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_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)
=== ===== === ==== ==== === === === ====
Sat 09/12 18Z 0.52 1807  65  16  10 0.00
Sat 09/12 19Z 0.69 1908  65  15  11 0.00
Sat 09/12 20Z 0.72 1910  63  15  11 0.00
Sat 09/12 21Z 0.44 1912  60  12  11 0.00
Sat 09/12 22Z 0.29 1913  57  10  11 0.00
Sat 09/12 23Z 0.28 1914  55   6  12 0.00
Sun 09/13 00Z 0.34 1918  57   3  12 0.00
Sun 09/13 01Z 0.41 2020  61   2  12 0.00
Sun 09/13 02Z 0.51 2023  72  14  12 0.00
Sun 09/13 03Z 0.51 2123  82  44  13 0.00
Sun 09/13 04Z 0.49 2124  88  76  13 0.00
Sun 09/13 05Z 0.49 2125  93  92  13 0.01
Sun 09/13 06Z 0.51 2228  93  90  13 0.10
Sun 09/13 07Z 0.46 2225  95  87  14 0.05
Sun 09/13 08Z 0.49 2227  97  94  13 0.21
Sun 09/13 09Z 0.46 2225  95  91  14 0.12
Sun 09/13 10Z 0.42 2126  97  89  14 0.16
Sun 09/13 11Z 0.56 2132  99  91  14 0.32
Sun 09/13 12Z 0.62 2230  99  89  14 0.16
Sun 09/13 13Z 0.63 2426  99  91  14 0.07
Sun 09/13 14Z 0.60 2423  98  83  14 0.06
Sun 09/13 15Z 0.57 2520  97  54  14 0.04
Sun 09/13 16Z 0.51 2518  93  32  14 0.01
Sun 09/13 17Z 0.48 2516  91  38  14 0.00
Sun 09/13 18Z 0.45 2514  91  59  15 0.00
Sun 09/13 19Z 0.48 2513  92  57  15 0.00
Sun 09/13 20Z 0.54 2513  94  32  14 0.00
Sun 09/13 21Z 0.58 2414  96  34  14 0.01
Sun 09/13 22Z 0.66 2417  96  53  15 0.01
Sun 09/13 23Z 0.80 2521  95  65  14 0.02
Mon 09/14 00Z 0.69 2621  90  62  15 0.02
Mon 09/14 01Z 0.69 2621  91  67  14 0.03
Mon 09/14 02Z 0.63 2621  81  73  14 0.02
Mon 09/14 03Z 0.69 2721  75  77  13 0.02
Mon 09/14 04Z 0.81 2824  68  75  12 0.00
Mon 09/14 05Z 0.70 2924  74  74  11 0.00
Mon 09/14 06Z 0.49 2920  73  88  11 0.01
Mon 09/14 07Z 0.45 2919  79  72  10 0.00
Mon 09/14 08Z 0.53 2921  85  70   9 0.00
Mon 09/14 09Z 0.60 3023  92  41   8 0.02
Mon 09/14 10Z 0.54 3024  93  25   7 0.01
Mon 09/14 11Z 0.45 3124  88  18   7 0.01
Mon 09/14 12Z 0.45 3124  88  14   6 0.01
Mon 09/14 13Z 0.34 3223  88  16   5 0.01
Mon 09/14 14Z 0.27 3222  85  16   5 0.00
Mon 09/14 15Z 0.25 3320  83  16   5 0.00
Mon 09/14 16Z 0.25 3320  82  13   5 0.00
Mon 09/14 17Z 0.28 3319  81   9   5 0.00
Mon 09/14 18Z 0.28 3318  79  12   5 0.00
Mon 09/14 19Z 0.32 3317  80  14   5 0.00
Mon 09/14 20Z 0.31 3318  79  17   5 0.00
Mon 09/14 21Z 0.25 3317  78  20   5 0.00
Mon 09/14 22Z 0.19 3317  76  17   5 0.00
Mon 09/14 23Z 0.10 3418  73  13   5 0.00
Tue 09/15 00Z 0.07 3419  74  14   6 0.00
Tue 09/15 01Z 0.03 3419  77  14   6 0.00
Tue 09/15 02Z 0.05 3518  71  14   7 0.00
Tue 09/15 03Z 0.08 0017  68  13   8 0.00
Tue 09/15 04Z 0.12 0115  61  12   9 0.00
Tue 09/15 05Z 0.12 0113  58  11   9 0.00

Run total areal avg QPF for the Central_Greens is: 1.51 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