NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260510_0000
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 05/10 00Z 0.14 1815  97  53   2 0.00
Sun 05/10 01Z 0.19 1918  96  39   3 0.01
Sun 05/10 02Z 0.25 1919  96  35   3 0.01
Sun 05/10 03Z 0.27 1920  96  33   3 0.01
Sun 05/10 04Z 0.38 2021  97  33   3 0.01
Sun 05/10 05Z 0.44 2122  96  35   3 0.00
Sun 05/10 06Z 0.50 2123  94  46   4 0.00
Sun 05/10 07Z 0.52 2223  92  49   4 0.01
Sun 05/10 08Z 0.56 2323  93  64   5 0.01
Sun 05/10 09Z 0.61 2322  94  82   5 0.02
Sun 05/10 10Z 0.61 2422  96  81   5 0.01
Sun 05/10 11Z 0.58 2421  94  59   5 0.01
Sun 05/10 12Z 0.55 2321  91  53   5 0.01
Sun 05/10 13Z 0.55 2421  88  69   5 0.01
Sun 05/10 14Z 0.59 2421  86  73   5 0.00
Sun 05/10 15Z 0.66 2420  87  81   5 0.00
Sun 05/10 16Z 0.96 2419  92  92   4 0.00
Sun 05/10 17Z 0.76 2417  88  73   4 0.02
Sun 05/10 18Z 1.75 2414  88  28   4 0.00
Sun 05/10 19Z 3.58 2514  91  23   4 0.00
Sun 05/10 20Z 4.14 2515  81  14   4 0.01
Sun 05/10 21Z 7.22 2617  68  16   4 0.00
Sun 05/10 22Z 10.23 2719  46  17   4 0.00
Sun 05/10 23Z 5.18 2720  43  19   3 0.00
Mon 05/11 00Z 2.08 2721  39  25   2 0.00
Mon 05/11 01Z 1.50 2822  42  26   1 0.00
Mon 05/11 02Z 1.11 2921  52  24   0 0.00
Mon 05/11 03Z 0.99 2920  64  29   0 0.00
Mon 05/11 04Z 1.00 3020  74  22  -1 0.00
Mon 05/11 05Z 0.87 3020  76  19  -1 0.00
Mon 05/11 06Z 0.63 3119  80  17  -2 0.00
Mon 05/11 07Z 0.52 3117  81  16  -2 0.00
Mon 05/11 08Z 0.41 3114  82  17  -2 0.00
Mon 05/11 09Z 0.35 3113  84  17  -2 0.00
Mon 05/11 10Z 0.31 3111  85  19  -3 0.00
Mon 05/11 11Z 0.30 3009  85  20  -3 0.00
Mon 05/11 12Z 0.34 2908  85  21  -3 0.00
Mon 05/11 13Z 0.47 2908  84  26  -3 0.00
Mon 05/11 14Z 1.83 2908  79  29  -3 0.00
Mon 05/11 15Z 3.63 2808  68  32  -2 0.00
Mon 05/11 16Z 5.15 2809  69  38  -2 0.00
Mon 05/11 17Z 5.46 2909  69  45  -1 0.00
Mon 05/11 18Z 5.61 2810  67  66  -1 0.00
Mon 05/11 19Z 4.94 2910  63  65  -1 0.00
Mon 05/11 20Z 5.67 2911  62  84  -1 0.00
Mon 05/11 21Z 4.41 2911  68  82  -1 0.00
Mon 05/11 22Z 2.71 3012  73  77  -1 0.00
Mon 05/11 23Z 0.86 3113  77  65  -2 0.00
Tue 05/12 00Z 0.41 3216  72  69  -2 0.00
Tue 05/12 01Z 0.40 3217  74  64  -2 0.00
Tue 05/12 02Z 0.41 3217  77  60  -3 0.00
Tue 05/12 03Z 0.56 3218  79  50  -3 0.00
Tue 05/12 04Z 0.57 3219  80  44  -4 0.00
Tue 05/12 05Z 0.51 3220  75  46  -4 0.00
Tue 05/12 06Z 0.46 3220  73  35  -4 0.00
Tue 05/12 07Z 0.40 3320  74  25  -4 0.00
Tue 05/12 08Z 0.35 3318  74  31  -5 0.00
Tue 05/12 09Z 0.32 3317  74  45  -5 0.00
Tue 05/12 10Z 0.31 3216  72  48  -5 0.00
Tue 05/12 11Z 0.36 3216  72  33  -5 0.00

Run total areal avg QPF for the Central_Greens is: 0.15 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