NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261005_1200
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)
=== ===== === ==== ==== === === === ====
Mon 10/05 12Z 0.61 2521  98  95   6 0.00
Mon 10/05 13Z 0.77 2625  95  81   5 0.08
Mon 10/05 14Z 0.81 2825  93  59   4 0.05
Mon 10/05 15Z 0.93 2824  92  70   3 0.03
Mon 10/05 16Z 2.28 2824  91  56   3 0.01
Mon 10/05 17Z 10.32 2824  85  73   2 0.01
Mon 10/05 18Z 10.38 2823  83  55   2 0.00
Mon 10/05 19Z 15.34 2723  77  33   1 0.00
Mon 10/05 20Z 9.89 2826  82  64   1 0.02
Mon 10/05 21Z 5.58 2930  86  53   0 0.03
Mon 10/05 22Z 2.08 2929  88  39   0 0.01
Mon 10/05 23Z 1.70 2930  90  43  -1 0.00
Tue 10/06 00Z 1.34 3031  89  45  -2 0.00
Tue 10/06 01Z 1.05 3032  90  42  -2 0.00
Tue 10/06 02Z 0.86 3032  89  39  -2 0.00
Tue 10/06 03Z 0.80 3031  90  34  -2 0.00
Tue 10/06 04Z 0.76 3030  91  29  -2 0.00
Tue 10/06 05Z 0.69 3029  90  24  -2 0.00
Tue 10/06 06Z 0.61 3029  87  22  -2 0.00
Tue 10/06 07Z 0.56 3029  84  20  -2 0.00
Tue 10/06 08Z 0.52 3030  82  18  -2 0.00
Tue 10/06 09Z 0.47 3029  80  17  -2 0.00
Tue 10/06 10Z 0.45 3030  78  15  -2 0.00
Tue 10/06 11Z 0.42 3030  76  14  -1 0.00
Tue 10/06 12Z 0.40 3029  75  15  -1 0.00
Tue 10/06 13Z 0.38 3129  74  13  -1 0.00
Tue 10/06 14Z 0.37 3127  74  12  -1 0.00
Tue 10/06 15Z 0.40 3026  70  11   0 0.00
Tue 10/06 16Z 0.44 3025  61  10   0 0.00
Tue 10/06 17Z 0.49 3024  52   6   0 0.00
Tue 10/06 18Z 0.55 3023  46   5   0 0.00
Tue 10/06 19Z 0.66 3023  43   3   0 0.00
Tue 10/06 20Z 0.94 3023  47   2   0 0.00
Tue 10/06 21Z 1.32 2922  46   3   0 0.00
Tue 10/06 22Z 1.33 2924  43   8   0 0.00
Tue 10/06 23Z 1.00 3024  39  20   0 0.00
Wed 10/07 00Z 0.78 3024  36  33   0 0.00
Wed 10/07 01Z 0.58 3023  32  45   0 0.00
Wed 10/07 02Z 0.47 3020  31  49   0 0.00
Wed 10/07 03Z 0.48 2918  32  73   0 0.00
Wed 10/07 04Z 0.45 2817  30  82   1 0.00
Wed 10/07 05Z 0.42 2716  29  83   2 0.00
Wed 10/07 06Z 0.42 2716  28  78   2 0.00
Wed 10/07 07Z 0.42 2617  26  83   3 0.00
Wed 10/07 08Z 0.41 2718  31  90   4 0.00
Wed 10/07 09Z 0.41 2618  32  88   4 0.00
Wed 10/07 10Z 0.45 2619  34  88   4 0.00
Wed 10/07 11Z 0.51 2522  38  91   5 0.00
Wed 10/07 12Z 0.55 2523  46  94   5 0.00
Wed 10/07 13Z 0.52 2522  58  95   6 0.00
Wed 10/07 14Z 0.52 2423  49  89   6 0.00
Wed 10/07 15Z 0.52 2324  51  92   6 0.00
Wed 10/07 16Z 0.53 2226  49  84   7 0.00
Wed 10/07 17Z 0.54 2226  40  79   7 0.00
Wed 10/07 18Z 0.58 2126  40  85   7 0.00
Wed 10/07 19Z 0.61 2125  44  75   7 0.00
Wed 10/07 20Z 0.72 2126  54  69   7 0.00
Wed 10/07 21Z 0.81 2128  64  89   7 0.00
Wed 10/07 22Z 0.87 2230  71  89   7 0.00
Wed 10/07 23Z 0.92 2232  75  88   6 0.01

Run total areal avg QPF for the Central_Greens is: 0.25 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