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_0600
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 06Z 0.39 0613  69   5   8 0.00
Fri 09/25 07Z 0.42 0614  63   5   9 0.00
Fri 09/25 08Z 0.42 0516  59   6   9 0.00
Fri 09/25 09Z 0.43 0517  56   6   9 0.00
Fri 09/25 10Z 0.54 0619  58   6   8 0.00
Fri 09/25 11Z 0.58 0720  55   6   8 0.00
Fri 09/25 12Z 0.53 0720  53   5   9 0.00
Fri 09/25 13Z 0.54 0720  53   5   9 0.00
Fri 09/25 14Z 0.54 0721  52   6   9 0.00
Fri 09/25 15Z 0.49 0719  46   7  10 0.00
Fri 09/25 16Z 0.45 0717  44   7  10 0.00
Fri 09/25 17Z 0.48 0816  47   8  10 0.00
Fri 09/25 18Z 0.51 0713  55  10   9 0.00
Fri 09/25 19Z 0.65 0613  61  11   8 0.00
Fri 09/25 20Z 0.84 0514  63  12   8 0.00
Fri 09/25 21Z 0.93 0517  60  12   8 0.00
Fri 09/25 22Z 1.01 0519  56  12   9 0.00
Fri 09/25 23Z 0.93 0520  53  13   9 0.00
Sat 09/26 00Z 0.88 0622  48  11   9 0.00
Sat 09/26 01Z 0.90 0623  44  10   9 0.00
Sat 09/26 02Z 0.90 0725  43   9   9 0.00
Sat 09/26 03Z 0.80 0725  38   7  10 0.00
Sat 09/26 04Z 0.75 0625  35   6  10 0.00
Sat 09/26 05Z 0.74 0626  36   5  10 0.00
Sat 09/26 06Z 0.75 0727  37   6  10 0.00
Sat 09/26 07Z 0.72 0726  38   6  10 0.00
Sat 09/26 08Z 0.68 0726  38   6  10 0.00
Sat 09/26 09Z 0.66 0725  38   6  10 0.00
Sat 09/26 10Z 0.66 0626  37   6  10 0.00
Sat 09/26 11Z 0.66 0626  36   7  10 0.00
Sat 09/26 12Z 0.67 0628  35   7  10 0.00
Sat 09/26 13Z 0.69 0628  37   9  10 0.00
Sat 09/26 14Z 0.70 0628  38  15  10 0.00
Sat 09/26 15Z 0.73 0627  40  22   9 0.00
Sat 09/26 16Z 0.81 0626  44  27   9 0.00
Sat 09/26 17Z 0.90 0623  47  32   9 0.00
Sat 09/26 18Z 1.07 0522  52  30   8 0.00
Sat 09/26 19Z 1.67 0521  58  32   8 0.00
Sat 09/26 20Z 2.14 0522  57  28   8 0.00
Sat 09/26 21Z 1.70 0523  56  25   8 0.00
Sat 09/26 22Z 1.53 0525  57  25   8 0.00
Sat 09/26 23Z 1.44 0527  56  40   8 0.00
Sun 09/27 00Z 1.39 0529  56  53   8 0.00
Sun 09/27 01Z 1.29 0531  56  55   8 0.00
Sun 09/27 02Z 1.14 0631  54  62   8 0.00
Sun 09/27 03Z 1.21 0634  56  67   8 0.00
Sun 09/27 04Z 1.26 0635  58  72   8 0.00
Sun 09/27 05Z 1.27 0735  61  79   7 0.00
Sun 09/27 06Z 1.17 0735  70  93   7 0.01
Sun 09/27 07Z 0.96 0736  76  92   7 0.02
Sun 09/27 08Z 0.92 0737  89  89   7 0.03
Sun 09/27 09Z 0.81 0738  86  68   8 0.02
Sun 09/27 10Z 0.76 0736  87  61   9 0.01
Sun 09/27 11Z 0.68 0835  89  61  11 0.01
Sun 09/27 12Z 0.64 0834  86  65  11 0.01
Sun 09/27 13Z 0.61 0834  88  57  12 0.01
Sun 09/27 14Z 0.59 0833  91  52  12 0.01
Sun 09/27 15Z 0.58 0832  92  44  12 0.01
Sun 09/27 16Z 0.60 0831  93  58  11 0.01
Sun 09/27 17Z 0.59 0829  93  49  11 0.01

Run total areal avg QPF for the Central_Greens is: 0.16 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