NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260608_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)
=== ===== === ==== ==== === === === ====
Mon 06/08 18Z 0.33 3101  72   7  10 0.00
Mon 06/08 19Z 0.78 2802  74   6  10 0.00
Mon 06/08 20Z 0.67 2803  77   5  10 0.00
Mon 06/08 21Z 0.65 2604  75   4  10 0.00
Mon 06/08 22Z 0.59 2505  69   4  11 0.00
Mon 06/08 23Z 0.37 2606  65   4  11 0.00
Tue 06/09 00Z 0.38 2508  63   4  11 0.00
Tue 06/09 01Z 0.38 2608  59   4  11 0.00
Tue 06/09 02Z 0.41 2609  57   4  11 0.00
Tue 06/09 03Z 0.44 2610  58   4  11 0.00
Tue 06/09 04Z 0.48 2612  59   4  11 0.00
Tue 06/09 05Z 0.52 2614  61   4  11 0.00
Tue 06/09 06Z 0.52 2714  65   4  11 0.00
Tue 06/09 07Z 0.56 2715  71   3  11 0.00
Tue 06/09 08Z 0.50 2714  77   3  11 0.00
Tue 06/09 09Z 0.37 2712  80   3  11 0.00
Tue 06/09 10Z 0.33 2611  81   3  11 0.00
Tue 06/09 11Z 0.30 2611  79   3  11 0.00
Tue 06/09 12Z 0.24 2409  77   3  11 0.00
Tue 06/09 13Z 0.21 2309  73   3  11 0.00
Tue 06/09 14Z 0.22 2308  71   3  11 0.00
Tue 06/09 15Z 0.23 2308  68   3  11 0.00
Tue 06/09 16Z 0.31 2308  69   3  11 0.00
Tue 06/09 17Z 0.43 2408  68   3  12 0.00
Tue 06/09 18Z 0.38 2507  65   2  12 0.00
Tue 06/09 19Z 0.43 2608  68   2  13 0.00
Tue 06/09 20Z 0.44 2610  74   2  13 0.00
Tue 06/09 21Z 0.46 2511  76   1  13 0.00
Tue 06/09 22Z 0.50 2514  79   1  14 0.00
Tue 06/09 23Z 0.44 2614  79   1  14 0.00
Wed 06/10 00Z 0.42 2615  77   0  15 0.00
Wed 06/10 01Z 0.39 2715  79   1  15 0.00
Wed 06/10 02Z 0.37 2714  82   1  15 0.00
Wed 06/10 03Z 0.32 2812  84   4  15 0.00
Wed 06/10 04Z 0.28 2710  86  21  15 0.00
Wed 06/10 05Z 0.29 2610  86  31  14 0.00
Wed 06/10 06Z 0.27 2509  85  48  15 0.00
Wed 06/10 07Z 0.29 2410  85  60  14 0.00
Wed 06/10 08Z 0.23 2408  84  54  15 0.00
Wed 06/10 09Z 0.22 2308  83  48  14 0.00
Wed 06/10 10Z 0.22 2209  81  59  15 0.00
Wed 06/10 11Z 0.21 2109  79  69  15 0.00
Wed 06/10 12Z 0.21 2110  76  76  15 0.00
Wed 06/10 13Z 0.16 2011  73  79  15 0.00
Wed 06/10 14Z 0.18 2011  72  78  15 0.00
Wed 06/10 15Z 0.17 2010  74  80  15 0.00
Wed 06/10 16Z 0.20 2011  75  67  15 0.00
Wed 06/10 17Z 0.25 2010  78  42  15 0.00
Wed 06/10 18Z 0.37 1910  82  55  15 0.00
Wed 06/10 19Z 0.32 1910  85  83  15 0.00
Wed 06/10 20Z 0.28 1911  89  86  15 0.00
Wed 06/10 21Z 0.23 1812  93  87  15 0.00
Wed 06/10 22Z 0.20 1814  95  92  15 0.01
Wed 06/10 23Z 0.12 1814  97  94  15 0.01
Thu 06/11 00Z 0.17 1913  98  93  15 0.02
Thu 06/11 01Z 0.23 2014  98  93  15 0.01
Thu 06/11 02Z 0.24 2014  99  96  15 0.13
Thu 06/11 03Z 0.25 2112  98  96  15 0.18
Thu 06/11 04Z 0.25 2310  98  91  15 0.03
Thu 06/11 05Z 0.25 2410  98  89  15 0.01

Run total areal avg QPF for the Central_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