NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260912_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)
=== ===== === ==== ==== === === === ====
Sat 09/12 12Z 0.05 1807  57  21  11 0.00
Sat 09/12 13Z 0.11 1909  55  19  11 0.00
Sat 09/12 14Z 0.15 1912  54  18  11 0.00
Sat 09/12 15Z 0.18 2013  54  18  11 0.00
Sat 09/12 16Z 0.24 2013  54  18  11 0.00
Sat 09/12 17Z 0.27 2012  55  15  12 0.00
Sat 09/12 18Z 0.32 2012  60  11  12 0.00
Sat 09/12 19Z 0.42 2012  63   7  11 0.00
Sat 09/12 20Z 0.36 1913  66   4  11 0.00
Sat 09/12 21Z 0.36 1914  69   4  12 0.00
Sat 09/12 22Z 0.33 1916  69   4  12 0.00
Sat 09/12 23Z 0.35 2018  69   5  12 0.00
Sun 09/13 00Z 0.37 2019  68   4  13 0.00
Sun 09/13 01Z 0.44 2022  70   5  13 0.00
Sun 09/13 02Z 0.47 2123  75  15  13 0.00
Sun 09/13 03Z 0.45 2124  80  45  13 0.00
Sun 09/13 04Z 0.44 2123  84  79  13 0.00
Sun 09/13 05Z 0.47 2223  93  91  13 0.00
Sun 09/13 06Z 0.45 2223  97  92  13 0.08
Sun 09/13 07Z 0.41 2222  95  88  14 0.06
Sun 09/13 08Z 0.35 2219  95  95  14 0.09
Sun 09/13 09Z 0.38 2123  96  97  13 0.12
Sun 09/13 10Z 0.37 2222  96  91  14 0.37
Sun 09/13 11Z 0.51 2228  98  93  14 0.20
Sun 09/13 12Z 0.54 2327  98  84  14 0.07
Sun 09/13 13Z 0.54 2325  98  78  14 0.03
Sun 09/13 14Z 0.55 2323  98  75  14 0.04
Sun 09/13 15Z 0.50 2420  97  71  14 0.04
Sun 09/13 16Z 0.45 2417  97  46  14 0.02
Sun 09/13 17Z 0.40 2414  95  40  14 0.01
Sun 09/13 18Z 0.41 2313  95  44  14 0.01
Sun 09/13 19Z 0.45 2413  94  43  14 0.00
Sun 09/13 20Z 0.41 2410  92  42  14 0.00
Sun 09/13 21Z 0.40 2510  92  42  14 0.00
Sun 09/13 22Z 0.37 2410  92  44  14 0.00
Sun 09/13 23Z 0.45 2413  94  40  14 0.00
Mon 09/14 00Z 0.52 2415  95  45  14 0.01
Mon 09/14 01Z 0.54 2517  91  46  14 0.01
Mon 09/14 02Z 0.63 2519  93  60  14 0.01
Mon 09/14 03Z 0.68 2520  95  59  14 0.01
Mon 09/14 04Z 0.76 2522  97  67  14 0.03
Mon 09/14 05Z 0.86 2824  95  82  12 0.08
Mon 09/14 06Z 0.50 3021  83  83  11 0.06
Mon 09/14 07Z 0.35 3017  81  70  11 0.07
Mon 09/14 08Z 0.32 3117  88  66  10 0.01
Mon 09/14 09Z 0.31 3117  88  62  10 0.01
Mon 09/14 10Z 0.40 3119  93  60   8 0.01
Mon 09/14 11Z 0.48 3122  95  42   7 0.01
Mon 09/14 12Z 0.46 3125  95  27   7 0.02
Mon 09/14 13Z 0.45 3225  93  18   6 0.02
Mon 09/14 14Z 0.36 3223  89  20   5 0.01
Mon 09/14 15Z 0.33 3323  90  24   5 0.01
Mon 09/14 16Z 0.37 3321  91  29   4 0.00
Mon 09/14 17Z 0.58 3319  88  33   4 0.00
Mon 09/14 18Z 0.63 3319  87  35   4 0.00
Mon 09/14 19Z 0.60 3319  79  24   4 0.00
Mon 09/14 20Z 1.19 3319  80   9   4 0.00
Mon 09/14 21Z 1.12 3219  84   8   4 0.00
Mon 09/14 22Z 0.37 3220  82  17   4 0.00
Mon 09/14 23Z 0.34 3222  79  23   4 0.00

Run total areal avg QPF for the Central_Greens is: 1.52 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