NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260924_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)
=== ===== === ==== ==== === === === ====
Thu 09/24 12Z 0.26 0610  62   3   7 0.00
Thu 09/24 13Z 0.29 0612  62   3   7 0.00
Thu 09/24 14Z 0.29 0612  61   3   7 0.00
Thu 09/24 15Z 0.30 0612  58   3   7 0.00
Thu 09/24 16Z 0.29 0512  53   2   8 0.00
Thu 09/24 17Z 0.34 0612  48   3   7 0.00
Thu 09/24 18Z 0.39 0711  46   3   7 0.00
Thu 09/24 19Z 0.43 0810  52   3   7 0.00
Thu 09/24 20Z 0.44 0809  58   3   7 0.00
Thu 09/24 21Z 0.47 0709  64   3   7 0.00
Thu 09/24 22Z 0.45 0710  67   4   7 0.00
Thu 09/24 23Z 0.44 0611  66   4   7 0.00
Fri 09/25 00Z 0.48 0512  69   5   7 0.00
Fri 09/25 01Z 0.55 0512  73   5   6 0.00
Fri 09/25 02Z 0.64 0515  75   5   6 0.00
Fri 09/25 03Z 0.65 0516  76   6   6 0.00
Fri 09/25 04Z 0.63 0616  73   6   7 0.00
Fri 09/25 05Z 0.60 0616  70   6   7 0.00
Fri 09/25 06Z 0.52 0616  63   6   8 0.00
Fri 09/25 07Z 0.47 0616  59   7   9 0.00
Fri 09/25 08Z 0.44 0616  56   7   9 0.00
Fri 09/25 09Z 0.42 0616  55   7   9 0.00
Fri 09/25 10Z 0.44 0616  57   7   8 0.00
Fri 09/25 11Z 0.49 0617  57   6   8 0.00
Fri 09/25 12Z 0.52 0618  57   6   8 0.00
Fri 09/25 13Z 0.48 0717  55   7   8 0.00
Fri 09/25 14Z 0.47 0718  54   7   9 0.00
Fri 09/25 15Z 0.49 0717  51   8   9 0.00
Fri 09/25 16Z 0.47 0815  52  10   9 0.00
Fri 09/25 17Z 0.48 0713  59  11   9 0.00
Fri 09/25 18Z 0.56 0711  65  12   8 0.00
Fri 09/25 19Z 0.78 0510  69  12   8 0.00
Fri 09/25 20Z 0.83 0510  69  11   8 0.00
Fri 09/25 21Z 0.74 0511  67  11   8 0.00
Fri 09/25 22Z 0.73 0413  68  11   8 0.00
Fri 09/25 23Z 0.79 0515  68   9   8 0.00
Sat 09/26 00Z 0.76 0516  67   8   9 0.00
Sat 09/26 01Z 0.74 0618  62   7   9 0.00
Sat 09/26 02Z 0.72 0718  57   7   9 0.00
Sat 09/26 03Z 0.74 0718  56   7   9 0.00
Sat 09/26 04Z 0.73 0719  52   7   9 0.00
Sat 09/26 05Z 0.67 0718  48   7   9 0.00
Sat 09/26 06Z 0.62 0717  46   7   9 0.00
Sat 09/26 07Z 0.63 0618  45   6   9 0.00
Sat 09/26 08Z 0.65 0618  47   6   9 0.00
Sat 09/26 09Z 0.68 0619  49   6   8 0.00
Sat 09/26 10Z 0.66 0619  49   6   8 0.00
Sat 09/26 11Z 0.64 0520  51   6   8 0.00
Sat 09/26 12Z 0.62 0521  49   6   9 0.00
Sat 09/26 13Z 0.65 0523  49   6   9 0.00
Sat 09/26 14Z 0.65 0523  50   5   9 0.00
Sat 09/26 15Z 0.65 0522  50   5   9 0.00
Sat 09/26 16Z 0.69 0621  52   6   9 0.00
Sat 09/26 17Z 0.70 0620  56  16   9 0.00
Sat 09/26 18Z 0.74 0520  60  26   8 0.00
Sat 09/26 19Z 0.87 0520  62  29   8 0.00
Sat 09/26 20Z 0.99 0522  62  28   8 0.00
Sat 09/26 21Z 1.18 0623  64  43   7 0.00
Sat 09/26 22Z 1.20 0624  64  49   7 0.00
Sat 09/26 23Z 1.18 0625  64  75   7 0.01

Run total areal avg QPF for the Central_Greens is: 0.01 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