NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261006_1200
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)
=== ===== === ==== ==== === === === ====
Tue 10/06 12Z 0.48 3025  97  21  -2 0.00
Tue 10/06 13Z 0.50 3027  95  15  -1 0.01
Tue 10/06 14Z 0.49 3026  95  12  -1 0.01
Tue 10/06 15Z 0.48 3024  90   8  -1 0.00
Tue 10/06 16Z 0.53 3022  87   6   0 0.00
Tue 10/06 17Z 0.65 2921  80   5   0 0.00
Tue 10/06 18Z 0.80 2919  73   4   0 0.00
Tue 10/06 19Z 0.94 2919  62   5   0 0.00
Tue 10/06 20Z 1.01 2919  56   8   0 0.00
Tue 10/06 21Z 1.01 2919  55  14   0 0.00
Tue 10/06 22Z 1.06 3020  53  23   0 0.00
Tue 10/06 23Z 0.92 3021  49  35   0 0.00
Wed 10/07 00Z 0.72 3021  50  45   0 0.00
Wed 10/07 01Z 0.52 3020  48  52   0 0.00
Wed 10/07 02Z 0.39 3019  44  51   1 0.00
Wed 10/07 03Z 0.33 3017  42  47   1 0.00
Wed 10/07 04Z 0.28 3014  41  49   2 0.00
Wed 10/07 05Z 0.26 2812  39  55   2 0.00
Wed 10/07 06Z 0.28 2712  35  56   3 0.00
Wed 10/07 07Z 0.33 2614  34  63   3 0.00
Wed 10/07 08Z 0.36 2616  29  79   4 0.00
Wed 10/07 09Z 0.43 2619  25  83   4 0.00
Wed 10/07 10Z 0.43 2619  21  88   5 0.00
Wed 10/07 11Z 0.41 2619  30  95   6 0.00
Wed 10/07 12Z 0.41 2519  41  93   6 0.00
Wed 10/07 13Z 0.42 2420  48  96   6 0.00
Wed 10/07 14Z 0.43 2322  51  93   7 0.00
Wed 10/07 15Z 0.41 2223  50  86   7 0.00
Wed 10/07 16Z 0.48 2225  52  84   7 0.00
Wed 10/07 17Z 0.54 2226  45  73   7 0.00
Wed 10/07 18Z 0.51 2125  39  63   8 0.00
Wed 10/07 19Z 0.54 2124  40  65   8 0.00
Wed 10/07 20Z 0.56 2123  48  44   8 0.00
Wed 10/07 21Z 0.65 2124  62  46   7 0.00
Wed 10/07 22Z 0.73 2126  76  90   7 0.00
Wed 10/07 23Z 0.66 2227  82  95   7 0.01
Thu 10/08 00Z 0.73 2229  85  93   7 0.01
Thu 10/08 01Z 0.80 2331  88  93   7 0.03
Thu 10/08 02Z 0.83 2332  95  92   7 0.02
Thu 10/08 03Z 0.85 2332  96  93   7 0.03
Thu 10/08 04Z 0.82 2332  96  87   8 0.03
Thu 10/08 05Z 0.75 2330  97  90   8 0.03
Thu 10/08 06Z 0.74 2429  97  93   8 0.04
Thu 10/08 07Z 0.80 2431  97  92   8 0.07
Thu 10/08 08Z 0.86 2431  97  90   8 0.12
Thu 10/08 09Z 0.83 2527  93  84   7 0.07
Thu 10/08 10Z 0.81 2526  92  75   7 0.02
Thu 10/08 11Z 0.76 2524  89  58   7 0.01
Thu 10/08 12Z 0.83 2624  88  49   6 0.01
Thu 10/08 13Z 0.77 2622  84  48   6 0.01
Thu 10/08 14Z 0.70 2720  76  44   6 0.01
Thu 10/08 15Z 0.77 2720  74  54   5 0.00
Thu 10/08 16Z 0.92 2719  78  58   5 0.00
Thu 10/08 17Z 2.19 2619  87  50   4 0.00
Thu 10/08 18Z 6.51 2618  86  32   5 0.00
Thu 10/08 19Z 7.96 2518  83  28   5 0.00
Thu 10/08 20Z 8.77 2520  82  42   5 0.00
Thu 10/08 21Z 3.15 2622  79  27   4 0.03
Thu 10/08 22Z 2.79 2625  80  25   4 0.00
Thu 10/08 23Z 2.56 2627  81  30   4 0.00

Run total areal avg QPF for the Central_Greens is: 0.57 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