Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261015_0000
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 00Z 0.67 3024  98  43   4 0.00
Thu 10/15 01Z 0.70 3128  98  29   3 0.01
Thu 10/15 02Z 0.54 3129  97  22   3 0.01
Thu 10/15 03Z 0.44 3229  96   7   3 0.01
Thu 10/15 04Z 0.45 3230  96   3   3 0.01
Thu 10/15 05Z 0.48 3232  97   1   2 0.01
Thu 10/15 06Z 0.42 3232  96   1   2 0.01
Thu 10/15 07Z 0.36 3232  94   2   1 0.01
Thu 10/15 08Z 0.24 3332  86   2   2 0.01
Thu 10/15 09Z 0.18 3330  77   2   2 0.01
Thu 10/15 10Z 0.11 3328  67   3   2 0.01
Thu 10/15 11Z 0.03 3427  61   3   3 0.01
Thu 10/15 12Z 0.02 3525  59   3   2 0.00
Thu 10/15 13Z 0.02 3523  58   3   2 0.00
Thu 10/15 14Z 0.03 3520  56   3   2 0.00
Thu 10/15 15Z 0.04 3517  53   3   2 0.00
Thu 10/15 16Z 0.06 0014  50   3   3 0.00
Thu 10/15 17Z 0.04 3511  47   3   4 0.00
Thu 10/15 18Z 0.02 3509  45   3   4 0.00
Thu 10/15 19Z 0.01 3507  46   4   4 0.00
Thu 10/15 20Z 0.02 3405  45   4   4 0.00
Thu 10/15 21Z 0.04 3204  44   4   4 0.00
Thu 10/15 22Z 0.04 3003  38   5   5 0.00
Thu 10/15 23Z 0.04 2802  34   5   5 0.00
Fri 10/16 00Z 0.03 2201  33   4   6 0.00
Fri 10/16 01Z 0.02 1804  35   4   6 0.00
Fri 10/16 02Z 0.02 1706  36   3   6 0.00
Fri 10/16 03Z 0.05 1810  38   4   6 0.00
Fri 10/16 04Z 0.09 1813  42  11   6 0.00
Fri 10/16 05Z 0.10 1817  46  17   6 0.00
Fri 10/16 06Z 0.16 1920  50  38   5 0.00
Fri 10/16 07Z 0.18 1924  47  78   5 0.00
Fri 10/16 08Z 0.21 1826  55  90   4 0.00
Fri 10/16 09Z 0.20 1827  69  96   4 0.00
Fri 10/16 10Z 0.15 1830  77  98   4 0.01
Fri 10/16 11Z 0.17 1835  80  99   3 0.03
Fri 10/16 12Z 0.19 1838  97  97   5 0.14
Fri 10/16 13Z 0.29 1841  98  94   6 0.12
Fri 10/16 14Z 0.39 1942  98  87   7 0.07
Fri 10/16 15Z 0.45 2040  98  91   9 0.08
Fri 10/16 16Z 0.52 2139  99  86  10 0.05
Fri 10/16 17Z 0.54 2236  99  81  12 0.04
Fri 10/16 18Z 0.57 2235  99  82  13 0.04
Fri 10/16 19Z 0.62 2233  98  89  13 0.03
Fri 10/16 20Z 0.71 2332  98  88  12 0.03
Fri 10/16 21Z 0.79 2334  98  82  12 0.02
Fri 10/16 22Z 1.05 2435  96  88  11 0.04
Fri 10/16 23Z 1.24 2434  95  91  10 0.05
Sat 10/17 00Z 1.43 2534  97  82   9 0.08
Sat 10/17 01Z 1.24 2729  96  66   6 0.05
Sat 10/17 02Z 0.78 2826  95  60   5 0.02
Sat 10/17 03Z 0.58 2927  96  47   2 0.02
Sat 10/17 04Z 0.54 3027  96  56   0 0.01
Sat 10/17 05Z 0.47 3125  95  42  -1 0.01
Sat 10/17 06Z 0.40 3226  95  42  -2 0.01
Sat 10/17 07Z 0.33 3226  95  41  -4 0.00
Sat 10/17 09Z 0.22 3328  93  41  -5 0.00
Sat 10/17 10Z 0.16 3428  91  40  -5 0.00
Sat 10/17 11Z 0.19 3428  92  38  -6 0.00

Run total areal avg QPF for the Central_Greens is: 1.06 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