Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260616_0000
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 06/16 00Z 0.47 3114  86  20   6 0.00
Tue 06/16 01Z 0.66 3118  86  23   6 0.00
Tue 06/16 02Z 0.77 3021  89  22   5 0.00
Tue 06/16 03Z 0.64 3021  95  17   5 0.00
Tue 06/16 04Z 0.48 3121  95  12   5 0.01
Tue 06/16 05Z 0.45 3122  96  12   5 0.00
Tue 06/16 06Z 0.44 3121  97  14   4 0.01
Tue 06/16 07Z 0.48 3121  97  13   4 0.01
Tue 06/16 08Z 0.45 3121  97  15   4 0.01
Tue 06/16 09Z 0.41 3221  93  13   4 0.00
Tue 06/16 10Z 0.32 3219  86   9   4 0.00
Tue 06/16 11Z 0.24 3217  80   7   5 0.00
Tue 06/16 12Z 0.17 3215  75   7   5 0.00
Tue 06/16 13Z 0.18 3212  74  14   6 0.00
Tue 06/16 14Z 0.33 3109  72  26   6 0.00
Tue 06/16 15Z 1.23 2908  69  35   6 0.00
Tue 06/16 16Z 3.13 2808  68  38   7 0.00
Tue 06/16 17Z 4.34 2808  66  44   7 0.00
Tue 06/16 18Z 5.00 2708  65  48   8 0.00
Tue 06/16 19Z 5.66 2508  71  59   8 0.00
Tue 06/16 20Z 4.98 2508  74  62   8 0.00
Tue 06/16 21Z 4.02 2409  75  54   9 0.00
Tue 06/16 22Z 3.16 2410  75  54   9 0.00
Tue 06/16 23Z 1.18 2412  76  46   9 0.00
Wed 06/17 00Z 0.79 2413  77  47   9 0.00
Wed 06/17 01Z 0.68 2513  75  45   9 0.00
Wed 06/17 02Z 0.80 2514  74  37   9 0.00
Wed 06/17 03Z 0.88 2416  80  30   8 0.00
Wed 06/17 04Z 0.87 2416  81  27   8 0.00
Wed 06/17 05Z 0.81 2515  79  37   8 0.00
Wed 06/17 06Z 0.64 2513  75  43   8 0.00
Wed 06/17 07Z 0.59 2512  75  36   8 0.00
Wed 06/17 08Z 0.60 2412  77  35   8 0.00
Wed 06/17 09Z 0.56 2411  78  39   8 0.00
Wed 06/17 10Z 0.46 2309  78  35   8 0.00
Wed 06/17 11Z 0.40 2209  79  33   8 0.00
Wed 06/17 12Z 0.40 2108  81  30   8 0.00
Wed 06/17 13Z 1.33 2008  82  24   8 0.00
Wed 06/17 14Z 1.81 1907  81  19   8 0.00
Wed 06/17 15Z 2.05 1908  81  23   8 0.01
Wed 06/17 16Z 1.47 1908  81  17   9 0.01
Wed 06/17 17Z 0.93 1808  80  14   9 0.00
Wed 06/17 18Z 0.69 1708  79  18   9 0.00
Wed 06/17 19Z 0.72 1809  77  20  10 0.00
Wed 06/17 20Z 1.11 1809  74  28  10 0.00
Wed 06/17 21Z 0.92 1809  73  48  10 0.00
Wed 06/17 22Z 0.28 1811  74  43  10 0.00
Wed 06/17 23Z 0.20 1812  75  36  10 0.00
Thu 06/18 00Z 0.39 1914  74  42  10 0.00
Thu 06/18 01Z 0.55 2016  73  50  10 0.00
Thu 06/18 02Z 0.52 1917  76  51  10 0.00
Thu 06/18 03Z 0.64 2018  84  44  10 0.00
Thu 06/18 04Z 0.51 2021  84  50  10 0.00
Thu 06/18 05Z 0.41 2021  79  58  11 0.00
Thu 06/18 06Z 0.38 2022  80  61  11 0.00
Thu 06/18 07Z 0.36 1923  83  56  11 0.00
Thu 06/18 08Z 0.33 1923  84  65  11 0.00
Thu 06/18 09Z 0.27 1921  85  90  11 0.01
Thu 06/18 10Z 0.15 1823  90  96  10 0.02
Thu 06/18 11Z 0.07 1726  94  96  10 0.11

Run total areal avg QPF for the Central_Greens is: 0.20 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