NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20250501_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)
=== ===== === ==== ==== === === === ====
Thu 05/01 12Z 0.13 2806  30   6   5 0.00
Thu 05/01 13Z 0.15 2806  31   4   5 0.00
Thu 05/01 14Z 0.14 2705  35   3   4 0.00
Thu 05/01 15Z 0.18 2504  39   2   4 0.00
Thu 05/01 16Z 0.56 2204  42   1   4 0.00
Thu 05/01 17Z 0.88 2105  39   2   4 0.00
Thu 05/01 18Z 1.07 2106  35   6   5 0.00
Thu 05/01 19Z 1.38 2107  32  21   6 0.00
Thu 05/01 20Z 1.12 2108  27  31   7 0.00
Thu 05/01 21Z 0.60 2008  24  42   7 0.00
Thu 05/01 22Z 0.22 1908  23  50   8 0.00
Thu 05/01 23Z 0.11 1809  27  70   9 0.00
Fri 05/02 00Z 0.15 1813  37  82   9 0.00
Fri 05/02 01Z 0.14 1815  44  82   9 0.00
Fri 05/02 02Z 0.18 1918  50  90  10 0.00
Fri 05/02 03Z 0.32 1923  62  98   9 0.00
Fri 05/02 04Z 0.33 2027  66  91  10 0.01
Fri 05/02 05Z 0.38 2032  67  89  11 0.00
Fri 05/02 06Z 0.39 2034  73  94  11 0.01
Fri 05/02 07Z 0.50 2137  81  87  10 0.03
Fri 05/02 08Z 0.36 2030  89  75  11 0.04
Fri 05/02 09Z 0.31 2029  96  65  11 0.01
Fri 05/02 10Z 0.31 2025  96  61  11 0.01
Fri 05/02 11Z 0.37 2126  98  87  11 0.01
Fri 05/02 12Z 0.43 2224  98  93  11 0.05
Fri 05/02 13Z 0.50 2324  99  94  10 0.05
Fri 05/02 14Z 0.52 2421  94  88   9 0.06
Fri 05/02 15Z 0.55 2420  94  57  10 0.00
Fri 05/02 16Z 0.67 2420  92  44  10 0.00
Fri 05/02 17Z 0.92 2419  91  54  10 0.00
Fri 05/02 18Z 1.67 2418  91  48   9 0.00
Fri 05/02 19Z 3.20 2417  90  55  10 0.00
Fri 05/02 20Z 3.51 2315  89  57  10 0.00
Fri 05/02 21Z 2.96 2217  91  73  10 0.01
Fri 05/02 22Z 1.06 2219  92  87  11 0.05
Fri 05/02 23Z 0.86 2421  89  67  11 0.21
Sat 05/03 00Z 0.93 2523  91  79  10 0.11
Sat 05/03 01Z 0.95 2524  91  62  10 0.02
Sat 05/03 02Z 0.85 2624  79  66  10 0.03
Sat 05/03 03Z 0.85 2624  77  76  10 0.00
Sat 05/03 04Z 0.86 2623  85  58   9 0.01
Sat 05/03 05Z 0.84 2522  88  30   9 0.00
Sat 05/03 06Z 0.82 2522  91  59   8 0.01
Sat 05/03 07Z 0.81 2622  92  72   8 0.01
Sat 05/03 08Z 0.79 2622  93  66   7 0.01
Sat 05/03 09Z 0.73 2621  93  29   7 0.01
Sat 05/03 10Z 0.63 2621  92  41   7 0.01
Sat 05/03 11Z 0.52 2620  86  32   7 0.01
Sat 05/03 12Z 0.45 2720  77  43   7 0.00
Sat 05/03 13Z 0.34 2716  62  51   8 0.00
Sat 05/03 14Z 0.30 2714  57  55   8 0.00
Sat 05/03 15Z 0.20 2709  52  74   9 0.00
Sat 05/03 16Z 0.21 2707  53  72   8 0.00
Sat 05/03 17Z 0.28 2505  55  72   7 0.00
Sat 05/03 18Z 0.26 2504  58  74   7 0.00
Sat 05/03 19Z 0.12 2403  66  95   6 0.00
Sat 05/03 20Z 0.05 2102  81  94   6 0.03
Sat 05/03 21Z 0.05 1603  87  94   7 0.02
Sat 05/03 22Z 0.02 3302  93  93   7 0.07
Sat 05/03 23Z 0.04 3303  95  99   7 0.09

Run total areal avg QPF for the Central_Greens is: 0.99 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