NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260524_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 05/24 00Z 0.40 1413  72   7   4 0.00
Sun 05/24 01Z 0.39 1416  71   9   4 0.00
Sun 05/24 02Z 0.38 1419  66  14   5 0.00
Sun 05/24 03Z 0.34 1421  59  27   5 0.00
Sun 05/24 04Z 0.33 1422  57  46   5 0.00
Sun 05/24 05Z 0.34 1523  56  56   5 0.00
Sun 05/24 06Z 0.40 1426  56  68   5 0.01
Sun 05/24 07Z 0.41 1428  61  83   5 0.01
Sun 05/24 08Z 0.36 1528  66  84   5 0.01
Sun 05/24 09Z 0.36 1430  67  85   6 0.01
Sun 05/24 10Z 0.34 1531  73  89   6 0.03
Sun 05/24 11Z 0.31 1531  82  96   6 0.06
Sun 05/24 12Z 0.34 1533  88  98   6 0.06
Sun 05/24 13Z 0.36 1535  91  99   5 0.05
Sun 05/24 14Z 0.32 1535  91  99   5 0.05
Sun 05/24 15Z 0.29 1535  92  98   5 0.05
Sun 05/24 16Z 0.28 1535  93  97   5 0.03
Sun 05/24 17Z 0.27 1535  94  98   5 0.03
Sun 05/24 18Z 0.25 1534  94  98   5 0.03
Sun 05/24 19Z 0.22 1635  95  98   5 0.03
Sun 05/24 20Z 0.20 1635  94  97   6 0.04
Sun 05/24 21Z 0.18 1635  95  97   6 0.03
Sun 05/24 22Z 0.15 1635  95  96   6 0.04
Sun 05/24 23Z 0.12 1634  95  97   7 0.04
Mon 05/25 00Z 0.11 1634  95  89   8 0.02
Mon 05/25 01Z 0.10 1734  95  87   8 0.01
Mon 05/25 02Z 0.09 1733  95  90   8 0.02
Mon 05/25 03Z 0.07 1732  96  91   9 0.02
Mon 05/25 04Z 0.04 1730  96  91  10 0.03
Mon 05/25 05Z 0.03 1728  96  91  11 0.02
Mon 05/25 06Z 0.05 1827  96  89  11 0.02
Mon 05/25 07Z 0.08 1828  97  89  12 0.02
Mon 05/25 08Z 0.12 1928  97  90  12 0.04
Mon 05/25 09Z 0.14 1928  98  91  12 0.06
Mon 05/25 10Z 0.16 1928  99  97  11 0.13
Mon 05/25 11Z 0.28 2029  99  95  10 0.32
Mon 05/25 12Z 0.39 2226  99  97   9 0.20
Mon 05/25 13Z 0.39 2419  98  92   9 0.12
Mon 05/25 14Z 0.37 2616  98  90   9 0.05
Mon 05/25 15Z 0.29 2814  96  82  10 0.02
Mon 05/25 16Z 0.31 2916  95  81  10 0.00
Mon 05/25 17Z 0.33 2916  94  76  10 0.00
Mon 05/25 18Z 0.39 2917  93  62   9 0.00
Mon 05/25 19Z 0.49 2918  92  43   9 0.00
Mon 05/25 20Z 0.59 2819  94  11   9 0.00
Mon 05/25 21Z 0.64 2819  96   7   9 0.01
Mon 05/25 22Z 0.64 2820  92  16   9 0.01
Mon 05/25 23Z 0.62 2921  81  16   9 0.01
Tue 05/26 00Z 0.56 3021  73  17   9 0.00
Tue 05/26 01Z 0.60 2922  71   9   9 0.00
Tue 05/26 02Z 0.59 3022  73   6   9 0.00
Tue 05/26 03Z 0.59 3124  75   6   8 0.00
Tue 05/26 04Z 0.63 3022  80   6   8 0.00
Tue 05/26 05Z 0.79 2922  84   7   8 0.00
Tue 05/26 06Z 0.77 2922  81   9   8 0.00
Tue 05/26 07Z 0.80 2921  76  13   9 0.00
Tue 05/26 08Z 0.64 2921  72  13   9 0.00
Tue 05/26 09Z 0.54 3022  64  17  10 0.00
Tue 05/26 10Z 0.47 3022  53  17  10 0.00
Tue 05/26 11Z 0.49 3022  51  18  10 0.00

Run total areal avg QPF for the greens is: 1.74 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