NAM12 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20260823_1200
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 08/23 12Z 0.12 1618  92  85  12 0.00
Sun 08/23 15Z 0.04 1718  94  87  12 0.01
Sun 08/23 18Z 0.04 1818  93  91  12 0.04
Sun 08/23 21Z 0.18 1917  93  82  12 0.07
Mon 08/24 00Z 0.38 2116  89  66  12 0.05
Mon 08/24 03Z 0.67 2318  83  70  10 0.01
Mon 08/24 06Z 0.54 2416  79  48   9 0.00
Mon 08/24 09Z 0.38 2214  78  44   9 0.00
Mon 08/24 12Z 0.28 2114  78  58   8 0.00
Mon 08/24 15Z 0.33 2015  81  67   8 0.00
Mon 08/24 18Z 3.17 2113  83  74   8 0.02
Mon 08/24 21Z 2.60 2112  77  79   9 0.01
Tue 08/25 00Z 1.49 2216  81  84   8 0.02
Tue 08/25 03Z 0.86 2317  83  85   8 0.00
Tue 08/25 06Z 0.52 2416  90  90   8 0.00
Tue 08/25 09Z 0.37 2611  92  72   8 0.00
Tue 08/25 12Z 0.22 2506  92  72   8 0.00
Tue 08/25 15Z 0.28 2408  95  80   8 0.00
Tue 08/25 18Z 0.30 2408  93  90   9 0.02
Tue 08/25 21Z 0.31 2609  91  87   9 0.03
Wed 08/26 00Z 0.38 2812  94  84   9 0.01
Wed 08/26 03Z 0.43 3013  96  81   8 0.00
Wed 08/26 06Z 0.40 3013  95  70   8 0.00
Wed 08/26 09Z 0.41 2913  95  78   8 0.00
Wed 08/26 12Z 0.41 2913  96  34   7 0.00
Wed 08/26 15Z 0.36 2809  91  22   7 0.00
Wed 08/26 18Z 1.58 2808  87  17   8 0.00
Wed 08/26 21Z 1.00 2806  82   8   9 0.00
Thu 08/27 00Z 0.29 2505  78   7  10 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