NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260517_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 05/17 00Z 0.95 2222  62  72  11 0.00
Sun 05/17 01Z 1.19 2327  63  86  11 0.01
Sun 05/17 02Z 1.51 2430  66  85  11 0.00
Sun 05/17 03Z 1.69 2534  78  74  11 0.00
Sun 05/17 04Z 1.59 2636  90  11  10 0.01
Sun 05/17 05Z 1.28 2734  94  17  10 0.03
Sun 05/17 06Z 1.13 2734  92   7  10 0.02
Sun 05/17 07Z 0.90 2833  85   7  10 0.01
Sun 05/17 08Z 0.82 2934  83   6  10 0.00
Sun 05/17 09Z 0.66 2931  70  15  10 0.00
Sun 05/17 10Z 0.54 2927  54  17  11 0.00
Sun 05/17 11Z 0.48 2923  49  16  11 0.00
Sun 05/17 12Z 0.48 2923  50  53  10 0.00
Sun 05/17 13Z 0.52 3022  54  82  10 0.00
Sun 05/17 14Z 0.50 2918  53  57  10 0.00
Sun 05/17 15Z 0.60 2816  63  33  10 0.00
Sun 05/17 16Z 0.69 2715  69  30  10 0.00
Sun 05/17 17Z 4.01 2613  81  33  10 0.00
Sun 05/17 18Z 2.41 2617  92  28  10 0.02
Sun 05/17 19Z 1.09 2717  93  18  10 0.01
Sun 05/17 20Z 0.89 2816  92  21  10 0.01
Sun 05/17 21Z 0.56 2914  89  19  10 0.01
Sun 05/17 22Z 0.47 2913  88  19  10 0.01
Sun 05/17 23Z 0.34 3013  84  16  10 0.00
Mon 05/18 00Z 0.29 3113  84  14  10 0.00
Mon 05/18 01Z 0.26 3113  80  17   9 0.00
Mon 05/18 02Z 0.28 3113  73  18   9 0.00
Mon 05/18 03Z 0.27 3013  69  22  10 0.00
Mon 05/18 04Z 0.26 3012  65  27  10 0.00
Mon 05/18 05Z 0.18 3010  61  34  10 0.00
Mon 05/18 06Z 0.14 3007  58  31  11 0.00
Mon 05/18 07Z 0.15 2706  56  39  12 0.00
Mon 05/18 08Z 0.18 2607  54  67  12 0.00
Mon 05/18 09Z 0.24 2509  57  84  12 0.00
Mon 05/18 10Z 0.18 2407  64  88  12 0.00
Mon 05/18 11Z 0.10 2006  73  86  12 0.00
Mon 05/18 12Z 0.12 1911  88  91  11 0.02
Mon 05/18 13Z 0.14 1919  95  88  12 0.02
Mon 05/18 14Z 0.26 2024  97  78  12 0.04
Mon 05/18 15Z 0.36 2126  98  72  12 0.05
Mon 05/18 16Z 0.46 2225  98  55  12 0.05
Mon 05/18 17Z 0.47 2223  97  41  12 0.02
Mon 05/18 18Z 0.52 2222  94  40  13 0.00
Mon 05/18 19Z 0.59 2322  95  18  13 0.00
Mon 05/18 20Z 0.59 2221  93  13  14 0.00
Mon 05/18 21Z 0.57 2221  93  14  14 0.00
Mon 05/18 22Z 0.66 2223  94  18  15 0.01
Mon 05/18 23Z 0.70 2224  95  21  15 0.01
Tue 05/19 00Z 0.71 2226  94  22  15 0.02
Tue 05/19 01Z 0.77 2328  92  14  16 0.02
Tue 05/19 02Z 0.79 2331  89   9  17 0.02
Tue 05/19 03Z 0.87 2433  85  28  17 0.02
Tue 05/19 04Z 1.01 2436  88  30  17 0.02
Tue 05/19 05Z 1.11 2438  88  45  17 0.04
Tue 05/19 06Z 1.26 2638  90  52  15 0.07
Tue 05/19 07Z 1.03 2733  81  55  15 0.03
Tue 05/19 08Z 1.02 2731  86  56  15 0.00
Tue 05/19 09Z 0.94 2729  86  54  15 0.00
Tue 05/19 10Z 1.00 2729  87  46  14 0.00
Tue 05/19 11Z 1.00 2629  88  51  14 0.00

Run total areal avg QPF for the Central_Greens is: 0.60 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