NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260516_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)
=== ===== === ==== ==== === === === ====
Sat 05/16 06Z 0.43 2612  89  54   5 0.00
Sat 05/16 07Z 0.54 2615  87  34   5 0.00
Sat 05/16 08Z 0.56 2715  83  11   5 0.00
Sat 05/16 09Z 0.57 2716  76   3   5 0.00
Sat 05/16 10Z 0.60 2716  73   7   5 0.00
Sat 05/16 11Z 0.68 2718  72  18   5 0.00
Sat 05/16 12Z 0.74 2620  69  36   5 0.00
Sat 05/16 13Z 0.74 2620  64  74   5 0.00
Sat 05/16 14Z 0.77 2519  57  56   6 0.00
Sat 05/16 15Z 0.81 2418  54  48   6 0.00
Sat 05/16 16Z 0.85 2416  51  54   7 0.00
Sat 05/16 17Z 1.01 2314  50  39   8 0.00
Sat 05/16 18Z 1.33 2215  51  26   9 0.00
Sat 05/16 19Z 2.93 2216  58  28   9 0.00
Sat 05/16 20Z 3.72 2118  69  24   9 0.00
Sat 05/16 21Z 2.11 2120  75  15   9 0.00
Sat 05/16 22Z 0.93 2122  73  11  10 0.00
Sat 05/16 23Z 0.75 2126  75  11  10 0.00
Sun 05/17 00Z 0.79 2130  74  81  11 0.00
Sun 05/17 01Z 1.03 2236  84  88  10 0.03
Sun 05/17 02Z 1.12 2340  89  74  10 0.01
Sun 05/17 03Z 1.20 2439  94  75  10 0.03
Sun 05/17 04Z 1.20 2636  96  49  10 0.05
Sun 05/17 05Z 1.13 2733  98  20   9 0.03
Sun 05/17 06Z 1.05 2831  94   3   9 0.01
Sun 05/17 07Z 0.83 2931  77   4   9 0.01
Sun 05/17 08Z 0.81 2932  69   5   9 0.01
Sun 05/17 09Z 0.87 2934  66   8   8 0.00
Sun 05/17 10Z 0.85 2935  57   8   8 0.00
Sun 05/17 11Z 0.78 2934  58  31   8 0.00
Sun 05/17 12Z 0.76 3032  62  31   7 0.00
Sun 05/17 13Z 0.77 3030  62  62   7 0.00
Sun 05/17 14Z 0.96 3030  66  70   6 0.00
Sun 05/17 15Z 1.38 2928  73  66   6 0.00
Sun 05/17 16Z 2.78 2926  77  64   6 0.00
Sun 05/17 17Z 4.26 2925  80  56   5 0.00
Sun 05/17 18Z 4.36 2923  80  35   5 0.00
Sun 05/17 19Z 4.67 2922  80  32   5 0.00
Sun 05/17 20Z 4.10 2919  80  28   6 0.00
Sun 05/17 21Z 3.32 2918  82  26   6 0.00
Sun 05/17 22Z 1.02 3017  80  21   6 0.00
Sun 05/17 23Z 0.74 3017  79  18   6 0.00
Mon 05/18 00Z 0.64 3017  78  14   6 0.00
Mon 05/18 01Z 0.56 3118  76  11   6 0.00
Mon 05/18 02Z 0.45 3118  71  11   7 0.00
Mon 05/18 03Z 0.37 3016  66  12   7 0.00
Mon 05/18 04Z 0.32 3014  61  15   7 0.00
Mon 05/18 05Z 0.26 3012  57  22   8 0.00
Mon 05/18 06Z 0.23 2910  50  39   9 0.00
Mon 05/18 07Z 0.22 2810  46  23   9 0.00
Mon 05/18 08Z 0.23 2810  45  27  10 0.00
Mon 05/18 09Z 0.21 2809  43  28  10 0.00
Mon 05/18 10Z 0.17 2707  41  30  11 0.00
Mon 05/18 11Z 0.15 2507  37  30  12 0.00
Mon 05/18 12Z 0.20 2310  40  35  12 0.00
Mon 05/18 13Z 0.25 2313  53  42  12 0.00
Mon 05/18 14Z 0.27 2217  70  48  12 0.00
Mon 05/18 15Z 0.36 2221  82  55  12 0.00
Mon 05/18 16Z 0.43 2223  91  57  12 0.00
Mon 05/18 17Z 0.47 2321  91  43  13 0.00

Run total areal avg QPF for the greens is: 0.18 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