NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260613_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)
=== ===== === ==== ==== === === === ====
Sat 06/13 06Z 0.78 2923  74  10  12 0.00
Sat 06/13 07Z 0.77 3028  74  10  12 0.00
Sat 06/13 08Z 0.57 3027  72  10  12 0.00
Sat 06/13 09Z 0.43 3126  70   9  12 0.00
Sat 06/13 10Z 0.40 3127  72   8  12 0.00
Sat 06/13 11Z 0.39 3228  71   9  11 0.00
Sat 06/13 12Z 0.35 3226  69  10  11 0.00
Sat 06/13 13Z 0.36 3222  71  12  11 0.00
Sat 06/13 14Z 0.38 3219  70  12  11 0.00
Sat 06/13 15Z 0.46 3115  71  12  11 0.00
Sat 06/13 16Z 1.22 3012  73  13  11 0.00
Sat 06/13 17Z 3.21 2911  77  13  11 0.00
Sat 06/13 18Z 4.46 2810  80  13  12 0.00
Sat 06/13 19Z 4.49 2710  82  14  12 0.00
Sat 06/13 20Z 3.42 2710  77  15  12 0.00
Sat 06/13 21Z 3.35 2612  77  12  12 0.00
Sat 06/13 22Z 3.14 2613  74  10  12 0.00
Sat 06/13 23Z 1.76 2615  75  13  12 0.00
Sun 06/14 00Z 0.93 2615  72  30  13 0.00
Sun 06/14 01Z 0.94 2618  70  39  13 0.00
Sun 06/14 02Z 1.03 2520  65  51  13 0.00
Sun 06/14 03Z 0.98 2521  61  52  13 0.00
Sun 06/14 04Z 0.84 2621  62  52  13 0.00
Sun 06/14 05Z 0.80 2523  74  57  13 0.00
Sun 06/14 06Z 0.79 2522  72  59  13 0.00
Sun 06/14 07Z 0.74 2522  67  42  14 0.00
Sun 06/14 08Z 0.77 2522  69  57  13 0.00
Sun 06/14 09Z 0.89 2524  75  61  13 0.00
Sun 06/14 10Z 1.02 2526  80  29  13 0.00
Sun 06/14 11Z 0.98 2525  82  25  12 0.01
Sun 06/14 12Z 0.83 2522  82  23  13 0.01
Sun 06/14 13Z 0.77 2419  81  22  13 0.01
Sun 06/14 14Z 0.89 2318  79  30  13 0.00
Sun 06/14 15Z 1.93 2216  78  29  13 0.00
Sun 06/14 16Z 3.89 2117  75  28  14 0.00
Sun 06/14 17Z 3.77 2118  71  33  14 0.00
Sun 06/14 18Z 4.57 2018  68  41  14 0.00
Sun 06/14 19Z 3.60 2020  68  46  15 0.00
Sun 06/14 20Z 6.15 2023  71  61  15 0.01
Sun 06/14 21Z 1.45 2124  74  42  15 0.02
Sun 06/14 22Z 1.53 2126  76  37  15 0.00
Sun 06/14 23Z 1.29 2026  79  54  15 0.00
Mon 06/15 00Z 1.06 2130  84  81  15 0.05
Mon 06/15 01Z 0.87 2030  83  66  15 0.03
Mon 06/15 02Z 0.94 2132  81  85  15 0.00
Mon 06/15 03Z 1.04 2132  84  90  14 0.00
Mon 06/15 04Z 1.11 2231  91  95  13 0.01
Mon 06/15 05Z 0.98 2230  95  97  13 0.04
Mon 06/15 06Z 0.70 2225  97  91  13 0.10
Mon 06/15 07Z 0.69 2320  99  97  12 0.20
Mon 06/15 08Z 0.58 2717  98  98  11 0.26
Mon 06/15 09Z 0.42 2816  97  91  11 0.05
Mon 06/15 10Z 0.55 2820  97  53   9 0.02
Mon 06/15 11Z 0.51 2819  92  30   8 0.01
Mon 06/15 12Z 0.41 2918  82   7   7 0.00
Mon 06/15 13Z 0.34 3017  81   2   7 0.00
Mon 06/15 14Z 0.30 3014  75   1   7 0.00
Mon 06/15 15Z 0.34 3014  75   1   7 0.00
Mon 06/15 16Z 0.67 2913  83   1   6 0.00
Mon 06/15 17Z 2.33 2913  88   8   6 0.00

Run total areal avg QPF for the Central_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