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_1800
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 18Z 0.12 3308  91   8   4 0.00
Sat 10/03 19Z 0.06 3409  89   8   4 0.00
Sat 10/03 20Z 0.05 3507  86   8   4 0.00
Sat 10/03 21Z 0.07 0007  85   8   4 0.00
Sat 10/03 22Z 0.09 0106  84   8   4 0.00
Sat 10/03 23Z 0.11 0206  81   8   5 0.00
Sun 10/04 00Z 0.14 0306  77   8   5 0.00
Sun 10/04 01Z 0.15 0505  75   9   5 0.00
Sun 10/04 02Z 0.19 0806  74   9   5 0.00
Sun 10/04 03Z 0.18 1107  75   8   4 0.00
Sun 10/04 04Z 0.14 1307  76   8   4 0.00
Sun 10/04 05Z 0.11 1408  79   8   4 0.00
Sun 10/04 06Z 0.08 1510  84   7   4 0.00
Sun 10/04 07Z 0.06 1614  90   7   4 0.00
Sun 10/04 08Z 0.04 1715  92   8   4 0.00
Sun 10/04 09Z 0.05 1715  94   8   4 0.00
Sun 10/04 10Z 0.07 1715  96   8   4 0.00
Sun 10/04 11Z 0.08 1615  96   8   4 0.01
Sun 10/04 12Z 0.09 1618  95   6   4 0.01
Sun 10/04 13Z 0.10 1619  94   5   4 0.00
Sun 10/04 14Z 0.11 1619  93   5   4 0.00
Sun 10/04 15Z 0.12 1520  92  10   4 0.00
Sun 10/04 16Z 0.14 1520  91  28   4 0.00
Sun 10/04 17Z 0.16 1520  89  39   4 0.00
Sun 10/04 18Z 0.13 1520  83  64   5 0.00
Sun 10/04 19Z 0.09 1620  72  66   5 0.00
Sun 10/04 20Z 0.05 1619  67  82   6 0.00
Sun 10/04 21Z 0.04 1719  64  81   6 0.00
Sun 10/04 22Z 0.07 1721  65  54   6 0.00
Sun 10/04 23Z 0.10 1720  71  40   6 0.00
Mon 10/05 00Z 0.11 1818  79  23   6 0.00
Mon 10/05 01Z 0.18 1915  85  27   6 0.00
Mon 10/05 02Z 0.21 2013  90  48   7 0.00
Mon 10/05 03Z 0.25 2113  94  72   7 0.00
Mon 10/05 04Z 0.30 2313  95  72   7 0.00
Mon 10/05 05Z 0.36 2414  94  74   6 0.00
Mon 10/05 06Z 0.39 2515  91  81   7 0.01
Mon 10/05 07Z 0.43 2617  91  78   7 0.01
Mon 10/05 08Z 0.49 2618  93  65   6 0.01
Mon 10/05 09Z 0.56 2620  96  30   6 0.02
Mon 10/05 10Z 0.71 2724  96  43   5 0.03
Mon 10/05 11Z 0.74 2724  83  80   5 0.01
Mon 10/05 12Z 0.81 2725  74  55   4 0.01
Mon 10/05 13Z 0.88 2725  72  19   3 0.01
Mon 10/05 14Z 0.86 2825  67  24   2 0.01
Mon 10/05 15Z 1.20 2825  72  23   1 0.01
Mon 10/05 16Z 6.58 2825  66  25   1 0.00
Mon 10/05 17Z 15.18 2825  66  21   0 0.00
Mon 10/05 18Z 13.32 2827  75  52   0 0.00
Mon 10/05 19Z 9.45 2826  83  52   0 0.01
Mon 10/05 20Z 9.40 2926  82  51  -1 0.01
Mon 10/05 21Z 3.89 2924  86  46  -1 0.00
Mon 10/05 22Z 2.09 2926  90  44  -2 0.00
Mon 10/05 23Z 1.40 2927  91  47  -3 0.00
Tue 10/06 00Z 1.34 2928  93  51  -3 0.00
Tue 10/06 01Z 1.31 2929  93  58  -4 0.00
Tue 10/06 02Z 1.23 3030  93  56  -4 0.00
Tue 10/06 03Z 1.11 3033  92  36  -5 0.00
Tue 10/06 04Z 0.99 3034  88  24  -4 0.00
Tue 10/06 05Z 0.94 3034  79  15  -4 0.00

Run total areal avg QPF for the Central_Greens is: 0.17 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