NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20251123_1800
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 11/23 18Z 0.27 2209  97  87  -5 0.00
Sun 11/23 19Z 0.25 2209  97  93  -5 0.01
Sun 11/23 20Z 0.26 2209  98  93  -5 0.02
Sun 11/23 21Z 0.32 2210  99  93  -5 0.02
Sun 11/23 22Z 0.33 2310  99  94  -5 0.02
Sun 11/23 23Z 0.31 2510  98  87  -4 0.02
Mon 11/24 00Z 0.30 2710  98  74  -4 0.01
Mon 11/24 01Z 0.27 2810  96  62  -4 0.01
Mon 11/24 02Z 0.27 2910  95  72  -4 0.00
Mon 11/24 03Z 0.31 2912  95  72  -4 0.00
Mon 11/24 04Z 0.33 2913  96  72  -4 0.00
Mon 11/24 05Z 0.35 2913  97  74  -5 0.01
Mon 11/24 06Z 0.39 3015  96  76  -5 0.01
Mon 11/24 07Z 0.44 3016  96  76  -5 0.01
Mon 11/24 08Z 0.46 3018  97  81  -5 0.01
Mon 11/24 09Z 0.45 3119  98  81  -5 0.02
Mon 11/24 10Z 0.46 3121  97  76  -5 0.01
Mon 11/24 11Z 0.52 3123  97  66  -6 0.01
Mon 11/24 12Z 0.53 3123  97  52  -6 0.01
Mon 11/24 13Z 0.52 3123  97  46  -6 0.01
Mon 11/24 14Z 0.50 3123  96  50  -6 0.01
Mon 11/24 15Z 0.38 3121  94  47  -6 0.00
Mon 11/24 16Z 0.42 3120  94  18  -6 0.00
Mon 11/24 17Z 0.44 3017  94   2  -6 0.00
Mon 11/24 18Z 0.45 2916  90   2  -5 0.00
Mon 11/24 19Z 0.33 2916  78   8  -4 0.00
Mon 11/24 20Z 0.31 3017  67  11  -2 0.00
Mon 11/24 21Z 0.25 3017  56  22  -1 0.00
Mon 11/24 22Z 0.25 3017  44  32   0 0.00
Mon 11/24 23Z 0.27 2917  39  56   0 0.00
Tue 11/25 00Z 0.28 2916  33  70   0 0.00
Tue 11/25 01Z 0.30 2816  23  85   1 0.00
Tue 11/25 02Z 0.35 2817  18  91   1 0.00
Tue 11/25 03Z 0.36 2715  15  91   1 0.00
Tue 11/25 04Z 0.39 2517  14  93   2 0.00
Tue 11/25 05Z 0.48 2421  13  92   2 0.00
Tue 11/25 06Z 0.56 2426  15  91   2 0.00
Tue 11/25 07Z 0.62 2429  16  88   2 0.00
Tue 11/25 08Z 0.64 2529  15  86   2 0.00
Tue 11/25 09Z 0.65 2529  15  85   2 0.00
Tue 11/25 10Z 0.63 2528  16  90   2 0.00
Tue 11/25 11Z 0.60 2526  18  82   2 0.00
Tue 11/25 12Z 0.56 2524  23  64   2 0.00
Tue 11/25 13Z 0.52 2522  28  69   2 0.00
Tue 11/25 14Z 0.43 2518  29  82   2 0.00
Tue 11/25 15Z 0.39 2417  35  75   3 0.00
Tue 11/25 16Z 0.39 2419  38  65   3 0.00
Tue 11/25 17Z 0.41 2320  45  64   3 0.00
Tue 11/25 18Z 0.44 2321  47  71   3 0.00
Tue 11/25 19Z 0.42 2320  46  64   3 0.00
Tue 11/25 20Z 0.38 2319  48  60   4 0.00
Tue 11/25 21Z 0.36 2319  54  65   4 0.00
Tue 11/25 22Z 0.38 2319  54  61   4 0.00
Tue 11/25 23Z 0.38 2319  62  63   4 0.00
Wed 11/26 00Z 0.39 2319  73  65   3 0.00
Wed 11/26 01Z 0.39 2319  81  77   3 0.01
Wed 11/26 02Z 0.41 2320  85  94   3 0.01
Wed 11/26 03Z 0.38 2219  90  98   3 0.02
Wed 11/26 04Z 0.31 2117  94  98   3 0.01
Wed 11/26 05Z 0.24 2017  94  98   3 0.01

Run total areal avg QPF for the Central_Greens is: 0.28 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