NAM12 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20260601_1800
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)
=== ===== === ==== ==== === === === ====
Mon 06/01 18Z 1.00 0105  74  69   3 0.00
Mon 06/01 21Z 1.01 3405  69  58   4 0.01
Tue 06/02 00Z 0.56 3307  69  63   4 0.00
Tue 06/02 03Z 0.23 3310  66  59   4 0.00
Tue 06/02 06Z 0.26 3311  65  47   5 0.00
Tue 06/02 09Z 0.37 3213  63  52   5 0.00
Tue 06/02 12Z 0.41 3216  55  46   6 0.00
Tue 06/02 15Z 0.55 3316  49  17   6 0.00
Tue 06/02 18Z 5.33 3318  49  18   6 0.00
Tue 06/02 21Z 4.47 3318  52  66   7 0.00
Wed 06/03 00Z 0.49 3421  51  64   7 0.00
Wed 06/03 03Z 0.12 3519  47  23   8 0.00
Wed 06/03 06Z 0.08 3514  43  14   8 0.00
Wed 06/03 09Z 0.11 3512  42  28   8 0.00
Wed 06/03 12Z 0.20 3411  42  54   9 0.00
Wed 06/03 15Z 0.50 3211  46  68   9 0.00
Wed 06/03 18Z 2.40 3008  50  68  10 0.00
Wed 06/03 21Z 1.41 2910  51  49  11 0.00
Thu 06/04 00Z 0.57 2911  54  35  11 0.00
Thu 06/04 03Z 0.58 2911  55  29  11 0.00
Thu 06/04 06Z 0.37 2910  50  33  11 0.00
Thu 06/04 09Z 0.37 2909  46  40  11 0.00
Thu 06/04 12Z 0.33 2908  47  38  12 0.00
Thu 06/04 15Z 0.35 2909  48  37  11 0.00
Thu 06/04 18Z 1.27 2410  52  32  12 0.00
Thu 06/04 21Z 2.96 2512  50  24  13 0.00
Fri 06/05 00Z 1.29 2716  55  23  12 0.00
Fri 06/05 03Z 0.67 2919  54  20  12 0.00
Fri 06/05 06Z 0.78 3121  67  18  11 0.00

Run total areal avg QPF for the greens is: 0.01 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