NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260516_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)
=== ===== === ==== ==== === === === ====
Sat 05/16 06Z 0.39 2511  90  50   6 0.00
Sat 05/16 07Z 0.48 2614  87  30   5 0.00
Sat 05/16 08Z 0.47 2714  84  10   5 0.00
Sat 05/16 09Z 0.47 2815  79   3   5 0.00
Sat 05/16 10Z 0.50 2714  75   6   5 0.00
Sat 05/16 11Z 0.59 2717  73   8   5 0.00
Sat 05/16 12Z 0.65 2619  72  28   5 0.00
Sat 05/16 13Z 0.69 2619  69  74   5 0.00
Sat 05/16 14Z 0.74 2519  59  57   6 0.00
Sat 05/16 15Z 0.78 2418  57  50   6 0.00
Sat 05/16 16Z 0.88 2417  53  62   7 0.00
Sat 05/16 17Z 1.11 2315  50  42   8 0.00
Sat 05/16 18Z 1.42 2216  50  30   9 0.00
Sat 05/16 19Z 3.43 2217  57  32   9 0.00
Sat 05/16 20Z 4.89 2219  71  25   9 0.00
Sat 05/16 21Z 2.66 2221  76  14   9 0.00
Sat 05/16 22Z 1.18 2122  74  10  10 0.00
Sat 05/16 23Z 1.00 2126  76  12  10 0.00
Sun 05/17 00Z 0.92 2130  73  74  11 0.00
Sun 05/17 01Z 1.26 2237  80  83  10 0.02
Sun 05/17 02Z 1.21 2340  89  71  10 0.01
Sun 05/17 03Z 1.26 2440  93  80  10 0.05
Sun 05/17 04Z 1.19 2536  94  66  10 0.06
Sun 05/17 05Z 1.08 2732  97  28   9 0.02
Sun 05/17 06Z 1.05 2831  95   3   9 0.01
Sun 05/17 07Z 0.77 2930  81   4  10 0.01
Sun 05/17 08Z 0.68 2931  68   5   9 0.00
Sun 05/17 09Z 0.75 2933  63   8   9 0.00
Sun 05/17 10Z 0.73 2936  47   7   9 0.00
Sun 05/17 11Z 0.68 3036  46  20   9 0.00
Sun 05/17 12Z 0.65 3033  52  17   8 0.00
Sun 05/17 13Z 0.61 3031  55  52   8 0.00
Sun 05/17 14Z 0.76 3030  61  61   7 0.00
Sun 05/17 15Z 0.90 3028  66  61   7 0.00
Sun 05/17 16Z 1.31 2927  70  66   7 0.00
Sun 05/17 17Z 5.01 2926  74  57   6 0.00
Sun 05/17 18Z 5.38 2923  73  34   6 0.00
Sun 05/17 19Z 5.81 2921  73  29   7 0.00
Sun 05/17 20Z 5.11 2919  74  25   7 0.00
Sun 05/17 21Z 4.15 2917  76  25   7 0.00
Sun 05/17 22Z 1.01 2917  75  21   7 0.00
Sun 05/17 23Z 0.67 3017  75  20   7 0.00
Mon 05/18 00Z 0.51 3017  76  16   7 0.00
Mon 05/18 01Z 0.45 3117  77  12   7 0.00
Mon 05/18 02Z 0.37 3117  73  11   7 0.00
Mon 05/18 03Z 0.31 3015  68  13   8 0.00
Mon 05/18 04Z 0.28 3014  62  18   8 0.00
Mon 05/18 05Z 0.25 2912  57  29   9 0.00
Mon 05/18 06Z 0.23 2911  51  41  10 0.00
Mon 05/18 07Z 0.22 2810  46  21  10 0.00
Mon 05/18 08Z 0.24 2710  44  30  11 0.00
Mon 05/18 09Z 0.21 2809  44  30  11 0.00
Mon 05/18 10Z 0.17 2708  43  28  12 0.00
Mon 05/18 11Z 0.17 2508  40  27  12 0.00
Mon 05/18 12Z 0.23 2311  44  19  13 0.00
Mon 05/18 13Z 0.29 2214  62  24  12 0.00
Mon 05/18 14Z 0.32 2217  84  36  12 0.00
Mon 05/18 15Z 0.41 2221  91  52  12 0.00
Mon 05/18 16Z 0.48 2222  92  55  13 0.00
Mon 05/18 17Z 0.53 2321  90  50  13 0.00

Run total areal avg QPF for the Central_Greens is: 0.18 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