NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261004_1800
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 10/04 18Z 0.14 1714  93  42   4 0.00
Sun 10/04 19Z 0.22 1617  94  66   4 0.00
Sun 10/04 20Z 0.17 1619  94  86   4 0.00
Sun 10/04 21Z 0.08 1720  93  85   4 0.00
Sun 10/04 22Z 0.04 1722  93  46   5 0.00
Sun 10/04 23Z 0.09 1823  92  42   5 0.00
Mon 10/05 00Z 0.18 1923  91  48   6 0.00
Mon 10/05 01Z 0.24 2023  93  69   6 0.00
Mon 10/05 02Z 0.29 2023  96  71   6 0.01
Mon 10/05 03Z 0.35 2122  97  71   6 0.01
Mon 10/05 04Z 0.43 2223  97  70   7 0.02
Mon 10/05 05Z 0.44 2221  97  59   7 0.01
Mon 10/05 06Z 0.45 2321  94  61   7 0.01
Mon 10/05 07Z 0.47 2321  92  78   8 0.01
Mon 10/05 08Z 0.50 2321  91  82   8 0.02
Mon 10/05 09Z 0.57 2324  94  93   7 0.04
Mon 10/05 10Z 0.72 2426  96  91   7 0.14
Mon 10/05 11Z 0.84 2626  96  94   6 0.10
Mon 10/05 12Z 0.95 2725  94  84   5 0.06
Mon 10/05 13Z 1.02 2826  84  54   4 0.04
Mon 10/05 14Z 0.95 2825  82  52   4 0.02
Mon 10/05 15Z 1.18 2825  88  67   3 0.02
Mon 10/05 16Z 5.50 2826  82  70   1 0.02
Mon 10/05 17Z 10.02 2824  79  40   1 0.01
Mon 10/05 18Z 10.33 2825  77  22   1 0.01
Mon 10/05 19Z 10.14 2825  77  55   0 0.01
Mon 10/05 20Z 3.80 2926  85  51   0 0.01
Mon 10/05 21Z 2.44 2927  90  53   0 0.01
Mon 10/05 22Z 1.74 2930  92  52  -1 0.01
Mon 10/05 23Z 1.72 2931  94  54  -2 0.01
Tue 10/06 00Z 1.34 3031  92  54  -2 0.00
Tue 10/06 01Z 1.17 3031  92  54  -2 0.00
Tue 10/06 02Z 1.13 3032  90  57  -2 0.01
Tue 10/06 03Z 1.05 3032  88  57  -2 0.00
Tue 10/06 04Z 1.02 2932  89  40  -3 0.01
Tue 10/06 05Z 0.98 2931  90  31  -3 0.01
Tue 10/06 06Z 0.87 3031  88  30  -3 0.01
Tue 10/06 07Z 0.78 3031  86  28  -3 0.01
Tue 10/06 08Z 0.68 3031  84  27  -3 0.01
Tue 10/06 09Z 0.64 3031  85  25  -3 0.01
Tue 10/06 10Z 0.60 3031  84  24  -3 0.01
Tue 10/06 11Z 0.58 3030  83  26  -2 0.01
Tue 10/06 12Z 0.55 3029  77  24  -2 0.01
Tue 10/06 13Z 0.48 3029  72  21  -1 0.01
Tue 10/06 14Z 0.45 3028  69  18  -1 0.00
Tue 10/06 15Z 0.46 3027  66  15   0 0.00
Tue 10/06 16Z 0.48 3026  58  12   0 0.00
Tue 10/06 17Z 0.55 3025  54   9   0 0.00
Tue 10/06 18Z 0.70 3025  51   6   0 0.00
Tue 10/06 19Z 0.99 2924  51   5   0 0.00
Tue 10/06 20Z 2.37 2923  51   7   0 0.00
Tue 10/06 21Z 2.37 2923  49  11   0 0.00
Tue 10/06 22Z 1.25 2923  44  25   0 0.00
Tue 10/06 23Z 0.96 2925  40  38   0 0.00
Wed 10/07 00Z 0.90 2924  42  42   0 0.00
Wed 10/07 01Z 0.84 2924  42  61   0 0.00
Wed 10/07 02Z 0.75 2922  43  61   0 0.00
Wed 10/07 03Z 0.67 2920  43  65   0 0.00
Wed 10/07 04Z 0.62 2919  41  74   0 0.00
Wed 10/07 05Z 0.59 2818  44  90   1 0.00

Run total areal avg QPF for the greens is: 0.71 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