NAM12 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20261004_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)
=== ===== === ==== ==== === === === ====
Sun 10/04 18Z 0.15 1615  94  40   4 0.00
Sun 10/04 21Z 0.09 1724  93  86   5 0.00
Mon 10/05 00Z 0.24 1925  95  44   5 0.00
Mon 10/05 03Z 0.42 2125  97  87   7 0.00
Mon 10/05 06Z 0.51 2321  95  77   7 0.00
Mon 10/05 09Z 0.65 2426  96  92   7 0.02
Mon 10/05 12Z 1.13 2828  97  97   4 0.11
Mon 10/05 15Z 1.64 2823  92  59   1 0.01
Mon 10/05 18Z 13.32 2825  80  27   0 0.02
Mon 10/05 21Z 14.63 2828  80  61   0 0.00
Tue 10/06 00Z 3.84 2930  85  59  -2 0.00
Tue 10/06 03Z 1.54 3032  87  56  -3 0.00
Tue 10/06 06Z 1.97 3033  85  33  -5 0.00
Tue 10/06 09Z 1.00 3032  83  27  -4 0.00
Tue 10/06 12Z 0.72 3031  81  19  -3 0.00
Tue 10/06 15Z 0.56 3026  69  16  -1 0.00
Tue 10/06 18Z 0.68 2923  51   7   0 0.00
Tue 10/06 21Z 1.24 2922  47  11   0 0.00
Wed 10/07 00Z 0.95 2824  46  41   0 0.00
Wed 10/07 03Z 0.54 2920  35  75   1 0.00
Wed 10/07 06Z 0.43 2718  31  72   3 0.00
Wed 10/07 09Z 0.59 2623  43  92   4 0.00
Wed 10/07 12Z 0.59 2525  72  92   6 0.00
Wed 10/07 15Z 0.53 2621  49  85   5 0.00
Wed 10/07 18Z 0.78 2330  58  93   9 0.00
Wed 10/07 21Z 0.83 2430  75  97   7 0.01
Thu 10/08 00Z 0.77 2529  91  95   7 0.03
Thu 10/08 03Z 0.79 2627  93  77   6 0.02
Thu 10/08 06Z 0.98 2725  88  17   4 0.02

Run total areal avg QPF for the greens is: 0.24 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