NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261007_0000
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 10/07 00Z 0.68 2917  58  30   0 0.00
Wed 10/07 01Z 0.69 3017  61  43   0 0.00
Wed 10/07 02Z 0.55 3017  60  54   0 0.00
Wed 10/07 03Z 0.41 3017  54  61   1 0.00
Wed 10/07 04Z 0.33 3015  48  66   2 0.00
Wed 10/07 05Z 0.29 2913  42  61   3 0.00
Wed 10/07 06Z 0.28 2812  38  53   3 0.00
Wed 10/07 07Z 0.29 2712  35  66   4 0.00
Wed 10/07 08Z 0.30 2713  34  67   4 0.00
Wed 10/07 09Z 0.31 2613  31  69   5 0.00
Wed 10/07 10Z 0.30 2613  25  81   5 0.00
Wed 10/07 11Z 0.29 2513  19  84   6 0.00
Wed 10/07 12Z 0.28 2413  17  83   7 0.00
Wed 10/07 13Z 0.29 2315  20  80   7 0.00
Wed 10/07 14Z 0.30 2217  28  86   7 0.00
Wed 10/07 15Z 0.32 2119  34  89   7 0.00
Wed 10/07 16Z 0.38 2121  39  87   7 0.00
Wed 10/07 17Z 0.41 2122  41  89   8 0.00
Wed 10/07 18Z 0.46 2122  42  91   8 0.00
Wed 10/07 19Z 0.52 2124  42  89   8 0.00
Wed 10/07 20Z 0.52 2124  44  84   8 0.00
Wed 10/07 21Z 0.59 2124  53  66   8 0.00
Wed 10/07 22Z 0.68 2125  63  32   7 0.00
Wed 10/07 23Z 0.73 2227  74  53   7 0.00
Thu 10/08 00Z 0.71 2228  80  82   7 0.00
Thu 10/08 01Z 0.72 2329  80  83   7 0.00
Thu 10/08 02Z 0.75 2330  83  67   7 0.00
Thu 10/08 03Z 0.83 2432  90  64   7 0.00
Thu 10/08 04Z 0.80 2431  92  75   7 0.00
Thu 10/08 05Z 0.75 2430  94  68   7 0.01
Thu 10/08 06Z 0.70 2428  95  67   8 0.01
Thu 10/08 07Z 0.66 2426  95  69   8 0.01
Thu 10/08 08Z 0.63 2325  96  73   8 0.01
Thu 10/08 09Z 0.56 2322  96  76   7 0.02
Thu 10/08 10Z 0.50 2321  97  83   8 0.02
Thu 10/08 11Z 0.55 2225  96  73   8 0.04
Thu 10/08 12Z 0.79 2332  97  70   7 0.05
Thu 10/08 13Z 0.97 2432  97  75   6 0.05
Thu 10/08 14Z 1.03 2529  94  88   6 0.02
Thu 10/08 15Z 1.18 2529  89  38   5 0.02
Thu 10/08 16Z 2.93 2529  92  23   5 0.02
Thu 10/08 17Z 7.04 2628  88  37   4 0.01
Thu 10/08 18Z 9.05 2728  86  36   4 0.01
Thu 10/08 19Z 9.28 2626  84  38   3 0.00
Thu 10/08 20Z 9.58 2626  83  31   3 0.00
Thu 10/08 21Z 4.40 2627  85  42   3 0.00
Thu 10/08 22Z 2.08 2728  84  43   3 0.01
Thu 10/08 23Z 1.64 2727  90  34   2 0.01
Fri 10/09 00Z 1.53 2726  92  36   2 0.01
Fri 10/09 01Z 1.16 2826  90  39   1 0.00
Fri 10/09 02Z 1.03 2826  86  33   1 0.00
Fri 10/09 03Z 0.91 2825  84  35   1 0.00
Fri 10/09 04Z 0.95 2825  89  39   1 0.00
Fri 10/09 05Z 0.91 2825  89  35   1 0.00
Fri 10/09 06Z 0.81 2825  86  36   1 0.00
Fri 10/09 07Z 0.89 2727  91  47   1 0.00
Fri 10/09 08Z 0.93 2727  92  61   1 0.00
Fri 10/09 09Z 0.90 2726  93  38   1 0.00
Fri 10/09 10Z 0.98 2727  91  49   1 0.00
Fri 10/09 11Z 0.96 2727  89  37   1 0.00

Run total areal avg QPF for the Central_Greens is: 0.33 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