Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260311_1200
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Wed 03/11 12Z 0.06 1625  84  86   9 0.00
Wed 03/11 13Z 0.06 1629  87  85  10 0.00
Wed 03/11 14Z 0.03 1730  83  78  11 0.00
Wed 03/11 15Z 0.06 1733  82  94  11 0.01
Wed 03/11 16Z 0.11 1834  82  93  11 0.02
Wed 03/11 17Z 0.17 1833  82  90  11 0.01
Wed 03/11 18Z 0.22 1935  80  79  11 0.00
Wed 03/11 19Z 0.26 1935  79  55  12 0.00
Wed 03/11 20Z 0.27 1934  79  74  12 0.00
Wed 03/11 21Z 0.32 1938  81  93  12 0.00
Wed 03/11 22Z 0.41 2039  91  86  11 0.01
Wed 03/11 23Z 0.50 2040  93  80  11 0.00
Thu 03/12 00Z 0.56 2041  93  85  12 0.01
Thu 03/12 02Z 0.62 2140  92  93  12 0.01
Thu 03/12 03Z 0.83 2238  96  94  10 0.01
Thu 03/12 04Z 1.03 2333  95  93   9 0.13
Thu 03/12 05Z 0.70 2325  87  86  10 0.14
Thu 03/12 06Z 0.76 2325  93  81   9 0.15
Thu 03/12 07Z 0.91 2328  97  64   8 0.01
Thu 03/12 08Z 0.92 2328  98  84   8 0.03
Thu 03/12 09Z 1.70 2631  98  88   4 0.04
Thu 03/12 10Z 0.92 2633  95  54   0 0.12
Thu 03/12 11Z 0.77 2731  89  56  -2 0.06
Thu 03/12 12Z 0.85 2731  89  41  -5 0.01
Thu 03/12 14Z 0.92 2829  89   6  -8 0.00
Thu 03/12 15Z 0.98 2827  89  12  -8 0.00
Thu 03/12 16Z 1.69 2727  92   4 -10 0.00
Thu 03/12 17Z 4.05 2826  91   3 -10 0.00
Thu 03/12 18Z 5.03 2826  89  11 -11 0.00
Thu 03/12 19Z 3.61 2923  87  26 -11 0.00
Thu 03/12 20Z 3.09 2921  87  16 -11 0.00
Thu 03/12 21Z 2.30 2920  87  27 -12 0.00
Thu 03/12 22Z 1.01 2919  87  37 -12 0.00
Thu 03/12 23Z 0.87 3020  87  42 -12 0.00
Fri 03/13 00Z 1.02 2922  88  52 -12 0.00
Fri 03/13 01Z 1.22 2923  90  56 -12 0.00
Fri 03/13 02Z 1.25 2924  91  57 -13 0.00
Fri 03/13 03Z 1.13 2923  92  55 -13 0.00
Fri 03/13 04Z 1.05 2922  94  53 -13 0.00
Fri 03/13 05Z 1.12 2923  95  54 -13 0.00
Fri 03/13 06Z 1.07 2921  95  49 -13 0.00
Fri 03/13 07Z 0.92 2919  95  35 -13 0.00
Fri 03/13 08Z 0.83 2816  96  25 -13 0.00
Fri 03/13 09Z 0.63 2814  94   7 -12 0.00
Fri 03/13 10Z 0.64 2714  93   3 -12 0.00
Fri 03/13 11Z 0.41 2612  87   2 -11 0.00
Fri 03/13 12Z 0.27 2509  77   4 -10 0.00
Fri 03/13 13Z 0.16 2108  66   8 -10 0.00
Fri 03/13 14Z 0.19 2011  56  12  -9 0.00
Fri 03/13 15Z 0.15 1814  45  22  -8 0.00
Fri 03/13 16Z 0.21 1915  44  60  -8 0.00
Fri 03/13 17Z 0.43 1918  48  87  -8 0.00
Fri 03/13 18Z 1.76 1821  59  90  -9 0.00
Fri 03/13 19Z 0.14 1726  93  88  -9 0.01
Fri 03/13 21Z 0.48 1932  94  87  -8 0.01
Fri 03/13 22Z 0.52 1931  91  73  -8 0.02
Fri 03/13 23Z 0.55 1931  90  90  -7 0.06

Run total areal avg QPF for the Central_Greens is: 0.87 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