NAM12 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20260215_0000
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 02/15 00Z 1.32 2820  87  20 -10 0.00
Sun 02/15 03Z 1.59 2927  88  19 -11 0.00
Sun 02/15 06Z 0.88 3125  84  15 -12 0.00
Sun 02/15 09Z 0.42 3122  76  14 -13 0.00
Sun 02/15 12Z 0.11 3419  40  12 -10 0.00
Sun 02/15 15Z 0.08 0210  24  15  -9 0.00
Sun 02/15 18Z 0.11 0905  27  29  -7 0.00
Sun 02/15 21Z 0.07 1506  26  37  -6 0.00
Mon 02/16 00Z 0.02 1713  20  22  -5 0.00
Mon 02/16 03Z 0.07 1914  30  62  -4 0.00
Mon 02/16 06Z 0.08 1916  76  85  -5 0.00
Mon 02/16 09Z 0.08 1915  92  88  -4 0.03
Mon 02/16 12Z 0.14 2014  93  85  -5 0.02
Mon 02/16 15Z 0.13 2111  94  61  -4 0.01
Mon 02/16 18Z 0.12 2110  93  42  -4 0.00
Mon 02/16 21Z 0.19 2112  94  35  -4 0.00
Tue 02/17 00Z 0.34 2217  95  61  -4 0.00
Tue 02/17 03Z 0.43 2419  94  88  -3 0.00
Tue 02/17 06Z 0.46 2419  94  88  -3 0.03
Tue 02/17 09Z 0.41 2417  96  94  -3 0.04
Tue 02/17 12Z 0.43 2615  97  80  -4 0.03
Tue 02/17 15Z 0.29 2811  96  19  -4 0.02
Tue 02/17 18Z 0.25 2909  94  18  -3 0.00
Tue 02/17 21Z 0.32 2711  96  39  -4 0.00
Wed 02/18 00Z 0.33 2812  83  22  -4 0.01
Wed 02/18 03Z 0.32 2712  80  40  -4 0.00
Wed 02/18 06Z 0.35 2813  85  35  -5 0.00
Wed 02/18 09Z 0.28 3012  84  43  -6 0.00
Wed 02/18 12Z 0.20 3111  82  50  -6 0.00

Run total areal avg QPF for the greens is: 0.19 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