NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260412_1200
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 04/12 12Z 0.03 0005  64  19  -3 0.00
Sun 04/12 13Z 0.02 3301  62  22  -3 0.00
Sun 04/12 14Z 0.05 2002  59  24  -2 0.00
Sun 04/12 15Z 0.09 1904  58  26  -2 0.00
Sun 04/12 16Z 0.26 1906  59  27  -2 0.00
Sun 04/12 17Z 0.80 1907  60  29  -2 0.00
Sun 04/12 18Z 1.01 2009  57  77  -1 0.00
Sun 04/12 19Z 0.33 1911  51  88   0 0.00
Sun 04/12 20Z 0.20 1813  48  97   0 0.00
Sun 04/12 21Z 0.13 1713  57  95  -1 0.00
Sun 04/12 22Z 0.14 1716  59  87   0 0.00
Sun 04/12 23Z 0.37 1920  67  99  -1 0.00
Mon 04/13 00Z 0.34 1922  87  98   0 0.02
Mon 04/13 01Z 0.37 2024  88  99   0 0.02
Mon 04/13 02Z 0.42 2027  88  99   1 0.02
Mon 04/13 03Z 0.44 2129  93  99   3 0.04
Mon 04/13 04Z 0.44 2230  95  95   5 0.03
Mon 04/13 05Z 0.47 2233  92  96   7 0.04
Mon 04/13 06Z 0.47 2232  90  96   8 0.03
Mon 04/13 07Z 0.51 2234  90  83   9 0.02
Mon 04/13 08Z 0.54 2335  89  31  10 0.00
Mon 04/13 09Z 0.59 2335  89  64   9 0.01
Mon 04/13 10Z 0.65 2438  93  86   9 0.03
Mon 04/13 11Z 0.70 2438  90  85  10 0.01
Mon 04/13 12Z 0.71 2438  91  68  10 0.01
Mon 04/13 13Z 0.76 2439  88  79  10 0.01
Mon 04/13 14Z 0.78 2438  92  85   9 0.03
Mon 04/13 15Z 0.89 2343  86  93   9 0.01
Mon 04/13 16Z 1.00 2246  97  96   8 0.09
Mon 04/13 17Z 1.12 2346  98  96   8 0.11
Mon 04/13 18Z 1.20 2445  98  95   8 0.11
Mon 04/13 19Z 1.19 2643  98  62   9 0.05
Mon 04/13 20Z 1.11 2639  97  53   9 0.02
Mon 04/13 21Z 1.14 2638  97  53  10 0.02
Mon 04/13 22Z 1.24 2637  98  54   9 0.02
Mon 04/13 23Z 1.37 2638  97  53   9 0.03
Tue 04/14 00Z 1.37 2638  98  42   9 0.03
Tue 04/14 01Z 1.49 2738  98  28   8 0.04
Tue 04/14 02Z 1.24 2835  97  27   8 0.02
Tue 04/14 03Z 0.97 2932  97  34   7 0.02
Tue 04/14 04Z 0.80 3028  96  36   7 0.01
Tue 04/14 05Z 0.59 3025  94  41   7 0.01
Tue 04/14 07Z 0.33 3020  83  46   8 0.01
Tue 04/14 08Z 0.26 3017  75  44   9 0.01
Tue 04/14 09Z 0.23 3014  70  42  10 0.01
Tue 04/14 10Z 0.23 2812  66  32  10 0.01
Tue 04/14 11Z 0.24 2612  62  36  10 0.00
Tue 04/14 12Z 0.25 2512  59  38  10 0.01
Tue 04/14 13Z 0.26 2513  57  50  10 0.00
Tue 04/14 14Z 0.27 2314  58  50  10 0.00
Tue 04/14 15Z 0.38 2318  63  56  11 0.00
Tue 04/14 16Z 0.47 2320  82  61  11 0.00
Tue 04/14 17Z 0.52 2322  85  51  11 0.00
Tue 04/14 18Z 0.62 2322  89  81  11 0.00
Tue 04/14 19Z 0.73 2327  87  82  11 0.00
Tue 04/14 20Z 0.76 2231  79  72  12 0.01
Tue 04/14 21Z 0.73 2330  70  61  13 0.02
Tue 04/14 22Z 0.71 2327  75  65  13 0.01
Tue 04/14 23Z 0.79 2230  83  65  13 0.00

Run total areal avg QPF for the Central_Greens is: 1.00 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