NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260410_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)
=== ===== === ==== ==== === === === ====
Fri 04/10 00Z 0.31 2028  33  53   7 0.00
Fri 04/10 01Z 0.41 2129  35  70   7 0.00
Fri 04/10 02Z 0.50 2231  39  77   7 0.00
Fri 04/10 03Z 0.60 2333  49  83   6 0.00
Fri 04/10 04Z 0.63 2432  56  79   6 0.00
Fri 04/10 05Z 0.68 2432  64  69   6 0.00
Fri 04/10 06Z 0.70 2432  70  60   6 0.00
Fri 04/10 07Z 0.72 2431  74  44   6 0.00
Fri 04/10 08Z 0.71 2530  75  32   6 0.00
Fri 04/10 09Z 0.71 2529  78  27   5 0.00
Fri 04/10 10Z 0.68 2527  82  19   5 0.00
Fri 04/10 11Z 0.64 2525  82  21   5 0.00
Fri 04/10 12Z 0.58 2522  78  29   5 0.00
Fri 04/10 13Z 0.49 2421  77  18   6 0.00
Fri 04/10 14Z 0.43 2419  78  47   6 0.00
Fri 04/10 15Z 0.39 2320  78  89   6 0.00
Fri 04/10 16Z 0.40 2222  75  87   7 0.00
Fri 04/10 17Z 0.45 2225  71  84   8 0.00
Fri 04/10 18Z 0.56 2224  67  74   8 0.00
Fri 04/10 19Z 0.61 2322  66  52   8 0.00
Fri 04/10 20Z 0.69 2323  65  39   8 0.00
Fri 04/10 21Z 0.73 2224  64  38   8 0.00
Fri 04/10 22Z 0.59 2224  70  52   8 0.00
Fri 04/10 23Z 0.54 2224  80  78   7 0.02
Sat 04/11 00Z 0.66 2423  92  96   6 0.10
Sat 04/11 01Z 0.51 2420  96  96   6 0.05
Sat 04/11 02Z 0.41 2318  97  98   5 0.07
Sat 04/11 03Z 0.39 2418  98  98   5 0.13
Sat 04/11 04Z 0.41 2718  98  96   3 0.11
Sat 04/11 05Z 0.41 3021  98  96   1 0.07
Sat 04/11 06Z 0.44 3126  97  83   0 0.04
Sat 04/11 07Z 0.54 3128  95  54  -2 0.03
Sat 04/11 08Z 0.67 3131  94  29  -3 0.02
Sat 04/11 09Z 0.72 3131  93  12  -4 0.01
Sat 04/11 10Z 0.71 3131  91   6  -5 0.01
Sat 04/11 11Z 0.71 3130  93   4  -5 0.01
Sat 04/11 12Z 0.77 3129  94   5  -6 0.01
Sat 04/11 13Z 0.77 3128  93   4  -6 0.01
Sat 04/11 14Z 0.78 3128  90   6  -7 0.01
Sat 04/11 15Z 0.76 3127  86   8  -7 0.00
Sat 04/11 16Z 0.77 3126  84   9  -7 0.00
Sat 04/11 18Z 1.02 3122  85  11  -7 0.00
Sat 04/11 19Z 1.53 3121  85  11  -7 0.00
Sat 04/11 20Z 2.76 3120  85  11  -6 0.00
Sat 04/11 21Z 3.01 3120  84  11  -6 0.00
Sat 04/11 22Z 2.51 3021  83  12  -6 0.00
Sat 04/11 23Z 1.90 3123  81  11  -6 0.00
Sun 04/12 00Z 1.77 3125  81  13  -6 0.00
Sun 04/12 01Z 1.31 3125  78  13  -6 0.00
Sun 04/12 02Z 0.92 3126  74  12  -6 0.00
Sun 04/12 03Z 0.65 3225  68  12  -6 0.00
Sun 04/12 04Z 0.52 3225  64  11  -5 0.00
Sun 04/12 05Z 0.40 3223  60   9  -5 0.00
Sun 04/12 06Z 0.33 3221  57  12  -5 0.00
Sun 04/12 07Z 0.25 3318  54  21  -4 0.00
Sun 04/12 08Z 0.23 3215  53  28  -4 0.00
Sun 04/12 09Z 0.23 3112  54  24  -4 0.00
Sun 04/12 10Z 0.18 3110  49  23  -3 0.00
Sun 04/12 11Z 0.12 3006  41  33  -2 0.00

Run total areal avg QPF for the greens is: 0.70 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