NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260824_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)
=== ===== === ==== ==== === === === ====
Mon 08/24 12Z 0.29 1915  80  42  10 0.00
Mon 08/24 13Z 0.43 2016  83  53   9 0.00
Mon 08/24 14Z 0.70 2117  89  65   9 0.00
Mon 08/24 15Z 2.26 2116  89  62   8 0.00
Mon 08/24 16Z 1.84 2217  92  58   9 0.00
Mon 08/24 17Z 0.87 2219  84  57   9 0.06
Mon 08/24 18Z 1.53 2219  82  49   9 0.02
Mon 08/24 19Z 3.85 2317  84  49   9 0.00
Mon 08/24 20Z 2.03 2315  83  55   9 0.00
Mon 08/24 21Z 1.65 2215  84  58   9 0.00
Mon 08/24 22Z 1.04 2315  83  60  10 0.00
Mon 08/24 23Z 0.98 2317  82  67   9 0.00
Tue 08/25 00Z 1.09 2318  80  66   9 0.00
Tue 08/25 01Z 1.13 2319  81  70   9 0.00
Tue 08/25 02Z 1.05 2319  83  64   9 0.00
Tue 08/25 03Z 0.85 2319  83  72   9 0.00
Tue 08/25 04Z 0.61 2316  84  68   9 0.00
Tue 08/25 05Z 0.43 2413  84  65   9 0.00
Tue 08/25 06Z 0.38 2312  85  70   9 0.00
Tue 08/25 07Z 0.37 2313  85  72   9 0.00
Tue 08/25 08Z 0.39 2413  87  73   9 0.00
Tue 08/25 09Z 0.39 2413  88  78   9 0.00
Tue 08/25 10Z 0.41 2414  90  70   9 0.00
Tue 08/25 11Z 0.43 2414  93  77   9 0.01
Tue 08/25 12Z 0.44 2415  94  70   9 0.01
Tue 08/25 13Z 0.41 2413  95  68   9 0.00
Tue 08/25 14Z 0.38 2511  96  63   9 0.00
Tue 08/25 15Z 0.40 2610  96  63   9 0.00
Tue 08/25 16Z 0.41 2709  96  80   8 0.00
Tue 08/25 17Z 0.45 2809  97  76   9 0.00
Tue 08/25 18Z 0.48 2811  96  70   9 0.00
Tue 08/25 19Z 0.42 2910  96  68   9 0.01
Tue 08/25 20Z 0.35 3010  95  77  10 0.03
Tue 08/25 21Z 0.30 3112  93  77  10 0.04
Tue 08/25 22Z 0.31 3112  94  66   9 0.00
Tue 08/25 23Z 0.26 3112  92  61  10 0.01
Wed 08/26 00Z 0.25 3113  91  56   9 0.01
Wed 08/26 01Z 0.29 3112  93  45   9 0.00
Wed 08/26 02Z 0.30 3012  95  46   9 0.01
Wed 08/26 03Z 0.29 3012  95  50   9 0.01
Wed 08/26 04Z 0.26 3112  95  51   9 0.01
Wed 08/26 05Z 0.23 3113  95  53   9 0.01
Wed 08/26 06Z 0.24 3112  96  52   9 0.01
Wed 08/26 07Z 0.22 3111  95  47   9 0.00
Wed 08/26 08Z 0.21 3011  93  45   9 0.00
Wed 08/26 09Z 0.19 3110  93  45   9 0.00
Wed 08/26 10Z 0.19 3110  92  42   9 0.00
Wed 08/26 11Z 0.15 3109  92  38   9 0.00
Wed 08/26 12Z 0.12 3107  90  36   9 0.00
Wed 08/26 13Z 0.10 3105  91  33   9 0.00
Wed 08/26 14Z 0.12 3005  90  28   9 0.00
Wed 08/26 15Z 0.12 2804  91  25   9 0.00
Wed 08/26 16Z 0.13 2704  91  22   9 0.00
Wed 08/26 17Z 0.13 2603  90  20   9 0.00
Wed 08/26 18Z 0.16 2603  89  18   9 0.00
Wed 08/26 19Z 0.14 2603  89  17   9 0.00
Wed 08/26 20Z 0.15 2503  88  15  10 0.00
Wed 08/26 21Z 0.17 2504  87  14  10 0.00
Wed 08/26 22Z 0.15 2504  84  14  10 0.00
Wed 08/26 23Z 0.13 2403  84  14  11 0.00

Run total areal avg QPF for the Central_Greens is: 0.25 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