Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261014_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)
=== ===== === ==== ==== === === === ====
Wed 10/14 18Z 0.69 2820  97  83   6 0.00
Wed 10/14 19Z 0.73 2822  97  75   6 0.01
Wed 10/14 20Z 0.77 2823  97  75   6 0.02
Wed 10/14 21Z 0.83 2925  97  74   5 0.02
Wed 10/14 22Z 0.85 2927  97  71   5 0.02
Wed 10/14 23Z 0.85 3028  97  57   4 0.02
Thu 10/15 00Z 0.81 3028  97  36   3 0.02
Thu 10/15 01Z 0.76 3128  96  29   3 0.02
Thu 10/15 02Z 0.70 3130  96  17   2 0.02
Thu 10/15 03Z 0.65 3130  95   3   2 0.01
Thu 10/15 04Z 0.58 3230  95   1   2 0.02
Thu 10/15 05Z 0.54 3230  93   2   2 0.01
Thu 10/15 06Z 0.48 3231  92   3   1 0.02
Thu 10/15 07Z 0.41 3330  90   1   1 0.01
Thu 10/15 08Z 0.34 3330  84   1   0 0.01
Thu 10/15 09Z 0.27 3329  78   1   0 0.01
Thu 10/15 10Z 0.19 3427  72   2   1 0.01
Thu 10/15 11Z 0.13 3426  67   2   1 0.01
Thu 10/15 12Z 0.09 3525  64   2   1 0.01
Thu 10/15 13Z 0.06 3523  61   2   0 0.00
Thu 10/15 14Z 0.06 3521  61   2   0 0.00
Thu 10/15 15Z 0.05 3518  58   3   1 0.00
Thu 10/15 16Z 0.05 3515  55   3   1 0.00
Thu 10/15 17Z 0.03 3513  52   3   2 0.00
Thu 10/15 18Z 0.02 3511  49   4   2 0.00
Thu 10/15 19Z 0.03 3509  49   4   3 0.00
Thu 10/15 20Z 0.02 3507  48   4   3 0.00
Thu 10/15 21Z 0.03 3405  47   5   4 0.00
Thu 10/15 22Z 0.05 3304  45   4   4 0.00
Thu 10/15 23Z 0.02 3402  36   4   4 0.00
Fri 10/16 00Z 0.02 3301  32   4   5 0.00
Fri 10/16 01Z 0.02 1501  31   5   5 0.00
Fri 10/16 02Z 0.04 1506  31   6   6 0.00
Fri 10/16 03Z 0.02 1709  32   6   5 0.00
Fri 10/16 04Z 0.03 1813  34   5   6 0.00
Fri 10/16 05Z 0.05 1817  37   4   6 0.00
Fri 10/16 06Z 0.08 1920  42  10   5 0.00
Fri 10/16 07Z 0.06 1824  43  39   5 0.00
Fri 10/16 08Z 0.10 1829  44  56   5 0.00
Fri 10/16 09Z 0.11 1833  46  77   5 0.00
Fri 10/16 10Z 0.12 1835  55  94   4 0.00
Fri 10/16 11Z 0.10 1835  86  99   4 0.04
Fri 10/16 12Z 0.13 1840  97  97   5 0.10
Fri 10/16 13Z 0.20 1942  98  95   5 0.25
Fri 10/16 14Z 0.26 1943  98  95   7 0.17
Fri 10/16 15Z 0.33 2042  98  95   9 0.08
Fri 10/16 16Z 0.36 2040  98  92  11 0.11
Fri 10/16 17Z 0.41 2139  98  93  12 0.10
Fri 10/16 18Z 0.46 2236  98  91  13 0.15
Fri 10/16 19Z 0.50 2234  97  84  13 0.04
Fri 10/16 20Z 0.59 2335  97  89  13 0.02
Fri 10/16 21Z 0.70 2334  95  93  13 0.03
Fri 10/16 22Z 0.83 2436  95  65  12 0.03
Fri 10/16 23Z 1.07 2437  97  52  11 0.03
Sat 10/17 00Z 1.24 2533  98  41   9 0.06
Sat 10/17 01Z 1.10 2732  96  41   6 0.06
Sat 10/17 02Z 0.81 2829  95  49   4 0.03
Sat 10/17 03Z 0.70 2927  96  45   1 0.02
Sat 10/17 04Z 0.66 2927  96  42   0 0.01
Sat 10/17 05Z 0.62 3026  96  38  -1 0.01

Run total areal avg QPF for the greens is: 1.61 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