NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260731_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)
=== ===== === ==== ==== === === === ====
Fri 07/31 12Z 0.02 3508  93  89  11 0.00
Fri 07/31 13Z 0.03 3407  88  84  12 0.00
Fri 07/31 14Z 0.02 3406  86  73  12 0.00
Fri 07/31 15Z 0.11 3206  89  76  12 0.00
Fri 07/31 16Z 0.23 3107  89  80  12 0.00
Fri 07/31 17Z 0.18 3206  86  81  12 0.00
Fri 07/31 18Z 0.20 3206  83  80  13 0.00
Fri 07/31 19Z 0.32 3205  81  75  13 0.00
Fri 07/31 20Z 0.70 3105  80  72  13 0.00
Fri 07/31 21Z 0.45 3105  78  67  13 0.00
Fri 07/31 22Z 0.36 3107  79  65  13 0.00
Fri 07/31 23Z 0.27 3007  83  65  13 0.00
Sat 08/01 00Z 0.14 3206  83  64  13 0.00
Sat 08/01 01Z 0.13 3206  81  63  13 0.00
Sat 08/01 02Z 0.05 3304  77  59  14 0.00
Sat 08/01 03Z 0.09 3104  77  59  14 0.00
Sat 08/01 04Z 0.13 3004  78  57  14 0.00
Sat 08/01 05Z 0.11 2903  78  49  14 0.00
Sat 08/01 06Z 0.10 3003  78  43  14 0.00
Sat 08/01 07Z 0.09 3104  77  39  14 0.00
Sat 08/01 08Z 0.11 3004  77  38  13 0.00
Sat 08/01 09Z 0.14 3004  78  37  13 0.00
Sat 08/01 10Z 0.11 3004  76  37  13 0.00
Sat 08/01 11Z 0.11 3004  75  37  13 0.00
Sat 08/01 12Z 0.13 2903  75  37  13 0.00
Sat 08/01 13Z 0.14 2703  75  38  13 0.00
Sat 08/01 14Z 0.17 2503  77  38  13 0.00
Sat 08/01 15Z 0.42 2303  79  35  13 0.00
Sat 08/01 16Z 0.76 2203  79  32  13 0.00
Sat 08/01 17Z 1.29 2205  79  31  14 0.00
Sat 08/01 18Z 1.64 2205  79  32  14 0.00
Sat 08/01 19Z 1.23 2105  78  34  14 0.00
Sat 08/01 20Z 0.95 2005  75  31  14 0.00
Sat 08/01 21Z 0.61 1906  71  24  15 0.00
Sat 08/01 22Z 0.32 2008  67  15  15 0.00
Sat 08/01 23Z 0.34 2009  65  12  15 0.00
Sun 08/02 00Z 0.34 2011  66  15  15 0.00
Sun 08/02 01Z 0.51 2013  75  19  15 0.00
Sun 08/02 02Z 0.70 2115  83  24  14 0.00
Sun 08/02 03Z 0.67 2117  86  32  14 0.00
Sun 08/02 04Z 0.60 2120  86  48  15 0.00
Sun 08/02 05Z 0.69 2222  92  46  14 0.00
Sun 08/02 06Z 0.66 2221  92  40  14 0.00
Sun 08/02 07Z 0.71 2322  93  40  14 0.00
Sun 08/02 08Z 0.67 2421  90  41  14 0.01
Sun 08/02 09Z 0.56 2319  87  52  15 0.02
Sun 08/02 10Z 0.59 2321  92  60  14 0.02
Sun 08/02 11Z 0.63 2321  91  65  14 0.02
Sun 08/02 12Z 0.64 2321  92  68  14 0.01
Sun 08/02 13Z 0.61 2220  95  66  14 0.01
Sun 08/02 14Z 0.60 2218  92  39  14 0.01
Sun 08/02 15Z 0.74 2117  94  44  14 0.00
Sun 08/02 16Z 0.67 2116  93  44  14 0.01
Sun 08/02 17Z 0.92 2017  91  46  14 0.00
Sun 08/02 18Z 1.38 2018  89  31  14 0.02
Sun 08/02 19Z 0.91 1919  87  30  15 0.00
Sun 08/02 20Z 1.14 1921  88  53  15 0.00
Sun 08/02 21Z 1.48 2021  85  69  14 0.00
Sun 08/02 22Z 1.11 2023  79  90  14 0.00
Sun 08/02 23Z 0.74 2024  68  96  15 0.00

Run total areal avg QPF for the Central_Greens is: 0.13 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