NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260524_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 05/24 12Z 0.27 1431  90  99   4 0.00
Sun 05/24 13Z 0.26 1431  92  99   4 0.04
Sun 05/24 14Z 0.27 1432  95  99   4 0.05
Sun 05/24 15Z 0.29 1433  94  99   4 0.06
Sun 05/24 16Z 0.26 1534  93  98   5 0.04
Sun 05/24 17Z 0.21 1533  93  98   6 0.02
Sun 05/24 18Z 0.18 1533  93  99   6 0.02
Sun 05/24 19Z 0.15 1533  95  99   6 0.02
Sun 05/24 20Z 0.13 1532  96  98   6 0.03
Sun 05/24 21Z 0.09 1631  96  95   6 0.02
Sun 05/24 22Z 0.10 1632  96  94   7 0.02
Sun 05/24 23Z 0.10 1634  95  94   8 0.01
Mon 05/25 00Z 0.10 1634  95  94   8 0.01
Mon 05/25 01Z 0.08 1631  95  87   8 0.02
Mon 05/25 02Z 0.07 1629  96  86   9 0.01
Mon 05/25 03Z 0.05 1626  96  90   9 0.01
Mon 05/25 04Z 0.03 1724  96  95  10 0.01
Mon 05/25 05Z 0.04 1721  97  96  10 0.02
Mon 05/25 06Z 0.08 1820  98  93  10 0.02
Mon 05/25 07Z 0.14 1920  98  92  11 0.03
Mon 05/25 08Z 0.16 1919  99  96  11 0.08
Mon 05/25 09Z 0.18 2018  98  91  11 0.11
Mon 05/25 10Z 0.24 2019  99  94  11 0.12
Mon 05/25 11Z 0.30 2218  99  97  10 0.14
Mon 05/25 12Z 0.39 2418  98  96   9 0.16
Mon 05/25 13Z 0.37 2616  98  91   9 0.08
Mon 05/25 14Z 0.27 2814  96  84   9 0.02
Mon 05/25 15Z 0.25 3016  96  75   9 0.00
Mon 05/25 16Z 0.23 3116  93  68  10 0.00
Mon 05/25 17Z 0.29 3016  91  66  10 0.00
Mon 05/25 18Z 0.36 3017  91  50   9 0.00
Mon 05/25 19Z 0.45 2917  93  13   9 0.00
Mon 05/25 20Z 0.51 2917  94   6   9 0.00
Mon 05/25 21Z 0.50 3017  93  10   9 0.00
Mon 05/25 22Z 0.49 3018  89   8   9 0.00
Mon 05/25 23Z 0.44 3017  84   8   9 0.00
Tue 05/26 00Z 0.37 3017  77  12  10 0.00
Tue 05/26 01Z 0.28 3117  68  10  10 0.00
Tue 05/26 02Z 0.28 3118  66   5  10 0.00
Tue 05/26 03Z 0.26 3117  62   5  10 0.00
Tue 05/26 04Z 0.22 3115  57   7  10 0.00
Tue 05/26 05Z 0.22 3115  56  10  10 0.00
Tue 05/26 06Z 0.21 3215  57  11   9 0.00
Tue 05/26 07Z 0.21 3215  56  13   9 0.00
Tue 05/26 08Z 0.24 3216  58  14   9 0.00
Tue 05/26 09Z 0.24 3215  60  16   9 0.00
Tue 05/26 10Z 0.28 3115  62  14  10 0.00
Tue 05/26 11Z 0.30 3014  60  20  10 0.00
Tue 05/26 12Z 0.29 3013  59  26  10 0.00
Tue 05/26 13Z 0.30 2911  60  31  10 0.00
Tue 05/26 14Z 0.38 2811  65  41  10 0.00
Tue 05/26 15Z 0.46 2711  66  51  10 0.00
Tue 05/26 16Z 0.66 2610  65  45  10 0.00
Tue 05/26 17Z 0.90 2511  63  55  11 0.00
Tue 05/26 18Z 1.21 2413  67  60  11 0.00
Tue 05/26 19Z 1.62 2416  66  53  12 0.00
Tue 05/26 20Z 1.47 2317  70  58  12 0.00
Tue 05/26 21Z 1.51 2321  73  70  12 0.00
Tue 05/26 22Z 1.22 2325  68  80  12 0.00
Tue 05/26 23Z 1.39 2429  62  81  13 0.00

Run total areal avg QPF for the Central_Greens is: 1.17 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