NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260909_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)
=== ===== === ==== ==== === === === ====
Wed 09/09 06Z 0.13 2205  89  15  11 0.00
Wed 09/09 07Z 0.19 2207  92  15  10 0.00
Wed 09/09 08Z 0.16 2008  93  37  10 0.00
Wed 09/09 09Z 0.20 2010  94  73  10 0.00
Wed 09/09 10Z 0.25 2013  94  70  11 0.00
Wed 09/09 11Z 0.28 2016  91  64  12 0.00
Wed 09/09 12Z 0.31 2020  90  63  12 0.00
Wed 09/09 13Z 0.39 2024  91  51  12 0.00
Wed 09/09 14Z 0.43 2124  93  47  12 0.00
Wed 09/09 15Z 0.47 2123  91  54  12 0.00
Wed 09/09 16Z 0.49 2123  86  43  13 0.00
Wed 09/09 17Z 0.51 2221  89  12  13 0.00
Wed 09/09 18Z 0.51 2121  93  30  12 0.00
Wed 09/09 19Z 0.52 2124  96  81  12 0.02
Wed 09/09 20Z 0.49 2024  96  97  13 0.04
Wed 09/09 21Z 0.48 2026  96  98  13 0.03
Wed 09/09 22Z 0.51 2029  99  98  14 0.17
Wed 09/09 23Z 0.78 2133  99  99  14 0.15
Thu 09/10 00Z 0.91 2234  99  98  14 0.15
Thu 09/10 01Z 1.02 2333  98  92  15 0.08
Thu 09/10 02Z 1.01 2435  97  94  15 0.07
Thu 09/10 03Z 1.00 2436  96  94  16 0.03
Thu 09/10 04Z 0.99 2338  97  91  16 0.03
Thu 09/10 05Z 1.09 2340  97  95  16 0.13
Thu 09/10 06Z 1.22 2443  97  95  15 0.24
Thu 09/10 07Z 1.17 2538  97  89  15 0.17
Thu 09/10 08Z 1.10 2534  98  89  15 0.20
Thu 09/10 09Z 0.97 2630  98  72  15 0.13
Thu 09/10 10Z 0.93 2627  97  35  14 0.07
Thu 09/10 11Z 0.97 2727  95  35  14 0.04
Thu 09/10 12Z 1.01 2827  93  42  12 0.02
Thu 09/10 13Z 1.07 2827  89  26  12 0.01
Thu 09/10 14Z 1.06 2727  83   9  12 0.00
Thu 09/10 15Z 1.54 2727  81   5  12 0.00
Thu 09/10 16Z 7.00 2725  77   5  11 0.00
Thu 09/10 17Z 15.60 2724  71   5  11 0.00
Thu 09/10 18Z 17.11 2725  63   7  11 0.00
Thu 09/10 19Z 17.76 2726  58   8  11 0.00
Thu 09/10 20Z 16.08 2725  57   5  11 0.00
Thu 09/10 21Z 11.58 2825  63   6  10 0.00
Thu 09/10 22Z 4.28 2925  76   9   9 0.00
Thu 09/10 23Z 1.52 2926  87   5   8 0.00
Fri 09/11 00Z 1.08 3026  94   6   7 0.01
Fri 09/11 01Z 0.79 3026  96  11   6 0.01
Fri 09/11 02Z 0.66 3025  96  12   6 0.01
Fri 09/11 03Z 0.66 3025  94  14   5 0.01
Fri 09/11 04Z 0.62 3124  92  15   4 0.00
Fri 09/11 05Z 0.61 3024  91  16   3 0.00
Fri 09/11 06Z 0.53 3024  90  15   3 0.00
Fri 09/11 07Z 0.40 3123  86  11   4 0.00
Fri 09/11 08Z 0.36 3123  81   6   4 0.00
Fri 09/11 09Z 0.31 3123  78   2   5 0.00
Fri 09/11 10Z 0.26 3123  73   1   5 0.00
Fri 09/11 11Z 0.25 3122  68   2   6 0.00
Fri 09/11 12Z 0.25 3122  66   3   6 0.00
Fri 09/11 13Z 0.24 3121  62   3   6 0.00
Fri 09/11 14Z 0.27 3120  59   2   5 0.00
Fri 09/11 15Z 0.30 3120  56   2   5 0.00
Fri 09/11 16Z 0.33 3120  53   1   5 0.00
Fri 09/11 17Z 0.35 3119  51   2   5 0.00

Run total areal avg QPF for the Central_Greens is: 1.82 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