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_1200
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 12Z 0.38 3220  84   9  10 0.00
Sat 06/13 13Z 0.33 3219  84  12  11 0.00
Sat 06/13 14Z 0.31 3215  80  13  11 0.00
Sat 06/13 15Z 0.52 3112  79  13  11 0.00
Sat 06/13 16Z 1.30 3010  80  14  12 0.00
Sat 06/13 17Z 2.72 2911  84  15  12 0.00
Sat 06/13 18Z 3.45 2811  88  15  12 0.00
Sat 06/13 19Z 2.86 2712  87  15  12 0.01
Sat 06/13 20Z 2.52 2711  80  15  12 0.01
Sat 06/13 21Z 2.48 2712  79  15  12 0.00
Sat 06/13 22Z 1.76 2612  77  14  12 0.00
Sat 06/13 23Z 1.31 2515  76  20  12 0.00
Sun 06/14 00Z 1.42 2618  76  42  13 0.00
Sun 06/14 01Z 0.73 2717  68  41  13 0.00
Sun 06/14 02Z 0.77 2718  66  43  13 0.00
Sun 06/14 03Z 0.76 2618  71  44  13 0.00
Sun 06/14 04Z 0.63 2618  69  43  13 0.00
Sun 06/14 05Z 0.70 2520  68  42  13 0.00
Sun 06/14 06Z 0.76 2522  67  37  13 0.00
Sun 06/14 07Z 0.77 2423  57  35  14 0.00
Sun 06/14 08Z 0.86 2426  54  34  14 0.00
Sun 06/14 09Z 0.93 2427  62  37  14 0.00
Sun 06/14 10Z 0.96 2427  68  34  14 0.00
Sun 06/14 11Z 0.93 2426  70  21  14 0.00
Sun 06/14 12Z 0.91 2425  74  23  13 0.01
Sun 06/14 13Z 0.96 2422  77  29  13 0.00
Sun 06/14 14Z 1.11 2319  76  33  13 0.00
Sun 06/14 15Z 2.88 2320  79  36  13 0.00
Sun 06/14 16Z 4.72 2219  82  27  13 0.00
Sun 06/14 17Z 3.46 2218  80  30  14 0.00
Sun 06/14 18Z 4.29 2117  80  44  14 0.00
Sun 06/14 19Z 4.23 2118  78  48  14 0.00
Sun 06/14 20Z 1.81 2119  74  64  15 0.02
Sun 06/14 21Z 1.18 2123  77  82  15 0.03
Sun 06/14 22Z 0.80 2224  86  81  14 0.04
Sun 06/14 23Z 0.91 2326  91  87  14 0.03
Mon 06/15 00Z 0.70 2323  93  76  13 0.12
Mon 06/15 01Z 0.70 2324  91  81  13 0.01
Mon 06/15 02Z 0.61 2320  95  93  13 0.02
Mon 06/15 03Z 0.62 2419  99  95  12 0.08
Mon 06/15 04Z 0.55 2416  98  92  12 0.07
Mon 06/15 05Z 0.42 2813  99  98  11 0.13
Mon 06/15 06Z 0.43 2921  94  97  10 0.25
Mon 06/15 07Z 0.39 2917  89  98  10 0.05
Mon 06/15 08Z 0.50 2818  88  93   8 0.01
Mon 06/15 09Z 0.46 2817  87  76   8 0.01
Mon 06/15 10Z 0.42 2817  83  48   7 0.01
Mon 06/15 11Z 0.41 2918  78  12   7 0.00
Mon 06/15 12Z 0.39 2917  71   2   7 0.00
Mon 06/15 13Z 0.36 2917  76   2   7 0.00
Mon 06/15 14Z 0.32 3016  77   1   7 0.00
Mon 06/15 15Z 0.33 3016  79   3   6 0.00
Mon 06/15 16Z 0.41 3014  81   4   5 0.00
Mon 06/15 17Z 2.15 3014  84   6   4 0.00
Mon 06/15 18Z 5.09 3014  87  12   4 0.00
Mon 06/15 19Z 4.10 3013  87  15   5 0.00
Mon 06/15 20Z 3.06 3014  88  21   5 0.00
Mon 06/15 21Z 2.67 2914  89  20   5 0.00
Mon 06/15 22Z 1.41 3015  87   9   5 0.00
Mon 06/15 23Z 0.85 3016  85   4   5 0.00

Run total areal avg QPF for the Central_Greens is: 0.91 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