NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260712_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)
=== ===== === ==== ==== === === === ====
Sun 07/12 18Z 0.90 3203  73  15  12 0.00
Sun 07/12 19Z 0.72 3203  72  18  12 0.00
Sun 07/12 20Z 0.29 3202  72  21  12 0.01
Sun 07/12 21Z 0.24 3102  70  22  12 0.00
Sun 07/12 22Z 0.16 3203  67  17  13 0.00
Sun 07/12 23Z 0.08 3202  66  10  13 0.00
Mon 07/13 00Z 0.09 2501  66  14  13 0.00
Mon 07/13 01Z 0.13 2003  65  13  12 0.00
Mon 07/13 02Z 0.22 2005  65   9  12 0.00
Mon 07/13 03Z 0.44 2107  66   7  12 0.00
Mon 07/13 04Z 0.68 2210  72   8  12 0.00
Mon 07/13 05Z 0.86 2312  76   7  12 0.00
Mon 07/13 06Z 0.90 2413  76   6  12 0.00
Mon 07/13 07Z 0.86 2414  77   8  11 0.00
Mon 07/13 08Z 0.83 2514  75  13  11 0.00
Mon 07/13 09Z 0.86 2514  73  16  11 0.00
Mon 07/13 10Z 0.82 2514  71  19  11 0.00
Mon 07/13 11Z 0.69 2414  76  22  11 0.00
Mon 07/13 12Z 0.66 2415  75  26  12 0.00
Mon 07/13 13Z 0.67 2415  81  27  12 0.00
Mon 07/13 14Z 0.73 2415  84  28  12 0.00
Mon 07/13 15Z 0.95 2316  85  31  12 0.00
Mon 07/13 16Z 1.39 2415  81  38  12 0.00
Mon 07/13 17Z 1.01 2413  80  40  13 0.00
Mon 07/13 18Z 0.62 2413  85  43  13 0.01
Mon 07/13 19Z 0.62 2412  84  48  14 0.00
Mon 07/13 20Z 0.58 2413  87  56  14 0.01
Mon 07/13 21Z 0.61 2415  86  66  15 0.00
Mon 07/13 22Z 0.66 2418  89  77  15 0.01
Mon 07/13 23Z 0.79 2621  90  87  15 0.01
Tue 07/14 00Z 0.70 2721  85  83  15 0.01
Tue 07/14 01Z 0.82 2723  86  67  14 0.00
Tue 07/14 02Z 0.87 2723  82  57  14 0.01
Tue 07/14 03Z 0.79 2822  72  44  15 0.00
Tue 07/14 04Z 0.72 2721  69  36  15 0.00
Tue 07/14 05Z 0.63 2720  74  27  15 0.00
Tue 07/14 06Z 0.73 2825  82  24  15 0.00
Tue 07/14 07Z 0.72 2926  84  24  15 0.00
Tue 07/14 08Z 0.66 2927  84  28  16 0.00
Tue 07/14 09Z 0.58 2927  82  36  17 0.00
Tue 07/14 10Z 0.56 2926  78  41  17 0.00
Tue 07/14 11Z 0.60 2927  78  35  18 0.00
Tue 07/14 12Z 0.61 2827  78  36  18 0.00
Tue 07/14 13Z 0.60 2826  73  35  19 0.00
Tue 07/14 14Z 0.61 2827  71  35  19 0.00
Tue 07/14 15Z 0.63 2727  76  33  20 0.00
Tue 07/14 16Z 0.65 2728  77  32  21 0.00
Tue 07/14 17Z 0.76 2728  83  21  20 0.00
Tue 07/14 18Z 0.92 2628  84  11  20 0.00
Tue 07/14 19Z 1.23 2629  83  11  20 0.00
Tue 07/14 20Z 1.76 2629  83  11  20 0.00
Tue 07/14 21Z 1.70 2628  82  11  20 0.00
Tue 07/14 22Z 1.90 2529  87  14  20 0.00
Tue 07/14 23Z 1.54 2630  90  17  20 0.01
Wed 07/15 00Z 1.43 2633  92  23  20 0.01
Wed 07/15 01Z 1.42 2636  92  27  19 0.01
Wed 07/15 02Z 1.40 2639  91  28  19 0.00
Wed 07/15 03Z 1.14 2735  88  35  19 0.00
Wed 07/15 04Z 1.04 2831  90  50  18 0.00
Wed 07/15 05Z 0.87 3029  94  68  17 0.05

Run total areal avg QPF for the Central_Greens is: 0.15 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