NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260515_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)
=== ===== === ==== ==== === === === ====
Fri 05/15 00Z 0.12 0011  98  96   3 0.00
Fri 05/15 01Z 0.13 3512  98  97   3 0.07
Fri 05/15 02Z 0.14 0015  99  99   4 0.05
Fri 05/15 03Z 0.25 0117  99  99   4 0.06
Fri 05/15 04Z 0.33 0413  99  97   4 0.06
Fri 05/15 05Z 0.39 0612  99  97   4 0.05
Fri 05/15 06Z 0.38 0711  99  94   3 0.04
Fri 05/15 08Z 0.44 0712  99  92   3 0.05
Fri 05/15 09Z 0.42 0712  99  90   3 0.06
Fri 05/15 10Z 0.47 0613  99  87   3 0.04
Fri 05/15 11Z 0.49 0614  99  63   3 0.04
Fri 05/15 12Z 0.49 0615  99  63   3 0.03
Fri 05/15 13Z 0.55 0717  98  72   3 0.02
Fri 05/15 14Z 0.57 0817  98  74   3 0.02
Fri 05/15 15Z 0.63 0817  98  80   3 0.01
Fri 05/15 16Z 0.68 0815  98  88   3 0.01
Fri 05/15 17Z 0.67 0813  98  92   3 0.01
Fri 05/15 18Z 0.53 0910  98  93   3 0.01
Fri 05/15 19Z 0.49 0909  97  89   3 0.01
Fri 05/15 20Z 0.34 0907  97  85   3 0.00
Fri 05/15 21Z 0.17 1005  93  82   4 0.00
Fri 05/15 22Z 0.09 1102  90  84   5 0.00
Fri 05/15 23Z 0.07 1400  87  84   5 0.00
Sat 05/16 00Z 0.08 2702  84  80   5 0.00
Sat 05/16 01Z 0.10 2803  77  64   5 0.00
Sat 05/16 02Z 0.20 2706  76  49   5 0.00
Sat 05/16 03Z 0.30 2709  83  47   5 0.00
Sat 05/16 04Z 0.34 2811  88  43   5 0.00
Sat 05/16 05Z 0.38 2813  92  47   5 0.00
Sat 05/16 06Z 0.42 2713  93  49   5 0.00
Sat 05/16 07Z 0.48 2715  92  43   5 0.01
Sat 05/16 08Z 0.53 2717  87  17   6 0.01
Sat 05/16 09Z 0.61 2719  81  11   5 0.01
Sat 05/16 10Z 0.67 2820  70   9   5 0.00
Sat 05/16 11Z 0.71 2821  64  11   5 0.00
Sat 05/16 12Z 0.75 2721  65  21   5 0.00
Sat 05/16 13Z 0.83 2722  65  28   5 0.00
Sat 05/16 14Z 0.93 2621  61  48   5 0.00
Sat 05/16 15Z 0.73 2516  49  47   7 0.00
Sat 05/16 16Z 0.64 2513  43  38   8 0.00
Sat 05/16 17Z 0.73 2312  43  27   8 0.00
Sat 05/16 18Z 1.07 2315  45  26   9 0.00
Sat 05/16 19Z 1.39 2217  50  13   9 0.00
Sat 05/16 20Z 2.20 2220  59  14   9 0.00
Sat 05/16 21Z 1.15 2121  65  15   9 0.00
Sat 05/16 22Z 0.78 2123  65  19  10 0.00
Sat 05/16 23Z 0.81 2124  68  53  10 0.00
Sun 05/17 00Z 0.82 2127  78  92  10 0.00
Sun 05/17 01Z 0.95 2231  78  88  10 0.04
Sun 05/17 02Z 1.27 2335  75  94  10 0.03
Sun 05/17 03Z 1.28 2338  79  92  10 0.01
Sun 05/17 04Z 1.32 2438  87  91  10 0.03
Sun 05/17 05Z 0.98 2634  95  61  10 0.03
Sun 05/17 06Z 0.81 2730  90  30  10 0.03
Sun 05/17 07Z 0.68 2827  80   9  10 0.01
Sun 05/17 08Z 0.64 2827  70   6  10 0.01
Sun 05/17 09Z 0.71 2830  63   7   9 0.01
Sun 05/17 10Z 0.79 3036  55   9   8 0.01
Sun 05/17 11Z 0.83 3036  59   7   8 0.00

Run total areal avg QPF for the Central_Greens is: 0.88 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