NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260722_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)
=== ===== === ==== ==== === === === ====
Wed 07/22 00Z 0.23 1626  95  78  14 0.00
Wed 07/22 01Z 0.23 1631  92  86  15 0.01
Wed 07/22 02Z 0.10 1730  90  90  15 0.02
Wed 07/22 03Z 0.07 1830  93  90  15 0.04
Wed 07/22 04Z 0.16 1926  93  84  15 0.03
Wed 07/22 05Z 0.30 2025  96  83  15 0.10
Wed 07/22 06Z 0.45 2124  96  74  14 0.02
Wed 07/22 07Z 0.64 2325  96  81  14 0.01
Wed 07/22 08Z 0.70 2423  98  83  14 0.03
Wed 07/22 09Z 0.66 2420  96  74  13 0.02
Wed 07/22 10Z 0.59 2418  95  70  13 0.01
Wed 07/22 11Z 0.53 2418  93  70  14 0.01
Wed 07/22 12Z 0.52 2418  90  76  14 0.01
Wed 07/22 13Z 0.57 2419  89  85  14 0.01
Wed 07/22 14Z 0.65 2420  90  82  13 0.03
Wed 07/22 15Z 1.05 2421  87  68  13 0.01
Wed 07/22 16Z 1.36 2421  93  55  13 0.01
Wed 07/22 17Z 1.57 2524  90  49  12 0.08
Wed 07/22 18Z 4.93 2523  80  23  11 0.01
Wed 07/22 19Z 7.44 2522  78   5  10 0.00
Wed 07/22 20Z 10.64 2621  82  18   9 0.00
Wed 07/22 21Z 8.07 2622  85  28   9 0.00
Wed 07/22 22Z 3.87 2622  86  36   8 0.00
Wed 07/22 23Z 1.76 2722  85  38   8 0.00
Thu 07/23 00Z 1.29 2624  91  39   7 0.00
Thu 07/23 01Z 1.16 2725  92  40   7 0.01
Thu 07/23 02Z 1.08 2826  94  38   7 0.00
Thu 07/23 03Z 1.05 2927  93  35   6 0.00
Thu 07/23 04Z 0.91 2926  93  31   6 0.00
Thu 07/23 05Z 0.89 2926  93  30   5 0.00
Thu 07/23 06Z 0.83 3026  92  30   5 0.00
Thu 07/23 07Z 0.76 3025  87  29   5 0.00
Thu 07/23 08Z 0.70 3126  82  26   5 0.00
Thu 07/23 09Z 0.62 3124  74  32   5 0.00
Thu 07/23 10Z 0.61 3122  71  29   5 0.00
Thu 07/23 11Z 0.70 3020  74  21   5 0.00
Thu 07/23 12Z 0.81 2920  76  29   5 0.00
Thu 07/23 13Z 1.06 2820  80  37   5 0.00
Thu 07/23 14Z 1.45 2819  80  45   5 0.00
Thu 07/23 15Z 3.25 2818  81  59   5 0.00
Thu 07/23 16Z 6.16 2715  82  60   6 0.00
Thu 07/23 17Z 6.49 2714  81  41   6 0.00
Thu 07/23 18Z 6.95 2714  78  33   7 0.00
Thu 07/23 19Z 7.58 2714  73  21   8 0.00
Thu 07/23 20Z 7.54 2713  71  14   8 0.00
Thu 07/23 21Z 7.07 2712  71  13   8 0.00
Thu 07/23 22Z 4.35 2711  73  20   9 0.00
Thu 07/23 23Z 1.90 2710  73  23   9 0.00
Fri 07/24 00Z 1.38 2611  72  26   9 0.00
Fri 07/24 01Z 1.37 2611  72  25   9 0.00
Fri 07/24 02Z 1.66 2712  73  25   9 0.00
Fri 07/24 03Z 1.17 2711  72  26   9 0.00
Fri 07/24 04Z 0.87 2711  72  23   9 0.00
Fri 07/24 05Z 0.68 2810  71  23   9 0.00
Fri 07/24 06Z 0.58 2809  71  22   9 0.00
Fri 07/24 07Z 0.48 2707  70  21   9 0.00
Fri 07/24 08Z 0.41 2606  70  21   9 0.00
Fri 07/24 09Z 0.37 2506  69  22   9 0.00
Fri 07/24 10Z 0.34 2406  69  21   9 0.00
Fri 07/24 11Z 0.34 2406  70  18   8 0.00

Run total areal avg QPF for the greens is: 0.47 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