NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261009_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)
=== ===== === ==== ==== === === === ====
Fri 10/09 18Z 4.49 2817  84  63   2 0.00
Fri 10/09 19Z 6.46 2818  81  69   2 0.01
Fri 10/09 20Z 4.90 2818  77  45   2 0.00
Fri 10/09 21Z 3.84 2621  72  51   2 0.00
Fri 10/09 22Z 2.58 2522  67  29   3 0.00
Fri 10/09 23Z 2.17 2627  72  77   2 0.00
Sat 10/10 00Z 1.28 2828  82  86   2 0.03
Sat 10/10 01Z 0.80 2926  86  37   1 0.05
Sat 10/10 02Z 0.64 3025  81  33   1 0.02
Sat 10/10 03Z 0.67 3027  80  16   1 0.00
Sat 10/10 04Z 0.64 3028  81   6   0 0.00
Sat 10/10 05Z 0.63 3026  85   7   0 0.00
Sat 10/10 06Z 0.49 3026  80   8   0 0.00
Sat 10/10 07Z 0.42 3124  78   9   0 0.00
Sat 10/10 08Z 0.39 3124  74  13   1 0.00
Sat 10/10 09Z 0.34 3124  69  14   1 0.01
Sat 10/10 10Z 0.30 3124  61  15   1 0.01
Sat 10/10 11Z 0.26 3225  54  16   1 0.00
Sat 10/10 12Z 0.23 3226  47  13   2 0.00
Sat 10/10 13Z 0.19 3225  45   9   2 0.00
Sat 10/10 14Z 0.18 3224  45   9   2 0.00
Sat 10/10 15Z 0.15 3321  47  12   2 0.00
Sat 10/10 16Z 0.11 3316  51  18   1 0.00
Sat 10/10 17Z 0.10 3312  52  26   1 0.00
Sat 10/10 18Z 0.12 3312  48  31   2 0.00
Sat 10/10 19Z 0.12 3211  42  48   3 0.00
Sat 10/10 20Z 0.13 3211  37  55   4 0.00
Sat 10/10 21Z 0.10 3210  31  63   5 0.00
Sat 10/10 22Z 0.10 3209  26  65   6 0.00
Sat 10/10 23Z 0.09 3107  23  59   6 0.00
Sun 10/11 01Z 0.09 2804  23  45   7 0.00
Sun 10/11 03Z 0.13 2306  25  33   8 0.00
Sun 10/11 04Z 0.12 2206  24  26   8 0.00
Sun 10/11 05Z 0.15 2108  26  28   8 0.00
Sun 10/11 06Z 0.19 2210  25  28   8 0.00
Sun 10/11 07Z 0.21 2211  23  29   8 0.00
Sun 10/11 08Z 0.21 2212  21  30   9 0.00
Sun 10/11 09Z 0.22 2113  20  31   9 0.00
Sun 10/11 10Z 0.23 2114  19  32  10 0.00
Sun 10/11 11Z 0.22 2114  18  29  10 0.00
Sun 10/11 12Z 0.21 2115  18  28  11 0.00
Sun 10/11 13Z 0.21 2116  19  27  11 0.00
Sun 10/11 14Z 0.22 2018  21  25  11 0.00
Sun 10/11 15Z 0.23 2018  20  25  10 0.00
Sun 10/11 16Z 0.21 2018  20  25  10 0.00
Sun 10/11 17Z 0.22 2019  23  28  10 0.00
Sun 10/11 18Z 0.22 2019  27  30   9 0.00
Sun 10/11 19Z 0.22 2018  36  41   9 0.00
Sun 10/11 20Z 0.21 1917  55  70   7 0.00
Sun 10/11 21Z 0.21 1918  63  92   6 0.00
Sun 10/11 22Z 0.17 1920  55  92   6 0.00
Sun 10/11 23Z 0.13 1822  60  96   6 0.00
Mon 10/12 00Z 0.08 1722  85  98   6 0.00
Mon 10/12 01Z 0.08 1723  95  99   7 0.00
Mon 10/12 02Z 0.09 1722  96  97   8 0.03
Mon 10/12 03Z 0.10 1820  97  98   8 0.10
Mon 10/12 04Z 0.11 1817  97  99   9 0.09
Mon 10/12 05Z 0.09 1813  97  99   9 0.07

Run total areal avg QPF for the Central_Greens is: 0.42 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