NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260721_1200
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 07/21 12Z 0.46 2022  69   2  13 0.00
Tue 07/21 13Z 0.46 2023  65   4  13 0.00
Tue 07/21 14Z 0.34 1921  70   6  14 0.00
Tue 07/21 15Z 0.33 1821  79  30  14 0.00
Tue 07/21 16Z 0.33 1825  90  70  13 0.01
Tue 07/21 17Z 0.21 1831  92  75  14 0.07
Tue 07/21 18Z 0.19 1832  92  44  14 0.00
Tue 07/21 19Z 0.12 1731  93  43  14 0.01
Tue 07/21 20Z 0.07 1733  97  46  14 0.04
Tue 07/21 21Z 0.11 1736  96  26  15 0.01
Tue 07/21 22Z 0.07 1733  96  40  16 0.02
Tue 07/21 23Z 0.08 1731  96  49  16 0.02
Wed 07/22 00Z 0.13 1730  95  76  16 0.02
Wed 07/22 01Z 0.24 1829  96  79  16 0.01
Wed 07/22 02Z 0.52 2030  93  86  15 0.10
Wed 07/22 03Z 0.45 2121  86  82  15 0.15
Wed 07/22 04Z 0.36 2021  95  89  15 0.02
Wed 07/22 05Z 0.47 2024  98  87  15 0.06
Wed 07/22 06Z 0.70 2226  99  55  15 0.03
Wed 07/22 07Z 0.73 2225  97  54  15 0.02
Wed 07/22 08Z 0.83 2326  96  67  14 0.02
Wed 07/22 09Z 0.85 2425  97  64  14 0.02
Wed 07/22 10Z 0.88 2424  98  65  14 0.02
Wed 07/22 11Z 0.86 2524  97  61  13 0.02
Wed 07/22 12Z 0.85 2523  95  59  13 0.01
Wed 07/22 13Z 0.83 2622  93  62  13 0.01
Wed 07/22 14Z 0.80 2521  91  58  13 0.01
Wed 07/22 15Z 0.92 2521  92  56  13 0.01
Wed 07/22 16Z 1.02 2420  93  55  13 0.01
Wed 07/22 17Z 1.22 2421  93  29  13 0.01
Wed 07/22 18Z 1.65 2420  92  10  12 0.01
Wed 07/22 19Z 1.82 2420  87   7  11 0.01
Wed 07/22 20Z 1.48 2522  85  17  11 0.01
Wed 07/22 21Z 1.68 2623  88  17  10 0.01
Wed 07/22 22Z 1.26 2622  87  17   9 0.00
Wed 07/22 23Z 1.15 2722  89  18   8 0.00
Thu 07/23 00Z 1.07 2722  90  17   8 0.00
Thu 07/23 01Z 0.97 2823  90  16   7 0.00
Thu 07/23 02Z 0.85 2823  91  18   7 0.00
Thu 07/23 03Z 0.74 2922  94  19   6 0.00
Thu 07/23 04Z 0.57 3022  90  21   6 0.00
Thu 07/23 05Z 0.44 3121  87  18   6 0.00
Thu 07/23 06Z 0.37 3122  83  14   6 0.00
Thu 07/23 07Z 0.34 3222  83  12   6 0.00
Thu 07/23 08Z 0.26 3220  82  14   6 0.00
Thu 07/23 09Z 0.21 3216  77  18   6 0.00
Thu 07/23 10Z 0.25 3113  74  29   6 0.00
Thu 07/23 11Z 0.32 3011  73  38   6 0.00
Thu 07/23 12Z 0.36 2811  73  39   6 0.00
Thu 07/23 13Z 0.38 2812  72  36   7 0.00
Thu 07/23 14Z 0.45 2812  71  30   7 0.00
Thu 07/23 15Z 0.54 2812  69  23   7 0.00
Thu 07/23 16Z 0.72 2811  63  23   8 0.00
Thu 07/23 17Z 1.09 2809  62  23   8 0.00
Thu 07/23 18Z 1.78 2808  67  22   8 0.00
Thu 07/23 19Z 3.22 2708  72  20   9 0.00
Thu 07/23 20Z 4.04 2708  75  18   9 0.00
Thu 07/23 21Z 3.56 2707  77  18   9 0.00
Thu 07/23 22Z 2.63 2706  78  18   9 0.00
Thu 07/23 23Z 1.18 2806  78  18   9 0.00

Run total areal avg QPF for the Central_Greens is: 0.77 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