NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260830_0600
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 08/30 06Z 0.77 2722  79  74  12 0.00
Sun 08/30 07Z 0.89 2825  81  85  12 0.00
Sun 08/30 08Z 0.94 2726  85  85  12 0.01
Sun 08/30 09Z 0.94 2626  86  66  12 0.00
Sun 08/30 10Z 0.91 2625  85  55  12 0.00
Sun 08/30 11Z 0.84 2624  87  51  12 0.00
Sun 08/30 12Z 0.83 2625  88  50  12 0.01
Sun 08/30 13Z 0.79 2625  88  60  12 0.03
Sun 08/30 14Z 0.75 2522  88  67  12 0.02
Sun 08/30 15Z 0.86 2523  87  71  12 0.06
Sun 08/30 16Z 0.88 2622  90  82  11 0.11
Sun 08/30 17Z 0.79 2721  90  80  11 0.04
Sun 08/30 18Z 0.66 2718  90  75  11 0.03
Sun 08/30 19Z 0.64 2616  93  74  11 0.01
Sun 08/30 20Z 0.63 2617  96  81  11 0.04
Sun 08/30 21Z 0.72 2619  94  92  11 0.02
Sun 08/30 22Z 0.77 2719  94  84  11 0.01
Sun 08/30 23Z 0.76 2820  96  85  11 0.01
Mon 08/31 00Z 0.72 2921  97  75  10 0.01
Mon 08/31 01Z 0.56 3022  96  65  11 0.01
Mon 08/31 02Z 0.40 3122  94  49  11 0.01
Mon 08/31 03Z 0.27 3221  89  30  11 0.01
Mon 08/31 04Z 0.15 3321  81  22  11 0.01
Mon 08/31 05Z 0.07 3420  79  10  11 0.00
Mon 08/31 06Z 0.06 3415  86   4  10 0.00
Mon 08/31 07Z 0.08 3312  88   3  10 0.01
Mon 08/31 08Z 0.07 3310  86   5   9 0.00
Mon 08/31 09Z 0.13 3209  86   6   9 0.00
Mon 08/31 10Z 0.14 3210  81   8  10 0.00
Mon 08/31 11Z 0.14 3210  75  11  10 0.00
Mon 08/31 12Z 0.13 3211  74  12  11 0.00
Mon 08/31 13Z 0.09 3209  70  13  11 0.00
Mon 08/31 14Z 0.13 3108  68  13  11 0.00
Mon 08/31 15Z 0.15 2906  68  11  11 0.00
Mon 08/31 16Z 0.20 2807  69   8  11 0.00
Mon 08/31 17Z 0.25 2707  71   5  11 0.00
Mon 08/31 18Z 0.25 2605  69   2  11 0.00
Mon 08/31 19Z 0.38 2605  69   2  11 0.00
Mon 08/31 20Z 0.42 2505  67   7  12 0.00
Mon 08/31 21Z 0.32 2405  68  14  12 0.00
Mon 08/31 22Z 0.29 2207  73  18  12 0.00
Mon 08/31 23Z 0.29 2109  75  25  12 0.00
Tue 09/01 00Z 0.32 2210  77  34  12 0.00
Tue 09/01 01Z 0.33 2211  82  41  12 0.00
Tue 09/01 02Z 0.35 2211  87  66  12 0.00
Tue 09/01 03Z 0.30 2111  93  85  12 0.01
Tue 09/01 04Z 0.18 2010  97  98  13 0.04
Tue 09/01 05Z 0.20 1913  98  99  13 0.07
Tue 09/01 06Z 0.36 2216 100  95  14 0.20
Tue 09/01 07Z 0.52 2517  99  99  13 0.15
Tue 09/01 08Z 0.52 2614  97  98  13 0.21
Tue 09/01 09Z 0.33 2115  98  97  14 0.30
Tue 09/01 10Z 0.61 2320  99  89  15 0.30
Tue 09/01 11Z 0.48 2512  99  94  15 0.24
Tue 09/01 12Z 0.23 2507  99  91  15 0.23
Tue 09/01 13Z 0.18 2507  99  81  15 0.08
Tue 09/01 14Z 0.18 2606  99  67  15 0.04
Tue 09/01 15Z 0.17 2706  99  58  15 0.02
Tue 09/01 16Z 0.15 2705  99  52  15 0.03
Tue 09/01 17Z 0.11 2101  99  48  15 0.05

Run total areal avg QPF for the Central_Greens is: 2.43 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