Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260306_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)
=== ===== === ==== ==== === === === ====
Fri 03/06 18Z 0.05 1511  93  63  -1 0.00
Fri 03/06 19Z 0.05 1512  92  61  -1 0.00
Fri 03/06 20Z 0.03 1613  90  58   0 0.00
Fri 03/06 21Z 0.02 1714  90  49   0 0.00
Fri 03/06 22Z 0.03 1716  90  28   0 0.00
Fri 03/06 23Z 0.08 1819  93  11   0 0.00
Sat 03/07 00Z 0.13 1821  94  11   0 0.00
Sat 03/07 01Z 0.19 1923  96  17   0 0.00
Sat 03/07 02Z 0.23 1926  97  38   0 0.01
Sat 03/07 03Z 0.24 1928  96  53   1 0.01
Sat 03/07 04Z 0.25 1927  96  59   2 0.01
Sat 03/07 05Z 0.25 2027  97  31   3 0.01
Sat 03/07 06Z 0.28 2027  97  23   3 0.01
Sat 03/07 07Z 0.28 2027  96  23   4 0.01
Sat 03/07 08Z 0.28 2028  95  62   5 0.00
Sat 03/07 09Z 0.31 2030  96  93   5 0.01
Sat 03/07 10Z 0.36 2133  96  90   7 0.01
Sat 03/07 11Z 0.39 2134  97  83   8 0.02
Sat 03/07 12Z 0.45 2236  97  68   9 0.02
Sat 03/07 13Z 0.52 2337  97  79   9 0.04
Sat 03/07 14Z 0.57 2338  98  67  10 0.03
Sat 03/07 15Z 0.56 2436  97  71  10 0.03
Sat 03/07 16Z 0.53 2333  96  61  10 0.03
Sat 03/07 17Z 0.56 2434  97  69  10 0.03
Sat 03/07 18Z 0.60 2435  95  79  10 0.04
Sat 03/07 19Z 0.59 2334  93  66  11 0.02
Sat 03/07 20Z 0.62 2335  96  62  11 0.01
Sat 03/07 21Z 0.63 2337  95  67  11 0.01
Sat 03/07 22Z 0.63 2338  95  66  12 0.01
Sat 03/07 23Z 0.66 2340  91  56  12 0.01
Sun 03/08 00Z 0.71 2342  94  45  12 0.01
Sun 03/08 01Z 0.75 2443  91  59  12 0.01
Sun 03/08 02Z 0.78 2445  90  80  12 0.01
Sun 03/08 03Z 0.84 2446  93  75  11 0.01
Sun 03/08 04Z 0.87 2444  96  88  10 0.03
Sun 03/08 05Z 0.89 2443  96  93  10 0.08
Sun 03/08 06Z 0.88 2542  95  83  10 0.04
Sun 03/08 07Z 0.86 2539  96  54   9 0.02
Sun 03/08 08Z 0.82 2537  94  52   9 0.02
Sun 03/08 09Z 0.82 2536  95  43   8 0.02
Sun 03/08 11Z 0.82 2533  93  14   7 0.02
Sun 03/08 12Z 0.97 2534  95   8   5 0.02
Sun 03/08 13Z 1.10 2534  94  10   4 0.02
Sun 03/08 14Z 1.24 2536  95  15   3 0.01
Sun 03/08 15Z 1.39 2636  95  45   1 0.02
Sun 03/08 16Z 1.24 2730  94  43   0 0.02
Sun 03/08 17Z 1.08 2730  93   4   0 0.02
Sun 03/08 18Z 1.20 2730  95   1  -1 0.01
Sun 03/08 19Z 1.31 2726  95   3  -1 0.00
Sun 03/08 20Z 1.27 2726  93   2  -2 0.00
Sun 03/08 21Z 0.98 2628  85   6  -1 0.00
Sun 03/08 22Z 0.76 2629  72  13   0 0.00
Sun 03/08 23Z 0.72 2632  62  45   0 0.00
Mon 03/09 00Z 0.73 2635  56  63   1 0.00
Mon 03/09 01Z 0.78 2637  54  63   1 0.00
Mon 03/09 02Z 0.82 2639  54  58   2 0.00
Mon 03/09 03Z 0.87 2640  59  45   2 0.00
Mon 03/09 04Z 0.91 2640  58  34   2 0.00
Mon 03/09 05Z 0.87 2739  58  29   2 0.00

Run total areal avg QPF for the Central_Greens is: 0.77 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