NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260829_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)
=== ===== === ==== ==== === === === ====
Sat 08/29 06Z 0.09 3415  82   7   7 0.00
Sat 08/29 07Z 0.07 3415  78   8   7 0.00
Sat 08/29 08Z 0.08 3413  77   6   6 0.00
Sat 08/29 09Z 0.11 3313  76   6   6 0.00
Sat 08/29 10Z 0.15 3312  74   5   6 0.00
Sat 08/29 11Z 0.22 3212  71   4   6 0.00
Sat 08/29 12Z 0.28 3112  73   5   6 0.00
Sat 08/29 13Z 0.31 3110  75   5   6 0.00
Sat 08/29 14Z 0.36 3008  78   5   6 0.00
Sat 08/29 15Z 0.81 2807  80   5   6 0.00
Sat 08/29 16Z 1.17 2706  79   5   7 0.00
Sat 08/29 17Z 1.34 2606  76   5   7 0.00
Sat 08/29 18Z 1.45 2606  73   5   8 0.00
Sat 08/29 19Z 1.74 2507  72   4   8 0.00
Sat 08/29 20Z 2.11 2508  76   3   8 0.00
Sat 08/29 21Z 1.36 2410  83   5   9 0.00
Sat 08/29 22Z 0.61 2412  79   5   9 0.00
Sat 08/29 23Z 0.56 2414  72   8  10 0.00
Sun 08/30 00Z 0.69 2518  74  18  10 0.00
Sun 08/30 01Z 0.81 2521  72  34  10 0.00
Sun 08/30 02Z 0.83 2623  66  35  11 0.00
Sun 08/30 03Z 0.99 2626  71  39  11 0.00
Sun 08/30 04Z 1.09 2629  76  46  11 0.00
Sun 08/30 05Z 1.08 2730  75  58  11 0.00
Sun 08/30 06Z 1.20 2731  74  53  11 0.00
Sun 08/30 07Z 1.24 2731  77  60  11 0.00
Sun 08/30 08Z 1.09 2829  76  46  11 0.00
Sun 08/30 09Z 1.06 2828  75  44  11 0.00
Sun 08/30 10Z 0.96 2827  77  38  11 0.00
Sun 08/30 11Z 0.91 2825  71  31  12 0.00
Sun 08/30 12Z 0.99 2725  74  30  11 0.00
Sun 08/30 13Z 0.98 2723  76  41  11 0.00
Sun 08/30 14Z 0.95 2622  78  39  11 0.00
Sun 08/30 15Z 0.94 2621  74  60  11 0.00
Sun 08/30 16Z 1.04 2522  72  56  12 0.00
Sun 08/30 17Z 1.21 2423  70  53  12 0.00
Sun 08/30 18Z 1.48 2423  70  49  12 0.00
Sun 08/30 19Z 1.50 2421  74  43  13 0.00
Sun 08/30 20Z 2.54 2419  85  51  12 0.00
Sun 08/30 21Z 1.65 2520  85  72  12 0.07
Sun 08/30 22Z 1.14 2620  87  87  12 0.01
Sun 08/30 23Z 0.84 2622  90  89  12 0.05
Mon 08/31 00Z 0.95 2824  91  94  11 0.00
Mon 08/31 01Z 0.80 2821  92  92  11 0.01
Mon 08/31 02Z 0.76 2820  95  96  11 0.01
Mon 08/31 03Z 0.70 2819  97  97  11 0.07
Mon 08/31 04Z 0.42 3017  96  92  11 0.04
Mon 08/31 05Z 0.27 3115  94  89  11 0.01
Mon 08/31 06Z 0.17 3213  88  78  11 0.01
Mon 08/31 07Z 0.09 3413  82  52  10 0.00
Mon 08/31 08Z 0.06 3411  78  20  10 0.00
Mon 08/31 09Z 0.04 3409  74   7  11 0.00
Mon 08/31 10Z 0.04 3410  70   3  11 0.00
Mon 08/31 11Z 0.05 3310  66   2  11 0.00
Mon 08/31 12Z 0.06 3311  63   2  11 0.00
Mon 08/31 13Z 0.05 3410  60   3  11 0.00
Mon 08/31 14Z 0.06 3308  60   4  11 0.00
Mon 08/31 15Z 0.06 3307  62   5  11 0.00
Mon 08/31 16Z 0.05 3305  65   7  11 0.00
Mon 08/31 17Z 0.08 3104  69   8  11 0.00

Run total areal avg QPF for the Central_Greens is: 0.28 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