NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260527_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 05/27 00Z 1.47 2426  59  46  14 0.00
Wed 05/27 01Z 2.10 2431  59  55  14 0.00
Wed 05/27 02Z 1.87 2535  59  66  13 0.00
Wed 05/27 03Z 1.50 2537  55  66  14 0.00
Wed 05/27 04Z 1.44 2638  56  63  14 0.00
Wed 05/27 05Z 1.39 2637  61  61  14 0.00
Wed 05/27 06Z 1.25 2735  67  60  13 0.00
Wed 05/27 07Z 1.07 2833  70  53  13 0.01
Wed 05/27 08Z 0.98 2830  74  46  12 0.01
Wed 05/27 09Z 0.86 2926  83  41  12 0.00
Wed 05/27 10Z 0.74 2923  85  42  12 0.00
Wed 05/27 11Z 0.58 2920  84  43  12 0.00
Wed 05/27 12Z 0.50 2918  83  41  12 0.00
Wed 05/27 13Z 0.43 2916  79  40  11 0.00
Wed 05/27 14Z 0.43 2915  77  35  11 0.00
Wed 05/27 15Z 0.47 3014  78  35  11 0.00
Wed 05/27 16Z 0.69 3013  78  31  10 0.00
Wed 05/27 17Z 1.71 3012  80  27  10 0.00
Wed 05/27 18Z 2.22 3012  83  29   9 0.00
Wed 05/27 19Z 1.59 3013  86  28   9 0.01
Wed 05/27 20Z 1.14 3114  83  23   9 0.01
Wed 05/27 21Z 1.38 3215  81  22   9 0.00
Wed 05/27 22Z 1.06 3316  80  21   8 0.00
Wed 05/27 23Z 0.51 3317  82  26   8 0.00
Thu 05/28 00Z 0.30 3418  83  29   7 0.00
Thu 05/28 01Z 0.21 3420  86  35   7 0.00
Thu 05/28 02Z 0.12 3520  88  37   6 0.00
Thu 05/28 03Z 0.10 3520  90  46   6 0.00
Thu 05/28 04Z 0.08 0018  91  52   5 0.00
Thu 05/28 05Z 0.06 0018  90  50   5 0.00
Thu 05/28 06Z 0.05 0018  91  55   5 0.00
Thu 05/28 07Z 0.06 0018  92  57   5 0.00
Thu 05/28 08Z 0.05 0018  93  53   4 0.00
Thu 05/28 09Z 0.04 0019  93  56   4 0.00
Thu 05/28 10Z 0.03 0019  94  64   4 0.00
Thu 05/28 11Z 0.03 3519  95  72   4 0.00
Thu 05/28 12Z 0.04 3518  96  78   3 0.01
Thu 05/28 13Z 0.05 3517  96  78   3 0.01
Thu 05/28 14Z 0.06 3516  96  78   3 0.00
Thu 05/28 15Z 0.10 3516  96  76   3 0.00
Thu 05/28 16Z 0.20 3417  95  78   3 0.00
Thu 05/28 17Z 0.34 3419  94  73   3 0.00
Thu 05/28 18Z 0.53 3420  93  66   3 0.00
Thu 05/28 19Z 0.60 3420  92  56   2 0.00
Thu 05/28 20Z 0.48 3419  91  45   3 0.00
Thu 05/28 21Z 0.37 3419  90  43   3 0.00
Thu 05/28 22Z 0.42 3420  91  49   3 0.01
Thu 05/28 23Z 0.32 3422  94  57   3 0.01
Fri 05/29 00Z 0.30 3423  91  56   3 0.01
Fri 05/29 01Z 0.21 3423  85  41   3 0.00
Fri 05/29 02Z 0.24 3422  89  34   3 0.00
Fri 05/29 03Z 0.25 3421  93  33   3 0.01
Fri 05/29 04Z 0.25 3420  95  32   2 0.01
Fri 05/29 05Z 0.27 3318  96  34   2 0.01
Fri 05/29 06Z 0.29 3317  96  39   2 0.01
Fri 05/29 07Z 0.32 3316  94  44   2 0.00
Fri 05/29 08Z 0.35 3316  93  48   2 0.00
Fri 05/29 09Z 0.38 3215  91  56   2 0.00
Fri 05/29 10Z 0.41 3115  90  64   3 0.00
Fri 05/29 11Z 0.42 3115  90  68   3 0.00

Run total areal avg QPF for the greens is: 0.13 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