NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260406_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)
=== ===== === ==== ==== === === === ====
Mon 04/06 06Z 1.92 2728  92  50  -7 0.00
Mon 04/06 07Z 2.37 2833  91  54  -8 0.00
Mon 04/06 08Z 1.45 2832  90  56  -8 0.00
Mon 04/06 09Z 1.30 2932  93  56  -8 0.00
Mon 04/06 10Z 1.41 2932  94  58  -8 0.00
Mon 04/06 11Z 1.54 2931  96  61  -9 0.00
Mon 04/06 12Z 1.66 2928  97  62  -9 0.00
Mon 04/06 13Z 2.04 2926  97  61 -10 0.00
Mon 04/06 14Z 3.26 2924  95  64 -10 0.00
Mon 04/06 15Z 5.97 2824  92  70 -10 0.00
Mon 04/06 16Z 9.52 2822  87  74  -9 0.00
Mon 04/06 17Z 11.70 2821  81  74  -9 0.00
Mon 04/06 18Z 12.03 2819  76  73  -9 0.00
Mon 04/06 19Z 11.67 2719  75  77  -8 0.00
Mon 04/06 20Z 11.31 2719  76  78  -8 0.00
Mon 04/06 21Z 11.96 2719  75  79  -8 0.00
Mon 04/06 22Z 9.06 2720  75  78  -8 0.00
Mon 04/06 23Z 6.21 2821  75  75  -8 0.00
Tue 04/07 00Z 3.23 2821  77  73  -9 0.00
Tue 04/07 01Z 1.54 2920  80  74  -9 0.00
Tue 04/07 02Z 1.03 2917  85  77  -9 0.00
Tue 04/07 03Z 0.75 3015  87  82  -9 0.00
Tue 04/07 04Z 0.52 3013  89  79 -10 0.00
Tue 04/07 05Z 0.44 3012  88  79 -10 0.00
Tue 04/07 06Z 0.40 3010  86  80 -10 0.00
Tue 04/07 07Z 0.36 2908  84  85 -10 0.00
Tue 04/07 08Z 0.34 2908  85  77 -10 0.00
Tue 04/07 09Z 0.31 2908  86  64 -10 0.00
Tue 04/07 10Z 0.27 2908  87  48 -10 0.00
Tue 04/07 11Z 0.23 2907  89  44 -10 0.00
Tue 04/07 12Z 0.21 2906  90  37 -10 0.00
Tue 04/07 13Z 0.34 2905  90  41 -11 0.00
Tue 04/07 14Z 0.69 2904  88  48 -11 0.00
Tue 04/07 15Z 1.47 2804  82  65 -10 0.00
Tue 04/07 16Z 2.22 2805  75  77 -10 0.00
Tue 04/07 17Z 2.51 2906  69  87  -9 0.00
Tue 04/07 18Z 3.02 2906  67  82  -9 0.00
Tue 04/07 19Z 2.94 3007  66  79  -9 0.00
Tue 04/07 20Z 2.54 3008  67  82  -8 0.00
Tue 04/07 21Z 2.17 3109  70  81  -8 0.00
Tue 04/07 22Z 1.19 3111  75  70  -9 0.00
Tue 04/07 23Z 0.36 3112  80  38  -9 0.00
Wed 04/08 00Z 0.37 3114  85  27 -10 0.00
Wed 04/08 01Z 0.45 3116  84  22 -11 0.00
Wed 04/08 02Z 0.54 3117  80  26 -12 0.00
Wed 04/08 03Z 0.45 3117  62  28 -12 0.00
Wed 04/08 04Z 0.42 3118  48  25 -12 0.00
Wed 04/08 05Z 0.38 3120  40  23 -12 0.00
Wed 04/08 06Z 0.36 3120  39  20 -12 0.00
Wed 04/08 07Z 0.33 3118  41  20 -12 0.00
Wed 04/08 08Z 0.30 3116  42  17 -12 0.00
Wed 04/08 09Z 0.26 3115  42  16 -11 0.00
Wed 04/08 10Z 0.22 3113  40  18 -10 0.00
Wed 04/08 11Z 0.21 3011  39  15 -10 0.00
Wed 04/08 12Z 0.19 2909  37  10  -9 0.00
Wed 04/08 13Z 0.17 2707  35   6  -8 0.00
Wed 04/08 14Z 0.18 2607  32   5  -7 0.00
Wed 04/08 15Z 0.20 2507  30   5  -7 0.00
Wed 04/08 16Z 0.24 2407  27   4  -7 0.00
Wed 04/08 17Z 0.35 2308  25   4  -6 0.00

Run total areal avg QPF for the Central_Greens is: 0.00 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