NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260226_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)
=== ===== === ==== ==== === === === ====
Thu 02/26 18Z 8.60 2612  82  30 -12 0.00
Thu 02/26 19Z 8.26 2614  81  31 -12 0.00
Thu 02/26 20Z 6.19 2712  81  32 -12 0.00
Thu 02/26 21Z 4.67 2612  82  26 -11 0.00
Thu 02/26 22Z 2.22 2713  84  26 -12 0.00
Thu 02/26 23Z 1.20 2714  83  29 -12 0.00
Fri 02/27 00Z 0.88 2815  83  33 -12 0.00
Fri 02/27 01Z 0.62 2916  80  38 -12 0.00
Fri 02/27 02Z 0.44 2915  77  40 -12 0.00
Fri 02/27 03Z 0.35 2914  70  44 -11 0.00
Fri 02/27 04Z 0.28 2913  66  39 -11 0.00
Fri 02/27 05Z 0.23 2911  65  41 -10 0.00
Fri 02/27 06Z 0.22 2911  65  50 -10 0.00
Fri 02/27 07Z 0.22 2811  66  57 -10 0.00
Fri 02/27 08Z 0.21 2810  64  60 -10 0.00
Fri 02/27 09Z 0.21 2710  61  57  -9 0.00
Fri 02/27 10Z 0.24 2712  59  56  -9 0.00
Fri 02/27 11Z 0.25 2713  56  52  -8 0.00
Fri 02/27 12Z 0.26 2613  54  57  -7 0.00
Fri 02/27 13Z 0.29 2515  53  60  -6 0.00
Fri 02/27 14Z 0.34 2517  52  60  -6 0.00
Fri 02/27 15Z 0.41 2519  52  73  -6 0.00
Fri 02/27 16Z 0.46 2420  58  83  -6 0.00
Fri 02/27 17Z 0.51 2420  60  89  -6 0.00
Fri 02/27 18Z 0.53 2419  63  92  -6 0.00
Fri 02/27 19Z 0.57 2419  64  91  -6 0.00
Fri 02/27 21Z 0.71 2419  72  61  -6 0.00
Fri 02/27 22Z 0.76 2421  76  41  -6 0.00
Fri 02/27 23Z 0.86 2423  74  36  -6 0.00
Sat 02/28 00Z 0.93 2425  76  43  -6 0.00
Sat 02/28 01Z 0.87 2524  82  41  -5 0.00
Sat 02/28 02Z 0.88 2426  83  35  -5 0.00
Sat 02/28 03Z 0.79 2327  78  24  -4 0.00
Sat 02/28 04Z 0.81 2230  74  19  -3 0.00
Sat 02/28 05Z 0.82 2232  74  25  -2 0.00
Sat 02/28 06Z 0.77 2233  73  29  -2 0.00
Sat 02/28 07Z 0.71 2134  65  26  -1 0.00
Sat 02/28 08Z 0.68 2137  61  26   0 0.00
Sat 02/28 09Z 0.74 2140  66  36   0 0.00
Sat 02/28 10Z 0.79 2242  66  45   0 0.00
Sat 02/28 11Z 0.81 2245  59  47   0 0.00
Sat 02/28 12Z 0.84 2245  57  92   0 0.00
Sat 02/28 13Z 0.92 2344  70  93   0 0.00
Sat 02/28 14Z 0.96 2342  83  93   0 0.00
Sat 02/28 15Z 1.00 2340  91  93  -1 0.01
Sat 02/28 16Z 0.95 2437  92  84  -1 0.01
Sat 02/28 17Z 0.92 2435  84  73  -1 0.01
Sat 02/28 18Z 0.89 2534  69  56  -1 0.01
Sat 02/28 19Z 0.91 2531  68  46  -1 0.01
Sat 02/28 20Z 1.05 2528  75  30  -2 0.01
Sat 02/28 21Z 1.42 2627  81  20  -4 0.01
Sat 02/28 22Z 1.02 2725  70  23  -4 0.01
Sat 02/28 23Z 0.82 2724  60  36  -5 0.00
Sun 03/01 00Z 0.71 2822  53  32  -5 0.00
Sun 03/01 01Z 0.51 2820  40  37  -5 0.00
Sun 03/01 02Z 0.38 2917  36  45  -6 0.00
Sun 03/01 03Z 0.34 2916  37  46  -6 0.00
Sun 03/01 04Z 0.32 2816  40  49  -6 0.00
Sun 03/01 05Z 0.27 2814  35  63  -6 0.00

Run total areal avg QPF for the Central_Greens is: 0.08 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