NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260913_1800
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 09/13 18Z 0.27 2210  98  30  13 0.00
Sun 09/13 19Z 0.27 2210  95  33  13 0.00
Sun 09/13 20Z 0.26 2210  93  30  14 0.00
Sun 09/13 21Z 0.32 2312  85  28  15 0.00
Sun 09/13 22Z 0.40 2515  81  30  15 0.00
Sun 09/13 23Z 0.49 2518  81  36  15 0.00
Mon 09/14 00Z 0.60 2621  85  39  15 0.00
Mon 09/14 01Z 0.69 2623  88  54  15 0.00
Mon 09/14 02Z 0.83 2526  94  62  14 0.01
Mon 09/14 03Z 0.83 2626  90  65  15 0.03
Mon 09/14 04Z 0.85 2725  91  72  13 0.05
Mon 09/14 05Z 0.78 2825  91  76  12 0.03
Mon 09/14 06Z 0.79 2925  92  80  11 0.02
Mon 09/14 07Z 0.63 2923  73  87  10 0.01
Mon 09/14 08Z 0.80 2924  80  69   9 0.00
Mon 09/14 09Z 0.73 2926  83  46   9 0.00
Mon 09/14 10Z 0.56 3028  82  21   8 0.00
Mon 09/14 11Z 0.41 3129  80  10   7 0.00
Mon 09/14 12Z 0.30 3229  79   9   5 0.00
Mon 09/14 13Z 0.24 3327  81   9   5 0.00
Mon 09/14 14Z 0.20 3325  83   9   5 0.00
Mon 09/14 15Z 0.20 3323  82   8   4 0.00
Mon 09/14 16Z 0.19 3320  80   9   4 0.00
Mon 09/14 17Z 0.24 3319  75   7   4 0.00
Mon 09/14 18Z 0.34 3218  71   6   4 0.00
Mon 09/14 19Z 0.98 3217  73   6   4 0.00
Mon 09/14 20Z 1.80 3216  80   9   4 0.00
Mon 09/14 21Z 0.96 3216  82  15   4 0.00
Mon 09/14 22Z 0.54 3218  82  18   4 0.00
Mon 09/14 23Z 0.45 3221  81  18   4 0.00
Tue 09/15 00Z 0.37 3221  81  17   4 0.00
Tue 09/15 01Z 0.21 3321  77  15   5 0.00
Tue 09/15 02Z 0.12 3320  72  12   6 0.00
Tue 09/15 03Z 0.02 3417  65   8   7 0.00
Tue 09/15 04Z 0.03 3518  68   8   7 0.00
Tue 09/15 05Z 0.07 0016  62   7   7 0.00
Tue 09/15 06Z 0.13 0114  58   6   8 0.00
Tue 09/15 07Z 0.11 0208  55   5   8 0.00
Tue 09/15 08Z 0.08 0306  52   5   8 0.00
Tue 09/15 09Z 0.02 0201  47   5   8 0.00
Tue 09/15 10Z 0.02 2000  42   4   9 0.00
Tue 09/15 11Z 0.02 1801  42   4   8 0.00
Tue 09/15 12Z 0.05 2003  44   4   8 0.00
Tue 09/15 13Z 0.05 1905  43   5   8 0.00
Tue 09/15 14Z 0.07 1906  45   5   8 0.00
Tue 09/15 15Z 0.10 2006  48   6   8 0.00
Tue 09/15 16Z 0.08 1906  49   6   9 0.00
Tue 09/15 17Z 0.09 1907  51   8  10 0.00
Tue 09/15 18Z 0.10 1908  54   9  10 0.00
Tue 09/15 19Z 0.08 1810  52  10  11 0.00
Tue 09/15 20Z 0.13 1911  52  12  11 0.00
Tue 09/15 21Z 0.17 1914  52  13  11 0.00
Tue 09/15 22Z 0.20 1916  49  15  12 0.00
Tue 09/15 23Z 0.23 2018  42  17  14 0.00
Wed 09/16 00Z 0.26 2020  37  27  14 0.00
Wed 09/16 01Z 0.31 2122  34  34  14 0.00
Wed 09/16 02Z 0.34 2123  31  48  14 0.00
Wed 09/16 03Z 0.39 2223  32  63  14 0.00
Wed 09/16 04Z 0.41 2323  33  72  15 0.00
Wed 09/16 05Z 0.42 2323  34  84  14 0.00

Run total areal avg QPF for the Central_Greens is: 0.15 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