NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260920_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)
=== ===== === ==== ==== === === === ====
Sun 09/20 06Z 0.26 2014  82  20   6 0.00
Sun 09/20 07Z 0.26 2014  85  25   6 0.00
Sun 09/20 08Z 0.20 1914  88  39   7 0.00
Sun 09/20 09Z 0.15 1914  86  74   7 0.00
Sun 09/20 10Z 0.17 1917  90  93   6 0.00
Sun 09/20 11Z 0.19 1918  92  98   6 0.01
Sun 09/20 12Z 0.14 1819  94  99   6 0.02
Sun 09/20 13Z 0.07 1718  94  99   6 0.03
Sun 09/20 14Z 0.05 1717  94  99   6 0.06
Sun 09/20 15Z 0.06 1715  96  99   7 0.07
Sun 09/20 16Z 0.09 1815  98 100   7 0.07
Sun 09/20 17Z 0.11 1815  98 100   7 0.06
Sun 09/20 18Z 0.12 1816  98  99   7 0.05
Sun 09/20 19Z 0.09 1817  98  99   8 0.05
Sun 09/20 20Z 0.09 1818  98  99   8 0.05
Sun 09/20 21Z 0.12 1817  99  93   8 0.06
Sun 09/20 22Z 0.10 1815  98  80   8 0.05
Sun 09/20 23Z 0.10 1812  98  65   8 0.03
Mon 09/21 00Z 0.05 1808  98  46   8 0.02
Mon 09/21 01Z 0.05 1804  99  41   7 0.01
Mon 09/21 02Z 0.03 1801  99  33   7 0.01
Mon 09/21 03Z 0.05 0501  99  37   6 0.00
Mon 09/21 04Z 0.05 0104  98  37   6 0.00
Mon 09/21 05Z 0.08 0108  97  36   6 0.00
Mon 09/21 06Z 0.09 0010  93  22   6 0.00
Mon 09/21 07Z 0.10 0011  88  10   6 0.00
Mon 09/21 08Z 0.11 0013  87   4   6 0.00
Mon 09/21 09Z 0.13 0016  87   2   5 0.00
Mon 09/21 10Z 0.15 0017  87   1   5 0.00
Mon 09/21 11Z 0.18 0118  89   1   4 0.00
Mon 09/21 12Z 0.19 0118  88   2   4 0.00
Mon 09/21 13Z 0.15 0018  84   2   4 0.00
Mon 09/21 14Z 0.13 0016  81   3   4 0.00
Mon 09/21 15Z 0.10 0013  79   2   4 0.00
Mon 09/21 16Z 0.13 0113  73   2   4 0.00
Mon 09/21 17Z 0.13 0112  70   2   4 0.00
Mon 09/21 18Z 0.13 0112  65   1   5 0.00
Mon 09/21 19Z 0.15 0112  58   1   5 0.00
Mon 09/21 20Z 0.15 0211  51   2   5 0.00
Mon 09/21 21Z 0.14 0211  47   2   6 0.00
Mon 09/21 22Z 0.15 0211  44   2   6 0.00
Mon 09/21 23Z 0.18 0312  41   2   6 0.00
Tue 09/22 00Z 0.19 0312  40   2   6 0.00
Tue 09/22 01Z 0.21 0413  38   2   6 0.00
Tue 09/22 02Z 0.22 0412  38   2   6 0.00
Tue 09/22 03Z 0.21 0510  38   2   6 0.00
Tue 09/22 04Z 0.19 0609  41   2   5 0.00
Tue 09/22 05Z 0.17 0807  47   2   4 0.00
Tue 09/22 06Z 0.14 0906  52   2   4 0.00
Tue 09/22 07Z 0.13 1106  56   2   4 0.00
Tue 09/22 08Z 0.11 1206  62   2   3 0.00
Tue 09/22 09Z 0.13 1207  67   2   3 0.00
Tue 09/22 10Z 0.15 1208  70   2   3 0.00
Tue 09/22 11Z 0.14 1207  71   2   3 0.00
Tue 09/22 12Z 0.16 1107  72   2   3 0.00
Tue 09/22 13Z 0.17 0907  71   2   3 0.00
Tue 09/22 14Z 0.19 0807  70   2   3 0.00
Tue 09/22 15Z 0.18 0706  71   3   3 0.00
Tue 09/22 16Z 0.22 0706  74   3   3 0.00
Tue 09/22 17Z 0.29 0606  73   3   2 0.00

Run total areal avg QPF for the Central_Greens is: 0.65 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