NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260814_0600
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)
=== ===== === ==== ==== === === === ====
Fri 08/14 06Z 0.37 3217  84  53   9 0.00
Fri 08/14 07Z 0.43 3218  87  47   9 0.00
Fri 08/14 08Z 0.43 3218  85  49   9 0.00
Fri 08/14 09Z 0.44 3119  82  49   9 0.00
Fri 08/14 10Z 0.43 3219  81  61   9 0.00
Fri 08/14 11Z 0.42 3219  79  66   9 0.00
Fri 08/14 12Z 0.41 3220  75  65   9 0.00
Fri 08/14 13Z 0.40 3219  73  68   9 0.00
Fri 08/14 14Z 0.36 3218  71  74   8 0.00
Fri 08/14 15Z 0.42 3216  70  78   8 0.00
Fri 08/14 16Z 0.90 3214  72  77   8 0.00
Fri 08/14 17Z 1.46 3212  73  75   8 0.00
Fri 08/14 18Z 1.94 3211  73  77   9 0.00
Fri 08/14 19Z 1.88 3211  74  77   9 0.00
Fri 08/14 20Z 1.45 3211  76  75   9 0.00
Fri 08/14 21Z 0.67 3210  80  64   9 0.01
Fri 08/14 22Z 0.62 3109  79  53   9 0.01
Fri 08/14 23Z 0.33 3209  79  48   9 0.00
Sat 08/15 00Z 0.29 3310  81  50   9 0.00
Sat 08/15 01Z 0.26 3312  81  44   9 0.00
Sat 08/15 02Z 0.32 3313  81  39   8 0.00
Sat 08/15 03Z 0.28 3313  82  34   8 0.00
Sat 08/15 04Z 0.21 3413  81  30   8 0.00
Sat 08/15 05Z 0.11 3412  78  22   8 0.00
Sat 08/15 06Z 0.16 3412  81  19   8 0.00
Sat 08/15 07Z 0.17 3310  80  14   8 0.00
Sat 08/15 08Z 0.16 3310  78  10   8 0.00
Sat 08/15 09Z 0.19 3310  79  10   8 0.00
Sat 08/15 10Z 0.27 3211  81   9   7 0.00
Sat 08/15 11Z 0.27 3213  81   9   7 0.00
Sat 08/15 12Z 0.26 3213  80   9   7 0.00
Sat 08/15 13Z 0.25 3313  81   9   7 0.00
Sat 08/15 14Z 0.24 3211  83   9   7 0.00
Sat 08/15 15Z 0.31 3211  83  11   7 0.00
Sat 08/15 16Z 0.30 3210  82  14   7 0.00
Sat 08/15 17Z 0.33 3211  80  18   7 0.00
Sat 08/15 18Z 0.56 3212  79  21   7 0.00
Sat 08/15 19Z 1.00 3213  79  23   7 0.00
Sat 08/15 20Z 1.26 3213  82  24   7 0.00
Sat 08/15 21Z 0.97 3213  85  22   7 0.00
Sat 08/15 22Z 0.47 3314  87  21   7 0.00
Sat 08/15 23Z 0.24 3313  86  18   7 0.00
Sun 08/16 00Z 0.14 3412  84  16   7 0.00
Sun 08/16 01Z 0.13 3412  83  16   7 0.00
Sun 08/16 02Z 0.09 3411  81  16   8 0.00
Sun 08/16 03Z 0.07 3511  81  16   8 0.00
Sun 08/16 04Z 0.04 0009  78  14   9 0.00
Sun 08/16 05Z 0.02 0008  77  15   9 0.00
Sun 08/16 06Z 0.03 0005  73  16   9 0.00
Sun 08/16 07Z 0.03 0003  64  15  10 0.00
Sun 08/16 08Z 0.01 0002  60  14  11 0.00
Sun 08/16 09Z 0.01 0000  59  14  11 0.00
Sun 08/16 10Z 0.02 1500  58  12  11 0.00
Sun 08/16 11Z 0.02 2002  57  11  10 0.00
Sun 08/16 12Z 0.04 2003  57  10  10 0.00
Sun 08/16 13Z 0.06 2104  55   9  10 0.00
Sun 08/16 14Z 0.06 2005  54   7  11 0.00
Sun 08/16 15Z 0.08 2106  58   7  11 0.00
Sun 08/16 16Z 0.11 2106  64   6  10 0.00
Sun 08/16 17Z 0.12 2006  67   5  10 0.00

Run total areal avg QPF for the greens is: 0.02 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