Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260923_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)
=== ===== === ==== ==== === === === ====
Wed 09/23 18Z 1.65 0706  81  10   3 0.00
Wed 09/23 19Z 1.43 0707  78   9   4 0.00
Wed 09/23 20Z 0.91 0707  78   8   4 0.00
Wed 09/23 21Z 0.58 0707  79   7   4 0.00
Wed 09/23 22Z 0.45 0708  79   6   4 0.00
Wed 09/23 23Z 0.40 0609  76   5   4 0.00
Thu 09/24 00Z 0.43 0611  74   4   5 0.00
Thu 09/24 01Z 0.46 0711  74   4   4 0.00
Thu 09/24 02Z 0.44 0712  70   4   5 0.00
Thu 09/24 03Z 0.41 0812  64   3   5 0.00
Thu 09/24 04Z 0.37 0812  57   4   5 0.00
Thu 09/24 05Z 0.32 0811  48   3   6 0.00
Thu 09/24 06Z 0.29 0711  41   3   7 0.00
Thu 09/24 07Z 0.26 0711  35   3   7 0.00
Thu 09/24 08Z 0.25 0611  32   3   7 0.00
Thu 09/24 09Z 0.26 0612  33   3   7 0.00
Thu 09/24 10Z 0.25 0611  33   3   7 0.00
Thu 09/24 11Z 0.25 0611  33   3   7 0.00
Thu 09/24 12Z 0.27 0712  32   3   7 0.00
Thu 09/24 13Z 0.26 0712  32   3   7 0.00
Thu 09/24 14Z 0.24 0711  31   3   7 0.00
Thu 09/24 15Z 0.21 0709  32   3   7 0.00
Thu 09/24 16Z 0.22 0709  33   4   7 0.00
Thu 09/24 17Z 0.22 0608  32   4   7 0.00
Thu 09/24 18Z 0.23 0608  31   4   8 0.00
Thu 09/24 19Z 0.23 0607  32   5   8 0.00
Thu 09/24 20Z 0.22 0607  35   5   8 0.00
Thu 09/24 21Z 0.26 0609  39   5   8 0.00
Thu 09/24 22Z 0.27 0609  44   5   8 0.00
Thu 09/24 23Z 0.31 0611  47   5   8 0.00
Fri 09/25 00Z 0.31 0611  48   5   8 0.00
Fri 09/25 01Z 0.33 0613  49   5   9 0.00
Fri 09/25 02Z 0.34 0613  50   5   9 0.00
Fri 09/25 03Z 0.33 0613  49   5   9 0.00
Fri 09/25 04Z 0.33 0613  46   6   9 0.00
Fri 09/25 05Z 0.31 0613  45   6   9 0.00
Fri 09/25 06Z 0.30 0613  45   6   9 0.00
Fri 09/25 07Z 0.30 0613  47   6   9 0.00
Fri 09/25 08Z 0.30 0513  48   6   9 0.00
Fri 09/25 09Z 0.31 0514  50   7   8 0.00
Fri 09/25 10Z 0.34 0515  52   7   8 0.00
Fri 09/25 11Z 0.38 0516  53   7   8 0.00
Fri 09/25 12Z 0.39 0517  51   8   8 0.00
Fri 09/25 13Z 0.43 0618  48   7   9 0.00
Fri 09/25 14Z 0.44 0617  50   8   8 0.00
Fri 09/25 15Z 0.47 0616  51   8   8 0.00
Fri 09/25 16Z 0.48 0614  49   7   8 0.00
Fri 09/25 17Z 0.41 0511  50   7   8 0.00
Fri 09/25 18Z 0.53 0410  55   7   8 0.00
Fri 09/25 19Z 1.20 0310  59   7   8 0.00
Fri 09/25 20Z 0.86 0311  60   7   8 0.00
Fri 09/25 21Z 0.56 0312  60   7   9 0.00
Fri 09/25 22Z 0.48 0314  59   7   9 0.00
Fri 09/25 23Z 0.43 0316  58   7   9 0.00
Sat 09/26 00Z 0.44 0417  57   7   9 0.00
Sat 09/26 01Z 0.46 0418  55   7   9 0.00
Sat 09/26 02Z 0.50 0518  51   6  10 0.00
Sat 09/26 03Z 0.52 0518  47   6  10 0.00
Sat 09/26 04Z 0.50 0518  42   6  10 0.00
Sat 09/26 05Z 0.49 0518  39   6   9 0.00

Run total areal avg QPF for the greens is: 0.00 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