NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261011_0000
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 10/11 00Z 0.12 2805  53  50   5 0.00
Sun 10/11 01Z 0.12 2704  52  52   6 0.00
Sun 10/11 02Z 0.12 2704  48  51   7 0.00
Sun 10/11 03Z 0.11 2404  44  50   8 0.00
Sun 10/11 04Z 0.12 2206  41  48   9 0.00
Sun 10/11 05Z 0.17 2109  39  45   9 0.00
Sun 10/11 06Z 0.21 2111  36  45   9 0.00
Sun 10/11 07Z 0.21 2111  32  44   9 0.00
Sun 10/11 08Z 0.26 2214  29  46   9 0.00
Sun 10/11 09Z 0.28 2216  38  43  10 0.00
Sun 10/11 10Z 0.29 2217  43  39  10 0.00
Sun 10/11 11Z 0.29 2216  48  36  10 0.00
Sun 10/11 12Z 0.32 2218  50  33  10 0.00
Sun 10/11 13Z 0.32 2217  52  31  10 0.00
Sun 10/11 14Z 0.31 2217  50  33  10 0.00
Sun 10/11 15Z 0.31 2217  51  35  10 0.00
Sun 10/11 16Z 0.30 2216  50  40   9 0.00
Sun 10/11 17Z 0.30 2215  52  60   9 0.00
Sun 10/11 18Z 0.20 2113  49  83   9 0.00
Sun 10/11 19Z 0.16 2013  48  94   9 0.00
Sun 10/11 20Z 0.18 2016  50  98   9 0.00
Sun 10/11 21Z 0.20 2017  52  99   8 0.00
Sun 10/11 22Z 0.14 1818  53  96   7 0.00
Sun 10/11 23Z 0.12 1820  55  94   7 0.00
Mon 10/12 00Z 0.15 1821  70  90   7 0.01
Mon 10/12 01Z 0.17 1920  89  90   8 0.02
Mon 10/12 02Z 0.22 2019  96  90   8 0.04
Mon 10/12 03Z 0.27 2117  98  93   8 0.03
Mon 10/12 04Z 0.26 2313  98  92   8 0.02
Mon 10/12 05Z 0.20 2509  98  94   8 0.02
Mon 10/12 06Z 0.17 2808  98  96   8 0.02
Mon 10/12 07Z 0.13 3007  97  93   8 0.03
Mon 10/12 08Z 0.10 3108  97  92   8 0.03
Mon 10/12 09Z 0.09 3209  97  92   8 0.01
Mon 10/12 10Z 0.09 3311  97  84   8 0.00
Mon 10/12 11Z 0.07 3311  96  81   8 0.00
Mon 10/12 12Z 0.08 3311  96  62   8 0.00
Mon 10/12 13Z 0.08 3312  94  44   9 0.00
Mon 10/12 14Z 0.09 3313  91  27  10 0.00
Mon 10/12 15Z 0.11 3315  85  32  11 0.00
Mon 10/12 16Z 0.08 3315  75  26  11 0.00
Mon 10/12 17Z 0.15 3216  78  45  11 0.00
Mon 10/12 18Z 0.21 3218  82  68  10 0.00
Mon 10/12 19Z 0.23 3218  84  74  10 0.00
Mon 10/12 20Z 0.25 3119  87  76  10 0.00
Mon 10/12 21Z 0.28 3120  91  71  10 0.00
Mon 10/12 22Z 0.24 3220  95  75   9 0.00
Mon 10/12 23Z 0.20 3219  97  79   8 0.01
Tue 10/13 00Z 0.15 3317  97  71   7 0.01
Tue 10/13 01Z 0.09 3315  97  69   7 0.00
Tue 10/13 02Z 0.03 3412  96  71   7 0.00
Tue 10/13 03Z 0.03 3508  97  77   7 0.01
Tue 10/13 04Z 0.02 3505  97  77   7 0.00
Tue 10/13 05Z 0.04 0102  96  74   8 0.00
Tue 10/13 06Z 0.06 1302  97  87   7 0.00
Tue 10/13 07Z 0.07 1606  98  95   7 0.00
Tue 10/13 08Z 0.05 1612  98  92   6 0.01
Tue 10/13 09Z 0.05 1716  98  90   6 0.01
Tue 10/13 10Z 0.04 1720  97  93   6 0.02
Tue 10/13 11Z 0.05 1722  96  97   7 0.01

Run total areal avg QPF for the Central_Greens is: 0.31 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