NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260716_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)
=== ===== === ==== ==== === === === ====
Thu 07/16 18Z 5.87 2925  79  83  13 0.00
Thu 07/16 19Z 4.47 3024  80  80  13 0.03
Thu 07/16 20Z 0.65 3223  89  79  12 0.08
Thu 07/16 21Z 0.57 3121  85  74  12 0.10
Thu 07/16 22Z 0.62 3024  89  74  11 0.17
Thu 07/16 23Z 0.58 3130  82  36  11 0.05
Fri 07/17 00Z 0.56 3232  79  14  10 0.01
Fri 07/17 01Z 0.66 3232  75  10   9 0.00
Fri 07/17 02Z 0.65 3232  71  20   9 0.00
Fri 07/17 03Z 0.58 3232  63  29   8 0.00
Fri 07/17 04Z 0.57 3231  61  31   8 0.00
Fri 07/17 05Z 0.58 3230  61  29   8 0.00
Fri 07/17 06Z 0.59 3229  61  28   7 0.00
Fri 07/17 07Z 0.62 3230  63  23   7 0.00
Fri 07/17 08Z 0.59 3229  67  17   7 0.00
Fri 07/17 09Z 0.57 3228  70  13   7 0.00
Fri 07/17 10Z 0.46 3228  72  12   7 0.00
Fri 07/17 11Z 0.37 3228  71  16   8 0.00
Fri 07/17 12Z 0.30 3226  67  19   9 0.00
Fri 07/17 13Z 0.21 3222  60  21   9 0.00
Fri 07/17 14Z 0.18 3219  56  17   9 0.00
Fri 07/17 15Z 0.19 3216  56  14   9 0.00
Fri 07/17 16Z 0.26 3214  55  17   9 0.00
Fri 07/17 17Z 0.37 3113  50  19   9 0.00
Fri 07/17 18Z 0.50 3013  49  20  10 0.00
Fri 07/17 19Z 0.79 2914  58  20  10 0.00
Fri 07/17 20Z 0.98 2813  60  18  10 0.00
Fri 07/17 21Z 1.31 2812  61  16  10 0.00
Fri 07/17 22Z 1.03 2811  59  12  11 0.00
Fri 07/17 23Z 0.69 2810  53  10  11 0.00
Sat 07/18 00Z 0.66 2810  47   9  11 0.00
Sat 07/18 01Z 0.64 2810  45   9  11 0.00
Sat 07/18 02Z 0.59 2710  45  10  11 0.00
Sat 07/18 03Z 0.58 2710  49  11  11 0.00
Sat 07/18 04Z 0.49 2609  50  10  11 0.00
Sat 07/18 05Z 0.49 2409  53   9  11 0.00
Sat 07/18 06Z 0.46 2410  56  11  11 0.00
Sat 07/18 07Z 0.49 2412  57  12  11 0.00
Sat 07/18 08Z 0.45 2414  44  22  12 0.00
Sat 07/18 09Z 0.52 2515  45  40  12 0.00
Sat 07/18 10Z 0.59 2416  59  78  12 0.00
Sat 07/18 11Z 0.61 2318  68  94  12 0.00
Sat 07/18 12Z 0.60 2220  67  81  13 0.00
Sat 07/18 13Z 0.66 2124  69  85  13 0.00
Sat 07/18 14Z 0.77 2125  69  64  14 0.00
Sat 07/18 15Z 0.98 2127  74  68  14 0.00
Sat 07/18 16Z 1.07 2128  78  64  15 0.00
Sat 07/18 17Z 4.74 2027  80  63  15 0.00
Sat 07/18 18Z 2.93 2129  86  84  15 0.01
Sat 07/18 19Z 0.88 2135  96  93  15 0.08
Sat 07/18 20Z 0.82 2135  98  91  15 0.13
Sat 07/18 21Z 0.79 2136  97  77  15 0.03
Sat 07/18 22Z 0.77 2138  97  78  15 0.02
Sat 07/18 23Z 0.80 2138  97  78  15 0.03
Sun 07/19 00Z 0.68 2133  96  65  16 0.02
Sun 07/19 01Z 0.70 2232  98  78  16 0.02
Sun 07/19 02Z 0.80 2232  96  84  16 0.22
Sun 07/19 03Z 0.87 2329  93  78  15 0.34
Sun 07/19 04Z 0.83 2327  95  75  15 0.05
Sun 07/19 05Z 0.79 2525  93  74  15 0.02

Run total areal avg QPF for the Central_Greens is: 1.41 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