NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260731_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)
=== ===== === ==== ==== === === === ====
Fri 07/31 00Z 0.06 0012  88  87  12 0.00
Fri 07/31 01Z 0.07 0012  87  88  12 0.00
Fri 07/31 02Z 0.07 0013  86  91  12 0.00
Fri 07/31 03Z 0.05 0013  86  90  12 0.00
Fri 07/31 04Z 0.04 0013  86  87  12 0.00
Fri 07/31 05Z 0.02 3512  85  87  12 0.00
Fri 07/31 06Z 0.06 3512  84  86  12 0.00
Fri 07/31 07Z 0.10 3412  84  86  12 0.00
Fri 07/31 08Z 0.13 3412  85  87  11 0.00
Fri 07/31 09Z 0.11 3412  86  84  11 0.00
Fri 07/31 10Z 0.12 3412  88  84  11 0.00
Fri 07/31 11Z 0.08 3412  89  84  11 0.00
Fri 07/31 12Z 0.09 3411  91  82  11 0.00
Fri 07/31 13Z 0.11 3410  92  77  11 0.00
Fri 07/31 14Z 0.18 3310  94  74  11 0.00
Fri 07/31 15Z 0.20 3309  96  72  11 0.00
Fri 07/31 16Z 0.15 3308  96  65  11 0.00
Fri 07/31 17Z 0.17 3307  95  57  11 0.01
Fri 07/31 18Z 0.17 3305  92  52  12 0.01
Fri 07/31 19Z 0.37 3208  91  54  12 0.01
Fri 07/31 20Z 0.49 3209  88  50  12 0.01
Fri 07/31 21Z 0.39 3209  83  50  13 0.00
Fri 07/31 22Z 0.31 3311  78  56  13 0.00
Fri 07/31 23Z 0.24 3313  74  57  13 0.00
Sat 08/01 00Z 0.18 3412  72  56  13 0.00
Sat 08/01 01Z 0.25 3313  73  59  13 0.00
Sat 08/01 02Z 0.18 3311  74  56  13 0.00
Sat 08/01 03Z 0.10 3410  74  52  13 0.00
Sat 08/01 04Z 0.17 3309  78  52  13 0.00
Sat 08/01 05Z 0.20 3208  79  50  13 0.00
Sat 08/01 06Z 0.22 3108  79  49  13 0.00
Sat 08/01 07Z 0.19 3106  78  47  13 0.00
Sat 08/01 08Z 0.21 3006  78  48  13 0.00
Sat 08/01 09Z 0.21 2905  78  49  13 0.00
Sat 08/01 10Z 0.22 2805  77  48  13 0.00
Sat 08/01 11Z 0.24 2705  76  49  13 0.00
Sat 08/01 12Z 0.26 2606  76  53  13 0.00
Sat 08/01 13Z 0.23 2505  76  52  13 0.00
Sat 08/01 14Z 0.20 2304  77  48  13 0.00
Sat 08/01 15Z 0.53 2305  80  46  13 0.00
Sat 08/01 16Z 0.49 2104  80  41  13 0.00
Sat 08/01 17Z 0.41 2004  80  35  13 0.00
Sat 08/01 18Z 0.60 2004  80  35  14 0.00
Sat 08/01 19Z 0.65 2005  79  34  14 0.00
Sat 08/01 20Z 0.40 1905  77  29  14 0.00
Sat 08/01 21Z 0.18 1806  77  23  14 0.00
Sat 08/01 22Z 0.15 1907  77  19  14 0.00
Sat 08/01 23Z 0.12 1909  76  14  14 0.00
Sun 08/02 00Z 0.18 1911  75  11  14 0.00
Sun 08/02 01Z 0.22 1913  76  10  14 0.00
Sun 08/02 02Z 0.28 2014  76  11  14 0.00
Sun 08/02 03Z 0.30 2016  79  12  15 0.00
Sun 08/02 04Z 0.33 2117  83  15  15 0.00
Sun 08/02 05Z 0.34 2118  88  18  15 0.00
Sun 08/02 06Z 0.37 2119  91  26  14 0.01
Sun 08/02 07Z 0.41 2219  92  33  14 0.01
Sun 08/02 08Z 0.40 2217  92  31  14 0.01
Sun 08/02 09Z 0.37 2216  91  28  14 0.01
Sun 08/02 10Z 0.33 2214  91  23  14 0.00
Sun 08/02 11Z 0.35 2215  92  26  14 0.01

Run total areal avg QPF for the greens is: 0.09 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