NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20250523_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)
=== ===== === ==== ==== === === === ====
Fri 05/23 18Z 0.41 2407  98  81   0 0.00
Fri 05/23 19Z 0.54 2508  97  81   0 0.00
Fri 05/23 20Z 0.49 2508  98  84   1 0.01
Fri 05/23 21Z 0.43 2508  98  88   1 0.01
Fri 05/23 22Z 0.41 2508  98  91   1 0.01
Fri 05/23 23Z 0.38 2509  99  94   1 0.01
Sat 05/24 00Z 0.37 2509  98  95   1 0.01
Sat 05/24 01Z 0.37 2510  97  96   1 0.01
Sat 05/24 02Z 0.38 2510  97  94   2 0.01
Sat 05/24 03Z 0.36 2510  98  93   2 0.01
Sat 05/24 04Z 0.35 2610  98  94   1 0.02
Sat 05/24 05Z 0.33 2610  98  95   1 0.02
Sat 05/24 06Z 0.32 2710  98  95   1 0.02
Sat 05/24 07Z 0.30 2910  98  97   1 0.02
Sat 05/24 08Z 0.27 3011  98  97   1 0.02
Sat 05/24 09Z 0.24 3111  97  96   0 0.02
Sat 05/24 10Z 0.23 3113  97  94   0 0.01
Sat 05/24 11Z 0.21 3214  97  94   0 0.01
Sat 05/24 12Z 0.22 3214  97  93   0 0.01
Sat 05/24 13Z 0.27 3215  97  94   0 0.01
Sat 05/24 14Z 0.29 3215  96  93   0 0.01
Sat 05/24 15Z 0.35 3215  95  92  -1 0.01
Sat 05/24 16Z 0.93 3216  94  96  -1 0.00
Sat 05/24 17Z 1.19 3216  93  96   0 0.00
Sat 05/24 18Z 0.62 3216  94  95   0 0.01
Sat 05/24 19Z 0.46 3216  91  93   0 0.00
Sat 05/24 20Z 0.63 3115  92  94   0 0.00
Sat 05/24 21Z 0.68 3115  93  93   0 0.00
Sat 05/24 22Z 0.43 3216  94  91   0 0.00
Sat 05/24 23Z 0.35 3216  92  91   0 0.00
Sun 05/25 00Z 0.37 3217  93  94   0 0.00
Sun 05/25 01Z 0.38 3118  93  93   0 0.00
Sun 05/25 02Z 0.38 3117  94  89   0 0.01
Sun 05/25 03Z 0.35 3117  94  88   0 0.01
Sun 05/25 04Z 0.34 3118  97  90   0 0.01
Sun 05/25 05Z 0.33 3218  98  93   0 0.01
Sun 05/25 06Z 0.33 3219  97  93  -1 0.02
Sun 05/25 07Z 0.26 3219  95  89  -1 0.01
Sun 05/25 08Z 0.24 3220  94  88  -1 0.01
Sun 05/25 09Z 0.26 3220  95  88  -1 0.01
Sun 05/25 10Z 0.30 3221  96  85  -1 0.01
Sun 05/25 11Z 0.29 3221  96  81  -1 0.01
Sun 05/25 12Z 0.28 3221  95  78   0 0.01
Sun 05/25 13Z 0.30 3220  95  74   0 0.01
Sun 05/25 14Z 0.31 3219  96  71   0 0.01
Sun 05/25 15Z 0.49 3218  97  71  -1 0.00
Sun 05/25 16Z 0.76 3218  96  69   0 0.00
Sun 05/25 17Z 0.97 3216  95  65   0 0.01
Sun 05/25 18Z 0.80 3316  94  64   0 0.00
Sun 05/25 19Z 0.74 3315  92  65   0 0.00
Sun 05/25 20Z 0.68 3315  89  66   0 0.00
Sun 05/25 21Z 0.40 3414  86  69   1 0.00
Sun 05/25 22Z 0.27 3514  83  75   1 0.00
Sun 05/25 23Z 0.10 3514  83  81   1 0.00
Mon 05/26 00Z 0.12 3516  82  80   2 0.00
Mon 05/26 01Z 0.09 3515  83  80   2 0.00
Mon 05/26 02Z 0.06 3513  87  84   2 0.00
Mon 05/26 03Z 0.03 3411  91  83   1 0.00
Mon 05/26 04Z 0.06 3411  93  80   1 0.00
Mon 05/26 05Z 0.08 3511  92  76   1 0.00

Run total areal avg QPF for the Central_Greens is: 0.42 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