Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260111_0000
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 01/11 00Z 0.08 1626  60  93   3 0.00
Sun 01/11 01Z 0.13 1532  85  99   2 0.01
Sun 01/11 02Z 0.17 1535  96  99   1 0.06
Sun 01/11 03Z 0.16 1534  96  99   2 0.11
Sun 01/11 04Z 0.14 1533  96  99   2 0.10
Sun 01/11 05Z 0.13 1532  96  99   2 0.09
Sun 01/11 06Z 0.11 1526  97  99   0 0.11
Sun 01/11 07Z 0.05 1622  97  97   0 0.06
Sun 01/11 08Z 0.05 1720  97  96   0 0.04
Sun 01/11 09Z 0.07 1815  97  85   0 0.02
Sun 01/11 10Z 0.23 2014  99  61  -1 0.02
Sun 01/11 11Z 0.40 2413  99  56  -3 0.03
Sun 01/11 12Z 0.48 2614  98  56  -4 0.02
Sun 01/11 13Z 0.51 2615  90  35  -4 0.01
Sun 01/11 14Z 0.45 2716  77  19  -4 0.00
Sun 01/11 15Z 0.44 2616  72  35  -4 0.00
Sun 01/11 16Z 0.47 2616  72  42  -4 0.00
Sun 01/11 17Z 0.72 2618  79  50  -6 0.00
Sun 01/11 18Z 1.05 2619  86  46  -7 0.01
Sun 01/11 19Z 0.94 2618  84  57  -8 0.01
Sun 01/11 20Z 1.05 2618  88  51  -9 0.00
Sun 01/11 21Z 1.42 2619  91  36  -9 0.00
Sun 01/11 22Z 1.87 2521  90  33 -10 0.00
Sun 01/11 23Z 1.41 2622  89  66 -10 0.00
Mon 01/12 00Z 1.17 2624  93  82 -10 0.01
Mon 01/12 01Z 1.10 2624  94  81  -9 0.01
Mon 01/12 02Z 1.38 2627  95  75 -10 0.02
Mon 01/12 03Z 1.66 2729  95  75 -11 0.02
Mon 01/12 04Z 1.87 2830  91  77 -12 0.02
Mon 01/12 05Z 1.65 2830  91  78 -13 0.01
Mon 01/12 06Z 2.37 2831  89  78 -15 0.01
Mon 01/12 07Z 1.49 2932  90  74 -15 0.01
Mon 01/12 08Z 0.98 2932  92  66 -14 0.00
Mon 01/12 09Z 0.76 2934  91  24 -13 0.00
Mon 01/12 10Z 0.64 3036  89  16 -12 0.00
Mon 01/12 11Z 0.61 3036  79  11 -11 0.00
Mon 01/12 12Z 0.61 3036  68  24 -10 0.00
Mon 01/12 13Z 0.62 3036  67  44 -10 0.00
Mon 01/12 14Z 0.61 3035  68  48 -10 0.00
Mon 01/12 15Z 0.67 2933  67  71 -10 0.00
Mon 01/12 16Z 0.75 2832  68  72 -10 0.00
Mon 01/12 17Z 0.79 2830  74  76  -9 0.00
Mon 01/12 18Z 0.78 2726  81  81  -9 0.00
Mon 01/12 19Z 0.81 2625  85  85  -9 0.00
Mon 01/12 20Z 0.92 2525  90  78  -9 0.00
Mon 01/12 21Z 1.14 2527  94  79 -10 0.00
Mon 01/12 22Z 1.44 2528  95  81 -10 0.00
Mon 01/12 23Z 1.65 2628  94  87 -10 0.00
Tue 01/13 00Z 1.49 2629  92  84 -10 0.00
Tue 01/13 01Z 1.32 2630  94  75 -10 0.00
Tue 01/13 02Z 1.20 2729  95  67 -10 0.00
Tue 01/13 03Z 1.12 2729  96  67 -10 0.00
Tue 01/13 04Z 0.95 2726  96  50  -9 0.00
Tue 01/13 05Z 0.84 2725  95  20  -9 0.01
Tue 01/13 06Z 0.75 2724  94  51  -8 0.01
Tue 01/13 07Z 0.73 2724  95  61  -8 0.01
Tue 01/13 08Z 0.70 2724  95  69  -7 0.01
Tue 01/13 09Z 0.72 2725  95  70  -7 0.00
Tue 01/13 10Z 0.67 2724  95  62  -7 0.00
Tue 01/13 11Z 0.70 2725  95  61  -7 0.01

Run total areal avg QPF for the Central_Greens is: 0.86 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