NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260415_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)
=== ===== === ==== ==== === === === ====
Wed 04/15 06Z 0.40 2715  88  31   8 0.00
Wed 04/15 07Z 0.36 2716  84  23  10 0.00
Wed 04/15 08Z 0.31 2816  77  18  11 0.00
Wed 04/15 09Z 0.28 2817  71  17  12 0.00
Wed 04/15 10Z 0.23 2915  66  17  13 0.00
Wed 04/15 11Z 0.16 2911  59  16  13 0.00
Wed 04/15 12Z 0.11 2907  55  17  13 0.00
Wed 04/15 13Z 0.18 2509  53  17  13 0.00
Wed 04/15 14Z 0.21 2311  53  15  13 0.00
Wed 04/15 15Z 0.19 2014  57  13  12 0.00
Wed 04/15 16Z 0.36 2120  72  70  11 0.00
Wed 04/15 17Z 0.35 2121  93  96  10 0.07
Wed 04/15 18Z 0.42 2125  98  95  11 0.07
Wed 04/15 19Z 0.63 2327  99  65  11 0.04
Wed 04/15 20Z 0.76 2426  98  44  11 0.02
Wed 04/15 21Z 0.96 2428  99  35  11 0.03
Wed 04/15 22Z 1.00 2527  98  35  11 0.02
Wed 04/15 23Z 0.98 2526  98  48  11 0.02
Thu 04/16 00Z 0.86 2625  97  58  11 0.01
Thu 04/16 01Z 0.87 2626  94  70  11 0.01
Thu 04/16 02Z 0.71 2624  90  82  12 0.01
Thu 04/16 03Z 0.59 2622  87  85  13 0.01
Thu 04/16 04Z 0.56 2620  86  94  12 0.00
Thu 04/16 05Z 0.49 2617  84  84  12 0.01
Thu 04/16 06Z 0.50 2616  89  93  11 0.03
Thu 04/16 07Z 0.23 2709  88  92  12 0.23
Thu 04/16 08Z 0.19 2707  88  96  12 0.04
Thu 04/16 09Z 0.22 2809  89  91  11 0.02
Thu 04/16 10Z 0.33 2813  93  81  11 0.00
Thu 04/16 11Z 0.37 2814  95  79  10 0.01
Thu 04/16 12Z 0.33 2914  94  83  10 0.01
Thu 04/16 13Z 0.30 2912  92  79  10 0.00
Thu 04/16 14Z 0.27 2911  94  75  10 0.00
Thu 04/16 15Z 0.29 2810  93  71  10 0.00
Thu 04/16 16Z 0.33 2609  93  85  10 0.00
Thu 04/16 17Z 0.33 2508  95  89  10 0.00
Thu 04/16 18Z 0.32 2409  96  92  10 0.01
Thu 04/16 19Z 0.37 2310  96  88  10 0.00
Thu 04/16 20Z 0.46 2212  97  84  10 0.00
Thu 04/16 21Z 0.55 2315  96  83  11 0.01
Thu 04/16 22Z 0.66 2318  95  93  11 0.00
Thu 04/16 23Z 0.54 2217  91  75  12 0.01
Fri 04/17 00Z 0.51 2119  92  82  12 0.00
Fri 04/17 01Z 0.47 2021  96  80  13 0.07
Fri 04/17 02Z 0.57 2120  93  88  12 0.04
Fri 04/17 03Z 0.42 2217  91  89  12 0.19
Fri 04/17 04Z 0.52 2517  96  93  11 0.43
Fri 04/17 05Z 0.74 2929  86  92  10 0.43
Fri 04/17 06Z 0.54 2419  62  57  12 0.01
Fri 04/17 07Z 0.70 2423  81  22  11 0.00
Fri 04/17 08Z 0.73 2525  84  33  10 0.00
Fri 04/17 09Z 0.74 2525  91  44  10 0.00
Fri 04/17 10Z 0.68 2624  94  34   9 0.00
Fri 04/17 11Z 0.63 2721  95  36   8 0.01
Fri 04/17 12Z 0.61 2821  96  59   8 0.02
Fri 04/17 13Z 0.59 2820  96  78   8 0.01
Fri 04/17 14Z 0.57 2819  96  86   8 0.01
Fri 04/17 15Z 0.59 2918  97  82   7 0.02
Fri 04/17 16Z 0.57 2918  98  76   7 0.03
Fri 04/17 17Z 0.40 3016  97  76   7 0.02

Run total areal avg QPF for the Central_Greens is: 1.98 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