NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261006_0000
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)
=== ===== === ==== ==== === === === ====
Tue 10/06 00Z 0.80 3128  93  82   0 0.00
Tue 10/06 01Z 0.82 3130  94  71   0 0.01
Tue 10/06 02Z 1.13 3133  91  47  -1 0.01
Tue 10/06 03Z 1.01 3132  88  25  -2 0.00
Tue 10/06 04Z 1.01 3132  87  19  -2 0.00
Tue 10/06 05Z 0.96 3032  84  13  -2 0.00
Tue 10/06 06Z 1.06 3031  84  13  -3 0.00
Tue 10/06 07Z 0.83 3031  82  14  -3 0.00
Tue 10/06 08Z 0.71 3031  83  16  -3 0.00
Tue 10/06 09Z 0.61 3031  84  17  -3 0.00
Tue 10/06 10Z 0.55 3030  84  16  -2 0.00
Tue 10/06 11Z 0.53 3030  84  15  -2 0.00
Tue 10/06 12Z 0.49 3030  81  13  -2 0.00
Tue 10/06 13Z 0.44 3130  78  10  -1 0.00
Tue 10/06 14Z 0.45 3129  76   8  -1 0.00
Tue 10/06 15Z 0.49 3027  74   6  -1 0.00
Tue 10/06 16Z 0.54 3025  66   5  -1 0.00
Tue 10/06 17Z 0.58 3023  58   4   0 0.00
Tue 10/06 18Z 0.74 3022  54   3   0 0.00
Tue 10/06 19Z 1.63 3021  53   3   0 0.00
Tue 10/06 20Z 2.89 2919  50   5   0 0.00
Tue 10/06 21Z 2.45 2920  47   8   0 0.00
Tue 10/06 22Z 1.52 2921  46  16   0 0.00
Tue 10/06 23Z 1.22 2921  45  25   0 0.00
Wed 10/07 00Z 0.89 2920  46  39   0 0.00
Wed 10/07 01Z 0.73 3020  46  53   0 0.00
Wed 10/07 02Z 0.52 3018  45  65   0 0.00
Wed 10/07 03Z 0.36 2914  41  59   1 0.00
Wed 10/07 04Z 0.37 2814  38  70   2 0.00
Wed 10/07 05Z 0.36 2714  34  80   2 0.00
Wed 10/07 06Z 0.34 2614  29  62   3 0.00
Wed 10/07 07Z 0.37 2516  26  80   4 0.00
Wed 10/07 08Z 0.41 2519  21  83   5 0.00
Wed 10/07 09Z 0.45 2521  23  83   6 0.00
Wed 10/07 10Z 0.47 2522  41  88   6 0.00
Wed 10/07 11Z 0.46 2522  49  87   6 0.00
Wed 10/07 12Z 0.47 2422  52  83   7 0.00
Wed 10/07 13Z 0.46 2421  45  83   7 0.00
Wed 10/07 14Z 0.52 2323  54  92   6 0.00
Wed 10/07 15Z 0.55 2323  63  92   5 0.00
Wed 10/07 16Z 0.51 2122  57  84   6 0.00
Wed 10/07 17Z 0.58 2123  53  78   6 0.00
Wed 10/07 18Z 0.68 2222  52  84   6 0.00
Wed 10/07 19Z 0.74 2221  55  74   6 0.00
Wed 10/07 20Z 0.66 2121  56  79   6 0.00
Wed 10/07 21Z 0.67 2124  64  83   7 0.00
Wed 10/07 22Z 0.86 2227  71  86   6 0.00
Wed 10/07 23Z 0.99 2230  78  81   6 0.00
Thu 10/08 00Z 1.05 2332  82  88   6 0.01
Thu 10/08 01Z 1.04 2333  87  81   6 0.01
Thu 10/08 02Z 0.99 2434  92  77   7 0.02
Thu 10/08 03Z 0.85 2432  96  42   7 0.02
Thu 10/08 04Z 0.80 2530  97  36   7 0.02
Thu 10/08 05Z 0.77 2528  93  19   7 0.02
Thu 10/08 06Z 0.74 2625  92  21   7 0.02
Thu 10/08 07Z 0.76 2625  89  16   6 0.01
Thu 10/08 08Z 0.72 2623  83  10   6 0.01
Thu 10/08 09Z 0.64 2721  78  21   6 0.01
Thu 10/08 10Z 0.59 2720  75  35   6 0.01
Thu 10/08 11Z 0.55 2619  73  35   6 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