NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260816_1200
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 08/16 12Z 0.05 1904  70   7  10 0.00
Sun 08/16 13Z 0.09 1906  69   7  10 0.00
Sun 08/16 14Z 0.17 2008  71   8  10 0.00
Sun 08/16 15Z 0.38 2010  76   9  10 0.00
Sun 08/16 16Z 0.81 2010  83   8  10 0.00
Sun 08/16 17Z 0.76 1909  86   8  10 0.00
Sun 08/16 18Z 0.48 1910  88   9  11 0.00
Sun 08/16 19Z 0.27 1812  88  17  12 0.00
Sun 08/16 20Z 0.29 1913  90  29  12 0.00
Sun 08/16 21Z 0.28 1916  94  48  12 0.01
Sun 08/16 22Z 0.36 2018  95  69  13 0.01
Sun 08/16 23Z 0.45 2021  95  81  13 0.01
Mon 08/17 00Z 0.45 2024  96  93  13 0.00
Mon 08/17 01Z 0.50 2026  98  91  13 0.01
Mon 08/17 02Z 0.59 2127  96  93  13 0.02
Mon 08/17 03Z 0.56 2127  97  91  13 0.01
Mon 08/17 04Z 0.55 2129  96  97  13 0.01
Mon 08/17 05Z 0.55 2132  96  96  13 0.02
Mon 08/17 06Z 0.58 2133  96  93  13 0.02
Mon 08/17 07Z 0.53 2131  97  93  12 0.02
Mon 08/17 08Z 0.57 2131  98  94  12 0.03
Mon 08/17 09Z 0.55 2129  98  96  13 0.04
Mon 08/17 10Z 0.52 2226  98  96  13 0.04
Mon 08/17 11Z 0.41 2220  97  92  14 0.03
Mon 08/17 12Z 0.35 2317  97  93  14 0.02
Mon 08/17 13Z 0.29 2214  97  91  15 0.01
Mon 08/17 14Z 0.25 2213  96  93  15 0.01
Mon 08/17 15Z 0.22 2112  96  93  15 0.01
Mon 08/17 16Z 0.20 2111  96  95  15 0.02
Mon 08/17 17Z 0.19 2109  96  93  15 0.01
Mon 08/17 18Z 0.20 2209  97  91  15 0.00
Mon 08/17 19Z 0.20 2208  98  83  15 0.00
Mon 08/17 20Z 0.22 2308  99  78  15 0.01
Mon 08/17 21Z 0.23 2408  99  64  15 0.02
Mon 08/17 22Z 0.21 2607  99  50  15 0.01
Mon 08/17 23Z 0.17 2906  99  49  14 0.00
Tue 08/18 00Z 0.18 3008  99  48  14 0.00
Tue 08/18 01Z 0.11 3209  99  37  14 0.00
Tue 08/18 02Z 0.08 3309  98  38  14 0.00
Tue 08/18 03Z 0.04 3409  97  44  14 0.00
Tue 08/18 04Z 0.02 3409  95  53  14 0.00
Tue 08/18 05Z 0.02 3409  95  26  13 0.00
Tue 08/18 06Z 0.02 3409  94  11  13 0.00
Tue 08/18 07Z 0.03 3408  94   6  13 0.00
Tue 08/18 08Z 0.04 3407  93   3  13 0.00
Tue 08/18 09Z 0.04 3407  93   2  13 0.00
Tue 08/18 10Z 0.05 3306  94   2  12 0.00
Tue 08/18 11Z 0.05 3307  94   2  12 0.00
Tue 08/18 12Z 0.05 3307  94   2  12 0.00
Tue 08/18 13Z 0.06 3307  95   2  12 0.00
Tue 08/18 14Z 0.07 3306  97   2  11 0.01
Tue 08/18 15Z 0.07 3404  97   2  11 0.01
Tue 08/18 16Z 0.09 3206  96   2  11 0.01
Tue 08/18 17Z 0.08 3306  95   3  12 0.01
Tue 08/18 18Z 0.10 3207  93   3  12 0.01
Tue 08/18 19Z 0.13 3207  91   3  12 0.01
Tue 08/18 20Z 0.12 3207  89   4  12 0.00
Tue 08/18 21Z 0.14 3207  87   4  12 0.00
Tue 08/18 22Z 0.15 3207  86   3  12 0.00
Tue 08/18 23Z 0.14 3207  87   3  12 0.00

Run total areal avg QPF for the Central_Greens is: 0.46 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