NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260731_1200
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 07/31 12Z 0.04 3507  91  88  11 0.00
Fri 07/31 13Z 0.06 3406  87  84  12 0.00
Fri 07/31 14Z 0.04 3505  86  76  12 0.00
Fri 07/31 15Z 0.12 3305  88  78  12 0.00
Fri 07/31 16Z 0.22 3106  88  80  12 0.00
Fri 07/31 17Z 0.18 3205  86  80  12 0.00
Fri 07/31 18Z 0.21 3205  83  78  13 0.00
Fri 07/31 19Z 0.33 3204  82  74  13 0.00
Fri 07/31 20Z 0.64 3104  81  72  13 0.00
Fri 07/31 21Z 0.44 3105  80  67  13 0.00
Fri 07/31 22Z 0.37 3107  80  65  13 0.00
Fri 07/31 23Z 0.26 3107  82  63  13 0.00
Sat 08/01 00Z 0.14 3205  80  62  14 0.00
Sat 08/01 01Z 0.12 3205  78  61  14 0.00
Sat 08/01 02Z 0.06 3303  75  58  14 0.00
Sat 08/01 03Z 0.10 3103  74  57  14 0.00
Sat 08/01 04Z 0.12 3003  75  55  14 0.00
Sat 08/01 05Z 0.12 3003  75  51  14 0.00
Sat 08/01 06Z 0.11 3003  74  47  14 0.00
Sat 08/01 07Z 0.12 3104  74  44  14 0.00
Sat 08/01 08Z 0.13 3004  75  44  13 0.00
Sat 08/01 09Z 0.17 3005  76  44  13 0.00
Sat 08/01 10Z 0.13 3104  75  44  13 0.00
Sat 08/01 11Z 0.14 3004  75  45  13 0.00
Sat 08/01 12Z 0.14 2903  74  47  13 0.00
Sat 08/01 13Z 0.14 2703  75  44  13 0.00
Sat 08/01 14Z 0.15 2402  77  39  13 0.00
Sat 08/01 15Z 0.31 2303  79  37  13 0.00
Sat 08/01 16Z 0.55 2203  80  33  13 0.00
Sat 08/01 17Z 0.96 2204  80  32  14 0.00
Sat 08/01 18Z 1.17 2204  79  30  14 0.00
Sat 08/01 19Z 0.82 2104  78  28  14 0.00
Sat 08/01 20Z 0.56 2005  76  26  14 0.00
Sat 08/01 21Z 0.36 2005  74  27  15 0.00
Sat 08/01 22Z 0.20 2007  71  26  15 0.00
Sat 08/01 23Z 0.21 2008  70  25  15 0.00
Sun 08/02 00Z 0.20 1909  70  26  15 0.00
Sun 08/02 01Z 0.32 2012  74  29  15 0.00
Sun 08/02 02Z 0.49 2115  78  28  14 0.00
Sun 08/02 03Z 0.50 2117  81  29  14 0.00
Sun 08/02 04Z 0.51 2120  85  41  14 0.00
Sun 08/02 05Z 0.60 2222  91  46  14 0.00
Sun 08/02 06Z 0.56 2221  91  45  14 0.00
Sun 08/02 07Z 0.63 2322  92  47  14 0.00
Sun 08/02 08Z 0.60 2321  90  48  14 0.00
Sun 08/02 09Z 0.49 2318  87  50  15 0.01
Sun 08/02 10Z 0.49 2319  90  56  14 0.01
Sun 08/02 11Z 0.54 2320  90  65  14 0.01
Sun 08/02 12Z 0.55 2320  92  65  14 0.01
Sun 08/02 13Z 0.53 2219  95  66  14 0.01
Sun 08/02 14Z 0.52 2217  93  52  13 0.00
Sun 08/02 15Z 0.54 2216  93  55  14 0.00
Sun 08/02 16Z 0.48 2115  93  55  14 0.00
Sun 08/02 17Z 0.59 2016  91  56  14 0.00
Sun 08/02 18Z 0.95 2018  89  47  14 0.02
Sun 08/02 19Z 0.58 1918  86  36  15 0.00
Sun 08/02 20Z 0.63 1919  87  59  15 0.00
Sun 08/02 21Z 0.80 1921  87  75  15 0.00
Sun 08/02 22Z 0.76 2024  83  89  14 0.08
Sun 08/02 23Z 0.60 2025  74  95  15 0.02

Run total areal avg QPF for the greens is: 0.17 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