NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260424_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)
=== ===== === ==== ==== === === === ====
Fri 04/24 18Z 2.80 3310  62  13  -3 0.00
Fri 04/24 19Z 2.57 3311  60  13  -2 0.00
Fri 04/24 20Z 1.52 3411  60  18  -2 0.00
Fri 04/24 21Z 0.70 3510  60  21  -2 0.00
Fri 04/24 22Z 0.44 0011  62  21  -2 0.00
Fri 04/24 23Z 0.77 0111  65  17  -2 0.00
Sat 04/25 00Z 0.85 0212  68  15  -2 0.00
Sat 04/25 01Z 0.93 0315  69  14  -3 0.00
Sat 04/25 02Z 0.85 0417  69  14  -3 0.00
Sat 04/25 03Z 0.78 0418  64  14  -3 0.00
Sat 04/25 04Z 0.68 0419  63  13  -3 0.00
Sat 04/25 05Z 0.52 0517  60  12  -3 0.00
Sat 04/25 06Z 0.44 0613  58  11  -3 0.00
Sat 04/25 07Z 0.38 0711  60  10  -3 0.00
Sat 04/25 08Z 0.31 0910  61   9  -3 0.00
Sat 04/25 09Z 0.26 1009  60   8  -2 0.00
Sat 04/25 10Z 0.20 1108  60   8  -2 0.00
Sat 04/25 11Z 0.16 1207  60   8  -2 0.00
Sat 04/25 12Z 0.15 1206  58   9  -2 0.00
Sat 04/25 13Z 0.17 1105  58   9  -2 0.00
Sat 04/25 14Z 0.25 1105  58   9  -2 0.00
Sat 04/25 15Z 1.11 1006  58  10  -2 0.00
Sat 04/25 16Z 1.87 1106  58  11  -2 0.00
Sat 04/25 17Z 2.09 1104  57  12  -1 0.00
Sat 04/25 18Z 1.70 1103  56  12   0 0.00
Sat 04/25 19Z 1.32 1103  56  13   0 0.00
Sat 04/25 20Z 1.09 1103  56  13   0 0.00
Sat 04/25 21Z 0.96 1103  56  13   0 0.00
Sat 04/25 22Z 0.42 1103  55  13   0 0.00
Sat 04/25 23Z 0.31 1004  54  13   0 0.00
Sun 04/26 00Z 0.34 1005  53  13   0 0.00
Sun 04/26 01Z 0.39 0907  54  13   0 0.00
Sun 04/26 02Z 0.42 0808  57  13   0 0.00
Sun 04/26 03Z 0.45 0808  59  14   0 0.00
Sun 04/26 04Z 0.44 0909  59  15   0 0.00
Sun 04/26 05Z 0.40 1008  59  18   0 0.00
Sun 04/26 06Z 0.37 1008  58  18   0 0.00
Sun 04/26 07Z 0.33 1007  57  19   0 0.00
Sun 04/26 08Z 0.31 1107  57  15   0 0.00
Sun 04/26 09Z 0.28 1206  58  18   0 0.00
Sun 04/26 10Z 0.30 1106  59  27   0 0.00
Sun 04/26 11Z 0.31 1106  61  33   0 0.00
Sun 04/26 12Z 0.31 1006  63  28   0 0.00
Sun 04/26 13Z 0.41 0906  64  26   0 0.00
Sun 04/26 14Z 0.72 0807  65  33   0 0.00
Sun 04/26 15Z 1.00 0806  66  47   0 0.00
Sun 04/26 16Z 1.74 0706  67  55   0 0.00
Sun 04/26 17Z 2.93 0606  68  59   0 0.00
Sun 04/26 18Z 2.51 0606  69  69   1 0.00
Sun 04/26 19Z 1.80 0606  70  81   1 0.00
Sun 04/26 20Z 1.18 0506  71  75   2 0.00
Sun 04/26 21Z 0.75 0406  71  69   2 0.00
Sun 04/26 22Z 0.38 0307  72  63   2 0.00
Sun 04/26 23Z 0.35 0308  72  59   3 0.00
Mon 04/27 00Z 0.49 0410  73  53   3 0.00
Mon 04/27 01Z 0.61 0512  75  47   3 0.00
Mon 04/27 02Z 0.72 0613  76  48   3 0.00
Mon 04/27 03Z 0.77 0714  76  55   3 0.00
Mon 04/27 04Z 0.66 0913  76  54   2 0.00
Mon 04/27 05Z 0.64 0915  76  60   2 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