NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260408_0000
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Wed 04/08 00Z 0.61 3120  91  56 -12 0.00
Wed 04/08 01Z 0.80 3122  89  45 -12 0.00
Wed 04/08 02Z 0.86 3122  88  40 -13 0.00
Wed 04/08 03Z 1.02 3122  78  40 -13 0.00
Wed 04/08 04Z 0.90 3122  65  31 -13 0.00
Wed 04/08 05Z 0.71 3121  54  26 -12 0.00
Wed 04/08 06Z 0.58 3220  52  24 -12 0.00
Wed 04/08 07Z 0.53 3220  51  22 -12 0.00
Wed 04/08 08Z 0.45 3219  51  21 -12 0.00
Wed 04/08 09Z 0.39 3218  51  21 -11 0.00
Wed 04/08 10Z 0.32 3116  49  20 -11 0.00
Wed 04/08 11Z 0.27 3114  46  20 -10 0.00
Wed 04/08 12Z 0.24 3112  45  15 -10 0.00
Wed 04/08 13Z 0.22 3010  45  11  -9 0.00
Wed 04/08 14Z 0.21 2908  43   8  -9 0.00
Wed 04/08 15Z 0.21 2807  40   5  -8 0.00
Wed 04/08 16Z 0.24 2706  36   4  -7 0.00
Wed 04/08 17Z 0.26 2605  33   4  -7 0.00
Wed 04/08 18Z 0.37 2605  30   4  -6 0.00
Wed 04/08 19Z 0.44 2505  29   5  -5 0.00
Wed 04/08 20Z 0.37 2505  27   5  -5 0.00
Wed 04/08 21Z 0.27 2505  26   5  -4 0.00
Wed 04/08 22Z 0.19 2405  26   6  -3 0.00
Wed 04/08 23Z 0.20 2208  26   6  -3 0.00
Thu 04/09 00Z 0.21 2210  24   6  -2 0.00
Thu 04/09 01Z 0.24 2212  22   6  -1 0.00
Thu 04/09 02Z 0.27 2215  20   8  -1 0.00
Thu 04/09 03Z 0.31 2217  19  14  -1 0.00
Thu 04/09 04Z 0.34 2219  20  25   0 0.00
Thu 04/09 05Z 0.35 2221  21  35   0 0.00
Thu 04/09 06Z 0.34 2221  21  42   1 0.00
Thu 04/09 07Z 0.31 2221  22  48   1 0.00
Thu 04/09 08Z 0.30 2221  19  53   2 0.00
Thu 04/09 09Z 0.30 2221  16  57   2 0.00
Thu 04/09 10Z 0.31 2221  13  57   2 0.00
Thu 04/09 11Z 0.32 2221  10  54   3 0.00
Thu 04/09 12Z 0.31 2222   7  49   3 0.00
Thu 04/09 13Z 0.31 2124   6  48   3 0.00
Thu 04/09 14Z 0.29 2124   6  57   3 0.00
Thu 04/09 15Z 0.27 2025   8  75   4 0.00
Thu 04/09 16Z 0.25 2025  10  55   4 0.00
Thu 04/09 17Z 0.26 2025  14  38   4 0.00
Thu 04/09 18Z 0.27 2025  17  33   4 0.00
Thu 04/09 19Z 0.29 1926  20  35   3 0.00
Thu 04/09 20Z 0.31 1927  22  25   3 0.00
Thu 04/09 21Z 0.35 2028  22  35   4 0.00
Thu 04/09 22Z 0.31 2030  21  39   5 0.00
Thu 04/09 23Z 0.30 2031  22  42   6 0.00
Fri 04/10 00Z 0.33 2032  28  47   6 0.00
Fri 04/10 01Z 0.40 2133  37  49   6 0.00
Fri 04/10 02Z 0.45 2233  46  52   6 0.00
Fri 04/10 03Z 0.50 2233  54  65   6 0.00
Fri 04/10 04Z 0.57 2334  58  73   6 0.00
Fri 04/10 05Z 0.63 2333  61  79   5 0.00
Fri 04/10 06Z 0.66 2433  67  69   5 0.00
Fri 04/10 07Z 0.67 2431  74  71   5 0.00
Fri 04/10 08Z 0.65 2529  76  55   4 0.00
Fri 04/10 09Z 0.62 2527  80  37   4 0.00
Fri 04/10 10Z 0.60 2626  82  30   3 0.00
Fri 04/10 11Z 0.65 2625  85  17   3 0.00

Run total areal avg QPF for the 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