NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260925_1800
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)
=== ===== === ==== ==== === === === ====
Fri 09/25 18Z 2.08 0507  74   4   8 0.00
Fri 09/25 19Z 3.01 0409  77   5   9 0.00
Fri 09/25 20Z 3.41 0411  79   6   9 0.00
Fri 09/25 21Z 2.26 0413  80   6   9 0.00
Fri 09/25 22Z 1.23 0415  80   8   9 0.00
Fri 09/25 23Z 1.39 0418  81  10   9 0.00
Sat 09/26 00Z 1.17 0519  81  11   9 0.00
Sat 09/26 01Z 1.07 0519  81  11   9 0.00
Sat 09/26 02Z 1.21 0621  78  11   9 0.00
Sat 09/26 03Z 1.27 0623  68  10   9 0.00
Sat 09/26 04Z 1.29 0625  63   8   9 0.00
Sat 09/26 05Z 1.09 0626  59   7   9 0.00
Sat 09/26 06Z 1.00 0627  55   5   9 0.00
Sat 09/26 07Z 0.98 0628  56   5   9 0.00
Sat 09/26 08Z 1.03 0628  63   5   8 0.00
Sat 09/26 09Z 0.96 0728  69   5   8 0.00
Sat 09/26 10Z 0.81 0628  66   5   8 0.00
Sat 09/26 11Z 0.76 0629  58   6   9 0.00
Sat 09/26 12Z 0.77 0630  53  25   9 0.00
Sat 09/26 13Z 0.80 0631  49  46   9 0.00
Sat 09/26 14Z 0.77 0630  45  49   9 0.00
Sat 09/26 15Z 0.82 0529  47  73   9 0.00
Sat 09/26 16Z 0.85 0528  52  63   9 0.00
Sat 09/26 17Z 1.13 0528  54  46   9 0.00
Sat 09/26 18Z 1.72 0527  54  64   8 0.00
Sat 09/26 19Z 3.80 0527  59  61   7 0.00
Sat 09/26 20Z 5.11 0529  60  68   7 0.01
Sat 09/26 21Z 1.25 0534  76  86   7 0.03
Sat 09/26 22Z 0.89 0540  81  84   8 0.06
Sat 09/26 23Z 1.02 0541  83  84   8 0.06
Sun 09/27 00Z 0.85 0542  95  93   8 0.07
Sun 09/27 01Z 0.84 0643  93  91   9 0.05
Sun 09/27 02Z 0.83 0643  93  89   9 0.04
Sun 09/27 03Z 0.79 0642  94  88  10 0.04
Sun 09/27 04Z 0.72 0738  95  82  11 0.04
Sun 09/27 05Z 0.64 0736  93  79  12 0.02
Sun 09/27 06Z 0.64 0736  93  80  12 0.01
Sun 09/27 07Z 0.64 0736  93  80  12 0.02
Sun 09/27 08Z 0.65 0736  94  80  12 0.04
Sun 09/27 09Z 0.65 0736  96  85  12 0.09
Sun 09/27 10Z 0.70 0738  97  90  11 0.12
Sun 09/27 11Z 0.70 0739  94  93  12 0.11
Sun 09/27 12Z 0.72 0740  96  90  12 0.11
Sun 09/27 13Z 0.70 0839  96  85  12 0.08
Sun 09/27 14Z 0.70 0839  96  89  12 0.06
Sun 09/27 15Z 0.67 0837  95  83  12 0.05
Sun 09/27 16Z 0.66 0936  96  86  12 0.04
Sun 09/27 17Z 0.66 0934  96  82  12 0.04
Sun 09/27 18Z 0.63 0933  96  76  12 0.03
Sun 09/27 19Z 0.60 0931  96  88  12 0.03
Sun 09/27 20Z 0.60 0931  95  87  12 0.05
Sun 09/27 21Z 0.60 0932  95  83  12 0.03
Sun 09/27 22Z 0.58 0932  95  71  12 0.03
Sun 09/27 23Z 0.57 0932  95  66  12 0.03
Mon 09/28 00Z 0.56 1032  95  55  12 0.02
Mon 09/28 01Z 0.54 0930  94  56  12 0.02
Mon 09/28 02Z 0.54 0931  93  60  12 0.02
Mon 09/28 03Z 0.54 0931  93  70  12 0.02
Mon 09/28 04Z 0.56 0932  93  73  12 0.01
Mon 09/28 05Z 0.53 0930  93  75  12 0.02

Run total areal avg QPF for the Central_Greens is: 1.50 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