NAM12 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20261102_0600
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 11/02 06Z 0.85 2823  60  84   6 0.00
Mon 11/02 09Z 1.08 2726  55  90   6 0.00
Mon 11/02 12Z 0.83 2823  54  86   7 0.00
Mon 11/02 15Z 0.77 2822  53  81   8 0.00
Mon 11/02 18Z 0.72 2722  48  81   9 0.00
Mon 11/02 21Z 0.76 2623  42  75   9 0.00
Tue 11/03 00Z 0.76 2723  47  79   9 0.00
Tue 11/03 03Z 0.59 2820  53  81   9 0.00
Tue 11/03 06Z 0.46 2816  56  83   9 0.00
Tue 11/03 09Z 0.43 2714  55  91   9 0.00
Tue 11/03 12Z 0.45 2614  52  92   9 0.00
Tue 11/03 15Z 0.54 2417  65  90   9 0.00
Tue 11/03 18Z 0.65 2422  73  85   9 0.00
Tue 11/03 21Z 0.65 2523  86  86  10 0.00
Wed 11/04 00Z 0.86 2528  86  70  10 0.00
Wed 11/04 03Z 0.92 2630  79  71  11 0.00
Wed 11/04 06Z 0.91 2630  76  58  11 0.00
Wed 11/04 09Z 0.75 2727  77  38  12 0.00
Wed 11/04 12Z 0.70 2725  79  40  11 0.00
Wed 11/04 15Z 0.62 2720  77  45  11 0.00
Wed 11/04 18Z 0.51 2616  69  45  12 0.00
Wed 11/04 21Z 0.40 2514  58  40  12 0.00
Thu 11/05 00Z 0.30 2512  53  39  12 0.00
Thu 11/05 03Z 0.40 2514  60  42  12 0.00
Thu 11/05 06Z 0.31 2316  47  49  13 0.00
Thu 11/05 09Z 0.36 2322  56  51  13 0.00
Thu 11/05 12Z 0.36 2323  64  34  14 0.01
Thu 11/05 15Z 0.42 2323  77  74  12 0.01
Thu 11/05 18Z 0.52 2520  96  92  10 0.01

Run total areal avg QPF for the greens is: 0.03 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