NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260419_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)
=== ===== === ==== ==== === === === ====
Sun 04/19 06Z 0.29 1927  92  96   9 0.00
Sun 04/19 07Z 0.40 2027  98  98   7 0.11
Sun 04/19 08Z 0.43 2124  98  96   8 0.12
Sun 04/19 09Z 0.45 2221  98  92   7 0.04
Sun 04/19 10Z 0.49 2319  99  97   6 0.04
Sun 04/19 11Z 0.29 2510  99  98   5 0.03
Sun 04/19 12Z 0.36 2711  99  99   4 0.04
Sun 04/19 13Z 0.38 3116  98  99   1 0.12
Sun 04/19 14Z 0.16 3324  96  99   0 0.15
Sun 04/19 15Z 0.23 3223  97  99  -1 0.11
Sun 04/19 16Z 0.26 3224  96  99  -3 0.12
Sun 04/19 17Z 0.22 3324  95  99  -4 0.10
Sun 04/19 18Z 0.25 3223  95  98  -5 0.08
Sun 04/19 19Z 0.34 3223  94  96  -6 0.02
Sun 04/19 20Z 0.36 3223  92  87  -6 0.02
Sun 04/19 21Z 0.42 3121  88  83  -6 0.01
Sun 04/19 22Z 0.62 3021  81  37  -6 0.00
Sun 04/19 23Z 0.66 3023  75  19  -6 0.00
Mon 04/20 00Z 0.74 2923  87  22  -6 0.00
Mon 04/20 01Z 0.90 2822  89  29  -6 0.00
Mon 04/20 02Z 1.30 2826  95  61  -6 0.02
Mon 04/20 03Z 1.01 2926  80  35  -6 0.01
Mon 04/20 04Z 0.95 2825  73  35  -6 0.00
Mon 04/20 05Z 0.86 2824  65  36  -6 0.00
Mon 04/20 06Z 0.89 2824  62  44  -7 0.00
Mon 04/20 07Z 0.80 2721  67  54  -7 0.00
Mon 04/20 08Z 0.78 2721  79  63  -7 0.00
Mon 04/20 09Z 0.79 2821  92  63  -8 0.00
Mon 04/20 10Z 0.86 2821  89  55  -8 0.00
Mon 04/20 11Z 0.87 2821  87  46  -9 0.00
Mon 04/20 12Z 0.67 2918  86  31  -9 0.01
Mon 04/20 13Z 0.89 3114  90  35 -10 0.01
Mon 04/20 14Z 1.18 3113  92  35 -10 0.00
Mon 04/20 15Z 0.35 3111  89  36 -10 0.00
Mon 04/20 16Z 1.11 3110  84  41 -10 0.00
Mon 04/20 17Z 2.56 3009  82  47 -10 0.00
Mon 04/20 18Z 3.35 3010  81  47 -10 0.00
Mon 04/20 19Z 4.34 3010  79  44 -10 0.00
Mon 04/20 20Z 3.79 3011  79  36 -10 0.00
Mon 04/20 21Z 3.57 3111  75  22 -10 0.00
Mon 04/20 22Z 2.36 3112  71  13 -10 0.00
Mon 04/20 23Z 0.94 3212  67   5 -10 0.00
Tue 04/21 00Z 0.48 3213  62   7 -10 0.00
Tue 04/21 01Z 0.55 3213  59  10 -10 0.00
Tue 04/21 02Z 0.85 3214  58  11 -11 0.00
Tue 04/21 03Z 0.95 3214  58   9 -11 0.00
Tue 04/21 04Z 0.72 3213  56   7 -11 0.00
Tue 04/21 05Z 0.61 3213  53   9 -11 0.00
Tue 04/21 06Z 0.60 3113  53  11 -11 0.00
Tue 04/21 07Z 0.55 3112  52  12 -11 0.00
Tue 04/21 08Z 0.52 3011  52  12 -11 0.00
Tue 04/21 09Z 0.39 3009  51  13 -11 0.00
Tue 04/21 10Z 0.39 2908  50  13 -11 0.00
Tue 04/21 11Z 0.38 2807  50  13 -11 0.00
Tue 04/21 12Z 0.43 2507  52  12 -11 0.00
Tue 04/21 13Z 1.48 2307  55  11 -11 0.00
Tue 04/21 14Z 3.28 2208  55  10 -10 0.00
Tue 04/21 15Z 3.72 2109  51   8  -9 0.00
Tue 04/21 16Z 4.09 2109  47  18  -8 0.00
Tue 04/21 17Z 4.97 2210  43  51  -8 0.00

Run total areal avg QPF for the Central_Greens is: 1.16 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