NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261003_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)
=== ===== === ==== ==== === === === ====
Sat 10/03 12Z 0.06 3310  94   5   4 0.00
Sat 10/03 13Z 0.07 3310  89   4   4 0.00
Sat 10/03 14Z 0.07 3308  87   4   4 0.00
Sat 10/03 15Z 0.09 3207  87   4   4 0.00
Sat 10/03 16Z 0.10 3208  84   4   4 0.00
Sat 10/03 17Z 0.11 3207  83   4   4 0.00
Sat 10/03 18Z 0.09 3306  83   4   4 0.00
Sat 10/03 19Z 0.08 3306  83   4   4 0.00
Sat 10/03 20Z 0.09 3306  83   4   4 0.00
Sat 10/03 21Z 0.07 3305  81   4   4 0.00
Sat 10/03 22Z 0.04 3304  79   4   4 0.00
Sat 10/03 23Z 0.03 3402  76   5   4 0.00
Sun 10/04 00Z 0.03 3402  74   4   4 0.00
Sun 10/04 01Z 0.04 0300  74   4   4 0.00
Sun 10/04 02Z 0.04 1501  73   4   4 0.00
Sun 10/04 03Z 0.03 1603  74   4   4 0.00
Sun 10/04 04Z 0.03 1705  77   4   4 0.00
Sun 10/04 05Z 0.04 1707  79   4   4 0.00
Sun 10/04 06Z 0.05 1708  83   5   4 0.00
Sun 10/04 07Z 0.07 1809  86   4   4 0.00
Sun 10/04 08Z 0.10 1810  90   4   3 0.00
Sun 10/04 09Z 0.09 1811  94   5   3 0.00
Sun 10/04 10Z 0.07 1712  95   4   3 0.00
Sun 10/04 11Z 0.06 1713  94   3   3 0.00
Sun 10/04 12Z 0.07 1614  94   2   4 0.00
Sun 10/04 13Z 0.11 1616  94   3   4 0.00
Sun 10/04 14Z 0.10 1618  93   7   4 0.00
Sun 10/04 15Z 0.07 1620  91  10   4 0.00
Sun 10/04 16Z 0.07 1620  89  13   4 0.00
Sun 10/04 17Z 0.06 1620  88  24   5 0.00
Sun 10/04 18Z 0.07 1619  84  47   5 0.00
Sun 10/04 19Z 0.08 1618  81  84   5 0.00
Sun 10/04 20Z 0.06 1619  81  95   4 0.01
Sun 10/04 21Z 0.08 1721  85  94   4 0.01
Sun 10/04 22Z 0.12 1721  87  82   3 0.01
Sun 10/04 23Z 0.18 1820  88  67   4 0.00
Mon 10/05 00Z 0.19 1820  89  33   5 0.00
Mon 10/05 01Z 0.23 1918  90  40   6 0.00
Mon 10/05 02Z 0.23 2016  94  45   6 0.00
Mon 10/05 03Z 0.25 2016  96  59   6 0.00
Mon 10/05 04Z 0.32 2116  98  65   6 0.01
Mon 10/05 05Z 0.38 2216  99  71   6 0.02
Mon 10/05 06Z 0.44 2316  98  64   6 0.01
Mon 10/05 07Z 0.55 2418  97  57   5 0.01
Mon 10/05 08Z 0.61 2420  96  66   5 0.01
Mon 10/05 09Z 0.56 2520  88  33   6 0.01
Mon 10/05 10Z 0.59 2622  89  42   6 0.00
Mon 10/05 11Z 0.76 2626  96  68   5 0.03
Mon 10/05 12Z 0.96 2728  90  61   3 0.06
Mon 10/05 13Z 0.91 2827  81  40   3 0.01
Mon 10/05 14Z 1.09 2827  79  20   2 0.01
Mon 10/05 15Z 2.54 2826  69   6   1 0.00
Mon 10/05 16Z 11.81 2825  70  11   0 0.00
Mon 10/05 17Z 13.67 2725  80  33   0 0.00
Mon 10/05 18Z 13.38 2725  81  41   0 0.00
Mon 10/05 19Z 11.72 2724  82  54   0 0.00
Mon 10/05 20Z 3.94 2723  87  66   0 0.01
Mon 10/05 21Z 1.64 2825  92  70   0 0.04
Mon 10/05 22Z 1.76 2928  92  66   0 0.03
Mon 10/05 23Z 1.70 2928  92  66  -2 0.02

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