NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260506_0600
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)
=== ===== === ==== ==== === === === ====
Wed 05/06 06Z 0.42 2513  90  94   7 0.00
Wed 05/06 07Z 0.38 2414  88  87   8 0.02
Wed 05/06 08Z 0.31 2313  88  91   8 0.00
Wed 05/06 09Z 0.24 2112  89  92   8 0.00
Wed 05/06 10Z 0.18 2012  89  85   9 0.01
Wed 05/06 11Z 0.10 1814  89  79   9 0.00
Wed 05/06 12Z 0.22 1917  92  77   8 0.02
Wed 05/06 13Z 0.47 2121  96  88   7 0.06
Wed 05/06 14Z 0.52 2121  97  81   7 0.04
Wed 05/06 15Z 0.56 2121  98  98   7 0.06
Wed 05/06 16Z 0.46 2123  99  98   7 0.13
Wed 05/06 17Z 0.50 2123  98  98   7 0.17
Wed 05/06 18Z 0.61 2028  96  98   7 0.13
Wed 05/06 19Z 0.44 2121  99  99   8 0.12
Wed 05/06 20Z 0.35 2216  99  94   7 0.10
Wed 05/06 21Z 0.25 2511  98  97   7 0.04
Wed 05/06 22Z 0.24 2611  98  98   7 0.05
Wed 05/06 23Z 0.25 2813  97  98   6 0.05
Thu 05/07 00Z 0.24 2914  96  94   5 0.02
Thu 05/07 01Z 0.18 3012  93  90   4 0.00
Thu 05/07 02Z 0.19 3012  93  83   3 0.00
Thu 05/07 03Z 0.18 3112  88  84   3 0.00
Thu 05/07 04Z 0.22 3013  90  93   2 0.00
Thu 05/07 05Z 0.22 3114  92  84   2 0.01
Thu 05/07 06Z 0.22 3113  93  65   1 0.00
Thu 05/07 07Z 0.29 3013  93  65   0 0.00
Thu 05/07 08Z 0.36 2914  93  65   0 0.00
Thu 05/07 09Z 0.49 2917  95  51   0 0.01
Thu 05/07 10Z 0.52 2817  93  38  -1 0.01
Thu 05/07 11Z 0.61 2819  86  18  -2 0.01
Thu 05/07 12Z 0.56 2818  66   9  -2 0.00
Thu 05/07 13Z 0.62 2919  61  16  -2 0.00
Thu 05/07 14Z 0.73 2918  68  19  -2 0.00
Thu 05/07 15Z 5.81 2817  78  24  -3 0.00
Thu 05/07 16Z 11.00 2816  78  22  -3 0.00
Thu 05/07 17Z 11.31 2817  71  25  -2 0.00
Thu 05/07 18Z 11.35 2716  65  25  -1 0.00
Thu 05/07 19Z 11.79 2717  57  24   0 0.00
Thu 05/07 20Z 11.68 2817  52  21   0 0.00
Thu 05/07 21Z 11.42 2818  52  22   0 0.00
Thu 05/07 22Z 10.68 2818  56  21   0 0.00
Thu 05/07 23Z 7.67 2918  59  21  -1 0.00
Fri 05/08 00Z 2.31 2918  63  22  -1 0.00
Fri 05/08 01Z 1.70 2918  66  23  -2 0.00
Fri 05/08 02Z 1.50 2918  71  23  -2 0.00
Fri 05/08 03Z 1.33 2918  74  24  -3 0.00
Fri 05/08 04Z 0.99 2918  75  29  -3 0.00
Fri 05/08 05Z 0.73 2918  74  37  -3 0.00
Fri 05/08 06Z 0.64 3018  74  46  -3 0.00
Fri 05/08 07Z 0.58 3018  74  55  -3 0.00
Fri 05/08 08Z 0.57 3018  74  56  -3 0.00
Fri 05/08 09Z 0.54 3019  78  58  -3 0.00
Fri 05/08 10Z 0.55 3019  82  53  -3 0.00
Fri 05/08 11Z 0.60 3018  77  46  -4 0.00
Fri 05/08 12Z 0.92 2916  74  72  -4 0.00
Fri 05/08 13Z 5.13 2815  72  79  -4 0.00
Fri 05/08 14Z 8.59 2714  74  68  -4 0.00
Fri 05/08 15Z 9.33 2714  74  24  -3 0.00
Fri 05/08 16Z 10.31 2715  68  30  -3 0.00
Fri 05/08 17Z 10.18 2716  67  46  -2 0.00

Run total areal avg QPF for the Central_Greens is: 1.06 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