NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261004_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 10/04 18Z 0.07 1613  94  47   4 0.00
Sun 10/04 19Z 0.09 1615  95  73   4 0.00
Sun 10/04 20Z 0.06 1618  95  89   4 0.00
Sun 10/04 21Z 0.05 1718  93  82   5 0.00
Sun 10/04 22Z 0.12 1719  94  36   5 0.00
Sun 10/04 23Z 0.21 1820  93  53   5 0.00
Mon 10/05 00Z 0.26 1920  92  48   6 0.00
Mon 10/05 01Z 0.31 1920  94  60   6 0.00
Mon 10/05 02Z 0.35 2020  97  60   6 0.01
Mon 10/05 03Z 0.40 2120  98  63   6 0.01
Mon 10/05 04Z 0.45 2220  97  70   7 0.01
Mon 10/05 05Z 0.46 2219  96  70   7 0.01
Mon 10/05 06Z 0.48 2320  94  52   7 0.01
Mon 10/05 07Z 0.49 2420  91  75   8 0.01
Mon 10/05 08Z 0.52 2421  91  78   8 0.01
Mon 10/05 09Z 0.58 2324  91  91   8 0.02
Mon 10/05 10Z 0.73 2428  96  88   7 0.11
Mon 10/05 11Z 0.84 2627  97  95   6 0.11
Mon 10/05 12Z 0.92 2726  95  91   5 0.08
Mon 10/05 13Z 0.94 2826  77  60   5 0.02
Mon 10/05 14Z 0.85 2825  76  43   4 0.01
Mon 10/05 15Z 1.09 2824  86  65   3 0.02
Mon 10/05 16Z 7.29 2826  76  70   2 0.02
Mon 10/05 17Z 14.02 2824  71  38   2 0.00
Mon 10/05 18Z 14.37 2824  66  22   2 0.00
Mon 10/05 19Z 13.83 2825  68  61   1 0.00
Mon 10/05 20Z 4.29 2925  80  49   0 0.01
Mon 10/05 21Z 2.48 2925  88  54   0 0.01
Mon 10/05 22Z 1.46 2928  90  44   0 0.01
Mon 10/05 23Z 1.49 2930  93  49  -1 0.01
Tue 10/06 00Z 1.08 3030  90  52  -1 0.00
Tue 10/06 01Z 0.82 3029  91  51  -2 0.00
Tue 10/06 02Z 0.73 3030  87  54  -1 0.00
Tue 10/06 03Z 0.71 3030  84  58  -2 0.00
Tue 10/06 04Z 0.78 3030  86  36  -2 0.00
Tue 10/06 05Z 0.79 3030  86  23  -3 0.00
Tue 10/06 06Z 0.68 3029  84  21  -3 0.00
Tue 10/06 07Z 0.60 3029  82  19  -2 0.00
Tue 10/06 08Z 0.53 3029  79  18  -2 0.00
Tue 10/06 09Z 0.52 3030  80  18  -2 0.00
Tue 10/06 10Z 0.47 3029  79  16  -2 0.00
Tue 10/06 11Z 0.45 3028  77  17  -2 0.00
Tue 10/06 12Z 0.42 3028  69  17  -2 0.00
Tue 10/06 13Z 0.37 3027  62  15  -1 0.00
Tue 10/06 14Z 0.35 3127  58  13   0 0.00
Tue 10/06 15Z 0.37 3026  55   8   0 0.00
Tue 10/06 16Z 0.41 3025  48   5   0 0.00
Tue 10/06 17Z 0.49 3025  48   3   0 0.00
Tue 10/06 18Z 0.66 3025  47   3   0 0.00
Tue 10/06 19Z 1.02 2924  49   5   0 0.00
Tue 10/06 20Z 2.87 2922  49   8  -1 0.00
Tue 10/06 21Z 2.75 2922  47  16  -1 0.00
Tue 10/06 22Z 1.23 2922  41  36   0 0.00
Tue 10/06 23Z 0.86 2924  36  49   0 0.00
Wed 10/07 00Z 0.76 2923  39  37   0 0.00
Wed 10/07 01Z 0.66 3022  40  57   0 0.00
Wed 10/07 02Z 0.55 2920  41  67   0 0.00
Wed 10/07 03Z 0.48 2918  39  56   1 0.00
Wed 10/07 04Z 0.42 2816  37  84   1 0.00
Wed 10/07 05Z 0.43 2817  41  90   2 0.00

Run total areal avg QPF for the Central_Greens is: 0.50 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