Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261015_0600
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Thu 10/15 06Z 0.22 3326  99   2   2 0.00
Thu 10/15 07Z 0.30 3329  98   3   1 0.01
Thu 10/15 08Z 0.28 3329  96   2   1 0.01
Thu 10/15 09Z 0.24 3329  94   1   1 0.01
Thu 10/15 10Z 0.13 3328  83   1   2 0.01
Thu 10/15 11Z 0.05 3427  65   2   3 0.01
Thu 10/15 12Z 0.02 3525  55   2   3 0.00
Thu 10/15 13Z 0.03 3523  51   2   3 0.00
Thu 10/15 14Z 0.02 3521  48   2   3 0.00
Thu 10/15 15Z 0.02 3517  47   2   4 0.00
Thu 10/15 16Z 0.02 3514  46   2   4 0.00
Thu 10/15 17Z 0.04 3511  46   3   4 0.00
Thu 10/15 18Z 0.04 0008  46   4   4 0.00
Thu 10/15 19Z 0.03 0006  46   4   4 0.00
Thu 10/15 20Z 0.02 3504  47   5   4 0.00
Thu 10/15 21Z 0.02 3303  47   5   4 0.00
Thu 10/15 22Z 0.01 3402  43   5   5 0.00
Thu 10/15 23Z 0.01 1200  40   7   5 0.00
Fri 10/16 00Z 0.02 1702  38   4   5 0.00
Fri 10/16 01Z 0.03 1707  40   7   5 0.00
Fri 10/16 02Z 0.06 1811  42   5   5 0.00
Fri 10/16 03Z 0.11 1914  46   5   5 0.00
Fri 10/16 04Z 0.14 1917  53   6   5 0.00
Fri 10/16 05Z 0.13 1819  54  11   5 0.00
Fri 10/16 06Z 0.14 1822  56  30   5 0.00
Fri 10/16 07Z 0.16 1823  62  56   5 0.00
Fri 10/16 08Z 0.14 1825  66  79   5 0.00
Fri 10/16 09Z 0.14 1830  70  93   4 0.01
Fri 10/16 10Z 0.16 1834  85  99   4 0.02
Fri 10/16 11Z 0.17 1836  96  99   6 0.12
Fri 10/16 12Z 0.24 1839  97  98   7 0.06
Fri 10/16 13Z 0.32 1941  98  98   7 0.18
Fri 10/16 14Z 0.41 1943  98  98   8 0.30
Fri 10/16 15Z 0.49 2043  99  95  10 0.10
Fri 10/16 16Z 0.53 2140  99  69  11 0.05
Fri 10/16 17Z 0.54 2135  99  82  12 0.04
Fri 10/16 18Z 0.59 2233  98  82  13 0.03
Fri 10/16 19Z 0.65 2231  98  74  13 0.02
Fri 10/16 20Z 0.81 2333  98  55  12 0.01
Fri 10/16 21Z 1.05 2334  97  41  11 0.02
Fri 10/16 22Z 1.23 2435  97  36  11 0.02
Fri 10/16 23Z 1.57 2535  96  44   9 0.05
Sat 10/17 00Z 1.73 2733  94  31   6 0.04
Sat 10/17 01Z 1.31 2729  91  45   4 0.01
Sat 10/17 02Z 1.04 2928  93  42   2 0.01
Sat 10/17 03Z 0.76 3028  96  34   0 0.01
Sat 10/17 04Z 0.72 3028  95  18  -2 0.01
Sat 10/17 05Z 0.64 3127  94  34  -3 0.01
Sat 10/17 06Z 0.64 3228  96  38  -4 0.00
Sat 10/17 07Z 0.70 3228  97  44  -5 0.01
Sat 10/17 08Z 0.61 3229  96  44  -6 0.01
Sat 10/17 09Z 0.42 3330  94  42  -6 0.00
Sat 10/17 10Z 0.43 3330  95  41  -6 0.01
Sat 10/17 11Z 0.43 3329  96  40  -6 0.01
Sat 10/17 12Z 0.42 3328  97  38  -7 0.01
Sat 10/17 13Z 0.43 3327  97  28  -7 0.01
Sat 10/17 14Z 0.42 3326  97  17  -8 0.01
Sat 10/17 15Z 0.35 3324  96  11  -8 0.00
Sat 10/17 16Z 0.34 3223  95   7  -8 0.00
Sat 10/17 17Z 0.42 3224  94   3  -9 0.00

Run total areal avg QPF for the Central_Greens is: 1.24 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