NAM12 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20260731_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)
=== ===== === ==== ==== === === === ====
Fri 07/31 18Z 0.27 3206  94  82  12 0.00
Fri 07/31 21Z 0.35 3107  87  79  13 0.04
Sat 08/01 00Z 0.29 3109  83  75  13 0.01
Sat 08/01 03Z 0.11 3308  79  65  14 0.00
Sat 08/01 06Z 0.06 3404  80  67  13 0.00
Sat 08/01 09Z 0.17 2804  81  70  13 0.01
Sat 08/01 12Z 0.30 2707  78  57  13 0.01
Sat 08/01 15Z 0.27 2505  76  45  14 0.00
Sat 08/01 18Z 1.28 2104  76  35  14 0.00
Sat 08/01 21Z 1.19 1907  69  30  15 0.00
Sun 08/02 00Z 0.44 2112  57  21  15 0.00
Sun 08/02 03Z 0.49 2215  74  28  15 0.00
Sun 08/02 06Z 0.48 2316  84  42  15 0.01
Sun 08/02 09Z 0.56 2317  84  32  15 0.00
Sun 08/02 12Z 0.48 2216  83  31  15 0.00
Sun 08/02 15Z 0.37 2114  79  49  15 0.00
Sun 08/02 18Z 0.63 1913  77  43  15 0.01
Sun 08/02 21Z 0.38 2016  83  72  15 0.04
Mon 08/03 00Z 0.40 2019  90  65  15 0.02
Mon 08/03 03Z 0.39 2021  72  75  15 0.00
Mon 08/03 06Z 0.26 2019  68  87  16 0.00
Mon 08/03 09Z 0.23 2116  82  76  16 0.00
Mon 08/03 12Z 0.26 2115  95  56  15 0.01
Mon 08/03 15Z 0.25 2116  82  73  15 0.00
Mon 08/03 18Z 0.34 2310  95  89  16 0.00
Mon 08/03 21Z 0.33 2509  94  84  15 0.17
Tue 08/04 00Z 0.32 2509  93  84  15 0.08
Tue 08/04 03Z 0.29 2809  96  85  15 0.03
Tue 08/04 06Z 0.14 3311  93  61  14 0.01

Run total areal avg QPF for the greens is: 0.45 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