NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260325_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 03/25 00Z 1.21 2520  56  39  -7 0.00
Wed 03/25 01Z 3.21 2626  58  73  -7 0.00
Wed 03/25 02Z 5.85 2728  62  90  -8 0.00
Wed 03/25 03Z 4.14 2727  72  84  -9 0.00
Wed 03/25 04Z 1.79 2826  80  51  -9 0.00
Wed 03/25 05Z 1.11 2825  82  24  -9 0.00
Wed 03/25 06Z 0.89 2825  82  20  -9 0.00
Wed 03/25 07Z 0.87 2826  88  23  -8 0.00
Wed 03/25 08Z 0.91 2827  90  11  -8 0.00
Wed 03/25 09Z 0.83 2927  90  10  -8 0.00
Wed 03/25 10Z 0.71 2923  88  13  -8 0.00
Wed 03/25 11Z 0.59 2920  85  19  -8 0.00
Wed 03/25 12Z 0.55 2918  87  25  -8 0.00
Wed 03/25 13Z 0.52 2917  87  30  -8 0.01
Wed 03/25 14Z 0.44 2915  83  22  -8 0.00
Wed 03/25 15Z 0.36 2912  78  14  -7 0.00
Wed 03/25 16Z 0.37 2710  72  10  -7 0.00
Wed 03/25 17Z 0.41 2610  68  10  -6 0.00
Wed 03/25 18Z 0.42 2510  58  10  -5 0.00
Wed 03/25 19Z 0.53 2410  47   9  -4 0.00
Wed 03/25 20Z 0.55 2310  40   8  -4 0.00
Wed 03/25 21Z 0.45 2210  37   7  -3 0.00
Wed 03/25 22Z 0.37 2013  37   8  -3 0.00
Wed 03/25 23Z 0.42 1916  44  79  -3 0.00
Thu 03/26 00Z 0.54 1921  55  85  -3 0.00
Thu 03/26 01Z 0.73 2025  61  83  -2 0.00
Thu 03/26 02Z 1.10 2130  76  91  -3 0.00
Thu 03/26 03Z 0.97 2133  93  93  -3 0.01
Thu 03/26 04Z 0.82 2231  93  93  -2 0.01
Thu 03/26 05Z 0.85 2136  81  94  -2 0.00
Thu 03/26 06Z 0.74 2232  77  91  -1 0.00
Thu 03/26 07Z 0.61 2231  73  93   0 0.00
Thu 03/26 08Z 0.68 2233  76  94   0 0.00
Thu 03/26 09Z 0.67 2331  78  95   0 0.00
Thu 03/26 10Z 0.68 2332  78  94   0 0.01
Thu 03/26 11Z 0.66 2432  85  93   0 0.01
Thu 03/26 12Z 0.67 2433  82  87   1 0.01
Thu 03/26 13Z 0.70 2435  80  74   3 0.00
Thu 03/26 14Z 0.76 2436  85  47   3 0.00
Thu 03/26 15Z 0.86 2435  87  35   3 0.00
Thu 03/26 16Z 0.83 2532  87  24   3 0.00
Thu 03/26 17Z 0.87 2528  86  36   3 0.00
Thu 03/26 18Z 0.94 2526  81  47   4 0.00
Thu 03/26 19Z 1.08 2425  79  69   4 0.00
Thu 03/26 20Z 1.02 2423  81  94   5 0.00
Thu 03/26 21Z 0.98 2319  82  96   5 0.00
Thu 03/26 22Z 0.65 2120  93  98   5 0.06
Thu 03/26 23Z 0.46 2024  98  99   6 0.14
Fri 03/27 00Z 0.63 2129  98  98   7 0.25
Fri 03/27 01Z 0.77 2328  99  92   6 0.18
Fri 03/27 02Z 0.62 2522  99  94   6 0.14
Fri 03/27 03Z 0.46 2517  99  96   6 0.11
Fri 03/27 04Z 0.35 2515  99  93   6 0.08
Fri 03/27 05Z 0.27 2712  99  95   5 0.08
Fri 03/27 06Z 0.21 2912  98  96   4 0.10
Fri 03/27 07Z 0.20 3013  97  98   3 0.10
Fri 03/27 08Z 0.22 3114  98  98   2 0.08
Fri 03/27 09Z 0.23 3117  97  97   1 0.07
Fri 03/27 10Z 0.26 3120  97  96   0 0.04
Fri 03/27 11Z 0.28 3222  96  88  -1 0.03

Run total areal avg QPF for the Central_Greens is: 1.52 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