NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260511_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)
=== ===== === ==== ==== === === === ====
Mon 05/11 18Z 4.96 2809  63  80   0 0.00
Mon 05/11 19Z 6.15 2809  62  78   0 0.00
Mon 05/11 20Z 5.63 2809  64  90   0 0.00
Mon 05/11 21Z 2.83 2809  68  79   0 0.00
Mon 05/11 22Z 2.26 2909  70  77   0 0.00
Mon 05/11 23Z 0.66 2911  78  81   0 0.00
Tue 05/12 00Z 0.38 3213  78  69   0 0.00
Tue 05/12 01Z 0.20 3315  82  73  -1 0.00
Tue 05/12 02Z 0.17 3316  81  79  -1 0.00
Tue 05/12 03Z 0.11 3416  82  76  -2 0.00
Tue 05/12 04Z 0.05 3416  81  76  -2 0.00
Tue 05/12 05Z 0.07 3416  81  67  -2 0.00
Tue 05/12 06Z 0.08 3417  79  50  -2 0.00
Tue 05/12 07Z 0.05 3417  77  45  -2 0.00
Tue 05/12 08Z 0.03 3417  73  44  -2 0.00
Tue 05/12 09Z 0.04 3518  70  33  -3 0.00
Tue 05/12 10Z 0.04 3418  66  27  -3 0.00
Tue 05/12 11Z 0.07 3416  65  31  -3 0.00
Tue 05/12 12Z 0.14 3415  66  36  -3 0.00
Tue 05/12 13Z 1.19 3313  69  36  -4 0.00
Tue 05/12 14Z 1.95 3311  69  33  -3 0.00
Tue 05/12 15Z 3.28 3211  67  37  -3 0.00
Tue 05/12 16Z 3.99 3111  63  40  -2 0.00
Tue 05/12 17Z 6.00 3012  66  39  -2 0.00
Tue 05/12 18Z 6.53 2912  70  36  -2 0.00
Tue 05/12 19Z 6.22 2912  70  35  -1 0.00
Tue 05/12 20Z 4.53 3110  67  31  -1 0.00
Tue 05/12 21Z 3.36 3110  64  28   0 0.00
Tue 05/12 22Z 1.69 3207  63  27   0 0.00
Tue 05/12 23Z 0.90 3007  62  28   0 0.00
Wed 05/13 00Z 0.39 3007  62  28   0 0.00
Wed 05/13 01Z 0.32 2905  62  25   0 0.00
Wed 05/13 02Z 0.34 2505  62  24   0 0.00
Wed 05/13 03Z 0.36 2306  61  23   0 0.00
Wed 05/13 04Z 0.37 2207  62  20   0 0.00
Wed 05/13 05Z 0.41 2209  61  14   0 0.00
Wed 05/13 06Z 0.47 2211  60  11   0 0.00
Wed 05/13 07Z 0.50 2112  60   8   0 0.00
Wed 05/13 08Z 0.55 2214  62  34   1 0.00
Wed 05/13 09Z 0.54 2215  65  82   1 0.00
Wed 05/13 10Z 0.53 2214  65  96   1 0.00
Wed 05/13 11Z 0.37 2012  67  97   1 0.00
Wed 05/13 12Z 0.24 1914  77  99   1 0.00
Wed 05/13 13Z 0.10 1718  86  99   2 0.01
Wed 05/13 14Z 0.09 1725  91  98   2 0.01
Wed 05/13 15Z 0.21 1829  97  97   4 0.05
Wed 05/13 16Z 0.24 1928  97  97   4 0.06
Wed 05/13 17Z 0.27 1928  97  96   5 0.05
Wed 05/13 18Z 0.27 1929  93  86   5 0.04
Wed 05/13 19Z 0.32 1929  94  95   4 0.02
Wed 05/13 20Z 0.31 1928  96  98   4 0.03
Wed 05/13 21Z 0.37 1929  97  95   4 0.04
Wed 05/13 22Z 0.41 1929  96  96   5 0.06
Wed 05/13 23Z 0.42 2030  96  93   5 0.04
Thu 05/14 00Z 0.43 2030  96  90   5 0.02
Thu 05/14 01Z 0.40 1931  95  88   5 0.05
Thu 05/14 02Z 0.42 2032  93  87   5 0.01
Thu 05/14 03Z 0.44 2033  86  83   5 0.02
Thu 05/14 04Z 0.42 2032  81  86   5 0.01
Thu 05/14 05Z 0.37 1931  82  83   6 0.00

Run total areal avg QPF for the Central_Greens is: 0.52 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