Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20251102_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)
=== ===== === ==== ==== === === === ====
Sun 11/02 06Z 0.33 3117  92   5  -3 0.00
Sun 11/02 07Z 0.37 3018  91   6  -3 0.00
Sun 11/02 08Z 0.40 3019  90   6  -3 0.00
Sun 11/02 09Z 0.37 3019  90   6  -3 0.00
Sun 11/02 10Z 0.36 3019  88   7  -3 0.00
Sun 11/02 11Z 0.38 3020  86   8  -3 0.00
Sun 11/02 12Z 0.39 3020  85   9  -3 0.00
Sun 11/02 13Z 0.34 3020  84  11  -3 0.00
Sun 11/02 14Z 0.34 3019  85  12  -3 0.00
Sun 11/02 15Z 0.29 3016  81  11  -3 0.00
Sun 11/02 16Z 0.31 2915  80  11  -3 0.00
Sun 11/02 17Z 0.34 2813  82  10  -3 0.00
Sun 11/02 18Z 0.35 2813  80  10  -3 0.00
Sun 11/02 19Z 0.43 2715  81   9  -3 0.00
Sun 11/02 20Z 0.48 2716  83  10  -3 0.00
Sun 11/02 21Z 0.50 2718  81  10  -2 0.00
Sun 11/02 22Z 0.46 2719  76   9  -1 0.00
Sun 11/02 23Z 0.47 2721  69   9   0 0.00
Mon 11/03 00Z 0.47 2822  66   9   0 0.00
Mon 11/03 01Z 0.48 2823  63  10   0 0.00
Mon 11/03 02Z 0.48 2823  62  11   0 0.00
Mon 11/03 03Z 0.55 2824  63  11   0 0.00
Mon 11/03 04Z 0.58 2724  59  16   0 0.00
Mon 11/03 05Z 0.63 2724  61  18   0 0.00
Mon 11/03 06Z 0.69 2625  71  28   1 0.00
Mon 11/03 07Z 0.71 2624  81  43   1 0.00
Mon 11/03 08Z 0.74 2525  82  59   1 0.00
Mon 11/03 09Z 0.78 2425  80  55   2 0.00
Mon 11/03 10Z 0.88 2428  82  66   1 0.00
Mon 11/03 11Z 0.92 2430  85  71   1 0.00
Mon 11/03 12Z 0.89 2331  81  71   2 0.00
Mon 11/03 13Z 0.89 2332  74  67   2 0.00
Mon 11/03 14Z 0.90 2333  73  52   2 0.00
Mon 11/03 15Z 0.98 2333  73  47   2 0.00
Mon 11/03 16Z 1.07 2332  71  48   2 0.00
Mon 11/03 17Z 1.27 2232  73  37   2 0.00
Mon 11/03 18Z 1.75 2231  69  42   2 0.00
Mon 11/03 19Z 2.17 2130  72  85   1 0.00
Mon 11/03 20Z 1.27 2031  73  90   1 0.00
Mon 11/03 21Z 0.93 2032  73  87   1 0.00
Mon 11/03 22Z 0.90 2133  84  89   1 0.00
Mon 11/03 23Z 1.24 2333  97  95   0 0.08
Tue 11/04 00Z 1.43 2431  96  90   0 0.07
Tue 11/04 01Z 1.52 2531  97  54  -1 0.04
Tue 11/04 02Z 1.48 2631  96  61  -1 0.03
Tue 11/04 03Z 1.30 2629  95  73  -2 0.02
Tue 11/04 04Z 1.16 2731  96  80  -2 0.05
Tue 11/04 05Z 1.05 2730  96  82  -2 0.04
Tue 11/04 06Z 1.00 2729  96  87  -2 0.05
Tue 11/04 07Z 1.06 2831  97  81  -2 0.07
Tue 11/04 08Z 1.06 2831  97  81  -2 0.04
Tue 11/04 09Z 1.14 2933  97  79  -3 0.02
Tue 11/04 10Z 1.14 2934  96  75  -3 0.02
Tue 11/04 11Z 1.10 3035  96  70  -3 0.01
Tue 11/04 12Z 1.11 3035  96  77  -3 0.01
Tue 11/04 13Z 1.12 3034  96  79  -4 0.01
Tue 11/04 14Z 1.16 2932  95  26  -4 0.01
Tue 11/04 15Z 1.31 2928  95  20  -4 0.01
Tue 11/04 16Z 1.61 2927  93  23  -4 0.00
Tue 11/04 17Z 2.48 2926  87  22  -4 0.00

Run total areal avg QPF for the Central_Greens is: 0.58 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