NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260606_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)
=== ===== === ==== ==== === === === ====
Sat 06/06 18Z 0.73 2222  83  97  13 0.00
Sat 06/06 19Z 0.98 2223  81  90  14 0.03
Sat 06/06 20Z 2.73 2122  81  97  14 0.02
Sat 06/06 21Z 2.81 2021  81  66  14 0.02
Sat 06/06 22Z 0.97 1922  80  75  15 0.01
Sat 06/06 23Z 0.67 2225  90  83  14 0.36
Sun 06/07 00Z 0.87 2428  93  67  14 0.28
Sun 06/07 01Z 1.19 2432  94  59  12 0.07
Sun 06/07 04Z 0.91 2729  94  82  11 0.04
Sun 06/07 05Z 0.95 2730  96  79  11 0.02
Sun 06/07 06Z 0.98 2731  96  80  11 0.01
Sun 06/07 07Z 0.97 2731  97  78  11 0.02
Sun 06/07 08Z 0.97 2830  96  61  10 0.03
Sun 06/07 09Z 0.97 2830  96  64  10 0.02
Sun 06/07 10Z 0.96 2831  95  58  10 0.02
Sun 06/07 11Z 0.86 2831  93  50  10 0.01
Sun 06/07 12Z 0.79 2929  94  49  10 0.01
Sun 06/07 13Z 0.82 2927  96  54  10 0.01
Sun 06/07 14Z 0.87 2826  97  63   9 0.01
Sun 06/07 15Z 0.81 2925  98  76   9 0.01
Sun 06/07 16Z 0.65 3024  98  90   9 0.03
Sun 06/07 17Z 0.47 3225  98  95   8 0.04
Sun 06/07 18Z 0.25 3325  98  86   8 0.04
Sun 06/07 19Z 0.19 3427  97  89   8 0.04
Sun 06/07 20Z 0.17 3529  96  92   8 0.04
Sun 06/07 21Z 0.22 0026  94  78   8 0.02
Sun 06/07 22Z 0.22 0027  92  60   8 0.01
Sun 06/07 23Z 0.22 0028  82  22   9 0.00
Mon 06/08 00Z 0.35 0128  81   1   8 0.00
Mon 06/08 01Z 0.48 0129  88   1   6 0.00
Mon 06/08 02Z 0.60 0231  83   1   6 0.00
Mon 06/08 03Z 0.79 0432  67   0   7 0.00
Mon 06/08 04Z 0.93 0434  61   1   7 0.00
Mon 06/08 05Z 0.93 0433  60   0   7 0.00
Mon 06/08 06Z 0.84 0430  57   1   7 0.00
Mon 06/08 07Z 0.79 0329  54   1   8 0.00
Mon 06/08 08Z 0.69 0327  50   2   8 0.00
Mon 06/08 09Z 0.66 0328  51   3   8 0.00
Mon 06/08 10Z 0.62 0327  44   4   8 0.00
Mon 06/08 11Z 0.60 0427  38   6   9 0.00
Mon 06/08 12Z 0.59 0426  40  10   9 0.00
Mon 06/08 13Z 0.57 0422  44  10   8 0.00
Mon 06/08 14Z 0.55 0517  49  11   8 0.00
Mon 06/08 15Z 0.48 0412  47  12   8 0.00
Mon 06/08 16Z 0.57 0509  48  12   9 0.00
Mon 06/08 17Z 0.93 0403  52   9   9 0.00
Mon 06/08 18Z 0.29 0002  56   7   9 0.00
Mon 06/08 19Z 0.17 3501  59   6  10 0.00
Mon 06/08 20Z 0.54 3103  65   6  10 0.00
Mon 06/08 21Z 0.41 3003  68   6  10 0.00
Mon 06/08 22Z 0.22 3003  65   6  10 0.00
Mon 06/08 23Z 0.08 3103  58   4  11 0.00
Tue 06/09 00Z 0.13 3004  53   3  11 0.00
Tue 06/09 01Z 0.22 3006  50   1  11 0.00
Tue 06/09 02Z 0.20 3006  57   1  10 0.00
Tue 06/09 03Z 0.20 3006  62   1  10 0.00
Tue 06/09 04Z 0.19 2905  62   2  11 0.00
Tue 06/09 05Z 0.24 2606  61   4  11 0.00

Run total areal avg QPF for the Central_Greens is: 1.22 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