NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260719_1200
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)
=== ===== === ==== ==== === === === ====
Sun 07/19 12Z 0.65 3226  96  11   6 0.00
Sun 07/19 13Z 0.63 3226  95   7   6 0.01
Sun 07/19 14Z 0.74 3124  93   7   6 0.01
Sun 07/19 15Z 1.06 3123  90   7   6 0.01
Sun 07/19 16Z 4.59 3022  85   8   7 0.00
Sun 07/19 17Z 10.91 3022  80   9   7 0.00
Sun 07/19 18Z 12.00 3022  78   9   7 0.00
Sun 07/19 19Z 11.69 3023  76   9   7 0.00
Sun 07/19 20Z 11.71 3023  75  10   8 0.00
Sun 07/19 21Z 12.08 3023  73  10   8 0.00
Sun 07/19 22Z 11.01 3024  69  13   8 0.00
Sun 07/19 23Z 5.82 3025  68  16   8 0.00
Mon 07/20 00Z 2.68 3124  68  16   8 0.00
Mon 07/20 01Z 2.38 3024  71  16   8 0.00
Mon 07/20 02Z 2.34 3025  76  16   7 0.00
Mon 07/20 03Z 1.65 3125  80  15   7 0.00
Mon 07/20 04Z 1.27 3125  82  12   7 0.00
Mon 07/20 05Z 1.15 3124  83  13   7 0.00
Mon 07/20 06Z 0.98 3122  83  15   6 0.00
Mon 07/20 07Z 0.77 3121  83  18   6 0.00
Mon 07/20 08Z 0.64 3120  80  19   7 0.00
Mon 07/20 09Z 0.58 3119  80  26   7 0.00
Mon 07/20 10Z 0.58 3119  80  36   7 0.00
Mon 07/20 11Z 0.58 3119  76  36   7 0.00
Mon 07/20 12Z 0.53 3118  72  49   8 0.00
Mon 07/20 13Z 0.51 3016  71  57   8 0.00
Mon 07/20 14Z 0.57 3014  71  61   8 0.00
Mon 07/20 15Z 1.30 3012  72  51   8 0.00
Mon 07/20 16Z 2.71 3009  69  52   9 0.00
Mon 07/20 17Z 3.42 2807  68  49   9 0.00
Mon 07/20 18Z 3.50 2707  72  47  10 0.00
Mon 07/20 19Z 3.12 2507  75  45  10 0.00
Mon 07/20 20Z 2.83 2407  76  44  10 0.00
Mon 07/20 21Z 2.50 2309  77  38  11 0.00
Mon 07/20 22Z 1.63 2211  77  35  11 0.00
Mon 07/20 23Z 0.73 2213  75  34  11 0.00
Tue 07/21 00Z 0.60 2216  71  31  11 0.00
Tue 07/21 01Z 0.50 2116  67  29  12 0.00
Tue 07/21 02Z 0.51 2118  67  27  12 0.00
Tue 07/21 03Z 0.46 2118  68  26  12 0.00
Tue 07/21 04Z 0.51 2120  69  23  12 0.00
Tue 07/21 05Z 0.58 2221  70  18  12 0.00
Tue 07/21 06Z 0.63 2222  72  15  11 0.00
Tue 07/21 07Z 0.66 2224  70  14  11 0.00
Tue 07/21 08Z 0.67 2225  70  13  11 0.00
Tue 07/21 09Z 0.60 2224  67  14  11 0.00
Tue 07/21 10Z 0.51 2124  66  16  12 0.00
Tue 07/21 11Z 0.48 2124  77  14  12 0.00
Tue 07/21 12Z 0.41 2124  84  11  12 0.00
Tue 07/21 13Z 0.38 2026  91  11  12 0.00
Tue 07/21 14Z 0.33 2026  94   9  12 0.00
Tue 07/21 15Z 0.29 1925  94  19  12 0.00
Tue 07/21 16Z 0.22 1926  97  25  12 0.01
Tue 07/21 17Z 0.17 1827  97  20  13 0.01
Tue 07/21 18Z 0.12 1828  97  25  13 0.01
Tue 07/21 19Z 0.11 1829  97  41  13 0.01
Tue 07/21 20Z 0.05 1729  95  40  14 0.01
Tue 07/21 21Z 0.09 1731  95  35  14 0.02
Tue 07/21 22Z 0.06 1734  95  61  15 0.03
Tue 07/21 23Z 0.09 1833  97  78  14 0.11

Run total areal avg QPF for the greens is: 0.24 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