NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261102_1200
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 11/02 12Z 0.62 2822  56  87   7 0.00
Mon 11/02 13Z 0.63 2822  59  85   8 0.00
Mon 11/02 14Z 0.63 2821  57  80   8 0.00
Mon 11/02 15Z 0.61 2820  55  77   8 0.00
Mon 11/02 16Z 0.62 2721  53  79   8 0.00
Mon 11/02 17Z 0.62 2720  53  78   8 0.00
Mon 11/02 18Z 0.62 2720  52  75   8 0.00
Mon 11/02 19Z 0.63 2620  47  74   8 0.00
Mon 11/02 20Z 0.64 2620  46  76   9 0.00
Mon 11/02 21Z 0.70 2721  47  82   9 0.00
Mon 11/02 22Z 0.71 2721  47  81   9 0.00
Mon 11/02 23Z 0.70 2721  48  80   9 0.00
Tue 11/03 00Z 0.66 2720  49  75   9 0.00
Tue 11/03 01Z 0.63 2720  51  77   9 0.00
Tue 11/03 02Z 0.60 2719  52  81   9 0.00
Tue 11/03 03Z 0.56 2718  53  84   9 0.00
Tue 11/03 04Z 0.54 2718  54  87   9 0.00
Tue 11/03 05Z 0.51 2717  57  92   9 0.00
Tue 11/03 06Z 0.48 2816  58  91   9 0.00
Tue 11/03 07Z 0.46 2715  60  90   9 0.00
Tue 11/03 08Z 0.42 2714  61  90   9 0.00
Tue 11/03 09Z 0.40 2713  61  89   9 0.00
Tue 11/03 10Z 0.40 2712  62  91   9 0.00
Tue 11/03 11Z 0.37 2711  63  94   9 0.00
Tue 11/03 12Z 0.37 2611  64  96   9 0.00
Tue 11/03 13Z 0.34 2510  62  97   9 0.00
Tue 11/03 14Z 0.36 2511  62  97   8 0.00
Tue 11/03 15Z 0.38 2412  62  97   8 0.00
Tue 11/03 16Z 0.40 2314  65  96   8 0.00
Tue 11/03 17Z 0.43 2216  66  95   8 0.00
Tue 11/03 18Z 0.49 2219  68  96   8 0.00
Tue 11/03 19Z 0.50 2220  75  98   8 0.00
Tue 11/03 20Z 0.51 2322  86  97   9 0.01
Tue 11/03 21Z 0.58 2324  88  96   9 0.03
Tue 11/03 22Z 0.61 2425  91  94  10 0.05
Tue 11/03 23Z 0.66 2526  92  87  10 0.05
Wed 11/04 00Z 0.66 2525  93  78  10 0.03
Wed 11/04 01Z 0.69 2625  93  66  10 0.02
Wed 11/04 02Z 0.68 2624  89  59  11 0.01
Wed 11/04 03Z 0.68 2524  86  57  11 0.00
Wed 11/04 04Z 0.71 2526  82  53  11 0.00
Wed 11/04 05Z 0.76 2428  80  56  11 0.00
Wed 11/04 06Z 0.80 2429  79  53  11 0.00
Wed 11/04 07Z 0.85 2529  77  55  11 0.00
Wed 11/04 08Z 0.86 2529  73  53  11 0.00
Wed 11/04 09Z 0.84 2529  71  52  12 0.00
Wed 11/04 10Z 0.85 2529  69  54  12 0.00
Wed 11/04 11Z 0.84 2628  69  51  12 0.00
Wed 11/04 12Z 0.80 2627  67  52  12 0.00
Wed 11/04 13Z 0.74 2627  67  54  12 0.00
Wed 11/04 14Z 0.68 2626  68  53  12 0.00
Wed 11/04 15Z 0.61 2624  70  51  12 0.00
Wed 11/04 16Z 0.58 2721  73  52  12 0.00
Wed 11/04 17Z 0.55 2719  75  52  12 0.00
Wed 11/04 18Z 0.52 2718  76  57  12 0.00
Wed 11/04 19Z 0.52 2718  76  56  12 0.00
Wed 11/04 20Z 0.52 2717  76  53  13 0.00
Wed 11/04 21Z 0.52 2717  74  48  13 0.00
Wed 11/04 22Z 0.53 2718  74  50  13 0.00
Wed 11/04 23Z 0.54 2718  74  54  13 0.00

Run total areal avg QPF for the greens is: 0.20 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