NAM12 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20250314_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)
=== ===== === ==== ==== === === === ====
Fri 03/14 00Z 0.15 1917  69   5  -2 0.00
Fri 03/14 03Z 0.33 2119  61   7  -1 0.00
Fri 03/14 06Z 0.39 2216  57  10   0 0.00
Fri 03/14 09Z 0.35 2513  54  17   0 0.00
Fri 03/14 12Z 0.29 2610  50  33   1 0.00
Fri 03/14 15Z 0.23 2409  46  33   2 0.00
Fri 03/14 18Z 0.18 2209  45  30   3 0.00
Fri 03/14 21Z 0.23 2213  44  28   4 0.00
Sat 03/15 00Z 0.25 2215  42  32   5 0.00
Sat 03/15 03Z 0.25 2117  39  32   7 0.00
Sat 03/15 06Z 0.26 2121  36  30   8 0.00
Sat 03/15 09Z 0.30 2124  36  22   8 0.00
Sat 03/15 12Z 0.38 2128  39  18   9 0.00
Sat 03/15 15Z 0.44 2135  35  39  10 0.00
Sat 03/15 18Z 0.39 2135  39  60  10 0.00
Sat 03/15 21Z 0.33 2132  43  24  10 0.00
Sun 03/16 00Z 0.43 2142  56  13  10 0.00
Sun 03/16 03Z 0.38 2140  59  17   9 0.00
Sun 03/16 06Z 0.47 2143  84  47   9 0.00
Sun 03/16 09Z 0.64 2243  92  29   8 0.00
Sun 03/16 12Z 0.55 2042  87  16   8 0.00
Sun 03/16 15Z 0.47 2051  85  12   9 0.00
Sun 03/16 18Z 0.40 2047  90  10  10 0.00
Sun 03/16 21Z 0.47 2047  87  13   9 0.00
Mon 03/17 00Z 0.23 1951  95  81  10 0.00
Mon 03/17 03Z 0.33 1953  98  97   9 0.11
Mon 03/17 06Z 1.13 2529  94  94   4 0.21
Mon 03/17 09Z 0.60 2621  83  56   3 0.02
Mon 03/17 12Z 0.41 2615  92  39   0 0.00

Run total areal avg QPF for the greens is: 0.34 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