Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261024_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)
=== ===== === ==== ==== === === === ====
Sat 10/24 06Z 0.03 3204  23   2   6 0.00
Sat 10/24 07Z 0.07 3105  22   2   6 0.00
Sat 10/24 08Z 0.09 3106  21   1   6 0.00
Sat 10/24 09Z 0.11 3008  19   1   6 0.00
Sat 10/24 10Z 0.13 3109  18   1   6 0.00
Sat 10/24 11Z 0.13 3110  18   1   6 0.00
Sat 10/24 12Z 0.12 3110  19   1   5 0.00
Sat 10/24 13Z 0.13 3110  20   1   5 0.00
Sat 10/24 14Z 0.13 3110  21   1   5 0.00
Sat 10/24 15Z 0.13 3109  22   1   6 0.00
Sat 10/24 16Z 0.13 3009  23   1   6 0.00
Sat 10/24 17Z 0.14 3008  23   2   6 0.00
Sat 10/24 18Z 0.14 3008  23   3   6 0.00
Sat 10/24 19Z 0.13 3108  23   4   6 0.00
Sat 10/24 20Z 0.12 3109  23   7   6 0.00
Sat 10/24 21Z 0.10 3209  20  11   6 0.00
Sat 10/24 22Z 0.10 3208  17  16   6 0.00
Sat 10/24 23Z 0.09 3208  15  25   6 0.00
Sun 10/25 00Z 0.07 3208  15  34   7 0.00
Sun 10/25 01Z 0.06 3207  15  45   7 0.00
Sun 10/25 02Z 0.06 3105  15  51   7 0.00
Sun 10/25 03Z 0.10 2905  15  55   8 0.00
Sun 10/25 04Z 0.13 2806  17  58   8 0.00
Sun 10/25 05Z 0.13 2806  17  56   8 0.00
Sun 10/25 06Z 0.12 2906  15  49   8 0.00
Sun 10/25 07Z 0.12 2806  14  45   8 0.00
Sun 10/25 08Z 0.14 2706  14  46   8 0.00
Sun 10/25 09Z 0.16 2707  15  50   8 0.00
Sun 10/25 10Z 0.19 2809  14  51   8 0.00
Sun 10/25 11Z 0.17 2809  10  42   9 0.00
Sun 10/25 12Z 0.14 2907   7  34   9 0.00
Sun 10/25 13Z 0.13 2907   7  31   9 0.00
Sun 10/25 14Z 0.13 2806   6  27   9 0.00
Sun 10/25 15Z 0.14 2706   6  26   9 0.00
Sun 10/25 16Z 0.15 2606   8  30   9 0.00
Sun 10/25 17Z 0.16 2507   8  32   9 0.00
Sun 10/25 18Z 0.18 2508   8  36  10 0.00
Sun 10/25 19Z 0.20 2509   7  39  10 0.00
Sun 10/25 20Z 0.24 2510   7  36  10 0.00
Sun 10/25 21Z 0.28 2512   6  31  10 0.00
Sun 10/25 22Z 0.32 2514   5  27  10 0.00
Sun 10/25 23Z 0.32 2614   8  24  11 0.00
Mon 10/26 00Z 0.31 2614  10  21  11 0.00
Mon 10/26 01Z 0.30 2714  12  19  11 0.00
Mon 10/26 02Z 0.28 2713  11  18  11 0.00
Mon 10/26 03Z 0.28 2613   9  18  11 0.00
Mon 10/26 04Z 0.29 2613   7  17  11 0.00
Mon 10/26 05Z 0.30 2614  10  18  11 0.00
Mon 10/26 06Z 0.32 2615  11  20  11 0.00
Mon 10/26 07Z 0.34 2716   9  21  11 0.00
Mon 10/26 08Z 0.34 2716   8  21  11 0.00
Mon 10/26 09Z 0.34 2817   9  18  10 0.00
Mon 10/26 10Z 0.33 2917  13  19  10 0.00
Mon 10/26 11Z 0.33 2917  20  37  10 0.00
Mon 10/26 12Z 0.34 2917  23  36   9 0.00
Mon 10/26 13Z 0.34 2917  31  48   9 0.00
Mon 10/26 14Z 0.36 2917  43  67   9 0.00
Mon 10/26 15Z 0.39 2818  55  84   9 0.00
Mon 10/26 16Z 0.42 2920  84  93   8 0.00
Mon 10/26 17Z 0.39 2920  94  95   7 0.01

Run total areal avg QPF for the Central_Greens is: 0.01 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