NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261003_1800
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sat 10/03 18Z 0.17 3308  92   9   3 0.00
Sat 10/03 19Z 0.13 3409  88   8   3 0.00
Sat 10/03 20Z 0.05 3508  85   7   4 0.00
Sat 10/03 21Z 0.04 3507  83   7   4 0.00
Sat 10/03 22Z 0.04 0006  81   7   4 0.00
Sat 10/03 23Z 0.06 0105  77   7   4 0.00
Sun 10/04 00Z 0.09 0305  73   7   5 0.00
Sun 10/04 01Z 0.10 0504  70   7   5 0.00
Sun 10/04 02Z 0.15 0805  68   7   5 0.00
Sun 10/04 03Z 0.16 1105  68   7   4 0.00
Sun 10/04 04Z 0.14 1306  68   7   4 0.00
Sun 10/04 05Z 0.13 1407  70   7   4 0.00
Sun 10/04 06Z 0.11 1510  74   7   4 0.00
Sun 10/04 07Z 0.11 1613  82   7   4 0.00
Sun 10/04 08Z 0.07 1715  89   7   4 0.00
Sun 10/04 09Z 0.05 1716  92   7   4 0.00
Sun 10/04 10Z 0.07 1716  93   7   4 0.00
Sun 10/04 11Z 0.09 1716  93   7   4 0.01
Sun 10/04 12Z 0.12 1618  93   7   4 0.00
Sun 10/04 13Z 0.13 1720  94   6   4 0.00
Sun 10/04 14Z 0.15 1621  93   6   4 0.00
Sun 10/04 15Z 0.16 1621  93   8   4 0.00
Sun 10/04 16Z 0.18 1621  92  21   4 0.00
Sun 10/04 17Z 0.21 1620  90  33   4 0.00
Sun 10/04 18Z 0.20 1621  86  55   4 0.00
Sun 10/04 19Z 0.19 1621  78  65   5 0.00
Sun 10/04 20Z 0.12 1721  73  76   5 0.00
Sun 10/04 21Z 0.08 1721  69  70   6 0.00
Sun 10/04 22Z 0.07 1723  70  42   6 0.00
Sun 10/04 23Z 0.08 1823  71  31   6 0.00
Mon 10/05 00Z 0.09 1821  76  23   6 0.00
Mon 10/05 01Z 0.14 1919  83  39   6 0.00
Mon 10/05 02Z 0.20 2017  89  54   6 0.00
Mon 10/05 03Z 0.23 2115  93  71   7 0.00
Mon 10/05 04Z 0.29 2215  95  74   6 0.00
Mon 10/05 05Z 0.35 2315  93  75   6 0.00
Mon 10/05 06Z 0.40 2516  91  84   6 0.00
Mon 10/05 07Z 0.45 2517  92  83   6 0.01
Mon 10/05 08Z 0.52 2519  94  70   6 0.01
Mon 10/05 09Z 0.61 2621  96  37   6 0.03
Mon 10/05 10Z 0.74 2623  93  46   5 0.02
Mon 10/05 11Z 0.78 2724  85  65   5 0.01
Mon 10/05 12Z 0.90 2725  81  42   4 0.02
Mon 10/05 13Z 0.93 2726  78  18   3 0.02
Mon 10/05 14Z 0.91 2825  74  22   2 0.01
Mon 10/05 15Z 1.29 2826  78  25   1 0.01
Mon 10/05 16Z 4.90 2825  76  28   0 0.01
Mon 10/05 17Z 10.79 2826  77  36   0 0.01
Mon 10/05 18Z 9.65 2828  82  57   0 0.02
Mon 10/05 19Z 7.24 2828  87  56  -1 0.01
Mon 10/05 20Z 7.42 2928  87  52  -2 0.01
Mon 10/05 21Z 3.45 2927  89  49  -2 0.01
Mon 10/05 22Z 2.23 2928  92  49  -3 0.01
Mon 10/05 23Z 1.75 2929  92  50  -4 0.01
Tue 10/06 00Z 1.69 2930  94  54  -4 0.00
Tue 10/06 01Z 1.67 2931  94  61  -5 0.01
Tue 10/06 02Z 1.56 2932  94  62  -5 0.01
Tue 10/06 03Z 1.50 2934  94  44  -5 0.01
Tue 10/06 04Z 1.35 3034  90  28  -5 0.00
Tue 10/06 05Z 1.13 3035  80  17  -4 0.00

Run total areal avg QPF for the greens is: 0.27 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