NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260301_0000
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 03/01 00Z 1.01 2720  74  20  -3 0.00
Sun 03/01 01Z 0.81 2820  72  27  -3 0.00
Sun 03/01 04Z 0.31 3014  58  51  -5 0.00
Sun 03/01 05Z 0.24 3012  60  77  -6 0.00
Sun 03/01 06Z 0.24 3012  63  81  -7 0.00
Sun 03/01 07Z 0.30 3015  67  89  -8 0.00
Sun 03/01 08Z 0.25 3014  63  92  -8 0.00
Sun 03/01 09Z 0.23 3113  70  84  -9 0.00
Sun 03/01 10Z 0.21 3114  79  86 -11 0.00
Sun 03/01 11Z 0.19 3214  84  88 -12 0.00
Sun 03/01 12Z 0.21 3215  85  86 -14 0.00
Sun 03/01 13Z 0.23 3216  82  83 -14 0.00
Sun 03/01 14Z 0.29 3216  80  73 -15 0.01
Sun 03/01 15Z 0.31 3116  73  63 -15 0.00
Sun 03/01 16Z 0.36 3117  63  41 -16 0.00
Sun 03/01 17Z 0.42 3117  58  33 -17 0.00
Sun 03/01 18Z 0.45 3117  57  35 -17 0.00
Sun 03/01 19Z 0.62 3118  65  36 -18 0.00
Sun 03/01 20Z 0.66 3119  70  34 -18 0.00
Sun 03/01 21Z 0.69 3119  73  29 -19 0.00
Sun 03/01 22Z 0.68 3120  77  27 -19 0.00
Sun 03/01 23Z 0.64 3121  72  23 -20 0.00
Mon 03/02 00Z 0.55 3121  66  20 -20 0.00
Mon 03/02 02Z 0.40 3122  55  16 -20 0.00
Mon 03/02 03Z 0.37 3121  51  15 -20 0.00
Mon 03/02 04Z 0.35 3121  50  13 -20 0.00
Mon 03/02 05Z 0.34 3120  48  12 -20 0.00
Mon 03/02 06Z 0.32 3119  46  11 -20 0.00
Mon 03/02 07Z 0.31 3119  45  12 -20 0.00
Mon 03/02 08Z 0.30 3119  44  13 -20 0.00
Mon 03/02 09Z 0.31 3118  45  15 -20 0.00
Mon 03/02 10Z 0.31 3118  43  16 -20 0.00
Mon 03/02 11Z 0.34 3119  42  18 -20 0.00
Mon 03/02 12Z 0.33 3018  40  14 -20 0.00
Mon 03/02 13Z 0.35 3018  40  14 -20 0.00
Mon 03/02 14Z 0.34 3017  41  15 -20 0.00
Mon 03/02 15Z 0.37 2916  43  16 -20 0.00
Mon 03/02 16Z 0.34 2913  42  14 -19 0.00
Mon 03/02 17Z 0.35 2912  40  14 -18 0.00
Mon 03/02 18Z 0.36 2812  39  19 -18 0.00
Mon 03/02 19Z 0.39 2712  44  19 -17 0.00
Mon 03/02 20Z 0.39 2612  49  24 -16 0.00
Mon 03/02 21Z 0.38 2513  49  27 -15 0.00
Mon 03/02 22Z 0.36 2514  43  34 -14 0.00
Mon 03/02 23Z 0.38 2416  36  43 -12 0.00
Tue 03/03 00Z 0.38 2418  30  52 -11 0.00
Tue 03/03 01Z 0.40 2321  28  50 -10 0.00
Tue 03/03 02Z 0.45 2324  29  54 -10 0.00
Tue 03/03 03Z 0.50 2327  30  54  -9 0.00
Tue 03/03 04Z 0.53 2429  31  49  -8 0.00
Tue 03/03 05Z 0.55 2431  31  45  -7 0.00
Tue 03/03 06Z 0.57 2432  32  41  -6 0.00
Tue 03/03 07Z 0.58 2431  28  41  -6 0.00
Tue 03/03 08Z 0.57 2431  28  37  -5 0.00
Tue 03/03 09Z 0.55 2529  35  34  -5 0.00
Tue 03/03 10Z 0.52 2528  41  29  -4 0.00
Tue 03/03 11Z 0.50 2527  43  26  -4 0.00

Run total areal avg QPF for the greens is: 0.01 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