Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20260110_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)
=== ===== === ==== ==== === === === ====
Sat 01/10 00Z 0.58 2147  91  73   5 0.00
Sat 01/10 03Z 1.67 2450  98  19   0 0.01
Sat 01/10 06Z 1.03 2941  88   4  -1 0.00
Sat 01/10 09Z 0.50 3134  64   9   0 0.00
Sat 01/10 12Z 0.21 3327  48  12   0 0.00
Sat 01/10 15Z 0.02 3513  32  12   0 0.00
Sat 01/10 18Z 0.03 0502  23   7   1 0.00
Sat 01/10 21Z 0.17 1414  15  15   1 0.00
Sun 01/11 00Z 0.33 1530  25  53   0 0.00
Sun 01/11 03Z 0.32 1432  82  93   1 0.06
Sun 01/11 06Z 0.39 1438  94  97   2 0.07
Sun 01/11 09Z 0.17 1629  97  96  -1 0.07
Sun 01/11 12Z 0.23 2022  97  64  -4 0.05
Sun 01/11 15Z 0.63 2519  79  28  -6 0.01
Sun 01/11 18Z 12.47 2518  81  26 -10 0.00
Sun 01/11 21Z 6.98 2519  81  68 -10 0.00
Mon 01/12 00Z 1.09 2422  88  96 -10 0.00
Mon 01/12 03Z 1.15 2625  93  81 -10 0.04
Mon 01/12 06Z 1.25 2933  90  79 -13 0.06
Mon 01/12 09Z 0.89 2932  90  55 -14 0.02
Mon 01/12 12Z 0.64 3034  88  46 -13 0.01
Mon 01/12 15Z 0.58 2931  72   6 -11 0.00
Mon 01/12 18Z 0.61 2826  63  66  -9 0.00
Mon 01/12 21Z 0.61 2930  74  40 -11 0.00
Tue 01/13 00Z 1.13 2431  91  87  -9 0.00
Tue 01/13 03Z 1.22 2631  94  82  -9 0.05
Tue 01/13 06Z 1.27 2733  95  79  -9 0.03
Tue 01/13 09Z 1.35 2830  95  47 -10 0.02
Tue 01/13 12Z 1.26 2829  95  28 -10 0.01

Run total areal avg QPF for the greens is: 0.51 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