NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260414_0600
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)
=== ===== === ==== ==== === === === ====
Tue 04/14 06Z 0.57 2922  90  37   8 0.00
Tue 04/14 07Z 0.45 3021  92  23   8 0.00
Tue 04/14 08Z 0.38 3019  90  23   8 0.00
Tue 04/14 09Z 0.30 3017  86  23   9 0.00
Tue 04/14 10Z 0.26 2914  82  22  10 0.00
Tue 04/14 11Z 0.20 2810  77  22  10 0.00
Tue 04/14 12Z 0.19 2509  75  25  10 0.00
Tue 04/14 13Z 0.21 2311  75  25  10 0.00
Tue 04/14 14Z 0.31 2315  80  25  10 0.00
Tue 04/14 15Z 0.26 2213  69  22  11 0.00
Tue 04/14 16Z 0.38 2216  74  77  10 0.00
Tue 04/14 17Z 0.43 2118  90  97  10 0.01
Tue 04/14 18Z 0.44 2216  87  81  11 0.05
Tue 04/14 19Z 0.44 2021  81  78  11 0.01
Tue 04/14 20Z 0.56 2023  83  76  12 0.00
Tue 04/14 21Z 0.71 1924  84  67  12 0.00
Tue 04/14 22Z 0.99 2128  94  74  12 0.07
Tue 04/14 23Z 1.25 2436  93  41  12 0.08
Wed 04/15 00Z 1.40 2537  94  48  12 0.01
Wed 04/15 01Z 1.55 2537  96  51  11 0.01
Wed 04/15 03Z 1.37 2734  98  35  10 0.02
Wed 04/15 04Z 1.00 2831  97  34   9 0.03
Wed 04/15 05Z 0.67 2829  91  28   9 0.03
Wed 04/15 06Z 0.43 2926  80  22  11 0.02
Wed 04/15 07Z 0.33 2922  71  15  12 0.01
Wed 04/15 08Z 0.30 2921  65  13  13 0.01
Wed 04/15 09Z 0.26 2917  57  13  13 0.00
Wed 04/15 10Z 0.25 2814  55  11  13 0.00
Wed 04/15 11Z 0.29 2714  54  11  13 0.00
Wed 04/15 12Z 0.30 2514  56  14  13 0.00
Wed 04/15 13Z 0.37 2416  67  23  12 0.00
Wed 04/15 14Z 0.38 2316  86  40  12 0.00
Wed 04/15 15Z 0.56 2323  95  64  11 0.00
Wed 04/15 16Z 0.66 2226  90  89  11 0.01
Wed 04/15 17Z 0.64 2323  90  93  11 0.09
Wed 04/15 18Z 0.81 2424  88  93  11 0.06
Wed 04/15 19Z 2.00 2525  91  92  11 0.01
Wed 04/15 20Z 1.66 2524  90  74  11 0.01
Wed 04/15 21Z 1.04 2523  91  65  12 0.00
Wed 04/15 22Z 1.01 2523  94  76  12 0.00
Wed 04/15 23Z 0.98 2624  95  80  12 0.01
Thu 04/16 00Z 0.97 2723  97  79  11 0.02
Thu 04/16 01Z 0.77 2821  94  64  11 0.02
Thu 04/16 02Z 0.60 2819  96  53  11 0.01
Thu 04/16 03Z 0.47 2917  97  60  10 0.00
Thu 04/16 04Z 0.37 2914  94  63  11 0.01
Thu 04/16 05Z 0.40 2814  94  63  11 0.00
Thu 04/16 06Z 0.36 2813  93  61  11 0.01
Thu 04/16 07Z 0.39 2713  93  62  11 0.01
Thu 04/16 08Z 0.35 2713  91  56  11 0.01
Thu 04/16 09Z 0.30 2812  90  51  11 0.01
Thu 04/16 10Z 0.28 2711  86  40  12 0.01
Thu 04/16 11Z 0.27 2610  83  45  12 0.00
Thu 04/16 12Z 0.37 2514  88  66  11 0.00
Thu 04/16 13Z 0.38 2414  86  76  11 0.00
Thu 04/16 14Z 0.39 2415  86  94  11 0.00
Thu 04/16 15Z 0.45 2316  92  95  11 0.00
Thu 04/16 16Z 0.52 2319  95  93  11 0.02
Thu 04/16 17Z 0.64 2321  93  93  11 0.07

Run total areal avg QPF for the Central_Greens is: 0.75 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