0.54 3022  72  20  10 0.01
Tue 05/26 10Z 0.51 3122  74  20  10 0.01
Tue 05/26 11Z 0.47 3120  79  19  10 0.00
Tue 05/26 12Z 0.47 3019  79  20  10 0.00
Tue 05/26 13Z 0.45 3017  77  17  10 0.00
Tue 05/26 14Z 0.48 3015  75  29  11 0.00
Tue 05/26 15Z 0.59 2914  73  49  11 0.00
Tue 05/26 16Z 0.71 2813  70  60  11 0.00
Tue 05/26 17Z 0.98 2712  69  70  12 0.00
Tue 05/26 18Z 2.71 2613  73  61  12 0.00
Tue 05/26 19Z 4.31 2515  73  52  12 0.00
Tue 05/26 20Z 3.85 2417  71  40  12 0.00
Tue 05/26 21Z 3.15 2319  72  33  13 0.00
Tue 05/26 22Z 1.78 2321  69  31  13 0.00
Tue 05/26 23Z 1.30 2325  62  31  13 0.00
Wed 05/27 00Z 1.49 2428  60  29  13 0.00
Wed 05/27 01Z 1.57 2431  62  31  13 0.00
Wed 05/27 02Z 1.39 2532  62  35  13 0.00
Wed 05/27 03Z 1.22 2532  56  44  13 0.00
Wed 05/27 04Z 1.20 2633  54  58  13 0.00
Wed 05/27 05Z 1.23 2732  53  65  13 0.00
Wed 05/27 06Z 1.19 2730  59  60  12 0.00
Wed 05/27 07Z 1.06 2828  68  60  12 0.00
Wed 05/27 08Z 0.96 2826  72  61  11 0.00
Wed 05/27 09Z 0.87 2825  82  60  11 0.00
Wed 05/27 10Z 0.79 2824  86  60  11 0.00
Wed 05/27 11Z 0.70 2822  87  55  11 0.01
Wed 05/27 12Z 0.66 2820  88  55  10 0.01
Wed 05/27 13Z 0.59 2818  90  57  10 0.01
Wed 05/27 14Z 0.60 2817  91  46  10 0.01
Wed 05/27 15Z 0.67 2816  88  44  10 0.01
Wed 05/27 16Z 0.92 2815  89  45  10 0.01
Wed 05/27 17Z 1.66 2914  89  39  10 0.01
Wed 05/27 18Z 0.74 2913  90  39  10 0.01
Wed 05/27 19Z 0.64 3013  88  35  10 0.01
Wed 05/27 20Z 0.98 3113  87  32   9 0.01
Wed 05/27 21Z 0.89 3113  85  25   9 0.00
Wed 05/27 22Z 0.66 3214  84  19   9 0.00
Wed 05/27 23Z 0.43 3316  86  17   8 0.00

Run total areal avg QPF for the greens is: 0.24 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