NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260809_0600
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 08/09 06Z 0.69 2521  87  70  16 0.00
Sun 08/09 07Z 0.76 2623  91  66  15 0.00
Sun 08/09 08Z 0.77 2623  92  60  15 0.01
Sun 08/09 09Z 0.75 2722  95  67  15 0.01
Sun 08/09 10Z 0.63 2820  91  80  15 0.01
Sun 08/09 11Z 0.56 2818  90  66  15 0.00
Sun 08/09 12Z 0.50 2817  90  62  15 0.00
Sun 08/09 13Z 0.46 2816  87  62  15 0.00
Sun 08/09 14Z 0.47 2815  81  61  15 0.00
Sun 08/09 15Z 0.47 2815  72  31  15 0.00
Sun 08/09 16Z 0.52 2813  69   8  15 0.00
Sun 08/09 17Z 0.85 2812  76  14  14 0.00
Sun 08/09 18Z 2.50 2813  81  24  14 0.00
Sun 08/09 19Z 4.64 2813  81  28  14 0.00
Sun 08/09 20Z 5.51 2812  76  26  14 0.00
Sun 08/09 21Z 3.23 2812  74  26  14 0.00
Sun 08/09 22Z 1.44 2912  74  25  14 0.00
Sun 08/09 23Z 0.98 2911  76  27  14 0.00
Mon 08/10 00Z 0.89 2812  77  29  14 0.00
Mon 08/10 01Z 0.74 2913  79  29  14 0.00
Mon 08/10 02Z 0.46 3012  78  32  15 0.00
Mon 08/10 03Z 0.32 2911  72  29  16 0.00
Mon 08/10 04Z 0.26 2909  70  33  16 0.00
Mon 08/10 05Z 0.25 2809  68  30  16 0.00
Mon 08/10 06Z 0.21 2707  64  33  16 0.00
Mon 08/10 07Z 0.22 2707  60  35  16 0.00
Mon 08/10 08Z 0.17 2506  53  32  16 0.00
Mon 08/10 09Z 0.16 2306  50  31  16 0.00
Mon 08/10 10Z 0.21 2307  47  33  15 0.00
Mon 08/10 11Z 0.24 2408  46  31  15 0.00
Mon 08/10 12Z 0.20 2307  45  24  15 0.00
Mon 08/10 13Z 0.21 2208  45  16  15 0.00
Mon 08/10 14Z 0.19 2108  47  16  15 0.00
Mon 08/10 15Z 0.39 2211  58  16  14 0.00
Mon 08/10 16Z 0.59 2211  70  25  14 0.00
Mon 08/10 17Z 0.25 1911  74  41  14 0.00
Mon 08/10 18Z 0.50 1912  78  66  14 0.00
Mon 08/10 19Z 0.48 1912  77  83  14 0.00
Mon 08/10 20Z 0.26 1811  77  96  15 0.00
Mon 08/10 21Z 0.19 1911  88  90  14 0.06
Mon 08/10 22Z 0.27 1914  92  69  15 0.03
Mon 08/10 23Z 0.47 2117  93  76  15 0.00
Tue 08/11 00Z 0.69 2320  96  47  15 0.02
Tue 08/11 01Z 0.85 2422  97  30  15 0.03
Tue 08/11 02Z 0.80 2623  93  23  14 0.04
Tue 08/11 03Z 0.73 2724  94  27  14 0.02
Tue 08/11 04Z 0.73 2826  95  24  14 0.02
Tue 08/11 05Z 0.67 2926  93  24  13 0.02
Tue 08/11 06Z 0.58 2926  91  32  13 0.01
Tue 08/11 07Z 0.51 3025  90  42  13 0.01
Tue 08/11 08Z 0.50 3024  94  53  12 0.01
Tue 08/11 09Z 0.40 3122  94  39  12 0.01
Tue 08/11 10Z 0.36 3121  96  44  12 0.01
Tue 08/11 11Z 0.34 3119  96  41  11 0.01
Tue 08/11 12Z 0.34 3117  97  40  11 0.01
Tue 08/11 13Z 0.36 3015  98  36  11 0.02
Tue 08/11 14Z 0.36 3014  97  27  11 0.01
Tue 08/11 15Z 0.42 3015  96  21  11 0.01
Tue 08/11 16Z 0.44 3015  95  19  11 0.00
Tue 08/11 17Z 0.50 2914  89  21  12 0.01

Run total areal avg QPF for the Central_Greens is: 0.39 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