NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260615_0600
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 06/15 06Z 0.28 2310  96  95  12 0.00
Mon 06/15 07Z 0.35 2811  99  98  11 0.27
Mon 06/15 08Z 0.38 3117  97  98  10 0.14
Mon 06/15 09Z 0.41 3119  95  97   9 0.08
Mon 06/15 10Z 0.51 3022  93  88   9 0.02
Mon 06/15 11Z 0.56 3122  92  74   8 0.00
Mon 06/15 12Z 0.55 3122  88  64   8 0.01
Mon 06/15 13Z 0.62 3123  86  36   7 0.00
Mon 06/15 14Z 0.73 3020  90  22   7 0.00
Mon 06/15 15Z 1.46 3017  94  25   7 0.00
Mon 06/15 16Z 1.16 3016  95  26   7 0.01
Mon 06/15 17Z 1.21 3014  93  21   7 0.01
Mon 06/15 18Z 2.09 3013  93  14   7 0.00
Mon 06/15 19Z 1.64 3012  90  14   7 0.00
Mon 06/15 20Z 1.99 2912  92  13   7 0.00
Mon 06/15 21Z 1.21 2912  92  10   7 0.01
Mon 06/15 22Z 1.26 3014  91   7   6 0.00
Mon 06/15 23Z 0.71 3016  92   6   6 0.00
Tue 06/16 00Z 0.65 3018  90   7   6 0.00
Tue 06/16 01Z 0.66 3019  94   7   6 0.00
Tue 06/16 02Z 0.58 3019  93   6   6 0.00
Tue 06/16 03Z 0.50 3020  93   8   5 0.00
Tue 06/16 04Z 0.45 3120  93   7   5 0.00
Tue 06/16 05Z 0.46 3122  95   5   5 0.00
Tue 06/16 06Z 0.39 3121  93   2   5 0.00
Tue 06/16 07Z 0.30 3221  85   3   5 0.00
Tue 06/16 08Z 0.24 3222  80   4   5 0.00
Tue 06/16 09Z 0.19 3321  78   7   5 0.00
Tue 06/16 10Z 0.20 3321  77  11   5 0.00
Tue 06/16 11Z 0.20 3219  71  12   6 0.00
Tue 06/16 12Z 0.18 3216  64  14   6 0.00
Tue 06/16 13Z 0.17 3314  58  17   6 0.00
Tue 06/16 14Z 0.23 3212  56  16   6 0.00
Tue 06/16 15Z 0.89 3109  53  14   7 0.00
Tue 06/16 16Z 2.27 3008  50  14   7 0.00
Tue 06/16 17Z 3.37 2907  49  17   8 0.00
Tue 06/16 18Z 4.07 2706  52  20   8 0.00
Tue 06/16 19Z 4.56 2506  55  15   8 0.00
Tue 06/16 20Z 5.39 2408  57  16   9 0.00
Tue 06/16 21Z 5.00 2408  60  13   9 0.00
Tue 06/16 22Z 3.44 2309  61  12   9 0.00
Tue 06/16 23Z 0.86 2309  60  14   9 0.00
Wed 06/17 00Z 0.57 2210  55  14   9 0.00
Wed 06/17 01Z 0.59 2311  50  14   9 0.00
Wed 06/17 02Z 0.64 2312  53  16   9 0.00
Wed 06/17 03Z 0.67 2313  58  18   9 0.00
Wed 06/17 04Z 0.62 2313  61  15   8 0.00
Wed 06/17 05Z 0.56 2312  62  16   8 0.00
Wed 06/17 06Z 0.46 2211  62  16   8 0.00
Wed 06/17 07Z 0.44 2211  62  13   8 0.00
Wed 06/17 08Z 0.41 2111  64  13   8 0.00
Wed 06/17 09Z 0.36 2011  66  12   8 0.00
Wed 06/17 10Z 0.29 1912  67  11   8 0.00
Wed 06/17 11Z 0.28 1913  68  14   8 0.00
Wed 06/17 12Z 0.30 1913  68  14   7 0.00
Wed 06/17 13Z 1.01 1813  69  13   7 0.00
Wed 06/17 14Z 2.33 1813  71   8   8 0.00
Wed 06/17 15Z 2.00 1812  68   7   8 0.00
Wed 06/17 16Z 1.04 1712  66   8   9 0.00
Wed 06/17 17Z 1.05 1713  67  43   9 0.00

Run total areal avg QPF for the Central_Greens is: 0.55 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