NAM12 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20260920_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)
=== ===== === ==== ==== === === === ====
Sun 09/20 12Z 0.23 2019  92  97   6 0.00
Sun 09/20 15Z 0.14 1922  98  98   7 0.10
Sun 09/20 18Z 0.24 2026  98  97   7 0.16
Sun 09/20 21Z 0.30 2218  98  97   8 0.14
Mon 09/21 00Z 0.17 3007  97  65   7 0.04
Mon 09/21 03Z 0.02 3513  80  43   7 0.00
Mon 09/21 06Z 0.02 0018  75   1   6 0.00
Mon 09/21 09Z 0.02 0018  91   2   4 0.00
Mon 09/21 12Z 0.07 0018  90   2   2 0.00
Mon 09/21 15Z 0.06 0017  82   1   1 0.00
Mon 09/21 18Z 0.05 0015  73   2   3 0.00
Mon 09/21 21Z 0.06 0012  71   2   3 0.00
Tue 09/22 00Z 0.17 0215  64   2   4 0.00
Tue 09/22 03Z 0.30 0514  60   3   4 0.00
Tue 09/22 06Z 0.27 0810  63   3   3 0.00
Tue 09/22 09Z 0.18 0806  61   4   2 0.00
Tue 09/22 12Z 0.14 0604  61   4   2 0.00
Tue 09/22 15Z 0.19 0408  57   4   2 0.00
Tue 09/22 18Z 1.00 0407  67   4   2 0.00
Tue 09/22 21Z 1.67 0507  70   6   3 0.00
Wed 09/23 00Z 1.35 0711  68  10   2 0.00
Wed 09/23 03Z 0.85 0914  68  14   2 0.00
Wed 09/23 06Z 0.64 0916  62  18   2 0.00
Wed 09/23 09Z 0.69 0813  66  14   2 0.00
Wed 09/23 12Z 0.56 0920  56  23   3 0.00
Wed 09/23 15Z 0.54 0818  54  23   3 0.00
Wed 09/23 18Z 1.59 0714  68  20   2 0.00
Wed 09/23 21Z 6.42 0815  65  13   3 0.00
Thu 09/24 00Z 1.10 0920  60   4   3 0.00

Run total areal avg QPF for the greens is: 0.44 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