Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260629_0600
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 06/29 06Z 0.10 3505  69  69  13 0.00
Mon 06/29 07Z 0.15 3305  71  62  13 0.00
Mon 06/29 08Z 0.19 3206  73  61  13 0.00
Mon 06/29 09Z 0.23 3207  74  59  13 0.00
Mon 06/29 10Z 0.23 3208  75  54  13 0.00
Mon 06/29 11Z 0.21 3209  74  48  13 0.00
Mon 06/29 12Z 0.17 3309  73  36  13 0.00
Mon 06/29 13Z 0.14 3309  73  27  13 0.00
Mon 06/29 14Z 0.15 3409  74  25  13 0.00
Mon 06/29 15Z 0.23 3407  75  24  13 0.00
Mon 06/29 16Z 0.52 3307  74  27  13 0.00
Mon 06/29 17Z 0.57 3307  72  35  13 0.01
Mon 06/29 18Z 0.54 3307  68  33  13 0.01
Mon 06/29 19Z 0.76 3307  65  25  13 0.01
Mon 06/29 20Z 0.75 3306  61  17  14 0.00
Mon 06/29 21Z 0.54 3307  57  17  14 0.00
Mon 06/29 22Z 0.26 3306  54  17  14 0.00
Mon 06/29 23Z 0.22 3306  52  23  14 0.00
Tue 06/30 00Z 0.23 3206  51  16  14 0.00
Tue 06/30 01Z 0.35 3106  51   9  14 0.00
Tue 06/30 02Z 0.32 3005  53  13  14 0.00
Tue 06/30 03Z 0.43 2705  57  12  14 0.00
Tue 06/30 04Z 0.44 2605  61  16  14 0.00
Tue 06/30 05Z 0.52 2407  63  12  14 0.00
Tue 06/30 06Z 0.65 2409  63   9  14 0.00
Tue 06/30 07Z 0.78 2511  64  10  14 0.00
Tue 06/30 08Z 0.75 2512  62  14  14 0.00
Tue 06/30 09Z 0.75 2513  64  17  14 0.00
Tue 06/30 10Z 0.80 2613  65  22  13 0.00
Tue 06/30 11Z 0.67 2612  66  32  14 0.00
Tue 06/30 12Z 0.63 2512  69  40  14 0.00
Tue 06/30 13Z 0.58 2512  71  40  14 0.00
Tue 06/30 14Z 0.57 2412  73  54  14 0.00
Tue 06/30 15Z 0.63 2311  75  60  14 0.00
Tue 06/30 16Z 1.36 2311  77  71  14 0.00
Tue 06/30 17Z 1.40 2110  75  76  15 0.00
Tue 06/30 18Z 0.46 1916  73  87  15 0.00
Tue 06/30 19Z 0.90 2017  81  82  15 0.02
Tue 06/30 20Z 1.63 2119  88  84  15 0.02
Tue 06/30 21Z 0.69 2119  85  78  16 0.00
Tue 06/30 22Z 0.64 2221  89  61  16 0.00
Tue 06/30 23Z 0.69 2323  94  51  17 0.01
Wed 07/01 00Z 0.82 2326  95  45  17 0.01
Wed 07/01 01Z 0.84 2426  97  35  17 0.02
Wed 07/01 02Z 0.86 2527  98  36  17 0.03
Wed 07/01 03Z 0.91 2530  97  43  18 0.06
Wed 07/01 04Z 0.79 2630  87  49  19 0.08
Wed 07/01 05Z 0.83 2631  89  43  19 0.02
Wed 07/01 06Z 0.89 2732  91  36  19 0.02
Wed 07/01 07Z 0.83 2831  91  29  19 0.02
Wed 07/01 08Z 0.79 2830  92  19  19 0.03
Wed 07/01 09Z 0.69 2828  90  14  20 0.03
Wed 07/01 10Z 0.59 2825  83  20  20 0.03
Wed 07/01 11Z 0.50 2922  76  25  21 0.02
Wed 07/01 12Z 0.42 2920  67  25  22 0.02
Wed 07/01 13Z 0.36 2918  62  31  22 0.01
Wed 07/01 14Z 0.35 2816  61  33  22 0.01
Wed 07/01 15Z 0.38 2816  62  35  22 0.01
Wed 07/01 16Z 0.38 2815  63  39  22 0.00
Wed 07/01 17Z 0.35 2813  66  37  23 0.00

Run total areal avg QPF for the greens is: 0.50 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