NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260301_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 03/01 06Z 0.26 2911  59  87  -5 0.00
Sun 03/01 07Z 0.30 2913  67  82  -6 0.00
Sun 03/01 08Z 0.30 2913  74  90  -7 0.00
Sun 03/01 09Z 0.23 2912  76  81  -7 0.00
Sun 03/01 11Z 0.19 3115  86  93  -9 0.00
Sun 03/01 12Z 0.21 3118  89  89 -11 0.01
Sun 03/01 13Z 0.23 3220  87  86 -12 0.01
Sun 03/01 14Z 0.27 3123  81  77 -13 0.01
Sun 03/01 15Z 0.29 3123  62  62 -13 0.00
Sun 03/01 16Z 0.29 3123  53  46 -13 0.00
Sun 03/01 17Z 0.33 3122  57  36 -14 0.00
Sun 03/01 18Z 0.37 3120  61  28 -15 0.00
Sun 03/01 19Z 0.46 3120  67  31 -16 0.00
Sun 03/01 20Z 0.53 3119  71  34 -17 0.00
Sun 03/01 21Z 0.65 3020  76  39 -18 0.00
Sun 03/01 22Z 0.57 3021  74  38 -18 0.00
Sun 03/01 23Z 0.51 3122  70  31 -19 0.00
Mon 03/02 00Z 0.48 3122  69  22 -19 0.00
Mon 03/02 01Z 0.39 3122  64  16 -19 0.00
Mon 03/02 02Z 0.31 3122  56  13 -19 0.00
Mon 03/02 03Z 0.26 3222  51  11 -19 0.00
Mon 03/02 04Z 0.23 3221  47  11 -19 0.00
Mon 03/02 05Z 0.21 3220  45   9 -19 0.00
Mon 03/02 06Z 0.20 3219  44   7 -19 0.00
Mon 03/02 07Z 0.20 3219  43   5 -19 0.00
Mon 03/02 08Z 0.22 3118  43   5 -19 0.00
Mon 03/02 09Z 0.22 3117  43   7 -19 0.00
Mon 03/02 10Z 0.24 3116  41  10 -19 0.00
Mon 03/02 11Z 0.25 3016  39  12 -19 0.00
Mon 03/02 12Z 0.28 3017  38  17 -19 0.00
Mon 03/02 13Z 0.30 3017  39  20 -19 0.00
Mon 03/02 14Z 0.32 2916  43  18 -19 0.00
Mon 03/02 15Z 0.35 2815  45  20 -19 0.00
Mon 03/02 16Z 0.39 2815  41  15 -19 0.00
Mon 03/02 17Z 0.40 2815  38  11 -18 0.00
Mon 03/02 18Z 0.39 2914  41  16 -17 0.00
Mon 03/02 19Z 0.41 2814  47  19 -17 0.00
Mon 03/02 20Z 0.39 2813  51  12 -16 0.00
Mon 03/02 21Z 0.35 2812  52   9 -15 0.00
Mon 03/02 22Z 0.34 2712  51  16 -14 0.00
Mon 03/02 23Z 0.36 2613  50  25 -14 0.00
Tue 03/03 00Z 0.39 2515  44  38 -13 0.00
Tue 03/03 01Z 0.39 2417  35  58 -11 0.00
Tue 03/03 02Z 0.42 2419  28  56 -10 0.00
Tue 03/03 03Z 0.49 2423  23  55  -9 0.00
Tue 03/03 04Z 0.51 2425  23  67  -9 0.00
Tue 03/03 05Z 0.51 2425  28  60  -8 0.00
Tue 03/03 06Z 0.51 2426  29  64  -7 0.00
Tue 03/03 07Z 0.51 2526  28  57  -6 0.00
Tue 03/03 08Z 0.50 2526  29  54  -5 0.00
Tue 03/03 09Z 0.50 2426  28  53  -5 0.00
Tue 03/03 10Z 0.49 2425  26  43  -4 0.00
Tue 03/03 11Z 0.47 2424  27  35  -4 0.00
Tue 03/03 12Z 0.46 2425  32  32  -4 0.00
Tue 03/03 13Z 0.46 2426  40  27  -3 0.00
Tue 03/03 14Z 0.45 2326  45  23  -3 0.00
Tue 03/03 15Z 0.43 2326  53  19  -2 0.00
Tue 03/03 16Z 0.43 2326  63  16  -2 0.00
Tue 03/03 17Z 0.46 2326  79  15  -2 0.00

Run total areal avg QPF for the Central_Greens is: 0.03 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