NAM12 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20260906_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 09/06 12Z 0.08 3510  93  87   7 0.00
Sun 09/06 15Z 0.12 0114  88  72   6 0.01
Sun 09/06 18Z 0.20 3412  89  46   6 0.00
Sun 09/06 21Z 1.86 3315  85  10   7 0.00
Mon 09/07 00Z 0.51 3420  82  11   7 0.00
Mon 09/07 03Z 0.50 3419  80  15   7 0.00
Mon 09/07 06Z 0.45 3319  74  11   7 0.00
Mon 09/07 09Z 0.51 3423  69  22   7 0.00
Mon 09/07 12Z 0.44 3422  67  24   7 0.00
Mon 09/07 15Z 0.83 3320  69  14   7 0.00
Mon 09/07 18Z 7.02 3216  69   6   8 0.00
Mon 09/07 21Z 7.84 3218  70  10   8 0.00
Tue 09/08 00Z 0.93 3220  75  26   8 0.00
Tue 09/08 03Z 1.03 3223  81  47   9 0.00
Tue 09/08 06Z 0.78 3223  85  73   9 0.00
Tue 09/08 09Z 0.53 3221  94  49   8 0.00
Tue 09/08 12Z 0.38 3222  88   3   8 0.00
Tue 09/08 15Z 0.31 3221  73   6   8 0.00
Tue 09/08 18Z 0.19 3316  49   7   9 0.00
Tue 09/08 21Z 0.13 3412  37   5   9 0.00
Wed 09/09 00Z 0.13 3310  25   4  10 0.00
Wed 09/09 03Z 0.12 3206  24   4  10 0.00
Wed 09/09 06Z 0.20 2706  36  14  10 0.00
Wed 09/09 09Z 0.15 3106  29   7  10 0.00
Wed 09/09 12Z 0.32 2313  80  69  11 0.00
Wed 09/09 15Z 0.31 2120  82  45  12 0.00
Wed 09/09 18Z 0.26 2023  70  38  13 0.00
Wed 09/09 21Z 0.39 2028  91  91  13 0.02
Thu 09/10 00Z 0.44 2034  89  72  14 0.03

Run total areal avg QPF for the 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