NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260409_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)
=== ===== === ==== ==== === === === ====
Thu 04/09 18Z 0.64 1918  31  30   2 0.00
Thu 04/09 19Z 0.69 1921  32  23   3 0.00
Thu 04/09 20Z 0.64 1923  32  26   3 0.00
Thu 04/09 21Z 0.52 1926  30  36   4 0.00
Thu 04/09 22Z 0.46 2027  30  44   5 0.00
Fri 04/10 00Z 0.41 2129  33  53   7 0.00
Fri 04/10 01Z 0.48 2230  38  52   7 0.00
Fri 04/10 02Z 0.53 2331  43  64   7 0.00
Fri 04/10 03Z 0.58 2432  50  69   7 0.00
Fri 04/10 04Z 0.64 2433  62  67   6 0.00
Fri 04/10 05Z 0.65 2432  69  84   6 0.00
Fri 04/10 06Z 0.64 2532  70  57   6 0.00
Fri 04/10 07Z 0.60 2629  71  35   6 0.00
Fri 04/10 08Z 0.55 2625  72   7   5 0.00
Fri 04/10 09Z 0.53 2624  76   5   5 0.00
Fri 04/10 10Z 0.51 2522  83   4   5 0.00
Fri 04/10 11Z 0.53 2522  85   8   5 0.00
Fri 04/10 13Z 0.47 2420  85  20   6 0.00
Fri 04/10 14Z 0.46 2421  86  66   6 0.00
Fri 04/10 15Z 0.45 2321  83  86   7 0.00
Fri 04/10 16Z 0.49 2323  84  94   7 0.00
Fri 04/10 17Z 0.57 2324  83  80   7 0.00
Fri 04/10 18Z 0.64 2324  79  49   8 0.00
Fri 04/10 19Z 0.70 2325  76  36   8 0.00
Fri 04/10 20Z 0.79 2228  71  31   8 0.00
Fri 04/10 22Z 0.96 2231  71  62   8 0.00
Fri 04/10 23Z 1.14 2234  78  94   7 0.00
Sat 04/11 00Z 1.04 2433  95  96   6 0.00
Sat 04/11 01Z 0.92 2532  98  94   5 0.00
Sat 04/11 02Z 0.75 2626  98  95   5 0.01
Sat 04/11 03Z 0.56 2722  98  88   4 0.09
Sat 04/11 04Z 0.37 2818  99  94   3 0.13
Sat 04/11 05Z 0.35 3021  97  92   1 0.07
Sat 04/11 06Z 0.39 3024  96  55   0 0.04
Sat 04/11 07Z 0.46 3127  92  20  -2 0.03
Sat 04/11 08Z 0.46 3127  85   8  -3 0.03
Sat 04/11 09Z 0.49 3129  85   3  -3 0.01
Sat 04/11 10Z 0.52 3029  84   3  -4 0.01
Sat 04/11 11Z 0.48 3128  80   3  -4 0.01
Sat 04/11 12Z 0.45 3127  79   6  -5 0.01
Sat 04/11 13Z 0.46 3127  78   8  -5 0.01
Sat 04/11 14Z 0.46 3127  76   8  -6 0.01
Sat 04/11 15Z 0.50 3126  79   7  -6 0.01
Sat 04/11 16Z 0.51 3124  81   9  -6 0.00
Sat 04/11 17Z 0.54 3122  81  10  -6 0.00
Sat 04/11 18Z 0.57 3121  81  10  -6 0.00
Sat 04/11 19Z 0.74 3120  81   9  -6 0.00
Sat 04/11 21Z 1.63 3119  79   8  -6 0.00
Sat 04/11 22Z 1.23 3119  79   6  -6 0.00
Sat 04/11 23Z 0.94 3119  77   7  -6 0.00
Sun 04/12 00Z 0.78 3121  75   8  -5 0.00
Sun 04/12 01Z 0.52 3221  72   7  -5 0.00
Sun 04/12 02Z 0.33 3221  67   8  -5 0.00
Sun 04/12 03Z 0.25 3221  61   7  -4 0.00
Sun 04/12 04Z 0.23 3220  60   8  -4 0.00
Sun 04/12 05Z 0.19 3218  59   8  -4 0.00

Run total areal avg QPF for the Central_Greens is: 0.47 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