Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261019_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)
=== ===== === ==== ==== === === === ====
Mon 10/19 00Z 0.29 2411  57  23   5 0.00
Mon 10/19 01Z 0.27 2512  50  22   7 0.00
Mon 10/19 02Z 0.24 2611  42  21   8 0.00
Mon 10/19 03Z 0.21 2610  35  21   8 0.00
Mon 10/19 04Z 0.18 2608  30  21   9 0.00
Mon 10/19 05Z 0.17 2708  28  21   9 0.00
Mon 10/19 06Z 0.15 2707  27  21   9 0.00
Mon 10/19 07Z 0.15 2707  27  21   9 0.00
Mon 10/19 08Z 0.15 2807  28  20   9 0.00
Mon 10/19 09Z 0.14 2807  28  20   9 0.00
Mon 10/19 10Z 0.12 2906  26  20   9 0.00
Mon 10/19 11Z 0.10 2905  24  21   9 0.00
Mon 10/19 12Z 0.11 2906  24  21   9 0.00
Mon 10/19 13Z 0.11 2905  23  20   9 0.00
Mon 10/19 14Z 0.12 2805  22  21   9 0.00
Mon 10/19 15Z 0.12 2806  21  22  10 0.00
Mon 10/19 16Z 0.12 2705  20  21  10 0.00
Mon 10/19 17Z 0.13 2706  19  19  11 0.00
Mon 10/19 18Z 0.13 2806  19  18  11 0.00
Mon 10/19 19Z 0.12 2906  19  17  11 0.00
Mon 10/19 20Z 0.12 3007  18  16  11 0.00
Mon 10/19 21Z 0.14 3008  17  16  11 0.00
Mon 10/19 22Z 0.13 3109  17  18  10 0.00
Mon 10/19 23Z 0.11 3210  21  19  10 0.00
Tue 10/20 00Z 0.10 3311  26  18   9 0.00
Tue 10/20 01Z 0.07 3312  29  16   9 0.00
Tue 10/20 02Z 0.04 3412  31  13   9 0.00
Tue 10/20 03Z 0.03 3513  34   9   9 0.00
Tue 10/20 04Z 0.03 3515  37   6   9 0.00
Tue 10/20 05Z 0.05 3517  44   6   9 0.00
Tue 10/20 06Z 0.08 0018  52   7   9 0.00
Tue 10/20 07Z 0.11 0020  57  11   9 0.00
Tue 10/20 08Z 0.16 0122  56  13   8 0.00
Tue 10/20 09Z 0.22 0124  49  13   9 0.00
Tue 10/20 10Z 0.23 0124  39  10   9 0.00
Tue 10/20 11Z 0.25 0225  34   8   9 0.00
Tue 10/20 12Z 0.26 0225  32   4   9 0.00
Tue 10/20 13Z 0.27 0225  31   2   8 0.00
Tue 10/20 14Z 0.26 0224  32   2   8 0.00
Tue 10/20 15Z 0.25 0222  33   2   7 0.00
Tue 10/20 16Z 0.21 0120  37   3   7 0.00
Tue 10/20 17Z 0.19 0119  45   4   6 0.00
Tue 10/20 18Z 0.18 0119  51   5   6 0.00
Tue 10/20 19Z 0.20 0118  53   5   6 0.00
Tue 10/20 20Z 0.20 0118  52   6   6 0.00
Tue 10/20 21Z 0.21 0119  51   7   6 0.00
Tue 10/20 22Z 0.21 0120  48   8   7 0.00
Tue 10/20 23Z 0.22 0221  44   8   7 0.00
Wed 10/21 00Z 0.23 0221  41   9   7 0.00
Wed 10/21 01Z 0.24 0221  39  10   7 0.00
Wed 10/21 02Z 0.25 0320  36  11   7 0.00
Wed 10/21 03Z 0.25 0319  34  13   7 0.00
Wed 10/21 04Z 0.25 0418  34  14   7 0.00
Wed 10/21 05Z 0.23 0415  34  15   7 0.00
Wed 10/21 06Z 0.20 0413  35  15   7 0.00
Wed 10/21 07Z 0.17 0412  35  14   7 0.00
Wed 10/21 08Z 0.15 0311  34  13   7 0.00
Wed 10/21 09Z 0.15 0311  30  11   7 0.00
Wed 10/21 10Z 0.16 0312  28   9   7 0.00
Wed 10/21 11Z 0.16 0312  28   7   8 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