Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20260114_0600
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)
=== ===== === ==== ==== === === === ====
Wed 01/14 06Z 0.52 2132  77  63  -1 0.00
Wed 01/14 09Z 0.70 2333  79  77  -1 0.00
Wed 01/14 12Z 0.71 2332  78  76   0 0.00
Wed 01/14 15Z 0.58 2326  77  60   0 0.00
Wed 01/14 18Z 0.62 2224  81  64  -1 0.00
Wed 01/14 21Z 0.55 2220  88  89  -1 0.00
Thu 01/15 00Z 0.32 2117  95  93  -1 0.01
Thu 01/15 03Z 0.10 1814  97  91  -1 0.05
Thu 01/15 06Z 0.11 1716  98  92  -1 0.10
Thu 01/15 09Z 0.07 1815  98  92  -1 0.08
Thu 01/15 12Z 0.16 2013  98  93  -2 0.08
Thu 01/15 15Z 0.33 2212  98  79  -3 0.04
Thu 01/15 18Z 0.41 2513  95  73  -7 0.03
Thu 01/15 21Z 5.24 2620  91  52 -14 0.04
Fri 01/16 00Z 8.01 2522  86  83 -17 0.02
Fri 01/16 03Z 7.56 2521  84  86 -19 0.01
Fri 01/16 06Z 8.90 2721  84  84 -21 0.01
Fri 01/16 09Z 0.85 2825  85  62 -20 0.01
Fri 01/16 12Z 0.51 2926  70  27 -18 0.00
Fri 01/16 15Z 0.27 3019  42   9 -13 0.00
Fri 01/16 18Z 0.21 2912  32  10 -12 0.00
Fri 01/16 21Z 0.17 2212  31  30 -10 0.00
Sat 01/17 00Z 0.24 2025  40  91 -11 0.00
Sat 01/17 03Z 0.20 2213  34  44 -11 0.00
Sat 01/17 06Z 0.67 2229  78  74 -10 0.00
Sat 01/17 09Z 0.61 2326  79  51  -9 0.00
Sat 01/17 12Z 0.61 2323  78  49  -9 0.00
Sat 01/17 15Z 0.52 2222  78  69  -8 0.00
Sat 01/17 18Z 0.74 2228  79  86  -8 0.00

Run total areal avg QPF for the greens is: 0.48 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