NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260330_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)
=== ===== === ==== ==== === === === ====
Mon 03/30 00Z 1.49 2519  58  19  -3 0.00
Mon 03/30 01Z 1.67 2620  58   9  -3 0.00
Mon 03/30 02Z 1.33 2519  58  13  -2 0.00
Mon 03/30 03Z 1.04 2420  54  43  -2 0.00
Mon 03/30 04Z 0.89 2421  48  81  -1 0.00
Mon 03/30 05Z 0.85 2324  45  87   0 0.00
Mon 03/30 06Z 1.47 2327  47  73   0 0.00
Mon 03/30 07Z 0.82 2232  52  75   0 0.00
Mon 03/30 08Z 0.80 2236  55  56   1 0.00
Mon 03/30 09Z 0.78 2336  56  29   2 0.00
Mon 03/30 10Z 0.75 2434  54  22   2 0.00
Mon 03/30 11Z 0.78 2432  54  49   2 0.00
Mon 03/30 12Z 0.79 2531  56  57   1 0.00
Mon 03/30 13Z 0.82 2531  56  63   1 0.00
Mon 03/30 14Z 0.85 2530  54  59   1 0.00
Mon 03/30 15Z 0.95 2530  55  60   1 0.00
Mon 03/30 16Z 1.05 2529  57  47   2 0.00
Mon 03/30 17Z 1.16 2529  59  52   2 0.00
Mon 03/30 18Z 1.29 2529  61  51   2 0.00
Mon 03/30 19Z 2.10 2530  64  60   3 0.00
Mon 03/30 20Z 2.21 2531  68  62   3 0.00
Mon 03/30 21Z 3.52 2530  65  63   3 0.00
Mon 03/30 22Z 3.72 2630  68  70   3 0.00
Mon 03/30 23Z 1.95 2629  78  82   3 0.01
Tue 03/31 00Z 1.24 2628  85  87   3 0.03
Tue 03/31 01Z 1.11 2728  91  82   3 0.03
Tue 03/31 02Z 1.02 2726  90  85   2 0.02
Tue 03/31 03Z 0.84 2823  91  86   2 0.02
Tue 03/31 04Z 0.70 2820  93  81   2 0.01
Tue 03/31 05Z 0.56 2816  95  81   2 0.01
Tue 03/31 06Z 0.46 2814  96  81   2 0.01
Tue 03/31 07Z 0.38 2713  96  78   3 0.01
Tue 03/31 08Z 0.28 2710  95  80   3 0.01
Tue 03/31 09Z 0.16 2506  95  76   3 0.00
Tue 03/31 10Z 0.09 2106  97  75   3 0.00
Tue 03/31 11Z 0.04 1808  98  70   4 0.01
Tue 03/31 12Z 0.03 1711  98  98   4 0.05
Tue 03/31 13Z 0.03 1813  99  98   4 0.15
Tue 03/31 14Z 0.10 1618  98  99   5 0.08
Tue 03/31 15Z 0.12 1720  99  99   5 0.11
Tue 03/31 16Z 0.16 1721  98  99   5 0.21
Tue 03/31 17Z 0.22 1920  98  97   5 0.11
Tue 03/31 18Z 0.24 2118  99  85   6 0.07
Tue 03/31 19Z 0.31 2319  99  67   7 0.05
Tue 03/31 20Z 0.36 2421  99  63   7 0.05
Tue 03/31 21Z 0.39 2322  99  61   8 0.06
Tue 03/31 22Z 0.42 2324  99  52   8 0.04
Tue 03/31 23Z 0.46 2326  99  87   9 0.06
Wed 04/01 00Z 0.48 2328  99  85   9 0.06
Wed 04/01 01Z 0.52 2331  99  86   9 0.09
Wed 04/01 02Z 0.55 2233  98  93   9 0.11
Wed 04/01 03Z 0.53 2234  98  87  10 0.10
Wed 04/01 04Z 0.62 2238  99  77  10 0.05
Wed 04/01 05Z 0.89 2340  99  43   9 0.08
Wed 04/01 06Z 1.00 2338  97  82   9 0.08
Wed 04/01 07Z 1.07 2439  98  94   9 0.14
Wed 04/01 08Z 0.98 2437  98  96   9 0.09
Wed 04/01 09Z 0.95 2537  99  93   9 0.15
Wed 04/01 10Z 0.97 2535  98  87   8 0.15
Wed 04/01 11Z 0.87 2731  98  76   7 0.10

Run total areal avg QPF for the greens is: 2.41 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