NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260218_0600
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)
=== ===== === ==== ==== === === === ====
Wed 02/18 06Z 0.55 2821  81  20  -2 0.00
Wed 02/18 07Z 0.54 2823  76  17  -2 0.01
Wed 02/18 08Z 0.51 2924  73  19  -3 0.01
Wed 02/18 09Z 0.44 3023  72  21  -3 0.00
Wed 02/18 10Z 0.39 3023  69  32  -3 0.00
Wed 02/18 11Z 0.35 3023  64  29  -3 0.01
Wed 02/18 12Z 0.32 3023  58  31  -3 0.01
Wed 02/18 13Z 0.25 3121  53  32  -3 0.00
Wed 02/18 14Z 0.21 3118  52  31  -4 0.00
Wed 02/18 15Z 0.19 3116  47  28  -4 0.00
Wed 02/18 16Z 0.17 3115  41  27  -3 0.00
Wed 02/18 17Z 0.15 3214  35  23  -3 0.00
Wed 02/18 18Z 0.10 3212  32  19  -3 0.00
Wed 02/18 19Z 0.06 3310  32  18  -3 0.00
Wed 02/18 20Z 0.04 3409  34  17  -4 0.00
Wed 02/18 21Z 0.04 3509  37  15  -4 0.00
Wed 02/18 22Z 0.07 0009  36  17  -4 0.00
Wed 02/18 23Z 0.15 0211  32  16  -4 0.00
Thu 02/19 00Z 0.18 0312  31   9  -4 0.00
Thu 02/19 01Z 0.15 0210  31  12  -5 0.00
Thu 02/19 02Z 0.18 0311  30  16  -5 0.00
Thu 02/19 03Z 0.21 0314  29  20  -5 0.00
Thu 02/19 04Z 0.21 0314  28  29  -5 0.00
Thu 02/19 05Z 0.14 0211  27  31  -5 0.00
Thu 02/19 06Z 0.15 0310  26  34  -5 0.00
Thu 02/19 07Z 0.12 0208  27  24  -5 0.00
Thu 02/19 08Z 0.13 0308  27  18  -5 0.00
Thu 02/19 09Z 0.10 0307  27  17  -6 0.00
Thu 02/19 10Z 0.10 0306  26  24  -5 0.00
Thu 02/19 11Z 0.05 0303  25  18  -5 0.00
Thu 02/19 12Z 0.02 0101  24  14  -5 0.00
Thu 02/19 13Z 0.02 0301  22   8  -4 0.00
Thu 02/19 14Z 0.02 0800  22   8  -4 0.00
Thu 02/19 15Z 0.01 1501  24  12  -4 0.00
Thu 02/19 16Z 0.01 1703  26  25  -4 0.00
Thu 02/19 17Z 0.05 1904  29  32  -3 0.00
Thu 02/19 18Z 0.10 2105  33  43  -3 0.00
Thu 02/19 19Z 0.15 2207  37  35  -3 0.00
Thu 02/19 20Z 0.19 2307  46  27  -3 0.00
Thu 02/19 21Z 0.19 2308  61  21  -3 0.00
Thu 02/19 22Z 0.22 2309  79  13  -3 0.00
Thu 02/19 23Z 0.23 2310  88  11  -3 0.00
Fri 02/20 00Z 0.24 2410  91  11  -2 0.00
Fri 02/20 01Z 0.19 2608  89  19  -1 0.00
Fri 02/20 02Z 0.12 2706  84  40   0 0.00
Fri 02/20 03Z 0.08 2704  82  52   0 0.00
Fri 02/20 04Z 0.10 2205  87  50   0 0.00
Fri 02/20 05Z 0.16 2111  89  48  -1 0.00
Fri 02/20 06Z 0.11 2108  80  44   0 0.00
Fri 02/20 07Z 0.11 2109  78  35   0 0.00
Fri 02/20 08Z 0.12 2010  76  28   0 0.00
Fri 02/20 09Z 0.11 2010  73  17   0 0.00
Fri 02/20 10Z 0.10 2011  71   5   1 0.00
Fri 02/20 11Z 0.10 2011  68   7   1 0.00
Fri 02/20 12Z 0.10 2010  65  12   1 0.00
Fri 02/20 13Z 0.08 1910  70  16   1 0.00
Fri 02/20 14Z 0.09 1911  74  15   1 0.00
Fri 02/20 15Z 0.08 1813  76  25   0 0.00
Fri 02/20 16Z 0.05 1715  84  63   0 0.00
Fri 02/20 17Z 0.02 1717  94  95   0 0.02

Run total areal avg QPF for the Central_Greens is: 0.06 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