NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260510_0000
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sun 05/10 00Z 0.06 1817  97  46   2 0.00
Sun 05/10 01Z 0.10 1820  95  34   3 0.01
Sun 05/10 02Z 0.15 1921  94  32   3 0.01
Sun 05/10 03Z 0.16 1922  94  29   3 0.01
Sun 05/10 04Z 0.27 2024  95  31   3 0.01
Sun 05/10 05Z 0.33 2024  93  32   4 0.00
Sun 05/10 06Z 0.40 2125  92  48   4 0.00
Sun 05/10 07Z 0.42 2225  91  57   5 0.01
Sun 05/10 08Z 0.51 2225  93  70   5 0.01
Sun 05/10 09Z 0.59 2323  92  88   4 0.04
Sun 05/10 10Z 0.56 2322  93  83   5 0.02
Sun 05/10 11Z 0.55 2322  93  64   5 0.01
Sun 05/10 12Z 0.54 2322  92  49   5 0.00
Sun 05/10 13Z 0.57 2322  91  58   5 0.01
Sun 05/10 14Z 0.63 2421  90  63   4 0.01
Sun 05/10 15Z 0.69 2420  88  74   4 0.01
Sun 05/10 16Z 1.02 2419  91  77   3 0.00
Sun 05/10 17Z 1.22 2416  89  60   3 0.01
Sun 05/10 18Z 1.78 2514  88  26   3 0.01
Sun 05/10 19Z 4.38 2514  86  23   3 0.01
Sun 05/10 20Z 5.88 2616  73  22   3 0.01
Sun 05/10 21Z 8.85 2617  61  20   3 0.00
Sun 05/10 22Z 9.64 2718  47  20   3 0.00
Sun 05/10 23Z 4.10 2819  51  21   2 0.00
Mon 05/11 00Z 1.74 2820  54  27   1 0.00
Mon 05/11 01Z 1.46 2921  59  28   0 0.00
Mon 05/11 02Z 1.29 2921  63  28   0 0.00
Mon 05/11 03Z 1.13 2920  71  32   0 0.00
Mon 05/11 04Z 1.04 3019  77  31  -1 0.00
Mon 05/11 05Z 0.98 3019  79  30  -2 0.00
Mon 05/11 06Z 0.75 3018  82  27  -2 0.00
Mon 05/11 07Z 0.66 3116  83  21  -2 0.00
Mon 05/11 08Z 0.55 3114  83  20  -2 0.00
Mon 05/11 09Z 0.47 3113  83  19  -3 0.00
Mon 05/11 10Z 0.42 3111  83  20  -3 0.00
Mon 05/11 11Z 0.41 3010  85  22  -3 0.00
Mon 05/11 12Z 0.47 2909  88  23  -3 0.00
Mon 05/11 13Z 0.59 2909  87  28  -3 0.00
Mon 05/11 14Z 2.02 2809  83  33  -3 0.00
Mon 05/11 15Z 3.49 2809  76  37  -3 0.00
Mon 05/11 16Z 4.36 2910  77  46  -2 0.01
Mon 05/11 17Z 5.00 2910  75  52  -2 0.00
Mon 05/11 18Z 4.43 2811  73  70  -2 0.01
Mon 05/11 19Z 4.17 2911  70  62  -1 0.00
Mon 05/11 20Z 4.39 2912  71  82  -1 0.01
Mon 05/11 21Z 3.45 3012  70  82  -1 0.00
Mon 05/11 22Z 2.57 3013  77  75  -2 0.00
Mon 05/11 23Z 0.98 3115  77  70  -2 0.01
Tue 05/12 00Z 0.68 3117  74  63  -2 0.00
Tue 05/12 01Z 0.81 3218  77  59  -3 0.00
Tue 05/12 02Z 0.73 3218  78  58  -3 0.00
Tue 05/12 03Z 0.84 3219  79  45  -3 0.00
Tue 05/12 04Z 0.80 3219  77  43  -4 0.00
Tue 05/12 05Z 0.70 3220  74  43  -4 0.00
Tue 05/12 06Z 0.60 3219  72  33  -4 0.00
Tue 05/12 07Z 0.52 3319  73  29  -4 0.00
Tue 05/12 08Z 0.50 3317  73  37  -5 0.00
Tue 05/12 09Z 0.47 3216  73  48  -5 0.00
Tue 05/12 10Z 0.46 3215  73  46  -5 0.00
Tue 05/12 11Z 0.53 3215  74  30  -6 0.00

Run total areal avg QPF for the greens is: 0.24 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