NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261002_1200
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Fri 10/02 12Z 0.73 2627  98  89  14 0.00
Fri 10/02 13Z 0.73 2626  97  87  13 0.09
Fri 10/02 14Z 0.78 2625  96  96  13 0.10
Fri 10/02 15Z 0.68 2721  98  95  12 0.10
Fri 10/02 16Z 0.61 2818  98  91  11 0.06
Fri 10/02 17Z 0.47 2915  97  85  11 0.03
Fri 10/02 18Z 0.47 2915  97  93  11 0.03
Fri 10/02 19Z 0.42 3015  96  91  10 0.03
Fri 10/02 20Z 0.46 3016  98  89  10 0.02
Fri 10/02 21Z 0.53 3020  98  77   9 0.03
Fri 10/02 22Z 0.57 3022  96  66   8 0.03
Fri 10/02 23Z 0.50 3122  90  36   8 0.01
Sat 10/03 00Z 0.44 3222  81  15   7 0.01
Sat 10/03 01Z 0.42 3222  81   7   7 0.01
Sat 10/03 02Z 0.44 3224  83   7   6 0.01
Sat 10/03 03Z 0.46 3324  86   3   5 0.01
Sat 10/03 04Z 0.46 3323  85   4   5 0.00
Sat 10/03 05Z 0.37 3323  83   4   4 0.00
Sat 10/03 06Z 0.32 3323  83   5   4 0.00
Sat 10/03 07Z 0.28 3321  86   4   3 0.00
Sat 10/03 08Z 0.26 3321  87   3   3 0.00
Sat 10/03 09Z 0.19 3318  85   2   3 0.00
Sat 10/03 10Z 0.14 3416  79   2   3 0.00
Sat 10/03 11Z 0.13 3415  76   2   3 0.00
Sat 10/03 12Z 0.11 3415  71   2   3 0.00
Sat 10/03 13Z 0.10 3415  68   2   4 0.00
Sat 10/03 14Z 0.08 3413  63   2   4 0.00
Sat 10/03 15Z 0.12 3312  61   2   4 0.00
Sat 10/03 16Z 0.11 3310  60   3   4 0.00
Sat 10/03 17Z 0.09 3408  61   3   3 0.00
Sat 10/03 18Z 0.12 3307  61   3   3 0.00
Sat 10/03 19Z 0.12 3307  59   4   4 0.00
Sat 10/03 20Z 0.07 3406  59   4   4 0.00
Sat 10/03 21Z 0.04 3505  60   5   3 0.00
Sat 10/03 22Z 0.03 0004  59   5   3 0.00
Sat 10/03 23Z 0.05 0103  57   4   3 0.00
Sun 10/04 00Z 0.05 0302  55   4   3 0.00
Sun 10/04 01Z 0.06 0702  52   4   4 0.00
Sun 10/04 02Z 0.09 1203  48   4   4 0.00
Sun 10/04 03Z 0.08 1405  47   4   4 0.00
Sun 10/04 04Z 0.07 1505  50   3   4 0.00
Sun 10/04 05Z 0.07 1607  51   3   4 0.00
Sun 10/04 06Z 0.04 1709  54   3   4 0.00
Sun 10/04 07Z 0.03 1810  60   3   3 0.00
Sun 10/04 08Z 0.04 1812  63   2   4 0.00
Sun 10/04 09Z 0.06 1813  68   2   4 0.00
Sun 10/04 10Z 0.05 1814  71   2   4 0.00
Sun 10/04 11Z 0.06 1816  75   2   3 0.00
Sun 10/04 12Z 0.08 1816  79   2   3 0.00
Sun 10/04 13Z 0.08 1817  81   1   3 0.00
Sun 10/04 14Z 0.08 1718  81   2   3 0.00
Sun 10/04 15Z 0.08 1717  82   1   3 0.00
Sun 10/04 16Z 0.11 1716  82   2   3 0.00
Sun 10/04 17Z 0.22 1715  84   5   3 0.00
Sun 10/04 18Z 0.26 1715  85   8   3 0.00
Sun 10/04 19Z 0.21 1715  83  17   3 0.00
Sun 10/04 20Z 0.19 1617  80  11   4 0.00
Sun 10/04 21Z 0.14 1719  78   3   4 0.00
Sun 10/04 22Z 0.06 1722  78  24   5 0.00
Sun 10/04 23Z 0.06 1824  78  75   5 0.00

Run total areal avg QPF for the greens is: 0.57 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