Subject: NAM3 EXPERIMENTAL Froude Number for the Northern_Greens

Model run: BTV_GRID_D2D_NAM3_20260307_0600
Using the MB925 to MB850 layer.
Assumes Northern_Greens are orthogonal to 290 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Northern_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sat 03/07 06Z 0.08 2028  91  34   4 0.00
Sat 03/07 07Z 0.08 2031  88  40   5 0.00
Sat 03/07 08Z 0.10 2134  76  50   6 0.00
Sat 03/07 09Z 0.12 2135  75  95   8 0.00
Sat 03/07 10Z 0.13 2137  77  98   9 0.01
Sat 03/07 11Z 0.14 2139  80  87  10 0.01
Sat 03/07 12Z 0.18 2140  89  90  10 0.01
Sat 03/07 14Z 0.34 2341  97  97   9 0.08
Sat 03/07 15Z 0.38 2336  98  96   9 0.17
Sat 03/07 16Z 0.42 2433  97  91   9 0.11
Sat 03/07 17Z 0.45 2435  97  80  10 0.05
Sat 03/07 18Z 0.45 2436  93  91  11 0.01
Sat 03/07 19Z 0.44 2337  88  92  11 0.01
Sat 03/07 20Z 0.44 2340  92  83  11 0.01
Sat 03/07 21Z 0.43 2340  91  78  11 0.00
Sat 03/07 22Z 0.47 2342  89  25  11 0.00
Sat 03/07 23Z 0.55 2444  84  81  11 0.00
Sun 03/08 00Z 0.50 2342  78  86  12 0.00
Sun 03/08 01Z 0.58 2346  89  91  11 0.00
Sun 03/08 02Z 0.64 2446  96  94  10 0.01
Sun 03/08 03Z 0.78 2445  95  54   9 0.06
Sun 03/08 04Z 0.80 2542  95  49   9 0.05
Sun 03/08 05Z 0.69 2537  96  80   9 0.01
Sun 03/08 06Z 0.67 2536  96  80   9 0.02
Sun 03/08 07Z 0.62 2532  91  74   9 0.03
Sun 03/08 08Z 0.63 2533  90  73   9 0.02
Sun 03/08 09Z 0.70 2437  94  77   8 0.03
Sun 03/08 10Z 0.81 2436  96  11   6 0.03
Sun 03/08 11Z 1.14 2439  92  10   4 0.01
Sun 03/08 12Z 1.37 2539  94  11   2 0.01
Sun 03/08 13Z 1.23 2639  94   5   0 0.01
Sun 03/08 14Z 1.12 2637  94   3   0 0.02
Sun 03/08 15Z 1.11 2734  94   3  -1 0.01
Sun 03/08 16Z 1.10 2733  96   5  -2 0.01
Sun 03/08 17Z 1.14 2731  97   5  -3 0.01
Sun 03/08 18Z 0.98 2728  96   5  -3 0.01
Sun 03/08 19Z 0.72 2723  96   5  -3 0.01
Sun 03/08 20Z 0.63 2623  94   8  -2 0.00
Sun 03/08 21Z 0.70 2626  94  12  -2 0.00
Sun 03/08 22Z 0.68 2529  80  21  -1 0.00
Sun 03/08 23Z 0.63 2532  62  87   0 0.00
Mon 03/09 00Z 0.63 2535  60  83   0 0.00
Mon 03/09 01Z 0.94 2541  72  34  -2 0.00
Mon 03/09 02Z 1.18 2641  88  12  -3 0.00
Mon 03/09 03Z 1.14 2739  91  10  -3 0.00
Mon 03/09 04Z 1.03 2737  84  19  -2 0.00
Mon 03/09 05Z 0.84 2734  73  30  -1 0.00
Mon 03/09 06Z 0.81 2732  69  37   0 0.00
Mon 03/09 07Z 0.80 2731  66  44   0 0.00
Mon 03/09 08Z 0.74 2729  60  52   0 0.00
Mon 03/09 09Z 0.66 2629  58  61   1 0.00
Mon 03/09 10Z 0.56 2529  62  70   2 0.00
Mon 03/09 11Z 0.63 2532  72  84   2 0.00
Mon 03/09 12Z 0.58 2532  71  84   2 0.00
Mon 03/09 13Z 0.51 2433  67  78   4 0.00
Mon 03/09 14Z 0.46 2336  52  58   5 0.00
Mon 03/09 15Z 0.45 2340  48  32   6 0.00
Mon 03/09 16Z 0.50 2342  45  42   6 0.00
Mon 03/09 17Z 0.57 2341  45  51   7 0.00

Run total areal avg QPF for the Northern_Greens is: 0.83 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