NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261031_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)
=== ===== === ==== ==== === === === ====
Sat 10/31 18Z 0.90 2913  87  20  -4 0.00
Sat 10/31 19Z 1.02 2915  87  15  -4 0.00
Sat 10/31 20Z 0.96 2915  88  15  -4 0.00
Sat 10/31 21Z 0.92 2916  90  21  -4 0.00
Sat 10/31 22Z 1.01 2817  91  23  -4 0.00
Sat 10/31 23Z 1.15 2920  91  21  -4 0.00
Sun 11/01 00Z 1.09 2922  90  29  -4 0.00
Sun 11/01 01Z 1.04 3023  91  31  -4 0.00
Sun 11/01 02Z 0.92 3124  91  26  -4 0.00
Sun 11/01 03Z 0.74 3122  90  19  -4 0.00
Sun 11/01 04Z 0.65 3121  88  12  -4 0.00
Sun 11/01 05Z 0.60 3021  87  11  -3 0.00
Sun 11/01 06Z 0.51 3020  83  12  -2 0.00
Sun 11/01 07Z 0.45 3121  79  13  -1 0.00
Sun 11/01 08Z 0.41 3121  75  14  -1 0.00
Sun 11/01 09Z 0.37 3121  71  13   0 0.00
Sun 11/01 10Z 0.35 3121  64  13   0 0.00
Sun 11/01 11Z 0.35 3122  57  13   0 0.00
Sun 11/01 12Z 0.38 3123  50  13   1 0.00
Sun 11/01 13Z 0.45 3125  50  13   1 0.00
Sun 11/01 14Z 0.54 3028  64  10   1 0.00
Sun 11/01 15Z 0.60 3029  78   8   1 0.00
Sun 11/01 16Z 0.59 3028  79   8   1 0.00
Sun 11/01 17Z 0.58 3027  74  11   2 0.00
Sun 11/01 18Z 0.58 3026  73  16   3 0.00
Sun 11/01 19Z 0.62 2925  72  21   3 0.00
Sun 11/01 20Z 0.67 2926  70  22   3 0.00
Sun 11/01 21Z 0.71 2927  66  22   4 0.00
Sun 11/01 22Z 0.76 2927  60  22   4 0.00
Sun 11/01 23Z 0.76 2927  58  22   4 0.00
Mon 11/02 00Z 0.77 2927  56  23   4 0.00
Mon 11/02 01Z 0.81 2927  53  27   5 0.00
Mon 11/02 02Z 0.88 2828  50  26   5 0.00
Mon 11/02 03Z 0.91 2827  54  40   5 0.00
Mon 11/02 04Z 1.02 2828  59  70   4 0.00
Mon 11/02 05Z 1.05 2828  59  80   5 0.00
Mon 11/02 06Z 1.08 2829  51  82   5 0.00
Mon 11/02 07Z 1.09 2829  50  84   6 0.00
Mon 11/02 08Z 1.07 2829  47  84   6 0.00
Mon 11/02 09Z 1.03 2829  46  84   6 0.00
Mon 11/02 10Z 0.99 2829  44  85   6 0.00
Mon 11/02 11Z 0.92 2828  45  85   6 0.00
Mon 11/02 12Z 0.84 2827  47  87   7 0.00
Mon 11/02 13Z 0.77 2825  49  87   7 0.00
Mon 11/02 14Z 0.71 2723  50  81   7 0.00
Mon 11/02 15Z 0.70 2723  52  81   7 0.00
Mon 11/02 16Z 0.69 2723  60  83   7 0.00
Mon 11/02 17Z 0.67 2722  68  81   7 0.00
Mon 11/02 18Z 0.62 2820  71  77   7 0.00
Mon 11/02 19Z 0.57 2818  71  76   7 0.00
Mon 11/02 20Z 0.62 2819  73  80   7 0.00
Mon 11/02 21Z 0.64 2820  76  76   7 0.00
Mon 11/02 22Z 0.66 2820  81  78   7 0.00
Mon 11/02 23Z 0.65 2820  82  81   7 0.00
Tue 11/03 00Z 0.56 2819  79  75   8 0.00
Tue 11/03 01Z 0.54 2719  77  73   8 0.00
Tue 11/03 02Z 0.56 2820  76  71   8 0.00
Tue 11/03 03Z 0.55 2820  75  72   9 0.00
Tue 11/03 04Z 0.54 2820  72  75   9 0.00
Tue 11/03 05Z 0.53 2819  71  83   9 0.00

Run total areal avg QPF for the greens is: 0.00 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