NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20250308_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)
=== ===== === ==== ==== === === === ====
Sat 03/08 00Z 3.08 2826  74  48 -11 0.00
Sat 03/08 01Z 2.51 2730  73  43 -11 0.00
Sat 03/08 02Z 2.01 2732  70  20 -12 0.00
Sat 03/08 03Z 1.91 2733  71  22 -12 0.00
Sat 03/08 04Z 1.78 2832  72  27 -12 0.00
Sat 03/08 05Z 1.81 2732  73  33 -12 0.00
Sat 03/08 06Z 1.37 2831  73  46 -12 0.00
Sat 03/08 07Z 1.24 2730  77  67 -11 0.00
Sat 03/08 08Z 1.12 2729  83  87 -11 0.00
Sat 03/08 09Z 1.03 2727  91  85 -11 0.01
Sat 03/08 10Z 1.09 2725  94  75 -12 0.01
Sat 03/08 11Z 1.33 2825  93  53 -13 0.01
Sat 03/08 12Z 1.50 2827  87  33 -13 0.01
Sat 03/08 13Z 4.22 2826  88  49 -14 0.01
Sat 03/08 14Z 10.83 2826  86  55 -15 0.00
Sat 03/08 15Z 15.75 2826  80  57 -15 0.00
Sat 03/08 16Z 15.15 2827  80  64 -15 0.00
Sat 03/08 17Z 16.50 2827  75  68 -15 0.00
Sat 03/08 18Z 16.63 2828  76  70 -15 0.00
Sat 03/08 19Z 16.05 2828  77  71 -15 0.00
Sat 03/08 20Z 15.51 2829  76  71 -14 0.00
Sat 03/08 21Z 13.48 2930  78  73 -14 0.00
Sat 03/08 22Z 8.78 2932  79  74 -14 0.00
Sat 03/08 23Z 2.57 2934  74  72 -14 0.00
Sun 03/09 00Z 1.96 2935  72  70 -13 0.00
Sun 03/09 01Z 1.57 2935  73  58 -13 0.00
Sun 03/09 02Z 1.34 2935  72  47 -13 0.00
Sun 03/09 03Z 1.18 3035  72  36 -13 0.00
Sun 03/09 04Z 1.10 3034  75  32 -13 0.00
Sun 03/09 05Z 1.01 3033  77  27 -13 0.00
Sun 03/09 06Z 0.88 3032  79  20 -13 0.00
Sun 03/09 07Z 0.81 3030  82  18 -13 0.00
Sun 03/09 08Z 0.73 3028  84  16 -13 0.00
Sun 03/09 09Z 0.61 3026  82  25 -13 0.00
Sun 03/09 10Z 0.46 3024  77  40 -12 0.00
Sun 03/09 11Z 0.42 3021  76  47 -12 0.00
Sun 03/09 12Z 0.36 2918  74  56 -11 0.00
Sun 03/09 13Z 0.36 2816  72  59 -11 0.00
Sun 03/09 14Z 0.37 2814  69  77 -11 0.00
Sun 03/09 15Z 0.46 2713  66  85 -11 0.00
Sun 03/09 16Z 0.79 2713  73  85 -11 0.00
Sun 03/09 17Z 1.74 2712  85  89 -11 0.00
Sun 03/09 18Z 2.07 2613  90  86 -11 0.00
Sun 03/09 19Z 3.33 2515  91  68 -10 0.00
Sun 03/09 20Z 2.90 2516  92  33 -10 0.00
Sun 03/09 21Z 1.29 2620  96  31  -9 0.01
Sun 03/09 22Z 2.07 2823  95   4 -10 0.02
Sun 03/09 23Z 1.95 2925  91   2 -11 0.01
Mon 03/10 00Z 1.35 2922  87   2 -11 0.00
Mon 03/10 01Z 0.93 2921  92   4 -11 0.00
Mon 03/10 02Z 0.96 2721  97   9 -11 0.01
Mon 03/10 03Z 1.01 2822  94  20 -11 0.01
Mon 03/10 04Z 0.86 2822  89  56 -11 0.00
Mon 03/10 05Z 0.67 2720  83  84 -10 0.00
Mon 03/10 06Z 0.55 2721  70  85  -8 0.00
Mon 03/10 07Z 0.59 2624  74  87  -8 0.00
Mon 03/10 08Z 0.58 2624  92  92  -7 0.01
Mon 03/10 09Z 0.57 2526  95  95  -5 0.01
Mon 03/10 10Z 0.60 2528  95  94  -4 0.03
Mon 03/10 11Z 0.65 2531  93  82  -4 0.02

Run total areal avg QPF for the Central_Greens is: 0.18 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