NAM12 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20260712_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 07/12 12Z 0.26 0105  75  19  10 0.00
Sun 07/12 15Z 0.63 0004  80  12  10 0.00
Sun 07/12 18Z 1.31 3203  75  11  11 0.00
Sun 07/12 21Z 1.33 2902  70  17  12 0.00
Mon 07/13 00Z 0.31 2104  67  31  12 0.00
Mon 07/13 03Z 0.52 2309  64  17  12 0.00
Mon 07/13 06Z 0.77 2413  70  25  12 0.00
Mon 07/13 09Z 0.88 2616  65  30  12 0.00
Mon 07/13 12Z 0.76 2615  56  49  13 0.00
Mon 07/13 15Z 0.77 2415  56  83  13 0.00
Mon 07/13 18Z 2.13 2417  67  95  14 0.00
Mon 07/13 21Z 1.38 2421  75  93  15 0.00
Tue 07/14 00Z 2.10 2724  74  80  14 0.01
Tue 07/14 03Z 0.91 2820  77  36  15 0.00
Tue 07/14 06Z 0.84 3024  84  27  16 0.00
Tue 07/14 09Z 0.64 2921  87  56  16 0.00
Tue 07/14 12Z 0.75 2725  84  38  18 0.00
Tue 07/14 15Z 0.93 2732  78  22  20 0.00
Tue 07/14 18Z 2.43 2627  80  16  19 0.00
Tue 07/14 21Z 2.56 2728  74  27  21 0.00
Wed 07/15 00Z 1.29 2728  81  35  21 0.03
Wed 07/15 03Z 0.91 2828  83  52  19 0.35
Wed 07/15 06Z 0.98 2932  91  65  18 0.14
Wed 07/15 09Z 1.02 2829  85  51  19 0.03
Wed 07/15 12Z 0.34 3115  65  46  15 0.17
Wed 07/15 15Z 0.54 2916  72  15  14 0.00
Wed 07/15 18Z 5.07 2916  80   7  14 0.00
Wed 07/15 21Z 10.00 2917  63   9  15 0.00
Thu 07/16 00Z 2.10 2822  59  15  15 0.00

Run total areal avg QPF for the greens is: 0.73 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