NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260214_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)
=== ===== === ==== ==== === === === ====
Sat 02/14 12Z 0.45 2715  90  80 -10 0.00
Sat 02/14 13Z 0.50 2817  94  81 -10 0.00
Sat 02/14 14Z 0.52 2818  95  76 -10 0.00
Sat 02/14 15Z 0.52 2817  96  70 -10 0.00
Sat 02/14 16Z 0.50 2915  96  55 -10 0.00
Sat 02/14 17Z 0.54 2915  95  43 -10 0.00
Sat 02/14 18Z 0.66 2816  94  31 -10 0.00
Sat 02/14 19Z 0.78 2816  95  25 -10 0.00
Sat 02/14 20Z 0.88 2717  96  21 -10 0.00
Sat 02/14 21Z 0.97 2719  96  18 -10 0.00
Sat 02/14 22Z 1.00 2821  93  18 -10 0.01
Sat 02/14 23Z 0.94 2822  87  19 -10 0.01
Sun 02/15 00Z 0.85 2924  82  21 -10 0.01
Sun 02/15 01Z 0.87 2926  79  21 -10 0.00
Sun 02/15 02Z 0.94 3027  80  17 -11 0.00
Sun 02/15 03Z 0.96 3027  82  16 -11 0.01
Sun 02/15 04Z 0.98 3027  81  16 -12 0.00
Sun 02/15 05Z 0.76 3027  83  15 -12 0.00
Sun 02/15 06Z 0.59 3126  77  15 -12 0.00
Sun 02/15 07Z 0.48 3127  69  15 -12 0.00
Sun 02/15 08Z 0.38 3127  58  15 -11 0.00
Sun 02/15 09Z 0.27 3227  45  15 -11 0.00
Sun 02/15 10Z 0.18 3325  35  15 -10 0.00
Sun 02/15 11Z 0.13 3422  27  14 -10 0.00
Sun 02/15 12Z 0.08 3519  22  13  -9 0.00
Sun 02/15 13Z 0.06 0015  18  13  -9 0.00
Sun 02/15 14Z 0.07 0111  17  13  -8 0.00
Sun 02/15 15Z 0.09 0308  19  14  -8 0.00
Sun 02/15 16Z 0.11 0507  20  15  -7 0.00
Sun 02/15 17Z 0.08 0604  21  20  -7 0.00
Sun 02/15 18Z 0.08 0803  22  32  -6 0.00
Sun 02/15 19Z 0.09 1004  22  38  -6 0.00
Sun 02/15 20Z 0.07 1304  24  37  -6 0.00
Sun 02/15 21Z 0.03 1606  22  37  -6 0.00
Sun 02/15 22Z 0.03 1708  19  31  -5 0.00
Sun 02/15 23Z 0.02 1810  17  36  -4 0.00
Mon 02/16 00Z 0.03 1811  15  45  -4 0.00
Mon 02/16 01Z 0.02 1811  16  47  -4 0.00
Mon 02/16 02Z 0.03 1811  19  45  -4 0.00
Mon 02/16 03Z 0.03 1812  23  51  -4 0.00
Mon 02/16 04Z 0.05 1814  27  59  -4 0.00
Mon 02/16 05Z 0.07 1915  31  66  -5 0.00
Mon 02/16 06Z 0.08 1916  38  76  -5 0.00
Mon 02/16 07Z 0.06 1816  45  81  -5 0.00
Mon 02/16 08Z 0.04 1814  50  71  -4 0.00
Mon 02/16 09Z 0.04 1814  53  64  -4 0.00
Mon 02/16 10Z 0.04 1812  58  60  -4 0.00
Mon 02/16 11Z 0.04 1812  63  59  -4 0.00
Mon 02/16 12Z 0.04 1813  66  68  -4 0.00
Mon 02/16 13Z 0.05 1813  69  89  -4 0.00
Mon 02/16 14Z 0.04 1812  72  90  -4 0.00
Mon 02/16 15Z 0.05 1911  74  87  -3 0.00
Mon 02/16 16Z 0.06 1911  76  83  -4 0.00
Mon 02/16 17Z 0.06 1811  77  73  -4 0.00
Mon 02/16 18Z 0.07 1910  78  60  -4 0.00
Mon 02/16 19Z 0.08 2009  79  48  -4 0.00
Mon 02/16 20Z 0.08 2008  80  35  -4 0.00
Mon 02/16 21Z 0.08 2007  81  34  -4 0.00
Mon 02/16 22Z 0.08 2007  83  30  -4 0.00
Mon 02/16 23Z 0.11 2107  84  26  -4 0.00

Run total areal avg QPF for the greens is: 0.04 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