Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260620_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)
=== ===== === ==== ==== === === === ====
Sat 06/20 06Z 1.07 2727  93  91   7 0.00
Sat 06/20 07Z 1.15 2731  95  92   7 0.05
Sat 06/20 08Z 1.10 2831  96  93   7 0.09
Sat 06/20 09Z 0.92 2831  97  90   7 0.09
Sat 06/20 10Z 0.82 2931  97  86   7 0.06
Sat 06/20 11Z 0.72 3031  97  84   7 0.04
Sat 06/20 12Z 0.64 3130  97  83   7 0.03
Sat 06/20 13Z 0.62 3128  97  84   7 0.03
Sat 06/20 14Z 0.71 3126  96  80   7 0.01
Sat 06/20 15Z 0.87 3022  97  76   8 0.01
Sat 06/20 16Z 1.38 2921  96  82   8 0.04
Sat 06/20 17Z 1.28 2923  96  81   8 0.06
Sat 06/20 18Z 1.83 2922  96  74   9 0.03
Sat 06/20 19Z 2.58 2922  95  72   9 0.02
Sat 06/20 20Z 3.20 2921  92  67   9 0.01
Sat 06/20 21Z 3.13 2922  90  69   9 0.01
Sat 06/20 22Z 1.95 2922  90  64   9 0.00
Sat 06/20 23Z 1.09 2922  92  65   9 0.00
Sun 06/21 00Z 0.91 2922  94  64   9 0.00
Sun 06/21 01Z 0.73 2921  94  62   9 0.01
Sun 06/21 02Z 0.64 2920  95  62   9 0.00
Sun 06/21 03Z 0.54 3018  96  63   9 0.01
Sun 06/21 04Z 0.47 3016  96  68   9 0.01
Sun 06/21 05Z 0.42 3015  96  73   9 0.01
Sun 06/21 06Z 0.35 3014  94  75   9 0.00
Sun 06/21 07Z 0.36 3014  94  79   8 0.00
Sun 06/21 08Z 0.34 2913  94  84   9 0.01
Sun 06/21 09Z 0.32 3013  94  79   8 0.01
Sun 06/21 10Z 0.30 3012  93  74   8 0.00
Sun 06/21 11Z 0.31 2911  93  68   8 0.00
Sun 06/21 12Z 0.28 2910  92  63   8 0.00
Sun 06/21 13Z 0.28 2909  91  62   9 0.00
Sun 06/21 14Z 0.33 2810  89  55   9 0.00
Sun 06/21 15Z 0.41 2809  89  44   9 0.00
Sun 06/21 16Z 1.10 2809  89  43   8 0.00
Sun 06/21 17Z 1.59 2808  89  34   9 0.00
Sun 06/21 18Z 1.48 2909  89  40   9 0.01
Sun 06/21 19Z 0.71 3009  88  47   9 0.06
Sun 06/21 20Z 0.47 3011  82  41   9 0.08
Sun 06/21 21Z 0.74 3010  83  38   9 0.01
Sun 06/21 22Z 0.48 3010  85  39   9 0.01
Sun 06/21 23Z 0.40 3011  81  32   9 0.05
Mon 06/22 00Z 0.36 3011  82  34   9 0.00
Mon 06/22 01Z 0.46 2913  89  41   9 0.00
Mon 06/22 02Z 0.31 3012  84  51   9 0.00
Mon 06/22 03Z 0.32 3014  82  57   9 0.00
Mon 06/22 04Z 0.24 3215  83  45   9 0.00
Mon 06/22 05Z 0.25 3114  82  46   9 0.00
Mon 06/22 06Z 0.19 3212  82  37   9 0.00
Mon 06/22 07Z 0.24 3111  83  31   9 0.00
Mon 06/22 08Z 0.16 3208  79  27   9 0.00
Mon 06/22 09Z 0.13 3106  76  26  10 0.00
Mon 06/22 10Z 0.19 2806  76  28   9 0.00
Mon 06/22 11Z 0.23 2606  77  29   9 0.00
Mon 06/22 12Z 0.25 2507  76  29   9 0.00
Mon 06/22 13Z 0.28 2407  78  31   9 0.00
Mon 06/22 14Z 0.21 2306  74  30   9 0.00
Mon 06/22 15Z 0.21 2205  71  29  10 0.00
Mon 06/22 16Z 0.14 1906  70  26  10 0.00
Mon 06/22 17Z 0.20 1908  74  39  10 0.00

Run total areal avg QPF for the Central_Greens is: 0.86 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