NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260719_0600
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)
=== ===== === ==== ==== === === === ====
Sun 07/19 06Z 0.64 3124  97  75  11 0.00
Sun 07/19 07Z 0.52 3124  95  57  10 0.00
Sun 07/19 08Z 0.54 3128  96  34   9 0.02
Sun 07/19 09Z 0.58 3233  96  20   8 0.02
Sun 07/19 10Z 0.55 3233  94  10   7 0.01
Sun 07/19 11Z 0.52 3232  93   8   7 0.01
Sun 07/19 12Z 0.48 3230  93   9   7 0.01
Sun 07/19 13Z 0.47 3227  94   9   7 0.01
Sun 07/19 14Z 0.41 3225  93   7   7 0.01
Sun 07/19 15Z 0.39 3223  90   6   7 0.01
Sun 07/19 16Z 0.55 3221  88   5   7 0.00
Sun 07/19 17Z 2.27 3120  85   5   7 0.00
Sun 07/19 18Z 7.69 3120  77   6   7 0.00
Sun 07/19 19Z 8.42 3119  73   5   8 0.00
Sun 07/19 20Z 9.11 3019  72   5   8 0.00
Sun 07/19 21Z 9.23 3019  72   6   8 0.00
Sun 07/19 22Z 7.83 3019  71   7   8 0.00
Sun 07/19 23Z 3.39 3021  72   7   8 0.00
Mon 07/20 00Z 1.83 3023  68   8   8 0.00
Mon 07/20 01Z 1.93 3124  69  11   8 0.00
Mon 07/20 02Z 1.76 3024  75  14   7 0.00
Mon 07/20 03Z 1.01 3024  84  13   7 0.00
Mon 07/20 04Z 0.81 3124  88  12   7 0.00
Mon 07/20 05Z 0.77 3123  88  12   6 0.00
Mon 07/20 06Z 0.62 3224  83  14   6 0.00
Mon 07/20 07Z 0.51 3224  79  21   7 0.00
Mon 07/20 08Z 0.48 3223  78  25   7 0.00
Mon 07/20 09Z 0.44 3222  77  27   7 0.00
Mon 07/20 10Z 0.45 3221  74  29   7 0.00
Mon 07/20 11Z 0.39 3220  71  33   7 0.00
Mon 07/20 12Z 0.40 3218  70  42   8 0.00
Mon 07/20 13Z 0.42 3116  69  44   8 0.00
Mon 07/20 14Z 0.45 3113  68  44   8 0.00
Mon 07/20 15Z 0.88 3011  69  37   8 0.00
Mon 07/20 16Z 1.40 3010  68  37   9 0.00
Mon 07/20 17Z 1.76 2908  69  36   9 0.00
Mon 07/20 18Z 2.55 2806  72  41  10 0.00
Mon 07/20 19Z 2.99 2505  73  41  10 0.00
Mon 07/20 20Z 3.07 2306  73  44  10 0.00
Mon 07/20 21Z 2.78 2308  75  51  11 0.00
Mon 07/20 22Z 1.55 2209  77  50  11 0.00
Mon 07/20 23Z 0.86 2211  78  51  11 0.00
Tue 07/21 00Z 0.67 2214  74  44  11 0.00
Tue 07/21 01Z 0.64 2115  69  41  11 0.00
Tue 07/21 02Z 0.61 2117  67  33  11 0.00
Tue 07/21 03Z 0.54 2119  64  25  12 0.00
Tue 07/21 04Z 0.65 2121  70  20  11 0.00
Tue 07/21 05Z 0.64 2121  73  18  12 0.00
Tue 07/21 06Z 0.81 2223  73  12  11 0.00
Tue 07/21 07Z 0.76 2223  70  14  11 0.00
Tue 07/21 08Z 0.72 2223  69  24  11 0.00
Tue 07/21 09Z 0.61 2222  67  24  11 0.00
Tue 07/21 10Z 0.54 2122  69  22  11 0.00
Tue 07/21 11Z 0.52 2122  82  20  12 0.00
Tue 07/21 12Z 0.48 2122  87  14  12 0.00
Tue 07/21 13Z 0.41 2023  90  13  12 0.00
Tue 07/21 14Z 0.34 1924  94  15  12 0.00
Tue 07/21 15Z 0.28 1825  96  29  12 0.00
Tue 07/21 16Z 0.29 1827  97  39  13 0.01
Tue 07/21 17Z 0.31 1828  97  35  13 0.01

Run total areal avg QPF for the Central_Greens is: 0.12 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