NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260405_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)
=== ===== === ==== ==== === === === ====
Sun 04/05 00Z 0.09 1523  85  98   3 0.00
Sun 04/05 01Z 0.10 1628  89  95   4 0.01
Sun 04/05 02Z 0.07 1629  91  88   5 0.00
Sun 04/05 03Z 0.05 1631  92  95   6 0.01
Sun 04/05 04Z 0.05 1734  95  95   6 0.01
Sun 04/05 05Z 0.09 1737  96  92   7 0.01
Sun 04/05 06Z 0.12 1842  96  88   8 0.01
Sun 04/05 07Z 0.14 1844  96  72   9 0.01
Sun 04/05 08Z 0.18 1844  97  76   9 0.01
Sun 04/05 09Z 0.23 1942  97  83  10 0.01
Sun 04/05 10Z 0.30 1940  98  82  10 0.02
Sun 04/05 11Z 0.34 2036  98  91   9 0.04
Sun 04/05 12Z 0.37 2133  99  90   9 0.04
Sun 04/05 13Z 0.47 2230  99  96   7 0.07
Sun 04/05 14Z 0.47 2326  97  96   7 0.06
Sun 04/05 15Z 0.50 2326  97  97   6 0.07
Sun 04/05 16Z 0.66 2429  97  97   4 0.11
Sun 04/05 17Z 0.64 2527  92  93   4 0.06
Sun 04/05 18Z 0.71 2526  92  68   3 0.01
Sun 04/05 19Z 0.80 2625  91  30   1 0.01
Sun 04/05 20Z 1.00 2625  92  17   0 0.01
Sun 04/05 21Z 1.18 2624  89  20  -2 0.01
Sun 04/05 22Z 1.77 2724  91  16  -3 0.00
Sun 04/05 23Z 1.58 2727  94  11  -4 0.00
Mon 04/06 00Z 1.76 2728  93  10  -5 0.01
Mon 04/06 01Z 1.59 2730  88  15  -5 0.00
Mon 04/06 02Z 1.37 2729  87  20  -6 0.00
Mon 04/06 03Z 1.32 2729  92  25  -7 0.00
Mon 04/06 04Z 1.36 2729  94  28  -7 0.00
Mon 04/06 05Z 1.57 2729  96  35  -8 0.01
Mon 04/06 06Z 1.74 2830  94  45  -9 0.01
Mon 04/06 07Z 1.26 2831  92  53  -8 0.00
Mon 04/06 08Z 1.22 2831  93  51  -8 0.00
Mon 04/06 09Z 1.37 2831  93  52  -9 0.00
Mon 04/06 10Z 1.53 2831  96  57  -9 0.00
Mon 04/06 11Z 1.56 2829  96  62  -9 0.00
Mon 04/06 12Z 1.70 2828  96  67 -10 0.00
Mon 04/06 13Z 2.43 2827  95  73 -10 0.00
Mon 04/06 14Z 3.09 2826  95  75 -10 0.01
Mon 04/06 15Z 6.06 2825  92  74 -10 0.01
Mon 04/06 16Z 6.73 2824  91  72  -9 0.00
Mon 04/06 17Z 11.38 2823  83  71  -9 0.00
Mon 04/06 18Z 13.10 2822  74  71  -9 0.00
Mon 04/06 19Z 12.44 2821  70  71  -8 0.00
Mon 04/06 20Z 12.70 2820  65  73  -8 0.00
Mon 04/06 21Z 12.89 2821  64  73  -7 0.00
Mon 04/06 22Z 12.33 2822  68  72  -8 0.00
Mon 04/06 23Z 8.06 2823  73  73  -8 0.00
Tue 04/07 00Z 2.51 2823  79  74  -9 0.00
Tue 04/07 01Z 1.59 2820  82  75  -9 0.00
Tue 04/07 02Z 1.18 2818  88  76  -9 0.00
Tue 04/07 03Z 0.92 2817  89  80  -9 0.01
Tue 04/07 04Z 0.81 2917  89  79  -9 0.01
Tue 04/07 05Z 0.64 2916  90  81 -10 0.01
Tue 04/07 06Z 0.45 3014  91  84 -10 0.01
Tue 04/07 07Z 0.37 3013  87  83 -10 0.01
Tue 04/07 08Z 0.41 3013  83  75 -11 0.00
Tue 04/07 09Z 0.42 2913  84  72 -11 0.00
Tue 04/07 10Z 0.48 2913  85  83 -12 0.00
Tue 04/07 11Z 0.46 2913  89  76 -12 0.00

Run total areal avg QPF for the Central_Greens is: 0.69 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