NAM12 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20251001_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)
=== ===== === ==== ==== === === === ====
Wed 10/01 12Z 0.17 0313  68   9   3 0.00
Wed 10/01 15Z 0.09 0115  69  16   2 0.00
Wed 10/01 18Z 0.06 0015  72  13   2 0.00
Wed 10/01 21Z 0.46 0115  75   5   1 0.00
Thu 10/02 00Z 0.51 0218  71   2   1 0.00
Thu 10/02 03Z 0.37 0516  54   2   2 0.00
Thu 10/02 06Z 0.30 0711  44   3   3 0.00
Thu 10/02 09Z 0.17 0806  45   9   2 0.00
Thu 10/02 12Z 0.05 0202  43  25   3 0.00
Thu 10/02 15Z 0.06 0303  42  44   3 0.00
Thu 10/02 18Z 0.02 1601  48  53   4 0.00
Thu 10/02 21Z 0.08 2104  45  55   5 0.00
Fri 10/03 00Z 0.18 2308  33  52   7 0.00
Fri 10/03 03Z 0.23 2311  27  52   8 0.00
Fri 10/03 06Z 0.29 2513  33  51   8 0.00
Fri 10/03 09Z 0.37 2616  45  35   8 0.00
Fri 10/03 12Z 0.33 2614  48  41   9 0.00
Fri 10/03 15Z 0.34 2614  48  42   9 0.00
Fri 10/03 18Z 0.34 2612  45  37  10 0.00
Fri 10/03 21Z 0.36 2613  50  31  11 0.00
Sat 10/04 00Z 0.48 2718  52  29  12 0.00
Sat 10/04 03Z 0.45 2918  49  33  12 0.00
Sat 10/04 06Z 0.39 3117  63  38  11 0.00
Sat 10/04 09Z 0.44 2917  54  33  11 0.00
Sat 10/04 12Z 0.34 3113  70  46  10 0.00
Sat 10/04 15Z 0.35 3113  79  40   9 0.00
Sat 10/04 18Z 0.34 3110  82  33  10 0.00
Sat 10/04 21Z 0.24 3107  82  40  10 0.00
Sun 10/05 00Z 0.17 2905  80  39  11 0.00

Run total areal avg QPF for the greens is: 0.00 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