NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260913_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)
=== ===== === ==== ==== === === === ====
Sun 09/13 18Z 0.26 2210  98  35  13 0.00
Sun 09/13 19Z 0.25 2211  95  36  13 0.00
Sun 09/13 20Z 0.23 2111  92  33  14 0.00
Sun 09/13 21Z 0.31 2313  86  30  15 0.00
Sun 09/13 22Z 0.38 2415  81  35  15 0.00
Sun 09/13 23Z 0.48 2518  81  42  15 0.00
Mon 09/14 00Z 0.64 2521  86  42  15 0.00
Mon 09/14 01Z 0.74 2523  90  60  14 0.00
Mon 09/14 02Z 0.81 2525  95  67  14 0.04
Mon 09/14 03Z 0.80 2624  90  71  14 0.04
Mon 09/14 04Z 0.87 2824  90  71  13 0.04
Mon 09/14 05Z 1.00 2926  91  79  12 0.03
Mon 09/14 06Z 0.91 2925  90  83  10 0.03
Mon 09/14 07Z 0.81 2923  77  84  10 0.01
Mon 09/14 08Z 0.98 2826  85  62   9 0.01
Mon 09/14 09Z 0.88 2928  86  40   8 0.00
Mon 09/14 10Z 0.71 3029  85  21   7 0.02
Mon 09/14 11Z 0.55 3229  84  11   6 0.01
Mon 09/14 12Z 0.45 3228  84  10   5 0.01
Mon 09/14 13Z 0.38 3327  86  11   4 0.01
Mon 09/14 14Z 0.33 3324  87  10   4 0.01
Mon 09/14 15Z 0.32 3322  85   9   4 0.01
Mon 09/14 16Z 0.35 3320  83  10   4 0.01
Mon 09/14 17Z 0.44 3219  80   7   4 0.01
Mon 09/14 18Z 0.51 3218  76   7   4 0.00
Mon 09/14 19Z 1.14 3218  80   9   3 0.00
Mon 09/14 20Z 1.92 3217  84  14   3 0.00
Mon 09/14 21Z 1.18 3218  85  18   3 0.00
Mon 09/14 22Z 0.80 3218  85  20   3 0.00
Mon 09/14 23Z 0.72 3221  85  20   3 0.00
Tue 09/15 00Z 0.61 3221  84  19   3 0.00
Tue 09/15 01Z 0.40 3220  80  17   4 0.00
Tue 09/15 02Z 0.26 3320  76  14   5 0.00
Tue 09/15 03Z 0.10 3417  68   9   7 0.00
Tue 09/15 04Z 0.07 3517  69   9   6 0.00
Tue 09/15 05Z 0.06 3515  66   8   6 0.00
Tue 09/15 06Z 0.06 0112  58   6   7 0.00
Tue 09/15 07Z 0.06 0108  55   5   8 0.00
Tue 09/15 08Z 0.05 0205  52   5   8 0.00
Tue 09/15 09Z 0.04 3401  48   5   8 0.00
Tue 09/15 10Z 0.03 2801  43   5   8 0.00
Tue 09/15 11Z 0.03 2101  42   5   8 0.00
Tue 09/15 12Z 0.04 2003  43   5   8 0.00
Tue 09/15 13Z 0.05 2005  43   6   8 0.00
Tue 09/15 14Z 0.06 2006  44   6   8 0.00
Tue 09/15 15Z 0.09 2006  46   7   8 0.00
Tue 09/15 16Z 0.06 2007  47   7   9 0.00
Tue 09/15 17Z 0.07 1908  49   9  10 0.00
Tue 09/15 18Z 0.06 1909  51  10  10 0.00
Tue 09/15 19Z 0.04 1811  50  12  11 0.00
Tue 09/15 20Z 0.09 1912  51  13  11 0.00
Tue 09/15 21Z 0.11 1915  51  15  12 0.00
Tue 09/15 22Z 0.15 1917  48  16  12 0.00
Tue 09/15 23Z 0.18 2020  40  21  13 0.00
Wed 09/16 00Z 0.22 2022  35  29  14 0.00
Wed 09/16 01Z 0.26 2123  31  43  14 0.00
Wed 09/16 02Z 0.31 2124  30  60  14 0.00
Wed 09/16 03Z 0.37 2225  32  73  14 0.00
Wed 09/16 04Z 0.40 2324  34  77  14 0.00
Wed 09/16 05Z 0.42 2323  38  86  14 0.00

Run total areal avg QPF for the greens is: 0.29 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