NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260812_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)
=== ===== === ==== ==== === === === ====
Wed 08/12 18Z 1.55 2805  80  88  12 0.00
Wed 08/12 19Z 0.68 2707  77  90  12 0.04
Wed 08/12 20Z 0.61 2706  73  85  12 0.02
Wed 08/12 21Z 0.29 2506  79  91  12 0.03
Wed 08/12 22Z 0.29 2406  80  82  12 0.04
Wed 08/12 23Z 0.34 2408  80  81  12 0.03
Thu 08/13 00Z 0.45 2510  79  73  12 0.02
Thu 08/13 01Z 0.51 2512  82  79  12 0.00
Thu 08/13 02Z 0.49 2512  83  83  12 0.02
Thu 08/13 03Z 0.57 2513  84  82  12 0.00
Thu 08/13 04Z 0.63 2614  86  76  12 0.00
Thu 08/13 05Z 0.54 2613  84  79  12 0.00
Thu 08/13 06Z 0.49 2713  85  75  12 0.00
Thu 08/13 07Z 0.48 2713  87  74  12 0.00
Thu 08/13 08Z 0.44 2713  89  74  11 0.00
Thu 08/13 09Z 0.43 2813  88  78  11 0.00
Thu 08/13 10Z 0.39 2812  89  81  11 0.00
Thu 08/13 11Z 0.41 2913  94  83  11 0.04
Thu 08/13 12Z 0.33 3011  92  79  11 0.02
Thu 08/13 13Z 0.29 3010  91  76  11 0.01
Thu 08/13 14Z 0.28 3110  91  75  11 0.01
Thu 08/13 15Z 0.33 3110  93  59  11 0.00
Thu 08/13 16Z 0.41 3111  92  57  11 0.00
Thu 08/13 17Z 0.57 3110  89  55  11 0.00
Thu 08/13 18Z 1.24 3110  87  65  11 0.00
Thu 08/13 19Z 0.59 3011  88  56  11 0.01
Thu 08/13 20Z 0.59 3012  89  56  11 0.00
Thu 08/13 21Z 0.62 3013  88  48  11 0.01
Thu 08/13 22Z 0.76 3016  85  45  11 0.00
Thu 08/13 23Z 0.92 3018  87  46  11 0.01
Fri 08/14 00Z 0.90 3021  89  46  11 0.03
Fri 08/14 01Z 0.86 3124  87  50  10 0.04
Fri 08/14 02Z 0.74 3124  84  47  10 0.01
Fri 08/14 03Z 0.51 3224  82  43   9 0.01
Fri 08/14 04Z 0.41 3324  83  39   9 0.00
Fri 08/14 05Z 0.41 3323  85  33   9 0.00
Fri 08/14 06Z 0.42 3221  88  28   8 0.00
Fri 08/14 07Z 0.40 3221  88  25   8 0.00
Fri 08/14 08Z 0.45 3221  85  26   8 0.00
Fri 08/14 09Z 0.40 3221  82  24   8 0.00
Fri 08/14 10Z 0.38 3221  77  22   7 0.00
Fri 08/14 11Z 0.39 3222  76  21   7 0.00
Fri 08/14 12Z 0.42 3223  77  25   7 0.00
Fri 08/14 13Z 0.43 3222  79  18   7 0.00
Fri 08/14 14Z 0.45 3221  79  17   7 0.00
Fri 08/14 15Z 0.51 3120  77  15   7 0.00
Fri 08/14 16Z 0.57 3120  75  14   8 0.00
Fri 08/14 17Z 0.60 3119  76  13   8 0.00
Fri 08/14 18Z 0.82 3117  79  14   8 0.00
Fri 08/14 19Z 1.69 3016  80  16   8 0.00
Fri 08/14 20Z 1.91 3016  79  17   8 0.00
Fri 08/14 21Z 1.62 3016  77  17   8 0.00
Fri 08/14 22Z 1.12 3016  79  17   8 0.00
Fri 08/14 23Z 0.80 3017  80  18   8 0.00
Sat 08/15 00Z 0.76 3118  81  17   8 0.00
Sat 08/15 01Z 0.70 3119  84  18   7 0.00
Sat 08/15 02Z 0.62 3119  86  18   7 0.00
Sat 08/15 03Z 0.49 3220  88  19   7 0.00
Sat 08/15 04Z 0.42 3221  89  26   7 0.00
Sat 08/15 05Z 0.37 3222  85  47   7 0.00

Run total areal avg QPF for the greens is: 0.40 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