NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260808_0600
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sat 08/08 06Z 0.17 2108  85  88  16 0.00
Sat 08/08 07Z 0.20 2208  86  88  16 0.05
Sat 08/08 08Z 0.20 2506  89  88  15 0.12
Sat 08/08 09Z 0.19 2605  91  87  15 0.04
Sat 08/08 10Z 0.13 2704  91  87  15 0.02
Sat 08/08 11Z 0.08 2802  93  92  15 0.00
Sat 08/08 12Z 0.08 2502  94  92  15 0.00
Sat 08/08 13Z 0.10 2403  96  90  15 0.00
Sat 08/08 14Z 0.15 2305  97  90  15 0.00
Sat 08/08 15Z 0.11 2105  95  85  15 0.00
Sat 08/08 16Z 0.10 2006  95  80  15 0.00
Sat 08/08 17Z 0.20 2109  95  77  15 0.00
Sat 08/08 18Z 0.30 2210  94  72  15 0.00
Sat 08/08 19Z 0.37 2211  91  68  16 0.01
Sat 08/08 20Z 0.45 2311  89  60  16 0.00
Sat 08/08 21Z 0.63 2412  91  55  16 0.00
Sat 08/08 22Z 0.55 2513  93  57  16 0.01
Sat 08/08 23Z 0.45 2412  90  55  16 0.06
Sun 08/09 00Z 0.42 2512  90  64  16 0.01
Sun 08/09 01Z 0.44 2513  91  70  16 0.01
Sun 08/09 02Z 0.52 2515  89  73  16 0.01
Sun 08/09 03Z 0.59 2617  90  64  16 0.02
Sun 08/09 04Z 0.63 2618  92  53  15 0.02
Sun 08/09 05Z 0.58 2718  90  48  16 0.01
Sun 08/09 06Z 0.59 2719  91  44  15 0.00
Sun 08/09 07Z 0.57 2819  90  47  15 0.00
Sun 08/09 08Z 0.55 2818  90  55  15 0.00
Sun 08/09 09Z 0.51 2817  91  42  15 0.01
Sun 08/09 10Z 0.45 2815  89  22  15 0.01
Sun 08/09 11Z 0.40 2814  85  17  15 0.01
Sun 08/09 12Z 0.40 2714  85  20  15 0.01
Sun 08/09 13Z 0.43 2715  85  25  15 0.01
Sun 08/09 14Z 0.49 2815  87  30  14 0.01
Sun 08/09 15Z 0.50 2814  85  16  14 0.01
Sun 08/09 16Z 0.63 2714  85  12  14 0.00
Sun 08/09 17Z 0.77 2714  84  15  14 0.00
Sun 08/09 18Z 1.13 2815  84  19  14 0.02
Sun 08/09 19Z 1.20 2915  81  18  14 0.01
Sun 08/09 20Z 0.91 2914  74  25  14 0.01
Sun 08/09 21Z 0.51 2911  68  32  14 0.00
Sun 08/09 22Z 0.50 2911  68  35  15 0.00
Sun 08/09 23Z 0.39 2910  67  34  15 0.00
Mon 08/10 00Z 0.37 2810  65  35  15 0.00
Mon 08/10 01Z 0.41 2811  66  33  15 0.00
Mon 08/10 02Z 0.38 2811  66  35  15 0.00
Mon 08/10 03Z 0.42 2913  72  42  14 0.00
Mon 08/10 04Z 0.34 2911  71  37  15 0.00
Mon 08/10 05Z 0.29 2911  65  28  15 0.00
Mon 08/10 06Z 0.24 2909  63  20  15 0.00
Mon 08/10 07Z 0.18 2806  59  25  15 0.00
Mon 08/10 08Z 0.15 2605  54  31  16 0.00
Mon 08/10 09Z 0.12 2305  50  30  16 0.00
Mon 08/10 10Z 0.15 2208  48  32  16 0.00
Mon 08/10 11Z 0.19 2209  46  33  16 0.00
Mon 08/10 12Z 0.22 2211  43  33  16 0.00
Mon 08/10 13Z 0.24 2211  40  38  16 0.00
Mon 08/10 14Z 0.28 2312  42  46  15 0.00
Mon 08/10 15Z 0.31 2312  47  64  15 0.00
Mon 08/10 16Z 0.38 2312  55  64  15 0.00
Mon 08/10 17Z 0.46 2212  65  63  15 0.00

Run total areal avg QPF for the greens is: 0.50 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