Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20260111_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 01/11 00Z 0.18 1628  56  75   2 0.00
Sun 01/11 03Z 0.33 1540  97  97   1 0.10
Sun 01/11 06Z 0.19 1631  97  97   1 0.23
Sun 01/11 09Z 0.03 1821  97  89   0 0.08
Sun 01/11 12Z 0.47 2416  97  53  -4 0.03
Sun 01/11 15Z 0.62 2617  86  34  -6 0.00
Sun 01/11 18Z 1.75 2617  90  53  -9 0.00
Sun 01/11 21Z 4.74 2617  84  73  -9 0.00
Mon 01/12 00Z 1.34 2522  92  97  -9 0.00
Mon 01/12 03Z 1.82 2830  93  82 -11 0.05
Mon 01/12 06Z 2.15 2935  88  82 -15 0.03
Mon 01/12 09Z 0.97 2936  89  63 -14 0.02
Mon 01/12 12Z 0.66 3036  81  15 -11 0.00
Mon 01/12 15Z 0.66 2932  66  66 -10 0.00
Mon 01/12 18Z 0.70 2726  81  84  -9 0.00
Mon 01/12 21Z 0.78 2525  86  89  -9 0.00
Tue 01/13 00Z 1.67 2528  88  92 -10 0.01
Tue 01/13 03Z 1.30 2629  94  83 -10 0.01
Tue 01/13 06Z 1.25 2727  96  68 -10 0.01
Tue 01/13 09Z 1.19 2725  96  27 -10 0.00
Tue 01/13 12Z 1.12 2724  96  60  -9 0.01
Tue 01/13 15Z 0.72 2621  94  22  -7 0.00
Tue 01/13 18Z 0.65 2617  94  19  -7 0.00
Tue 01/13 21Z 0.79 2720  95  34  -8 0.00
Wed 01/14 00Z 0.28 2218  84  19  -3 0.00
Wed 01/14 03Z 0.23 2023  76  37  -1 0.00
Wed 01/14 06Z 0.22 2027  96  91  -2 0.02
Wed 01/14 09Z 0.29 2034  97  92  -1 0.10
Wed 01/14 12Z 0.57 2227  96  37  -3 0.07

Run total areal avg QPF for the greens is: 0.77 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