NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260302_1800
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 03/02 18Z 0.67 2610  55  19 -17 0.00
Mon 03/02 19Z 0.60 2712  50  17 -16 0.00
Mon 03/02 20Z 0.49 2610  51  24 -16 0.00
Mon 03/02 21Z 0.46 2610  55  35 -15 0.00
Mon 03/02 22Z 0.41 2610  59  44 -15 0.00
Mon 03/02 23Z 0.43 2512  61  46 -14 0.00
Tue 03/03 00Z 0.41 2613  59  37 -14 0.00
Tue 03/03 01Z 0.39 2613  54  30 -12 0.00
Tue 03/03 02Z 0.35 2614  48  27 -11 0.00
Tue 03/03 03Z 0.35 2515  41  33 -10 0.00
Tue 03/03 04Z 0.36 2516  35  41  -9 0.00
Tue 03/03 05Z 0.36 2517  31  46  -8 0.00
Tue 03/03 06Z 0.36 2418  30  43  -7 0.00
Tue 03/03 07Z 0.40 2420  31  42  -7 0.00
Tue 03/03 08Z 0.42 2421  33  45  -6 0.00
Tue 03/03 09Z 0.40 2420  36  46  -6 0.00
Tue 03/03 10Z 0.38 2419  35  47  -5 0.00
Tue 03/03 11Z 0.35 2318  33  46  -5 0.00
Tue 03/03 12Z 0.33 2318  31  46  -4 0.00
Tue 03/03 13Z 0.31 2218  31  43  -4 0.00
Tue 03/03 14Z 0.31 2219  35  40  -4 0.00
Tue 03/03 15Z 0.33 2220  59  38  -4 0.00
Tue 03/03 16Z 0.35 2221  77  36  -4 0.00
Tue 03/03 17Z 0.38 2222  86  29  -4 0.00
Tue 03/03 18Z 0.42 2222  94  38  -5 0.01
Tue 03/03 19Z 0.38 2220  96  63  -4 0.01
Tue 03/03 20Z 0.36 2221  97  85  -3 0.02
Tue 03/03 21Z 0.36 2222  98  97  -3 0.03
Tue 03/03 22Z 0.38 2125  98  96  -3 0.03
Tue 03/03 23Z 0.38 2026  98  97  -2 0.03
Wed 03/04 00Z 0.41 2127  98  94  -2 0.05
Wed 03/04 01Z 0.47 2127  98  95  -2 0.07
Wed 03/04 02Z 0.52 2226  98  95  -2 0.07
Wed 03/04 03Z 0.55 2325  98  92  -2 0.05
Wed 03/04 04Z 0.56 2523  98  92  -2 0.04
Wed 03/04 05Z 0.50 2621  98  90  -2 0.04
Wed 03/04 06Z 0.43 2820  97  78  -3 0.03
Wed 03/04 07Z 0.38 3021  96  59  -3 0.02
Wed 03/04 08Z 0.27 3120  83  41  -1 0.01
Wed 03/04 09Z 0.21 3119  64  46   0 0.00
Wed 03/04 10Z 0.23 3018  53  24   0 0.00
Wed 03/04 11Z 0.21 3117  47  13   0 0.00
Wed 03/04 12Z 0.26 3018  49   6   0 0.00
Wed 03/04 13Z 0.31 3019  52   4   0 0.00
Wed 03/04 14Z 0.34 3020  52   3   0 0.00
Wed 03/04 16Z 0.27 3015  45   3   0 0.00
Wed 03/04 17Z 0.27 2813  44   5   0 0.00
Wed 03/04 18Z 0.29 2712  42   6   0 0.00
Wed 03/04 19Z 0.34 2613  40   7   0 0.00
Wed 03/04 20Z 0.41 2515  37   8   0 0.00
Wed 03/04 21Z 0.44 2616  37  11   0 0.00
Wed 03/04 22Z 0.43 2616  36  12   1 0.00
Wed 03/04 23Z 0.40 2615  34  12   2 0.00
Thu 03/05 00Z 0.42 2616  34  14   2 0.00
Thu 03/05 01Z 0.43 2517  33  16   2 0.00
Thu 03/05 02Z 0.45 2518  31  16   3 0.00
Thu 03/05 03Z 0.48 2519  30  17   3 0.00
Thu 03/05 04Z 0.50 2620  28  20   3 0.00
Thu 03/05 05Z 0.52 2620  29  18   3 0.00

Run total areal avg QPF for the Central_Greens is: 0.51 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