NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261002_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)
=== ===== === ==== ==== === === === ====
Fri 10/02 12Z 0.86 2532  98  83  15 0.00
Fri 10/02 13Z 0.94 2534  97  81  14 0.07
Fri 10/02 14Z 0.96 2532  94  95  14 0.04
Fri 10/02 15Z 0.83 2626  97  93  13 0.07
Fri 10/02 16Z 0.68 2719  98  86  12 0.04
Fri 10/02 17Z 0.52 2816  97  80  12 0.02
Fri 10/02 18Z 0.48 2916  98  90  11 0.02
Fri 10/02 19Z 0.40 3016  96  88  11 0.03
Fri 10/02 20Z 0.45 3018  97  85  10 0.01
Fri 10/02 21Z 0.49 3021  98  84  10 0.03
Fri 10/02 22Z 0.46 3122  97  73   9 0.03
Fri 10/02 23Z 0.38 3122  91  35   8 0.01
Sat 10/03 00Z 0.33 3223  85  23   8 0.01
Sat 10/03 01Z 0.29 3223  76   9   7 0.00
Sat 10/03 02Z 0.25 3324  77   5   6 0.00
Sat 10/03 03Z 0.23 3325  84   1   6 0.00
Sat 10/03 04Z 0.22 3324  85   1   5 0.00
Sat 10/03 05Z 0.16 3324  85   2   5 0.00
Sat 10/03 06Z 0.11 3423  85   3   4 0.00
Sat 10/03 07Z 0.12 3422  84   2   4 0.00
Sat 10/03 08Z 0.13 3322  84   1   3 0.00
Sat 10/03 09Z 0.09 3419  82   1   3 0.00
Sat 10/03 10Z 0.06 3417  77   1   4 0.00
Sat 10/03 11Z 0.05 3417  73   2   4 0.00
Sat 10/03 12Z 0.02 3417  69   1   4 0.00
Sat 10/03 13Z 0.02 3516  65   2   5 0.00
Sat 10/03 14Z 0.01 3513  61   2   5 0.00
Sat 10/03 15Z 0.03 3412  61   3   5 0.00
Sat 10/03 16Z 0.03 3411  60   3   5 0.00
Sat 10/03 17Z 0.03 3408  64   3   4 0.00
Sat 10/03 18Z 0.06 3307  65   3   4 0.00
Sat 10/03 19Z 0.05 3407  62   3   4 0.00
Sat 10/03 20Z 0.03 3506  64   3   4 0.00
Sat 10/03 21Z 0.06 0004  67   4   3 0.00
Sat 10/03 22Z 0.06 0003  66   4   3 0.00
Sat 10/03 23Z 0.08 0203  64   4   3 0.00
Sun 10/04 00Z 0.08 0402  61   4   4 0.00
Sun 10/04 01Z 0.08 0702  56   4   4 0.00
Sun 10/04 02Z 0.09 1103  51   5   4 0.00
Sun 10/04 03Z 0.07 1405  50   4   4 0.00
Sun 10/04 04Z 0.05 1505  55   4   4 0.00
Sun 10/04 05Z 0.05 1507  58   4   4 0.00
Sun 10/04 06Z 0.03 1608  62   3   3 0.00
Sun 10/04 07Z 0.06 1810  68   3   3 0.00
Sun 10/04 08Z 0.07 1811  71   2   4 0.00
Sun 10/04 09Z 0.08 1812  74   2   4 0.00
Sun 10/04 10Z 0.08 1714  77   2   3 0.00
Sun 10/04 11Z 0.09 1716  80   2   3 0.00
Sun 10/04 12Z 0.09 1715  81   2   3 0.00
Sun 10/04 13Z 0.07 1715  83   1   3 0.00
Sun 10/04 14Z 0.05 1716  81   2   3 0.00
Sun 10/04 15Z 0.05 1716  81   2   3 0.00
Sun 10/04 16Z 0.05 1615  81   2   3 0.00
Sun 10/04 17Z 0.11 1614  85   7   3 0.00
Sun 10/04 18Z 0.13 1614  83  12   3 0.00
Sun 10/04 19Z 0.09 1614  79  23   3 0.00
Sun 10/04 20Z 0.08 1615  76  13   4 0.00
Sun 10/04 21Z 0.05 1618  76   3   4 0.00
Sun 10/04 22Z 0.08 1720  76  12   5 0.00
Sun 10/04 23Z 0.14 1722  77  67   5 0.00

Run total areal avg QPF for the Central_Greens is: 0.38 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