Subject: NAM3 EXPERIMENTAL Froude Number for the Northern_Greens

Model run: BTV_GRID_D2D_NAM3_20251102_0600
Using the MB925 to MB850 layer.
Assumes Northern_Greens are orthogonal to 290 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Northern_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sun 11/02 06Z 0.76 2918  94   9  -5 0.00
Sun 11/02 07Z 0.66 2920  89   9  -4 0.00
Sun 11/02 08Z 0.68 2921  89   8  -4 0.00
Sun 11/02 09Z 0.63 2921  92   7  -4 0.00
Sun 11/02 10Z 0.60 2920  91   7  -4 0.00
Sun 11/02 11Z 0.62 2921  91   8  -4 0.00
Sun 11/02 12Z 0.67 2921  91   9  -5 0.01
Sun 11/02 13Z 0.62 3021  89   8  -5 0.01
Sun 11/02 14Z 0.55 2919  87   8  -4 0.01
Sun 11/02 15Z 0.46 2917  84   8  -4 0.01
Sun 11/02 16Z 0.46 2917  84   8  -4 0.00
Sun 11/02 17Z 0.43 2816  85   7  -4 0.00
Sun 11/02 18Z 0.42 2715  85   7  -4 0.00
Sun 11/02 19Z 0.44 2716  86   7  -4 0.00
Sun 11/02 20Z 0.44 2616  85   7  -4 0.00
Sun 11/02 21Z 0.44 2617  82   6  -3 0.00
Sun 11/02 22Z 0.44 2619  80   5  -2 0.00
Sun 11/02 23Z 0.47 2719  79   6  -2 0.00
Mon 11/03 00Z 0.48 2719  78   6  -2 0.00
Mon 11/03 01Z 0.43 2717  74   5  -2 0.00
Mon 11/03 02Z 0.39 2717  70   8  -1 0.00
Mon 11/03 03Z 0.42 2719  69  13  -1 0.00
Mon 11/03 04Z 0.47 2720  68  14  -1 0.00
Mon 11/03 05Z 0.54 2622  63  18   0 0.00
Mon 11/03 06Z 0.58 2624  59  22   0 0.00
Mon 11/03 07Z 0.64 2525  63  27   0 0.00
Mon 11/03 08Z 0.75 2527  79  35   0 0.00
Mon 11/03 09Z 0.74 2427  81  48   1 0.00
Mon 11/03 10Z 0.79 2429  82  60   1 0.00
Mon 11/03 11Z 0.76 2332  83  65   1 0.00
Mon 11/03 12Z 0.77 2333  82  69   2 0.00
Mon 11/03 13Z 0.75 2334  78  80   2 0.00
Mon 11/03 14Z 0.68 2334  78  81   2 0.00
Mon 11/03 15Z 0.55 2234  76  79   2 0.00
Mon 11/03 16Z 0.56 2233  80  81   2 0.00
Mon 11/03 17Z 0.58 2234  81  78   2 0.00
Mon 11/03 18Z 0.53 2234  82  82   2 0.00
Mon 11/03 19Z 0.51 2134  82  91   2 0.00
Mon 11/03 20Z 0.30 2034  84  96   1 0.01
Mon 11/03 21Z 0.10 2033  85  91   1 0.02
Mon 11/03 22Z 0.39 2134  92  94   0 0.07
Mon 11/03 23Z 0.73 2335  98  96   0 0.10
Tue 11/04 00Z 1.22 2432  97  89  -1 0.09
Tue 11/04 01Z 1.06 2530  97  81  -1 0.04
Tue 11/04 02Z 1.04 2629  97  78  -1 0.05
Tue 11/04 03Z 1.08 2628  97  67  -1 0.03
Tue 11/04 04Z 1.07 2730  98  91  -2 0.05
Tue 11/04 05Z 1.18 2731  98  89  -2 0.06
Tue 11/04 06Z 1.25 2831  98  81  -2 0.05
Tue 11/04 07Z 1.37 2933  98  87  -2 0.08
Tue 11/04 08Z 1.40 2935  99  90  -2 0.07
Tue 11/04 09Z 1.45 2937  98  90  -3 0.08
Tue 11/04 10Z 1.44 2937  98  91  -3 0.07
Tue 11/04 11Z 1.44 3037  98  89  -3 0.06
Tue 11/04 12Z 1.50 3037  98  85  -4 0.05
Tue 11/04 13Z 1.51 3037  98  88  -4 0.07
Tue 11/04 14Z 1.49 3035  98  74  -4 0.07
Tue 11/04 15Z 1.47 2932  98  25  -4 0.05
Tue 11/04 16Z 1.57 2929  97  27  -5 0.04
Tue 11/04 17Z 1.71 2927  95  28  -5 0.02

Run total areal avg QPF for the Northern_Greens is: 1.27 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