NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260807_1800
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)
=== ===== === ==== ==== === === === ====
Fri 08/07 18Z 0.44 3004  88  41  16 0.00
Fri 08/07 19Z 0.26 3104  87  44  16 0.04
Fri 08/07 20Z 0.12 3303  86  44  16 0.03
Fri 08/07 21Z 0.09 0102  86  46  17 0.01
Fri 08/07 22Z 0.09 0600  87  47  17 0.02
Fri 08/07 23Z 0.08 2200  86  51  17 0.03
Sat 08/08 00Z 0.08 2301  86  50  17 0.03
Sat 08/08 01Z 0.03 1702  85  50  17 0.01
Sat 08/08 02Z 0.05 1704  85  51  17 0.00
Sat 08/08 03Z 0.04 1806  85  54  16 0.00
Sat 08/08 04Z 0.07 1805  86  60  16 0.00
Sat 08/08 05Z 0.10 2004  89  69  16 0.00
Sat 08/08 06Z 0.11 2203  91  76  16 0.00
Sat 08/08 07Z 0.08 2203  92  82  16 0.03
Sat 08/08 08Z 0.09 2302  92  84  16 0.07
Sat 08/08 09Z 0.09 2202  92  83  16 0.03
Sat 08/08 10Z 0.11 2303  91  80  16 0.02
Sat 08/08 11Z 0.11 2403  91  79  16 0.01
Sat 08/08 12Z 0.09 2203  90  80  16 0.02
Sat 08/08 13Z 0.10 2304  91  82  16 0.01
Sat 08/08 14Z 0.14 2404  91  81  16 0.01
Sat 08/08 15Z 0.10 2303  89  74  16 0.00
Sat 08/08 16Z 0.16 2305  89  72  16 0.00
Sat 08/08 17Z 0.26 2407  88  72  16 0.01
Sat 08/08 18Z 0.39 2509  87  70  16 0.01
Sat 08/08 19Z 0.48 2510  87  64  16 0.00
Sat 08/08 20Z 0.57 2612  88  65  16 0.01
Sat 08/08 21Z 0.56 2613  91  61  16 0.02
Sat 08/08 22Z 0.49 2612  91  61  16 0.06
Sat 08/08 23Z 0.50 2713  89  47  16 0.08
Sun 08/09 00Z 0.52 2714  91  41  16 0.01
Sun 08/09 01Z 0.46 2712  92  41  16 0.01
Sun 08/09 02Z 0.38 2812  90  43  16 0.04
Sun 08/09 03Z 0.36 2811  87  43  16 0.01
Sun 08/09 04Z 0.34 2812  80  36  17 0.01
Sun 08/09 05Z 0.32 2812  73  31  17 0.00
Sun 08/09 06Z 0.31 2811  67  36  17 0.00
Sun 08/09 07Z 0.34 2711  69  44  17 0.00
Sun 08/09 08Z 0.35 2711  75  45  16 0.00
Sun 08/09 09Z 0.37 2612  84  45  16 0.00
Sun 08/09 10Z 0.37 2512  89  42  16 0.00
Sun 08/09 11Z 0.37 2513  92  36  16 0.00
Sun 08/09 12Z 0.37 2513  90  36  16 0.01
Sun 08/09 13Z 0.39 2513  89  34  16 0.00
Sun 08/09 14Z 0.41 2513  91  49  16 0.00
Sun 08/09 15Z 0.46 2513  93  62  15 0.00
Sun 08/09 16Z 0.52 2513  93  67  15 0.00
Sun 08/09 17Z 0.60 2512  94  67  15 0.00
Sun 08/09 18Z 0.58 2511  96  64  15 0.01
Sun 08/09 19Z 0.56 2613  94  64  16 0.21
Sun 08/09 20Z 0.53 2613  93  39  16 0.12
Sun 08/09 21Z 0.57 2715  90  20  16 0.08
Sun 08/09 22Z 0.55 2816  88  23  16 0.03
Sun 08/09 23Z 0.53 2917  81  25  16 0.02
Mon 08/10 00Z 0.47 3017  79  32  15 0.01
Mon 08/10 01Z 0.38 3017  72  35  15 0.01
Mon 08/10 02Z 0.34 3016  76  33  15 0.01
Mon 08/10 03Z 0.33 3116  75  26  15 0.01
Mon 08/10 04Z 0.31 3117  73  29  15 0.01
Mon 08/10 05Z 0.27 3217  69  38  15 0.01

Run total areal avg QPF for the greens is: 1.18 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