NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260303_0600
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)
=== ===== === ==== ==== === === === ====
Tue 03/03 06Z 0.37 2319  44  57  -9 0.00
Tue 03/03 07Z 0.42 2321  41  55  -8 0.00
Tue 03/03 08Z 0.44 2422  38  51  -7 0.00
Tue 03/03 09Z 0.46 2422  33  50  -6 0.00
Tue 03/03 10Z 0.46 2521  33  50  -6 0.00
Tue 03/03 11Z 0.44 2421  33  51  -5 0.00
Tue 03/03 12Z 0.40 2419  34  49  -5 0.00
Tue 03/03 13Z 0.35 2418  36  46  -4 0.00
Tue 03/03 14Z 0.33 2318  41  42  -4 0.00
Tue 03/03 15Z 0.31 2219  48  40  -3 0.00
Tue 03/03 16Z 0.32 2220  59  35  -3 0.00
Tue 03/03 17Z 0.34 2222  70  34  -3 0.00
Tue 03/03 18Z 0.38 2224  80  34  -4 0.00
Tue 03/03 19Z 0.42 2225  89  36  -4 0.00
Tue 03/03 20Z 0.45 2127  95  43  -4 0.01
Tue 03/03 21Z 0.47 2129  97  57  -4 0.01
Tue 03/03 22Z 0.45 2130  98  71  -3 0.02
Tue 03/03 23Z 0.46 2131  98  83  -3 0.03
Wed 03/04 00Z 0.47 2130  98  95  -3 0.05
Wed 03/04 01Z 0.47 2228  98  95  -2 0.06
Wed 03/04 03Z 0.54 2327  98  95  -2 0.06
Wed 03/04 04Z 0.59 2525  98  94  -2 0.09
Wed 03/04 05Z 0.57 2623  98  83  -2 0.10
Wed 03/04 06Z 0.50 2823  94  61  -2 0.05
Wed 03/04 07Z 0.41 2921  84  53  -1 0.03
Wed 03/04 08Z 0.37 3021  68  45   0 0.01
Wed 03/04 09Z 0.36 3020  58  29   0 0.01
Wed 03/04 10Z 0.40 3022  53  22   0 0.01
Wed 03/04 11Z 0.45 3024  51  15   0 0.01
Wed 03/04 12Z 0.49 3026  52   8  -1 0.00
Wed 03/04 13Z 0.49 3026  56   3  -1 0.00
Wed 03/04 14Z 0.48 3026  59   4  -1 0.00
Wed 03/04 15Z 0.46 3025  62   7   0 0.00
Wed 03/04 16Z 0.42 3023  63  13   0 0.00
Wed 03/04 17Z 0.38 2921  63  18   0 0.00
Wed 03/04 18Z 0.35 2918  63  21   0 0.00
Wed 03/04 19Z 0.34 2916  63  24   0 0.00
Wed 03/04 20Z 0.34 2815  63  28   0 0.00
Wed 03/04 21Z 0.36 2716  62  35   0 0.00
Wed 03/04 22Z 0.36 2716  58  39   0 0.00
Wed 03/04 23Z 0.36 2716  55  38   0 0.00
Thu 03/05 00Z 0.33 2715  50  39   1 0.00
Thu 03/05 01Z 0.31 2614  45  41   2 0.00
Thu 03/05 02Z 0.31 2614  42  39   2 0.00
Thu 03/05 03Z 0.31 2514  39  36   2 0.00
Thu 03/05 04Z 0.33 2516  39  36   3 0.00
Thu 03/05 05Z 0.34 2516  37  31   3 0.00
Thu 03/05 06Z 0.38 2518  35  29   3 0.00
Thu 03/05 07Z 0.40 2518  35  26   3 0.00
Thu 03/05 08Z 0.40 2518  35  20   3 0.00
Thu 03/05 09Z 0.38 2617  36  14   2 0.00
Thu 03/05 10Z 0.37 2516  37  12   2 0.00
Thu 03/05 11Z 0.33 2514  36  10   2 0.00
Thu 03/05 12Z 0.28 2512  35  11   2 0.00
Thu 03/05 13Z 0.24 2411  36  12   2 0.00
Thu 03/05 14Z 0.23 2410  36  14   2 0.00
Thu 03/05 15Z 0.21 2409  37  16   2 0.00
Thu 03/05 16Z 0.16 2407  39  20   3 0.00
Thu 03/05 17Z 0.13 2306  43  33   3 0.00

Run total areal avg QPF for the greens is: 0.55 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