NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260807_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)
=== ===== === ==== ==== === === === ====
Fri 08/07 06Z 0.19 2906  89  75  17 0.00
Fri 08/07 07Z 0.25 2908  88  73  16 0.00
Fri 08/07 08Z 0.24 2908  88  69  16 0.00
Fri 08/07 09Z 0.23 2908  86  62  16 0.00
Fri 08/07 10Z 0.21 3008  84  53  16 0.00
Fri 08/07 11Z 0.18 3108  81  57  16 0.00
Fri 08/07 12Z 0.16 3208  84  61  16 0.00
Fri 08/07 13Z 0.13 3307  85  57  16 0.00
Fri 08/07 14Z 0.09 3406  86  55  15 0.00
Fri 08/07 15Z 0.06 3404  88  51  15 0.00
Fri 08/07 16Z 0.06 3502  88  46  16 0.00
Fri 08/07 17Z 0.08 3201  87  48  16 0.02
Fri 08/07 18Z 0.11 2601  86  48  16 0.03
Fri 08/07 19Z 0.19 2702  86  50  16 0.02
Fri 08/07 20Z 0.15 2701  85  51  17 0.01
Fri 08/07 21Z 0.16 2702  84  55  17 0.00
Fri 08/07 22Z 0.12 2602  83  54  17 0.00
Fri 08/07 23Z 0.06 2401  81  55  17 0.00
Sat 08/08 00Z 0.04 2201  79  56  17 0.00
Sat 08/08 01Z 0.03 2001  79  57  17 0.00
Sat 08/08 02Z 0.03 1902  79  60  17 0.00
Sat 08/08 03Z 0.03 1902  79  61  17 0.00
Sat 08/08 04Z 0.05 1903  80  66  16 0.00
Sat 08/08 05Z 0.05 1803  80  68  16 0.00
Sat 08/08 06Z 0.07 1704  81  69  16 0.00
Sat 08/08 07Z 0.06 1605  83  73  16 0.00
Sat 08/08 08Z 0.08 1606  82  77  16 0.00
Sat 08/08 09Z 0.09 1706  82  84  16 0.00
Sat 08/08 10Z 0.04 1706  83  85  16 0.00
Sat 08/08 11Z 0.06 1907  83  84  16 0.00
Sat 08/08 12Z 0.15 2008  86  85  16 0.00
Sat 08/08 13Z 0.19 2109  89  80  16 0.00
Sat 08/08 14Z 0.27 2111  93  82  16 0.00
Sat 08/08 15Z 0.29 2211  93  79  16 0.00
Sat 08/08 16Z 0.43 2313  90  61  16 0.03
Sat 08/08 17Z 0.47 2413  84  58  16 0.03
Sat 08/08 18Z 0.58 2414  88  63  16 0.01
Sat 08/08 19Z 0.70 2415  92  53  16 0.02
Sat 08/08 20Z 0.81 2518  91  53  16 0.10
Sat 08/08 21Z 0.85 2617  90  53  16 0.07
Sat 08/08 22Z 0.83 2616  91  59  16 0.03
Sat 08/08 23Z 0.77 2615  89  55  16 0.00
Sun 08/09 00Z 0.68 2614  89  57  16 0.00
Sun 08/09 01Z 0.59 2614  87  64  16 0.00
Sun 08/09 02Z 0.53 2613  85  69  16 0.00
Sun 08/09 03Z 0.48 2613  87  76  16 0.02
Sun 08/09 04Z 0.44 2713  86  73  16 0.08
Sun 08/09 05Z 0.44 2713  91  81  16 0.00
Sun 08/09 06Z 0.42 2713  90  68  16 0.00
Sun 08/09 07Z 0.43 2714  89  51  16 0.00
Sun 08/09 08Z 0.38 2714  86  34  16 0.00
Sun 08/09 09Z 0.38 2714  82  42  16 0.00
Sun 08/09 10Z 0.41 2715  85  47  16 0.00
Sun 08/09 11Z 0.43 2715  87  43  16 0.01
Sun 08/09 12Z 0.47 2716  91  40  15 0.01
Sun 08/09 13Z 0.50 2716  94  50  15 0.01
Sun 08/09 14Z 0.51 2715  96  52  15 0.01
Sun 08/09 15Z 0.57 2715  96  44  14 0.01
Sun 08/09 16Z 0.67 2715  97  38  14 0.01
Sun 08/09 17Z 0.69 2716  95  31  14 0.04

Run total areal avg QPF for the greens is: 0.57 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