NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260907_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)
=== ===== === ==== ==== === === === ====
Mon 09/07 12Z 0.07 3420  84  14   8 0.00
Mon 09/07 13Z 0.09 3422  82  13   8 0.00
Mon 09/07 14Z 0.07 3425  77  10   8 0.00
Mon 09/07 15Z 0.05 3425  71   8   9 0.00
Mon 09/07 16Z 0.05 3422  66   7   9 0.00
Mon 09/07 17Z 0.10 3419  65   5   9 0.00
Mon 09/07 18Z 0.31 3319  66   4   9 0.00
Mon 09/07 19Z 0.74 3318  65   4   9 0.00
Mon 09/07 20Z 1.16 3317  64   5   9 0.00
Mon 09/07 21Z 1.26 3316  67   6  10 0.00
Mon 09/07 22Z 0.76 3216  70   8   9 0.00
Mon 09/07 23Z 0.84 3116  71  12   9 0.00
Tue 09/08 00Z 0.83 3116  71  21   9 0.00
Tue 09/08 01Z 0.94 3217  74  24   9 0.00
Tue 09/08 02Z 0.74 3218  77  30   9 0.00
Tue 09/08 03Z 0.37 3215  75  46   9 0.00
Tue 09/08 04Z 0.30 3213  73  59  10 0.00
Tue 09/08 05Z 0.31 3113  72  66  10 0.00
Tue 09/08 06Z 0.44 3116  75  72   9 0.00
Tue 09/08 07Z 0.44 3115  75  59   9 0.00
Tue 09/08 08Z 0.49 3014  74  58   9 0.00
Tue 09/08 09Z 0.49 3014  72  54  10 0.00
Tue 09/08 10Z 0.57 3016  73  55   9 0.00
Tue 09/08 11Z 0.56 3017  72  59   9 0.00
Tue 09/08 12Z 0.46 3117  74  66   9 0.00
Tue 09/08 13Z 0.38 3117  77  76  10 0.00
Tue 09/08 14Z 0.33 3114  80  85  10 0.00
Tue 09/08 15Z 0.35 3114  86  87  10 0.00
Tue 09/08 16Z 0.31 3115  92  77  10 0.01
Tue 09/08 17Z 0.19 3314  93  62  10 0.00
Tue 09/08 18Z 0.11 3312  93  54  10 0.00
Tue 09/08 19Z 0.11 3311  88  50  10 0.00
Tue 09/08 20Z 0.10 3310  85  78  10 0.00
Tue 09/08 21Z 0.08 3309  81  90  11 0.00
Tue 09/08 22Z 0.08 3308  76  91  11 0.00
Tue 09/08 23Z 0.07 3306  72  85  11 0.00
Wed 09/09 00Z 0.11 3105  71  80  11 0.00
Wed 09/09 01Z 0.12 3105  75  81  11 0.00
Wed 09/09 02Z 0.15 2904  80  81  10 0.00
Wed 09/09 03Z 0.20 2705  86  87  11 0.00
Wed 09/09 04Z 0.22 2506  90  86  11 0.00
Wed 09/09 05Z 0.23 2307  94  77  11 0.00
Wed 09/09 06Z 0.26 2209  95  67  11 0.00
Wed 09/09 07Z 0.24 2111  94  59  11 0.00
Wed 09/09 08Z 0.32 2213  94  57  11 0.00
Wed 09/09 09Z 0.36 2214  94  59  11 0.00
Wed 09/09 10Z 0.34 2115  90  55  12 0.00
Wed 09/09 11Z 0.40 2118  89  61  12 0.00
Wed 09/09 12Z 0.46 2119  88  57  12 0.00
Wed 09/09 13Z 0.48 2120  87  48  11 0.00
Wed 09/09 14Z 0.50 2219  87  51  11 0.00
Wed 09/09 15Z 0.52 2119  82  45  11 0.00
Wed 09/09 16Z 0.56 2119  86  26  11 0.00
Wed 09/09 17Z 0.57 2119  88   7  12 0.00
Wed 09/09 18Z 0.56 2119  90  17  12 0.00
Wed 09/09 19Z 0.55 2120  89  43  12 0.00
Wed 09/09 20Z 0.58 2124  93  64  13 0.01
Wed 09/09 21Z 0.68 2127  92  61  13 0.02
Wed 09/09 22Z 0.78 2229  92  49  14 0.00
Wed 09/09 23Z 0.82 2231  93  39  14 0.00

Run total areal avg QPF for the Central_Greens is: 0.04 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