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_0600
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 06Z 0.87 2431  96  98  14 0.00
Fri 10/02 07Z 0.89 2434  93  92  15 0.02
Fri 10/02 08Z 0.93 2436  95  91  15 0.03
Fri 10/02 09Z 0.91 2535  94  80  15 0.01
Fri 10/02 10Z 0.93 2534  96  92  15 0.05
Fri 10/02 11Z 0.83 2530  95  88  14 0.03
Fri 10/02 12Z 0.92 2433  96  92  14 0.06
Fri 10/02 13Z 0.89 2531  95  91  14 0.12
Fri 10/02 14Z 0.80 2526  97  96  14 0.10
Fri 10/02 15Z 0.76 2523  98  97  13 0.09
Fri 10/02 16Z 0.68 2720  98  95  12 0.07
Fri 10/02 17Z 0.60 2919  98  95  12 0.09
Fri 10/02 18Z 0.47 3016  98  89  11 0.05
Fri 10/02 19Z 0.44 3018  98  87  11 0.04
Fri 10/02 20Z 0.44 3017  95  72  10 0.01
Fri 10/02 21Z 0.47 3017  88  62  10 0.01
Fri 10/02 22Z 0.59 3020  92  39   9 0.01
Fri 10/02 23Z 0.46 3121  93  17   8 0.02
Sat 10/03 00Z 0.35 3223  91  25   8 0.01
Sat 10/03 01Z 0.18 3323  81   7   7 0.01
Sat 10/03 02Z 0.18 3323  76   2   7 0.00
Sat 10/03 03Z 0.20 3324  76   1   6 0.00
Sat 10/03 04Z 0.25 3325  72   1   5 0.00
Sat 10/03 05Z 0.20 3324  74   1   5 0.00
Sat 10/03 06Z 0.19 3323  78   1   4 0.00
Sat 10/03 07Z 0.20 3322  76   2   4 0.00
Sat 10/03 08Z 0.17 3322  67   3   4 0.00
Sat 10/03 09Z 0.13 3321  60   2   4 0.00
Sat 10/03 10Z 0.09 3321  60   1   4 0.00
Sat 10/03 11Z 0.06 3421  62   0   4 0.00
Sat 10/03 12Z 0.02 3420  61   0   4 0.00
Sat 10/03 13Z 0.02 3419  58   0   4 0.00
Sat 10/03 14Z 0.02 3417  58   2   4 0.00
Sat 10/03 15Z 0.05 3415  59   2   4 0.00
Sat 10/03 16Z 0.05 3413  61   3   3 0.00
Sat 10/03 17Z 0.06 3411  63   3   3 0.00
Sat 10/03 18Z 0.10 3409  65   3   3 0.00
Sat 10/03 19Z 0.13 3408  66   4   3 0.00
Sat 10/03 20Z 0.13 3307  64   4   3 0.00
Sat 10/03 21Z 0.04 3408  60   5   3 0.00
Sat 10/03 22Z 0.03 3508  56   5   3 0.00
Sat 10/03 23Z 0.04 3508  51   5   4 0.00
Sun 10/04 00Z 0.06 0007  44   5   4 0.00
Sun 10/04 01Z 0.06 0104  40   4   4 0.00
Sun 10/04 02Z 0.08 0403  37   4   4 0.00
Sun 10/04 03Z 0.10 0903  35   3   5 0.00
Sun 10/04 04Z 0.09 1204  34   3   5 0.00
Sun 10/04 05Z 0.07 1406  35   4   5 0.00
Sun 10/04 06Z 0.04 1508  36   4   5 0.00
Sun 10/04 07Z 0.04 1610  41   4   5 0.00
Sun 10/04 08Z 0.04 1613  46   4   5 0.00
Sun 10/04 09Z 0.05 1715  53   4   4 0.00
Sun 10/04 10Z 0.13 1815  61   4   3 0.00
Sun 10/04 11Z 0.15 1815  68   3   3 0.00
Sun 10/04 12Z 0.11 1816  71   3   3 0.00
Sun 10/04 13Z 0.10 1817  71   3   3 0.00
Sun 10/04 14Z 0.11 1817  73   3   3 0.00
Sun 10/04 15Z 0.15 1816  77   3   3 0.00
Sun 10/04 16Z 0.14 1714  77   2   3 0.00
Sun 10/04 17Z 0.19 1715  77   0   3 0.00

Run total areal avg QPF for the Central_Greens is: 0.83 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