NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261003_0000
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)
=== ===== === ==== ==== === === === ====
Sat 10/03 00Z 0.30 3218  98  29   8 0.00
Sat 10/03 01Z 0.25 3322  91  17   8 0.02
Sat 10/03 02Z 0.17 3322  83  18   7 0.01
Sat 10/03 03Z 0.12 3422  83  22   6 0.00
Sat 10/03 04Z 0.14 3423  86   6   6 0.00
Sat 10/03 05Z 0.12 3423  87  12   6 0.01
Sat 10/03 06Z 0.07 3423  89  13   5 0.00
Sat 10/03 07Z 0.05 3421  84   4   5 0.00
Sat 10/03 08Z 0.04 3420  81   1   4 0.00
Sat 10/03 09Z 0.05 3418  79   0   4 0.00
Sat 10/03 10Z 0.04 3417  77   1   3 0.00
Sat 10/03 11Z 0.05 3417  73   1   3 0.00
Sat 10/03 12Z 0.04 3416  69   2   3 0.00
Sat 10/03 13Z 0.02 3415  65   2   4 0.00
Sat 10/03 14Z 0.02 3414  61   2   4 0.00
Sat 10/03 15Z 0.02 3413  59   3   5 0.00
Sat 10/03 16Z 0.02 3412  58   3   5 0.00
Sat 10/03 17Z 0.02 3412  58   2   4 0.00
Sat 10/03 18Z 0.02 3410  57   2   4 0.00
Sat 10/03 19Z 0.02 3508  58   3   4 0.00
Sat 10/03 20Z 0.03 3507  59   3   4 0.00
Sat 10/03 21Z 0.04 3507  57   5   4 0.00
Sat 10/03 22Z 0.07 0007  54   6   4 0.00
Sat 10/03 23Z 0.08 0106  48   4   4 0.00
Sun 10/04 00Z 0.13 0306  42   3   5 0.00
Sun 10/04 01Z 0.13 0405  38   5   5 0.00
Sun 10/04 02Z 0.16 0605  39   4   5 0.00
Sun 10/04 03Z 0.17 0906  43   5   5 0.00
Sun 10/04 04Z 0.18 1107  41   4   5 0.00
Sun 10/04 05Z 0.16 1208  42   4   5 0.00
Sun 10/04 06Z 0.13 1410  47   4   5 0.00
Sun 10/04 07Z 0.10 1513  53   4   4 0.00
Sun 10/04 08Z 0.09 1514  56   4   4 0.00
Sun 10/04 09Z 0.09 1514  55   4   5 0.00
Sun 10/04 10Z 0.10 1516  54   5   5 0.00
Sun 10/04 11Z 0.10 1517  56   6   5 0.00
Sun 10/04 12Z 0.09 1619  63   6   4 0.00
Sun 10/04 13Z 0.11 1520  64   4   5 0.00
Sun 10/04 14Z 0.09 1621  64   4   4 0.00
Sun 10/04 15Z 0.06 1620  62   7   4 0.00
Sun 10/04 16Z 0.04 1618  60   5   4 0.00
Sun 10/04 17Z 0.04 1616  62  14   4 0.00
Sun 10/04 18Z 0.09 1616  68  63   4 0.00
Sun 10/04 19Z 0.12 1616  75  89   4 0.00
Sun 10/04 20Z 0.05 1718  78  82   4 0.00
Sun 10/04 21Z 0.11 1719  80  74   4 0.00
Sun 10/04 22Z 0.19 1820  82  58   4 0.00
Sun 10/04 23Z 0.18 1821  83  53   5 0.00
Mon 10/05 00Z 0.26 1822  88  47   5 0.00
Mon 10/05 01Z 0.29 1922  95  60   5 0.01
Mon 10/05 02Z 0.28 1921  97  61   6 0.01
Mon 10/05 03Z 0.35 2021  98  64   7 0.01
Mon 10/05 04Z 0.42 2122  99  63   6 0.02
Mon 10/05 05Z 0.52 2123  99  67   6 0.03
Mon 10/05 06Z 0.61 2223  99  58   6 0.03
Mon 10/05 07Z 0.71 2323  98  58   6 0.02
Mon 10/05 08Z 0.64 2422  92  73   6 0.01
Mon 10/05 09Z 0.58 2520  90  78   6 0.01
Mon 10/05 10Z 0.68 2622  96  45   6 0.03
Mon 10/05 11Z 0.84 2624  97  57   5 0.04

Run total areal avg QPF for the Central_Greens is: 0.26 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