Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261017_1200
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)
=== ===== === ==== ==== === === === ====
Sat 10/17 12Z 0.54 3225  98   5  -5 0.00
Sat 10/17 13Z 0.59 3225  97   0  -6 0.01
Sat 10/17 14Z 0.55 3224  96   0  -7 0.01
Sat 10/17 15Z 0.59 3224  94   2  -7 0.00
Sat 10/17 16Z 0.75 3222  90   5  -7 0.00
Sat 10/17 17Z 0.87 3220  87   5  -8 0.00
Sat 10/17 18Z 0.66 3119  81  12  -7 0.00
Sat 10/17 19Z 0.71 3118  74  25  -7 0.00
Sat 10/17 20Z 0.79 3117  74  29  -7 0.00
Sat 10/17 21Z 0.61 3116  70  32  -7 0.00
Sat 10/17 22Z 0.56 3118  64  27  -6 0.00
Sat 10/17 23Z 0.45 3120  57  32  -5 0.00
Sun 10/18 00Z 0.36 3121  50  38  -5 0.00
Sun 10/18 01Z 0.29 3220  47  52  -4 0.00
Sun 10/18 02Z 0.24 3219  44  52  -3 0.00
Sun 10/18 03Z 0.24 3118  43  48  -3 0.00
Sun 10/18 04Z 0.25 3118  44  58  -3 0.00
Sun 10/18 05Z 0.25 3117  48  55  -3 0.00
Sun 10/18 06Z 0.25 3116  51  51  -3 0.00
Sun 10/18 07Z 0.28 3115  54  50  -3 0.00
Sun 10/18 08Z 0.33 3015  55  50  -3 0.00
Sun 10/18 09Z 0.36 3016  62  52  -3 0.00
Sun 10/18 10Z 0.33 3016  67  52  -2 0.00
Sun 10/18 11Z 0.28 3014  69  52  -1 0.00
Sun 10/18 12Z 0.25 3012  70  51  -1 0.00
Sun 10/18 13Z 0.24 2911  69  47   0 0.00
Sun 10/18 14Z 0.22 2911  68  42   0 0.00
Sun 10/18 15Z 0.21 2910  66  39   1 0.00
Sun 10/18 16Z 0.22 2809  62  37   1 0.00
Sun 10/18 17Z 0.26 2710  56  34   2 0.00
Sun 10/18 18Z 0.26 2710  48  32   3 0.00
Sun 10/18 19Z 0.25 2810  42  35   4 0.00
Sun 10/18 20Z 0.23 2710  37  33   5 0.00
Sun 10/18 21Z 0.22 2710  33  25   6 0.00
Sun 10/18 22Z 0.23 2711  30  16   7 0.00
Sun 10/18 23Z 0.23 2812  26  12   7 0.00
Mon 10/19 00Z 0.22 2711  22  10   8 0.00
Mon 10/19 01Z 0.21 2610  18  12   8 0.00
Mon 10/19 02Z 0.21 2609  13  17   9 0.00
Mon 10/19 03Z 0.22 2610  11  23   9 0.00
Mon 10/19 04Z 0.23 2610  10  28   9 0.00
Mon 10/19 05Z 0.23 2611  12  32  10 0.00
Mon 10/19 06Z 0.23 2611  14  32  10 0.00
Mon 10/19 07Z 0.23 2611  17  30  10 0.00
Mon 10/19 08Z 0.23 2611  20  27  10 0.00
Mon 10/19 09Z 0.22 2711  20  26  10 0.00
Mon 10/19 10Z 0.22 2710  20  25  10 0.00
Mon 10/19 11Z 0.21 2710  19  24  10 0.00
Mon 10/19 12Z 0.20 2709  17  23  10 0.00
Mon 10/19 13Z 0.21 2809  16  23  10 0.00
Mon 10/19 14Z 0.20 2809  16  23  10 0.00
Mon 10/19 15Z 0.21 2809  15  22  10 0.00
Mon 10/19 16Z 0.20 2809  15  22  11 0.00
Mon 10/19 17Z 0.19 2808  15  21  11 0.00
Mon 10/19 18Z 0.19 2909  14  20  11 0.00
Mon 10/19 19Z 0.19 2909  13  20  11 0.00
Mon 10/19 20Z 0.18 3010  13  20  11 0.00
Mon 10/19 21Z 0.16 3110  14  19  11 0.00
Mon 10/19 22Z 0.13 3211  16  18  11 0.00
Mon 10/19 23Z 0.09 3310  18  18  10 0.00

Run total areal avg QPF for the Central_Greens is: 0.02 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