NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260717_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)
=== ===== === ==== ==== === === === ====
Fri 07/17 06Z 0.36 3223  69  42   9 0.00
Fri 07/17 07Z 0.45 3225  65  45   9 0.00
Fri 07/17 08Z 0.47 3226  61  47   9 0.00
Fri 07/17 09Z 0.48 3226  63  35   8 0.00
Fri 07/17 10Z 0.42 3225  64  25   8 0.00
Fri 07/17 11Z 0.38 3225  64  18   9 0.00
Fri 07/17 12Z 0.36 3224  61  15   9 0.00
Fri 07/17 13Z 0.34 3222  60  14   9 0.00
Fri 07/17 14Z 0.32 3119  59  15   9 0.00
Fri 07/17 15Z 0.35 3117  58  17   9 0.00
Fri 07/17 16Z 0.43 3116  56  18   9 0.00
Fri 07/17 17Z 0.80 3014  59  19   9 0.00
Fri 07/17 18Z 1.66 2912  66  18   9 0.00
Fri 07/17 19Z 3.98 2912  67  18  10 0.00
Fri 07/17 20Z 4.65 2811  65  18  10 0.00
Fri 07/17 21Z 3.00 2810  59  16  10 0.00
Fri 07/17 22Z 1.50 2810  54  16  11 0.00
Fri 07/17 23Z 0.80 2911  51  14  11 0.00
Sat 07/18 00Z 0.62 2911  48  13  11 0.00
Sat 07/18 01Z 0.57 2810  47  12  11 0.00
Sat 07/18 02Z 0.56 2809  48  12  11 0.00
Sat 07/18 03Z 0.51 2709  51  12  11 0.00
Sat 07/18 04Z 0.43 2707  53  12  11 0.00
Sat 07/18 05Z 0.49 2608  56  11  10 0.00
Sat 07/18 06Z 0.51 2509  58  12  10 0.00
Sat 07/18 07Z 0.51 2409  59  12  10 0.00
Sat 07/18 08Z 0.45 2509  56  25  11 0.00
Sat 07/18 09Z 0.33 2508  52  77  11 0.00
Sat 07/18 10Z 0.25 2208  49  93  12 0.00
Sat 07/18 11Z 0.22 2109  43  92  13 0.00
Sat 07/18 12Z 0.34 2115  47  91  13 0.00
Sat 07/18 13Z 0.49 2120  62  84  13 0.00
Sat 07/18 14Z 0.70 2123  71  73  13 0.00
Sat 07/18 15Z 0.93 2125  71  63  14 0.00
Sat 07/18 16Z 1.16 2126  78  57  15 0.00
Sat 07/18 17Z 2.46 2027  81  61  15 0.00
Sat 07/18 18Z 3.47 2028  81  83  15 0.00
Sat 07/18 19Z 1.65 2032  91  75  15 0.02
Sat 07/18 20Z 0.72 2129  96  50  16 0.01
Sat 07/18 21Z 0.68 2127  96  56  16 0.01
Sat 07/18 22Z 0.68 2227  95  67  16 0.01
Sat 07/18 23Z 0.66 2130  94  63  17 0.01
Sun 07/19 00Z 0.98 2237  95  74  16 0.06
Sun 07/19 01Z 0.90 2235  94  62  16 0.03
Sun 07/19 02Z 1.14 2337  92  72  16 0.10
Sun 07/19 03Z 1.06 2433  93  57  15 0.08
Sun 07/19 04Z 1.08 2530  94  52  15 0.02
Sun 07/19 05Z 0.94 2729  95  69  13 0.06
Sun 07/19 06Z 0.77 3030  90  36  10 0.03
Sun 07/19 07Z 0.59 3029  87  19   9 0.00
Sun 07/19 08Z 0.61 3030  90  18   8 0.00
Sun 07/19 09Z 0.64 3031  90  20   7 0.00
Sun 07/19 10Z 0.66 3032  90  18   7 0.00
Sun 07/19 11Z 0.63 3133  91  18   7 0.00
Sun 07/19 12Z 0.70 3032  93  26   7 0.01
Sun 07/19 13Z 0.68 3031  91  26   7 0.01
Sun 07/19 14Z 0.74 3029  89  17   7 0.00
Sun 07/19 15Z 1.59 3027  82  18   7 0.00
Sun 07/19 16Z 9.74 3027  73  14   7 0.00
Sun 07/19 17Z 13.36 3027  64  14   8 0.00

Run total areal avg QPF for the Central_Greens is: 0.46 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